Model air car skims the ground By ROY L. CLOUGH, JR.

Working model of a ground-effect vehicle rides on a cushion of air from a model-airplane engine Tethered to a stake, the car will skim half an inch or so off the ground, around and around until it runs out of fuel WITH A hollow whistling note audible over the whine of its tiny engine, this advanced working model of a ground-effect vehicle skims across the floor supported on a cushion of air. What makes it go?

is a model, which can buzz along at a good clip Air is supplied by a prop to a peripheral slot, on any level surface with a minimum of sideslip which produces a high-speed wall of air around due to minor irregularities on the surface. the edge of the model to retain the lift. A Attached to a tether it will whiz merrily around in separate propulsion-system tube bleeds off air a circle until the fuel runs out. It rides a half-inch for reactive propulsion---from the blower section, or so off the floor even when running free. Any not the skirt. Supporting pressure is not reduced small airplane engine can be used to power it. If --- a major fault of ground-effect vehicles which you use the engine installed in the original propel by dumping air pressure and lifting the model, which is supplied with a three-blade skirt on the opposite side from the desired prop, you won't have to make a prop of sheet direction of travel. Stabilizers on each side act metal, a pattern of which is given. If the engine somewhat like the dihedralled wings of an is new, break it in by running on a test stand for airplane— if the model tilts to either side, air 15 or 20 minutes. pressure escaping from the skirt builds up under the vane and returns it to even keel. The result Top and rear views above and below show the engine mounted in the intake duct and the propulsion tube outlet at the rear. Note the wire hook on the door for tethering.

A squeeze bulb feeds fuel through the plastic fuel line connected to the tank. The dry cell plugs into the phono jack

First study the cutaway drawings given to become familiar with the various parts. Then begin construction by making up the base, top and diaphragm plate from edge-glued 3/32-in. balsa sheet. Use stiffeners where shown and allow to dry on a flat surface. Make up the 3 1/2- in. intake duct from art paper and use this as the first structural member to hold the top and base use this as a guide in centering the engine. together. When dry, add the 3/16-in. uprights, Actual installation is made by cementing the which form the supports for the side covering. diaphragm plate to the stators. Use a slow Next install the paper propulsion tube. Note the drying cement to allow time to even up the slot vane to direct airflow within it. around the skirt and center the engine shaft. The skirt is vertical grained 3/32-in. stock Run out the fuel filler tubes and engine lead glued around the bottom edge of the base. Use out wires and make up a needle valve extension basswood or balsawood and there will be no shaft. The glow-plug wires lead to a phonograph difficulty in making the bends. Cover the jack---a great convenience in starting. A recoil framework of the car body with art paper, one spring starter is a must and is installed before section at a time, beginning at the rear. Add the prop. dummy headlights and fin, stabilizing vanes and A length of 1/8-in. cord is cemented around handrails. Windows may be glazed with sheet the skirt as a buffer. (A round shoestring works acetate or left open. Finally turn the model over very nicely.) Suspend the model by the engine and install stator vanes. Coat the interior with at shaft and balance it so that it hangs evenly. least two coats of hot fuel proof dope (clear). Small bits of solder, coated with cement and Dope the exterior in your favorite color. The dropped inside the body on the light side or end original was painted light blue outside, fire red will do the trick. If tethered operation is desired, inside. cement a wire hook through the covering to the Make up the engine pedestal, mount the engine upright on the centerline. and cement the pedestal to the wires to the glow Scanned from: plug. Cut out a 3 1/4-in. disk of cardboard and Popular Mechanics Do it yourself Encyclopedia

MODEL CAR RACING AT ITS SIMPLEST

Deceptively simple in appearance, every line on his car has been carefully planned to make it easy to build and maintain and fun to race

By ROY L. CLOUGH, JR.

WIND WAGON • Here is the perfect project to absorb your old nothing flat. three-port .19-.29 engine that still has a few kicks Begin construction with the chassis. This is left in it despite being outmoded for flying use by carved from white pine or equivalent. The wheel newer and hotter engines. axles are 1/8" steel landing gear wire. It is not We wanted to find out if a really good air-drive difficult to drill holes in the chassis for these by car could be built to look like a real race car and hand if care is used, but a drill press makes the not a runaway fuselage. The results were job a cinch. Don't try to drill all the way through surprisingly good. With an old O&R side-port .19 from one side; drill in from each side so the holes it hit a zooming 62.8 mph. Even a beaten-up .14 meet in the middle. Note how the axles are held diesel engine kicked it up to 40 mph. This by soldered washers. It is not essential that the compares very favorably with wheel-drive cars, axles be held so firmly they cannot rotate, but and Wind Wagon is a lot simpler to operate and there should be no end-play. Do not put the cheaper to build. wheels on yet. The plan should be followed fairly closely. The body is carved from soft pine. Some Making an air-drive race car is not just a matter originality of line is permissible here, but don't of sticking a motor and prop on a wheeled depart too far from the plan and be sure the platform; balance and dynamic loadings are thrust line comes as shown. The motor mount is important. There are a couple of angles designed 1/2" plywood, cut to fit your particular engine. into this one which are essential to good Chassis, body and mount are assembled with 1- performance. For example, the wide under- 1/2" flat head wood screws and good wood chassis is not a matter of taste in style, but is glue—do not use model cement. The cockpit made that way to create an airflow pattern to details add realism. The driver is a ping pong prevent fine abrasive dust, present on concrete ball, painted to look like a helmeted head and the surfaces, from being thrown up to the engine rim of the pit is padded with heavy twine intake; the washer arrangement which holds the cemented in place. The fuel tank can be anything model plane type wheels came about because handy that suits the engine. Several types have other arrangements wore out aluminum hubs in been used on the original and all worked well provided the usual U-control fuel feed to the outside was observed. Be sure it is anchored We found that maximum speeds came from firmly. careful selection of propellers and by setting the Next bore a ballast hole, put in the screw- car off a bit rich so that it would start to lean out eyes and bridle and make a trial fit of the engine by about the tenth lap—presumably because the and tank and check the balance. The model rich start prevented the pusher engine from should hang the slightest trifle nose-down when overheating before the car got going fast enough suspended by the bridle, so pour in melted lead for the slipstream to provide sufficient cooling. or old bearing metal to balance. Pull the engine While this vehicle will never set the world on and tank and finish the model with fuel-proof fire from either the appearance or performance dope or enamel—incidentally, it seems easier to standpoint, it does bring auto racing within the clock a bright-colored car. reach of the average miniature engine owner When the paint job suits you install the who may not have access to a lathe or the other wheels, using the washer arrangement shown to specialized equipment so vital to AMRCA minimize wear on the hubs. Install the motor and followers. tank and check it over to make sure the wheels By limiting a group of racing enthusiasts to spin freely and track and foot well. Put a little #50 same size or maximum power plants any hobby oil on the axles every other run and clean them shop or model club can come up with a fleet of off whenever they seem to be picking up dirt. cars in jig-time for some informal, strictly-for-fun Because the engine is pushing instead of racing. Almost any smoothly surfaced parking lot pulling you must now check the shaft end play to will suffice (school yards frequently provide the make sure the push doesn't move the shaft in so type of running surface most desirable). A far that it puts a strain on the connecting rod or portable center post sandbagged in place and allows the crank throw to strike the back of the mounting a skate wheel well bolted to a sturdy crankcase. Usually on such engines as the O&R timber or piece of piping is about all that's .19 and .23 side-port jobs the hard steel propeller needed for "Sunday" drivers. A steel wire back plate running against the end of the bronze connects from the pivoting center piece to the car main bearing is all the thrust bearing required. If, bridle; be super sure that your lines are all of however, there is considerable end play, or gap, sufficient size and free of nicks. fill this in with thin brass or surface ground steel As with all projects presented in this shim washers until the play is just perceptible. Do publication, the editors welcome your comments not run the shaft tight and be sure to oil the and photos of completed models. Let your fellow shims well before the first run—see page will hobby fans see your handiwork; send along your take care of lubrication after that. model pictures

39 Air Trails HOBBIES for Young Men

By ROY L CLOUGH JR.

Unique gyrocopter-kite design

launches itself without towing,

costs less than $1 to build

HEN there's not enough room Wto run with a kite or too much wind to fly model airplanes, it's a perfect time and place to test fly this newly designed rotary-wing kite. All ma- terials you'll need are available at your local hobby shop and in one evening's time you can have your 'copter-kite ready to fly. First, layout the fuselage, stabil- izer, rotors, and vanes (Fig. 3) on balsa stock and cut them out with a sharp hobby knife or razor blade. To shape the rotors and stabilizer, first crack them along scored lines as in Fig. 3A, then fill the crack with cement and prop up the end of the part until the cement dries. Note that the rotors are not identical, but are a pair, having opposite pitch for counter- rotation and are oppositely coned. Now cement the stabilizer and landing gear support (Fig. SB) to the fuselage, reinforcing the joints with a fillet cut from the 1/4-in. balsa stock. Next cut the rotor mast from coat hanger wire and cement this to the right side of the fuselage, 12 3/4 in. from the aft end. Rein- force by sewing it to the balsa with a needle and heavy thread, then coat the threads" with more cement. After installing the eyelet MATERIALS LIST—WHIRLYBIRD KITE to which the tether attaches, sand Amt. Req. Size and Description Use the assembly with fine sandpaper 1 1/8 x 3 x 36" sheet balsa rotors and paint as in Fig. 3C, with model 1 1/4 x 3 x 20" sheet balsa fuselage 1 1/16 x 3 x 20" sheet balsa vane, stabilizer airplane dope. Do not apply dope 1 1/8 x 3/4 x 5" pine or basswood landing gear support to the rotors or vane. 2 1 1/4" Dia wooden wheels main wheels 1 3/4" Dia wooden wheel nose wheel The rotor bearings and hubs 1 10" x .030 wire axles (Fig. 3D) are made of 3/4-in. 1 9" length coat hanger wire rotor mast 3 #6-32 brass hex nuts rotor spacers lengths of tubing soldered to strips 1 3/32" id brass washer thread washer of tin can metal. Make two of 2 3/32" id x 3/4" brass tube rotor bearings 1 2 x 4" tin can stock rotor hubs these, form them over the blades, 2 3/16" id brass eyelets tether eye and cement them to the rotors as Misc. model airplane cement, red, black, and silver dope; and kite string in Fig. 3E.

74 SCIENCE and MECHANICS

Layout the motor mounting holes on a 3/4" disk of tin can stock, punch or drill them and solder the disk to the lower end of the tank. Next mount the engine with common pins, which are bent over and soldered securely in place. While doing this, care- fully check the alignment of the crank- shaft with the tank and the stud. A bit of 1/16" rod is soldered to the tin disk opposite the cylinder, the end of this be- ing wrapped with a few turns of tinned copper wire to serve as a counterweight. The counter-weighting may be done very exactly, as follows: wrap the wire on fairly tight until it seems correct; then slide the wrapping a bit one way or the other for fine balance. When you find it, heat the end of the rod briefly and the wire will "tin on" and stay put. Drill a new hole for the feed line near the top of the tank and on the opposite side from the filler valve. Solder the line in place carefully, to prevent leakage. The big rotor is made from a good springy variety of balsa, which may be finger-doped for added toughness. It is of left-hand pitch to permit the inter- change of various easy-to-obtain right- hand propellers on the motor end. We have used the Hillcrest adjustable plastic- blade prop and also Monogram kit props with fairly good results but top perform- ance will come from a wood propeller carved to fit the individual machine. The fairly small total area of the rotor system by ROY L. CLOUGH, Jr. results in a rather rapid descent, but is necessary because the engine must turn ONE evening of fairly intensive work of cellulose tape which can be flipped over up quite rapidly in order to develop will put this little whirligig-type the filler hole after charging, to keep dirt enough power to fly the machine. There helicopter aloft. out, is good performance insurance be- is, of course, a very favorable heat-ex- The construction is quite simple and cause of the exposed nature of the model. change setup because of the rapid motion offers no problems to the builder who is Begin construction by unscrewing the of the cylinder through the air as the handy with a soldering iron. Good balance filler valve. Put this in some safe place tank rotates, but set the motor at near without excessive weight is the primary until again needed, taking care not to lose maximum output to get the best results consideration, and care along this line will the tiny rubber plug which serves as a altitude-wise. One word of caution: be result in good flight performance. check valve. Unsolder the feed line at the absolutely certain the motor is running A Campus Bee was used for the origi- tank end. A 2-56 or 3-48 stud, an inch in the right direction when released! nal and proved to be very reliable. A bit long, is tapped, and then soldered in the hole.

34 MODEL AIRPLANE NEWS • April. 1950 WHAT'S THE SCORE ON helicopters?

By ROY L. CLOUGH, JR. • Easily the most fascinating thing that thing look so impossibly flies, the helicopter is making a name for complex that there seems to be itself in peace and war as the marvelous little point in trying it at all. The machine that can land or take off envisioning of complicated anywhere, hover over one spot or controls, pushrods, flap hinges, tuck its nose down and scoot away in dampers, complicated power any direction the pilot chooses. transmissions, hairline It is only natural then that model adjustments and impossibly builders have been attracted to the complex and delicate structures type, for here is a flying machine which places the designing and does its stuff close in where it may be building of a successful free observed and enjoyed, does not require flying model helicopter on the huge tracts over which to fly, and which level of a major engineering should give more solid hours of model feat—so the modeler puts the fun than anything ever invented. whole thing aside and starts Or so it would seem at first glance. sketching a new pylon job. However, as many a model builder The truth of the matter, as in who has tried it will testify, it isn't most cases, lies somewhere quite that simple. between the two extremes of To some who have tried it, at first it utter simplicity and impossible appears a rather straightforward complexity. A fair statement of proposition—merely arrange a prop to the case is that a good model pull upward, provide some method of helicopter is no more difficult to torque nullification, presto, there is a build and fly than any other type helicopter. And several bitter of fairly advanced model aircraft. disappointments later, the model What may appear to be builder sweeps up the shattered balsa difficult at first becomes at wood, lays aside his tools and tries to second glance merely dig up some information on the type. different. This is because there is Roughly speaking, the differences are In many cases a study of the very little in the way of carry-over of the same order as those between problems involved makes the whole analogy from fixed-wing models. building a hot engine into a speed job and building the same engine into a boat. The principles are approximately the same, but the factors are different. Helicopter information, in the empirical form in which it is most useful to model builders, has unfortunately been neither complete nor widely available. Therefore the design picture has been a bit clouded. Any up-to-date aviation fan, if he scratches his memory a bit, will recall having read that "articulation" is a good thing, that helicopters are inherently "unstable," that there are a great number of things like "cyclic" pitch and gyroscopic precessive forces to be dealt with. All of which contains elements of truth, yet just how these things apply to sitting down and actually building a flying model helicopter has been obscure. The writer scored considerable success in rubber-powered helicopter models with his development of the cage drive co-axial system, which allowed two rotors to revolve in opposite directions about a common center, thus canceling out both torque and gyroscopic effects. With this system, which first appeared in Air Trails some time ago, incorporated into the model, stable power-on free flight was possible for the first time winder-wound. Later a further development, a kit without the use of complex control However, these flights were very design manufactured in limited arrangements. Extremely steady in largely vertical; it was not possible to numbers, featured a stabilizing or flight, the machine and a later secure any marked forward flight with "damper" fin which permitted a fair variation of it were capable of the machine, barring the use of degree of forward flight, with great rather surprising duration when extreme nose-heavy trim. steadiness and every indication of stability. So consistent was this type that by counting the number of turns stored in the motor the model could be flown from one table-top to another, time after time alighting within an inch or two of the desired spot. Several further variations of this machine were built, performing well. Now, note that no blade articulation of any sort was used in these models. There was no provision for cyclic, pitch changes and gyroscopic action did not enter the picture. Yet they flew very well under rubber power. Keeping that empirical fact in mind, let us further examine the co-axial system. This system—meaning two rotors revolving in opposite directions, about a common center—is one of the oldest designers' answers to the question of what to do about torque reaction. Further, it appears to be ideal in many respects because it would seem that any disturbances, either aerodynamic or gyroscopic, which occur in one rotor would be balanced immediately by the reverse possible to stress the system all out of that the rubber models actually made of that reaction in the other. Now proportion to its size—models and tiny use of the oscillating tendency of stiff then, why, if this system is so man-carrying jobs. rotors to secure forward flight and that theoretically ideal, with equalized thrust, Now, what is this business about they were successful in doing this cycling and gyroscopic moments, has it cyclic pitch? Did we not just describe because the oscillation was damped at not appeared in any machine which has rubber models, which flew well without it? proper time by the motor running out. demonstrated itself to be of practical Why not merely eliminate cycling pitch Or, to put it a bit differently, the co- commercial importance? from the co-axial system and fly forward axial rubber model helicopters with by shifting the C.G. ahead? damper fins as developed by the writer The rubber models did fly forward by were simply highly modified co-axially means of the stabilizing fin and C.G. driven planes flown vertically. Have you shift. But don't overlook the fact that a ever seen Jim Walker do the Saber rubber model flies with continuously dance? The principle is the same. diminishing power after the rotors come Thus, to fly forward in a co-axial up to speed. This is very important machine, as in any other, requires that because it meant the writer could the pitch of the blades decrease in front eliminate cycling controls because of a and increase at the rear of the rotor characteristic of the power plant. Just disk. And, since we must be able to why this was so may be explained as control the pitch of the rotor blade follows: around the circumference of its sweep, Picture a purely hypothetical co-axial we may as well abandon the co-axial model helicopter in which the thrust configuration and its power transmission The answer lies in the fact that co- does not vary, which has stiff, fixed-pitch problems and go over to something axial systems have two major rotors, and which is trimmed nose simpler, the single rotor and torque requirements, and, from a practical heavy to make it fly forward. All set? prop. Either that, or power the rotor standpoint, these requirements tend to The machine, because of the unequal itself by means of tip jets or motors be mutually exclusive. loading of the disk (area covered by the which eliminate torque effects entirely. First, it is desirable that the two rotors rotors) begins to slide forward. It will not For most model work, and at this be mounted close together. The reason tip to either side since the advancing stage of the game, we will find the for this is that widely spaced rotors blade of one rotor, creating more lift as torque prop type more practical, since introduce great stresses in the mast and it encounters a relative wind due to this gives us a heading and trim control rotor system when the blades are cycled forward motion has a balancing and the boom helps to round out the for forward flight, that is, when the blade counterpart in the blade, which is design by balancing the weight of the angle is increased at the rear and rotating forward on the opposite side. power plant, which will be forward in reduced at the front each revolution of This, incidentally, is a major advantage most cases. the rotor. The uppermost blade will of the co-axial configuration. Which means we promptly dive head require a greater pitch change than the Now, as the machine gains speed first into the rotor head business—but lower blade in order to equalize the we find that the front edge of the rotor don't let it scare you. couple between the points of applied disk is entering the wind while the rear The earliest successful helicopters force and the center of gravity. Thus, if edge is leaving it. This means that the used a refinement of what is known as we wish to avoid excessive stressing of rotor is lifting more at the front than at the flapping, drag link rotor originated by the rotor and mast system, the rotors the back, and it will tilt upward, moving Juan de Cierva, the autogiro inventor. must be quite close together. the machine into what is actually a To Cierva's basic invention were added Second, the rotor blades of a co-axial stall—one of the few analogies which mechanisms to secure collective and machine must be spaced with a large occur between fixed and rotating wing cyclic pitch control and with such an gap from one set to the other because craft. Now this will happen no matter arrangement the first man-carrying otherwise they may clash together due how much weight is placed in the nose, machines flew. to the flexibility of the rotors. Blade consistent of course with the ability of This system (Fig. 2) makes use of a deflection due to gusts or even normal the machine to lift it. hinge between the blade root and rotor cycling pitch changes is great enough, Now, when this stall occurs, the mast. This allows the blade to flap up ordinarily speaking, to make any helicopter will slide backward and down relative to the plane of spacing of the rotors less than one increasing the lift at the rear of the rotor rotation and was originally introduced in third rotor diameter apart definitely disk until the model stalls tail up, the autogiro to permit the machine to fly hazardous. Thus, the rotors must be far whereupon it repeats the trick, forward without tipping over due to apart. oscillating back and forth with relative wind differentials. From these two requirements it can increasing amplitude and violence until Soon after this was invented it was be seen that the only way out of the it finally crashes. found necessary to add another hinge problem is not actually an "out" at all, for The reason the rubber-powered which would allow the blade to swing it will mean building the rotor systems models flew steadily ahead under C.G. fore and aft, since, as the blade coned impossibly heavy and rugged and thus shift is that the power gradually upward on the advancing side it would losing many, if not all, of the decreased as the machine flew forward tend to lag behind the retreating blade, advantages of the co-axial system. In and the damping fin provided a thus setting up terrific stresses in the the practical sense, then, this means stabilizing surface, which served to flap hinge. This drag hinge then had to that co-axial systems are limited in use maintain the proper angle. Thus it might be fitted with a dynamic damper—a to such cases as where it may be be said with considerable accuracy gadget similar to the device which closes doors without slamming —to absorb the progressive tipping of his stiff four-bladed factor in rotary wing flight, and the jolts and shocks that such a system was rotor. This appeared in Air Trails.—RLC. reader will find it of value if at this, point heir to and to assure a correct nominal (To be continued in subsequent issue.) he takes the trouble to make up a small circumferential position of the blade. "understanding tool" and follow along This system is in wide use among full- AIR TRAILS SEPTEMBER 1952 with the text. scale helicopter makers but it has some (Continued from previous issue) Cut out a six-inch circle of heavy limitations in that it is not truly stable, cardboard and mount it with a pin although quite flyable with a competent This initial model was soon followed through the center in the end of a short pilot. by others, simplified greatly by length of 1/4" stock which has its sides As far as model helicoptering is eliminating the springs and mast numbered consecutively: 1, 2, 3, 4. concerned the system is of interest rubbers, and using thin wood blades This represents a rotor—and a chiefly as background material. In attached to a stiff spar and a flexible gyroscope. If you wish, mark the disk practice it proves tricky to build, fragile wire mast. Models built here and in with an arrow showing left hand rotation and easily misaligned, and it falls down England proved the soundness of the (most model helicopter rotors will be left on a most important model requirement system. Fig. A. hand in rotation because of mechanical in that it will not fly "hands off." The articulated rotor mast was fine for considerations which will develop later As a matter of fact, it is not even a autogiros, with due restrictions on the on). satisfactory free flight autogiro articulation to prevent clipping the prop First, flick the disk with the fingers to arrangement as the writer discovered or the tail, because it permitted the make it spin rapidly, then poke gently some years ago, and this lack of initial tilting, which starts the gyroscopic under the rim of the spinning disk on satisfactory flight characteristics started wobble, to* damp out without running the side of the stick marked 1. . What a series of experiments, which led into through a cycle of self-excitation back happens? The edge of the disk rises, not contact with a type of rotor arrangement and forth through the mast. But, for where you poked at it, but at 90 that would perform satisfactorily on an model helicopter work a flexible mast degrees, the side, marked 4. Repeat autogiro. seems impractical. the experiment, only this time - poke it at Initial experiments with articulated If rotation is supplied by the rotor, as 3. It rises at 2. What is happening? rotors on rubber model autogiros in the case of the autogiro, it will run Simply this: the deflecting force is resulted consistently in dismal crack- concentric and true if in balance. But, if modified by a factor of 90 degrees. ups at the end of erratic flights of a few one tries to feed power into the rotor This is the first rule: that a feet. Apparently the fault was somehow through a flexible mast the whole thing gyroscope, if deflected, reacts with a connected with the articulation that was will jump out of line and wobble violently displacement proportional to the supposed to promote flight stability. So with the whole system acting as an deflection at 90 degrees in the direction we committed heresy. We stopped eccentric. of rotation from the impingement of the articulating the rotor blades.* This was In the practical sense, then, this deflecting force. (Of course it also better, but still not good, and then came means that a flexible mast cannot be deflects an equal amount in an opposite the inspiration—why not articulate the used on model helicopters except, direction 90 degrees back from point of blades in some other fashion, so that possibly, where the propulsive force impingement, but we're trying to keep the effect would be the same, but the originates in the rotor, as for example, this thing simple.) big bounce would be taken out? tip-jet propulsion. With the understanding tool at hand Why not, instead of allowing the blade At this point the writer became this becomes quite easy to understand, to flap upward, allow it to rotate span acquainted with the work done by or think of it this way: if a rotor blade is wise— that is, instead of letting the tip Arthur Young, who designed the Bell deflected at one point in its fly up, let the trailing edge flap upward? helicopters, and this takes us into a circumferential travel, it will tend to pop A new rotor was built with the blades discussion of the so-called "feathering up 90 degrees further along in the spring-loaded against their span wise rotor" system in which the blades neither direction of rotation. axis at zero pitch, and since the rotor cone upward nor drag back, and in Now, spin the disk again and gently was stiff, tip-to-tip, the mast, which held which, for the first time, we begin to see tilt the stick. Note that while the the rotor, was jointed, or articulated to inherent stability introduced into rotary gyroscope initially tends to remain in the fuselage to prevent the wing flight. its original plane, it will now gradually transmission of disturbances back and In order to understand the readjust itself until it is spinning with its forth. Aerodynamic pressures would differences between the fully plane perpendicular to its axis (the result in the slight negative pitch angle articulated and feathering systems it is stick). If the disk were mounted on a necessary for autorotation, and a sort necessary to look a bit more closely at universal joint and driven by rotation of of automatic cycling pitch would be gyroscopics, the seemingly puzzling, but the stick this effect would be even more obtained as the advancing blade actually rather simple set of pronounced. flattened to the relative wind, which shenanigans which take place when a This occurs because it is a function of would flip the trailing edge down as the rotating system is disturbed. centrifugal force to' cause the rim of the blade passed in front and started back Any rotating system, and this disk to recede as far as possible from dh the downwind side. applies with particular emphasis to the axis, and this condition is satisfied It worked. helicopter rotors, is a gyroscope, and at. 90 degrees. *Louis Garami built a successful non- jointing, hinging or springing it will not These two related phenomena are of articulated, non-feathering giro at about make it anything else; it will still extreme importance to helicopter the same time which flew by using observe the natural laws which govern designers: first, a deflection reacts at 90 torque of the motor to counteract the gyroscopic action. This is probably the degrees; second, a gyro seeks rotation most puzzling and least understood perpendicular to its axis. Now remove the stick and take the Fig. B illustrates such a rotor. The control over blade pitch becoming disk outside and scale it through the air simplicity of the thing is its beauty. With ineffectual and the drag of the system with a quick spinning motion. Note how it a little study of the sketch no reader will very high. tips over toward the advancing side. have trouble duplicating it. Note that the Note, of course, that it is possible to Two factors are responsible for this fly-bar is moved up level with the blades. use H series stable airfoils and behavior. The first is related to the This is simply a length of wire with a eliminate the trailers entirely; however, Magnus effect and is due to differing few turns of solder on the ends to if this is done the rotor system may pressure gradients on the surface of the provide operating momentum—not show a tendency to tip back in forward spinning disk, and the second, which is much weight is needed. flight, and cyclic control installation may our primary interest helicopter-wise, is Note that the function of the fly-bar is be more difficult. But for straight that the air pressure at the entering to steer the rotor blades back into the hovering or vertical flight this system is edge of the disk is producing a proper position with respect to the mast unmatched for stability. gyroscopic resultant at 90 degrees, thus through a damping interval, hence I have been asked, "How does the turning the disk over. cyclic control may be had by arranging Jetex kit helicopter work?" This model is Bear in mind these vital functions as the fly-bar in such fashion that it can be a good performer with a very fair we consider the requirements of a deflected into a new plane of rotation— duration for this type of craft and in flight stable helicopter rotor. One thing should but, very important, the fly-bar must not exhibits stability. If we examine the be evident, that forward flight produces be rigidly attached to the mast because machine we can find the answer. Two a problem in tip speed differentials, the this will cause rapid following; that is, the blades are used which are articulated to advancing blade in meeting a faster mast will tend to swing immediately the a supporting beam. These depend, as relative wind than the receding blade rotor is displaced, because the does the Cierva system, upon tends to tip the machine toward the independent nature of the system will centrifugal force to keep them at the retreating blade side due to, have been destroyed. proper angle in flight, without a rigid aerodynamic forces, but these In Fig. C we see a system developed connector. aerodynamic forces are balanced to a by the writer, which uses the Underneath the rotor is a thrust beam large extent by gyroscopic forces, independent rotor principle together with to which are mounted two Jetex engines provided the blades do no flap upward control "trailers" similar to the Kaman and the machine is driven by the or drag back circumference-wise and system. The advantages of this system reaction of these units. are free to rotate, within limits, about for model work is that it provides Now, please note that the mass of the their span-wise axis. automatic-rotation in addition to the jet motors is quite high in-regard to the And, if the rotor head is mounted in a stability of the Young system, plus the total mass of the ship; that is, it has a gimbal, rotor deflections will not be fact that cyclic control by trailer sort of high-momentum flywheel transmitted back and forth between deflection (only one trailer need be beneath an articulated rotor with the rotor and fuselage through the mast, connected) is very easy to arrange with mass of the pod, or fuselage being which means that the helicopter will be a line up through a hollow mast and out quite negligible. stable. By the addition of a stabilizing to a "loaded" trailer. Thus we see here a combination of fly-bar between mast and fuselage The other end of the line being the articulated blade system with the fly- connected by linkages, which can alter attached to a cam ring which may be set bar stabilizer, which operates well if we its plane of rotation, the rotor can be to produce the cyclic deflection at any confine activity to vertical flight. In made to take up any position desired by desired point. The drag of this system essence this machine is dynamically the pilot. is higher than others and it must be similar to the writer's little Infant job of a In other words, then, if we use a designed carefully if maximum lift is to couple years back, but being jet flapping blade with drag links we must be obtained, yet its many advantages powered it requires no damping fins or also include a device to alter the pitch make it attractive and it is certainly fuselage-rotor-mast brake to retain of the blades cyclically, mechanically; capable of much greater development, proper heading. but, if we eliminate the flap hinges and particularly since it is possible, with However, in its present form drag links and allow the blades to trailers, to make use of high lift sections forward, flight by changing the C.G. "feather" as it rotates, cyclic pitch is with less regard for pitching moments. trim will be found unreliable; the automatic in accordance with the gyro- This system is particularly attractive machine isn't designed for that sort of dynamics of the system. for jet work, and it should be noted that thing. It should prove a very interesting This basic discovery about the by placing the line of thrust of the jet experiment to move the power beam helicopter rotor was made by Arthur D. motor a bit below the center of the up level with the rotor blades, and Young of Bell helicopter fame. In this span-wise hinge the blade pitch will be rebuild the rotor along the lines shown in writer's opinion, based on literally controlled by the thrust output of the Fig. B. This should produce a model scores of experiments with flying engine. However, this factor must be capable of forward flight, as well as models, this discovery is one of the great used judiciously because too great a vertical, but the problem of auto- aerodynamic advances of the century. moment here will result in the blade rotational letdown will have to be solved Not only for the mechanism which mushing around slowly at a very high with some new mechanism to alter Young worked out, which is remarkably pitch, which will produce no lift at all. blade pitch. Also it may prove effective, but for the principles his work Remember too that trailers, in necessary to introduce a small amount outlines, which it is not extravagant to operation, should drop down into the of friction between the motor-fly-bar and state mark the greatest single rotor plane— don't seek to drive them its gimbal connection to the mast in contribution to rotary wing flight. either above or below the plane, since order that adding weight to the nose will From these principles we can arrive at this puts them at a great, mechanical make it go forward and not just alter the a stable rotor for model helicopter work. disadvantage and may result in their angle of dangle of the fuselage from the In general, then, we may sum it up as rather well, because design rotor. follows: It is better to use a shallow pitch considerations necessary for power On the basis of experiment the writer and run the rotor at a good clip; make location, landing gear, lateral areas, suggests that configurations for first the blades of high aspect ratio—and thin etc., work out so as to make it possible experiments be kept as simple as section. Be sure the pitch is equal on to locate the torque prop axis well down possible. The first helicopter should be both blades; mount the torque prop as out of the way. rubber powered, something along the far aft as practical—it will absorb less Assuming a left hand rotor, it will be lines of a simple stick model, probably power, and keep the design of the model noted that if the axis of the torque direct drive. It won't fly for very long with as simple as possible and the bearings prop is too high the machine will fly this limited power, but it can be fooled as near perfect as you can get them. sidewise to the left, and if the axis is too with indoors at great length and the There are several things to watch out low it will fly to the right. Properly rotor set-up ironed out. After you get the for. For one thing, the rotor blades located, the model shows no tendency "feel" of the rotor set-up and a bit of should be quite stiff. Balsa wood if hard to slide off in either direction. experience in handling rotary wings, try is pretty fair, but pine or even birch is This is a very happy circumstance something in gas or jet power. better. Because of the thin sections, because it means that by combining a The best bet for gas engines is the which must be used, and the high rotor few factors, such as level of the torque single rotor, or tandem rotor type—like speeds, an overly flexible rotor blade prop-axis with C.G. we may make a the Piasecki jobs with a rotor at each end may develop "whip" due to resonance. model of very simple design fly in any of a long fuselage. Coaxials, or rather This will make the blades run out of desired direction without a separate composite rotor jobs, such as the track, absorb a terrific amount of cyclic control mechanism. writer's little Infant machine, are very power and may result in tearing the This statement reads rather simply, simple and okay for direct vertical model apart, particularly if a whipping but go back and look it over again, for it flight, but they won't do well in forward blade connects with the drive string to contains the essential elements 'of flight and will return to earth with quite a the torque rotor. practical model helicopter flying in that thump unless some free-wheeling Some of the writer's early models we see how that adjustment of the arrangement, other than spin-in-reverse used exceptionally flexible blades model helicopter, and the mechanism is used. without articulation or feathering to make that adjustment possible, are Better than freewheeling, which will features, yet flew. How? By adding not a complicated mess of pushrods, mean pitch change too, is engine two- quite a bit of weight to the tips. Thus as cams and levers, but are in fact no speed control. Have a timer rigged to the rotor was spinning up for take-off as more complicated than the adjustment drop a partial obstruction into the the model sat on its wheels a of an ordinary free flight model of the venturi after a certain interval. This will gyroscopic plane or reference was conventional type, and in many ways bring the model down under power, quite established which held the model fairly simpler. gently. The really ambitious may use steady for the brief duration of the And, incidentally this is no spark ignition in conjunction with timer rubber power. condemnation of cyclic controls, as control—but watch the weight. It takes This won't work well if power is such, for they have much to offer the power to fly helicopters. continuous, as for a gas motor; the purist and the researcher. However, and It is impossible of course, in a 2-part model will gradually tip over a bit to analogically, the writer must point out article to cover all phases of helicopter one side and then jump violently at 90 that we do not find it necessary to build design. However, it is quite possible and degrees. The reason for this behavior is operating ailerons, rudder, elevator and the writer hopes he has been successful that a sort of cycling occurs due to flaps into a conventional free flight in this respect, to outline some primary blade flexibility, at the first small tilt, and model in order to enjoy it essentials. In answer to the question, this condition is rapidly excited back and tremendously. then: "What's the score on the forth until something disastrous Power transmission may scare the helicopters?" the reply is this: you can happens. uninitiated at first, particularly the bevel build them and fly them successfully if With single rotor and torque prop gear drive shown in one of the you understand the basic dynamics. models a change of heading may be pictures. It shouldn't. It does present a In this report are shown two stable noticeable immediately after jump-off. new problem, true, yet a simple drive of rotor designs. They work, they have This may be only a few degrees or a this nature is but the work of a few been flown, they do not hop and jump quarter circle, even if the balance of minutes to produce, requiring far less madly about and there is no element of thrust is correct. The way to minimize effort than the control system of, say, a luck about it; they can be duplicated by this is to hold the model for a second or team racer. any average modeler who will take the two to allow the rotors to come up to The gears are readily obtainable in time to understand just what forces are speed. For gas jobs use old friend any toy store; for 20 cents two toy involved and how they react. If, in times "stooge" to hold the model down until eggbeaters yield six gears, four small past, the reader has tried unsuccessfully ready. and two large ones. You can't even buy to design his own, or has purchased kits Theoretically the axis of the torque a good bell-crank for that. There are which did not perform as well as prop should lie in the plane of rotation dozens of ready sources of small gears, expected, he should re-examine his of the rotor. Practically it must be toys, old alarm clocks, etc. Fuel line experience in the light of the material he somewhat below this plane. This is due (brass) and landing gear wire takes has just read, make a couple more to fuselage effects, aerodynamically care of the shaft and bearing problems experiments and decide for himself that speaking, and to the mechanical nicely and adequately. practical model helicopters are not consideration that we must keep the To drive the torque prop use balsa only possible but downright fascinating. prop drive string (or shaft) well clear of wood pulleys faced with #1 sandpaper the rotor tips. Empirically it works out and a string belt. About 2½-to 3-1 is a practical ratio and slippage with this produce longer and better flights. It shelved in the interests of simplicity; use system is nil. won't. Power requirements will be flat blades of uniform pitch until you Gas power requires heavy reductions tremendous, which means a thicker build up a little experience at helicopter in speed and some sort of shock clutch motor will be required, meaning more flying. or take-up may be necessary if any weight, meaning it can't be wound as The sketches show general considerable weight or power is to be many turns, meaning a great deal more proportions and sound design practice. used. We hope to cover this phase power will be needed for torque Stick pretty closely to these layouts, at more fully at a later date and show correction—a vicious circle that adds least for your first machine, then strike some simple gas motor hook-ups, up fast. out on your own. which require no machining or difficult Rotor blades should be of fairly high work. density, thin in section and operated One pitfall to avoid is the idea that a fairly fast at low angles of attack. For large, high pitch, slow moving rotor will the present, helical pitch should be

ROY L. CLOUGH, JR.

AIR TRAILS SEPTEMBER and NOVEMBER, 1952

Water Bug By ROY L. CLOUGH, JR.

INSPIRED BY those little aquatic insects called "water striders," this unusual model boat flits along the surface of the water on three flipper shaped planing feet mounted at the ends of long legs.

Although it travels fastest on calm water, Water Bug can run through 4 to 5 in. ripples— the scale equivalent of 5-ft.waves---with no trouble. The struts simply slice through the wavelets and keep going. The boat is very remember to soak the sheeting, which covers stable and can be run with a guideline or turned the front section in hot water before bending. loose in small ponds where recovery is easy. Finish the boat with a couple of coats of sanding The original model showed no tendency to trip sealer and one of dope, or cover the bare wood or tip over, even with the rudder bent sharply for with a layer of lightweight model tissue laid on free-running turns. with heavy dope. The motor mount is a disc of plywood pinned The hull is a simple box structure of 1/8-in. and cemented to the rear leg. Drill for the engine sheet balsa. It should offer no problems, but mounting bolts, set the engine in place and build up the fairing on the rear of the bulkhead with scrap balsa left over from the hull planking.

Don't worry about access to the rear of the bulkhead to tighten up the nuts. If built-in blind this way, they'll stay put. The thrust line of the motor should be almost parallel to the bottom of the boat, but pointed slightly downward.

Cut the planing feet out of .019 sheet metal, then make up the holders and rudder and solder them to the feet at the angles shown. Attach the feet to the struts by lashing and cementing securely. Finish off the model with scale radio masts, running lights and foghorn. A couple of screw eyes are used for the restraining bridle. If you use a tether, attach it in such a fashion that the boat dangles level when suspended by it.

If you don't have a model boat basin with tether post, you can run Water Bug off a spinning rod from a rowboat.

To launch the boat hold it by the motor mount and give a gentle push. It should climb out of the water in about 6 ft. with an immediate increase in speed. If it doesn't, turn up the front edges of the forward planing feet slightly.

Scanned from: Popular Mechanics Do it yourself Encyclopedia

'TYPHOON-STEAM OR AIR EXPANSION ENGINE By Roy L. Clough Jr.

Of all the gadgets a hobbyist fly a plane with it. aside. can make, few offer greater kick Crankshaft is built up from than a homemade steam engine length of steel rod, threaded that really hums along smoothly. into heavy brass washer and Usually, however, making even a soldered. simple oscillating type engine Bearing is any handy bit of entails considerable machine brass or copper tubing, which work, lots of know-how and fits or can be reamed to size. experience—which keeps many Cut hole in front case and from trying it. solder it in. Make up wrist- This little expansion engine, pin bracket from scrap of which runs beautifully on air or .024 stock and set aside. steam pressure, was designed Find two bits of brass tubing especially for the hobbyist who for con rod bearings, one to fit would like to try this phase of Despite its extreme simplicity machine screw (around 6-32 model building with good the engine is very efficient and size), which forms crankpin. assurance of success, without a powerful, due chiefly to unique well-equipped machine shop at valve system worked out by the his disposal. author after much experimenting All difficult parts are adapted with rotary, ball valve and from readily obtainable things; oscillating cylinder engines. This the rest are odds and ends that system has all the simplicity of the everybody has kicking around. latter and none of its drawbacks. For instance the crankcase is Cylinder is stationary and made from a couple of catsup or valving is taken care of by chili-sauce bottle caps, the piston simple flat valve rocked back and and cylinder from an old fish-rod forth by means of slotted drive ferrule, bearings from odd bits over crankpin. of brass tubing. A little Feed line is flexible neoprene rummaging around in the scrap tubing, which moves with valve. On smooth board, box will probably turn up most Hunt up, or buy, a mating measure off con rod length of the rest in nearly finished pair of 9/16" fish-rod ferrules, and with appropriately sized shape. You don't have to stick cut to proper length and lap with nails hold bearings to board. very closely to the dimensions fine pumice and oil to smooth slide Then bend length of 1/16" either; just watch the fit. (Alternatively you may use brass or soft iron rod around proportions so you arrive at 9/16" tubing and turn a piston two bearings in shape shown enough clearance between the con from aluminum or brass.) Next on plan and solder in place. rod and cylinder sides at quarter- locate a couple of bottle caps of Melt a little solder into inside stroke. right size and cut out for of piston, heavily tin con-rod The completed engine fills the cylinder, which is then bracket, put rod in bracket, gap between gas engines and soldered in place in one. push pin through, then dangle clockwork drive for model boats, Other cap is cut back on bracket into piston, apply heat or if you're really ambitious and rim for about 1/4" to provide to piston until solder fuses. want to see what it was like back valve clearance and two 4-40 Drop piston into cylinder; in the compressed-air flying model bolts soldered in place to act poke crank pin into crankpin days, make up an air tank and as mounting studs. Put this bearing and screw lightly in

Typhoon Engine Now reassemble shaft cylinder head, a disk of tin can (Continued from page 26) and piston workings and metal or .024 brass, should fit quite place. Rotate shaft to check recheck for sticks or binds. well with a push fit. Then rotate for sticks and binds. Now Make up valve—but do not shaft so piston is at bottom stroke remove piston, shaft, etc. drill intake hole yet, just and carefully solder head in Make up a valve plate from rocker shaft hole. Put valve place. scrap of sheet brass, threading in place, holding with Attach 5" length of black and soldering valve rocker spring, washer and nut, and neoprene tubing to intake line stud in place and filing off rotate shaft to quarter-stroke (clear tubing is not even so as not to project in direction you wish engine satisfactory—steam hardens it against cylinder. Drill inlet to run. (Note valve can be turned and it works too stiffly for air) and hole. over at this point for left-hand put on flywheel or prop and apply Now wire valve plate to rotation.) a little pressure. A flip is cylinder in a couple of places With a scribe mark valve for necessary to start it, or else with enameled copper wire drilling through intake hole in simply rotate to valve "on" (which won't stick), line it cylinder. Then turn shaft 180° position for self-starting. If up carefully and run solder and make certain inlet hole is now everything works right, and it along both sides to hold in open, the edge of the valve having should, you may now solder rear place. Remove wire tie-down slid past it. Remove valve, drill case in place. Use lots of oil for and drill through cylinder wall marked spot, then with wood first few runs; when run in a bit, a through valve plate inlet peg in hole solder on short length few drops on valve plate and hole. (Doing it in this order of brass tubing for feed line. crankshaft bearing are sufficient. prevents distorting thin Polish valve face by rubbing Air pressure up to 100 p.s.i. cylinder tubing.) Carefully lightly on fine file, oil up and may be used, steam to 60-70 p.s.i. scrape off rough edges. reassemble the works. The

American Modeler — September I960 Try TURBINE

It's not too hard to convert your regular glow

plug engine into a passable jet power plant!

By ROY L. CLOUGH, JR.

The increasing importance of jet and rocket aircraft has focused interest on power plants which can be used to propel their scale model counterparts without the ear-splitting racket of a pulse jet, and with longer duration than is provided by current rocket motors. In an effort to achieve this, a number of builders have been experimenting with various arrangements whereby a conventional model engine is used to produce a jet blast. Although less thrust can be produced in this fashion with any given engine than that same engine would put out with a propeller, the results can often be satisfactory if the weight of the model is kept low due to the terrific power to weight ratio of small glow, plug engines. There are at least three types of possible piston-engine operated jet motors. These are 1) ducted fan, 2) pressure jet, 3) jets operated COMING ATTRACTION: scheduled for next "AT" by means of a positive displacement, or Rootes-type blower. is Roy's "Blow Bug" pressure jet basic F/F Since initial experimentation has been along the lines of the ducted fan system this type is best known. Basically the ducted fan is simply a model engine and propeller placed inside a tube. For optimum efficiency the tube should be so shaped that the ambient pressure is about the same on both sides of the propeller, or fan. This means that the ducted fan should produce a great increase in velocity of air flowing through it without producing a correspond- ing great increase in pressure. This is accomplished by proportion- ing the tail pipe and the intake pipe so that their difference in size matches the pressure/velocity of the air flow within each to the other, and by locating the fan in the necked-down portion between the two sections. In other words, the airflow behind the fan will be much faster than the flow ahead of the fan, so the tail pipe diameter will be proportionately less than the intake diameter, and the fan will be located at the transition point, or, where the air is speeded up. The sketch illustrates this. The reason for this proportioning is that pressures within the tube are functions of air velocity, and, the faster the air is moving, the less pressure it exerts on the walls. If we tried to build a ducted fan with the same diameter from intake to exhaust end we would find it very inefficient because the intake end would be operating at a much higher pressure than the exhaust end, the engine would tend to starve, race, and possibly overheat, and the thrust from the efflux would be small. The ducted fan obtains reactive propulsion by accelerating the column of air within it; it is the inertia of this column of air to being set in motion, which provides the thrust. Thus anything that impedes the flow of air within the system tends to reduce thrust. It is better, then, to have tail pipe a bit on the small side than too large, and, from the empirical approach, which is generally the best m model sizes, a variable area exhaust nozzle can be used to advantage. A very simple instrument which can be made from a two foot length of transparent fuel line and an oil bubble is helpful in determining pressures at various points within the duct. This is called a manometer. To work it simply suck up a slug of light oil an inch or two into the line and hold the other end first at the intake, then at the exhaust end. By comparing the behavior of the bubble in both positions a good idea can be gained of the pressure pattern. Even better, tap into the duct in several places and compare pressures. The tail pipe pressure should be higher than the intake pressure, but not a great amount higher, for ducted fan designs. Too great a pressure difference means that the fan is working against back pressure and is not handling all the air it can; which is in direct opposition to the basic philosophy of the ducted fan to move the greatest mass of air possible in the shortest possible tune. Simplicity is a great advantage of ducted fans, and of course, the tube can be used as the keel or central member of the airframe

AIR TRAILS 26 JETS for your Models

which supports the other assemblies. The tube may be con- which can be poked down the intake to flip the engine over structed of steamed sheet balsa or stiff hard-finished paper. will eliminate fiddling with strings or risking chopped The writer has found that aluminum foil makes the best fingertips to get the thing going. interior finish; being smooth and nonabsorbent it is easily The ducted fan motor works best in scale-type models wiped clean of oil from the engine. Stick it in place with hot flown at moderate speeds and may be used singly, as a fuel proof dope which has been allowed to thicken a bit The fuselage member, or mounted in external pods. If pod mounts necked down portion of the tube could mean making a are used, keep them as close together as possible. Some layout for each new motor built, but this can be avoided by adaptation to helicopter use is possible, but the bulk and building this portion using a dime store funnel for a form clumsiness of this type of model jet makes it less practical and trimming the section where it fits. The angle is just for rotary wing craft than our next consideration, the about right and the bother of laying out a conic section is by- pressure jet passed with plenty of trim allowance. The pressure jet system has not been widely employed in Standard practice with ducted fans is to angle the motor conjunction with model engines. This is quite a different supports to act as stator vanes to straighten out the airflow affair from a ducted fan The pressure jet consists essentially and reduce, or eliminate torque effects. In some cases it may of an impeller, or blower, which keeps a reservoir or plenum be necessary to add a vane or two to do the job. These chamber stuffed with compressed air, and from this reservoir should be adjustable to permit interchange of fans without lines are bled off to feed jet reaction nozzles which may be losing torque trim. located some distance away from, or at least angles to, the Small sheet metal "flower petal" fans are generally used blower. in ducted jobs, but try carving small wide-bladed props of Unlike the ducted fan, the idea is not to provide a large correct helical pitch for added thrust A carefully carved four- mass of air with velocity, but to supply a smaller mass of blader will move more air than metal fans A spinner is air at a relatively high pressure, to high velocity discharge another aid to accelerated flow Actually, the ideal ducted fan nozzles (or afterburners). would be a wheel-type plastic job with a well-shaped rim Pressure jet systems may use either an axial flow (propeller) to prevent tip losses and to provide a good flywheel fan, or a centrifugal blower, depending upon the general effect. Perhaps some manufacturer will read this and pro- layout and designer's discretion. They could also use duce one positive displacement blowers of the Rootes type, as Generally speaking, to get the most out of a ducted fan mentioned above. The chief objection to use of this type use as large a diameter as possible for any given model, blower is that there is none light enough for model use, and cutting down on the number of blades and pitch where in any event they operate at a slower shaft speed than necessary to maintain correct engine speed. Be sure to model engines provide, which seems to suggest infinite streamline the backside of the engine mount and lead-out complication, hence impracticality for our purpose. glow plug wires and needle valve extension for convenience Pressure jets offer intriguing possibilities for buried in- in operation. If the engine can be fueled and started without stallations, experiments with multiple jets, boundary layer using a removable section in the tube, so much the better. control, helicopter propulsion, etc. We may use a simple box An external fuel supply, or filler line, depending upon engine with a tightly fitting rotor for the plenum chamber and bleed used will simplify this part of operation, and a starting rod, off jet tubes wherever we wish. (Continued on page 69)

JULY. 1953 27 Turbine Jets (.Continued from page 27) Since high internal velocities are of less concern, This does not mean that extremely good performance internal streamlining of the system is relatively lies beyond the reach of our engine driven jets. unimportant within reasonable limits. We may simply Attention to the factors involved, minor adjustments, seal up a fuselage, or wing," and use it as the plenum care in detailing and improved operational experience chamber, locating the jets at handy points and placing can result in greatly improved thrust figures over what the air pickup, or intake, either at the top (at or slightly we are able to obtain at present. Such angles as variable behind the CG) the front, or split to the sides. Whether tail cones (in flight?), improved ram scoops and fans of we use axial or centrifugal blowers will depend upon improved design should be exploited more fully, and various considerations A centrifugal blower is good possibly the use of afterburners and the many problems where the air intake is "dead," that is, open to the they present can be licked inside of a ventilated fuselage, it may also leak less air A good rule for the experimenter to remember is that under high pressures. It can, however, be used in pod- the propulsive efficiency of any system is highest when type jet motors as shown in the sketch the exhaust efflux velocity most nearly matches the It is a characteristic of a centrifugal blower that air forward speed That is, the air should be blown rammed into it puts a load on the engine, just the backward about as fast as the model moves forward opposite of what happens with an axial or fan blower, Practically speaking, this means it is more efficient to which speeds up when rammed This means that in move a large mass of air at a moderate speed than it is applications where a centrifugal blower is to be used in to move a small mass of air at a very high speed, conjunction with ram air, the motor should run at its because moving the larger mass gives us the advantage optimum rpm under ram, which means it may race when of inertia. the model is not in motion. Since it is usually better to In the concrete application we can improve propulsion locate the engine within the plenum chamber to take efficiency in those systems where the exhaust velocity is advantage of its heat and exhaust gases this means that several times higher than the forward speed of the model it will operate in a supercharged condition by using augmenters, that is, devices which will The way a glow motor will wind up under such introduce more air into the efflux, increasing its reaction conditions may surprise the builder the first time he tries mass and slowing it down. it. Operating well above atmospheric pressure, the A tail pipe shroud, as shown in one of the engine really stuffs itself with air and water sketches, is a good way to do this. Another method, condensation and it can get very hot in the process. useful in ducted fan systems suspected of having low For this reason it is a very good idea to use cold tail pipe pressures is the simple clapper valve—a reed plugs and fuel in engines put to this use. of tough paper, which admits more air to the tail pipe if Pressure jets work to best advantage where its internal pressure drops below atmospheric mechanical advantage can be taken of their unique The essential thing to remember in designing engine- characteristics, one of the best applications being driving operated jets is that the basic problem is to put a gas helicopter rotors, where a stream of high speed air (air plus combustion products) in motion, in order to emerging from a blade tip can produce considerable get the opposite reaction (propulsion) produced by rotational speed and lift. For scale type models of doing work upon that selfsame gas. fighters they are not quite as good as ducted fans, except A good rule of thumb for empirical model jet design is where highly streamlined and fast jobs are to be used, "The greater the gob of gas you can grab, the less 'give' or where used in conjunction with a thrust augmenter, it's got and the more got you'll get " which we'll discuss in a moment From the above material the reader should be able to arrive at workable jet propulsion with a standard engine for his jet project As best thrust will not be as high with a propeller, so the weight must be kept down. But nevertheless, workable scale type jet models can be built and flown if a little attention is given to detail, and surprisingly "hot" models can be built by anybody willing to take a little extra care with internal finish and experiment a bit with intake and exhaust diameters Our interest in model jets is largely limited to such uses as scale model power-methods of the big ships, and for special model uses, such as helicopters, where, by sacrificing some mechanical efficiency we can do away with a great deal of mechanical complexity TRIAD...A Radial-Wing Flying Model

By ROY L. CLOUGH, Jr.

An interesting experiment in radial-wing ships, fact, turning and banking can be controlled en- this model is incapable of stalling out of a climbing tirely by warping the single aileron on this vertical turn. wing. Construction is extremely simple. The fuselage is built up of three sheets of 1/32" medium-hard balsa, all cut to the same shape. Stiffeners of 1/16" square balsa are cemented to the inner faces of these sheets. The nose end is reinforced with plates of 1/16" balsa, cemented on after assembly. Cut three identical wing frames from 1/16" medium soft balsa and install the 15 ribs, trimming a little from the trailing edges of the outer ribs to make them fit. Cover with regular model tissue and water-shrink, but do not dope. Wing design makes for speedy construction. The aileron shown on the plan is fitted to the vertical wing only. Other wings have landing wheels at their tips. A shallow groove cut chord-wise in the butt edge or root of each wing will make a stronger joint. Use cement liberally to attach the wings to the fuselage. The two lower wings, which take up the shock of landing, are reinforced with wire crosspieces as shown on the plans. DESIGNED with radially mounted wings as A notch in the elevator, reinforced by an found on some robot bombs, this novel model has additional thickness of stock, retains the rear rubber brought favorable comment wherever it has been hook. Mount a wide-bladed prop of fairly high flown. pitch and make test flights over tall grass on a Its surprising stability is due directly to the calm day. The sturdy fuselage permits use of a vertical wing. In straight and level flight, the two powerful enough rubber motor to give the ship a lower wings provide lift. Should the model tend skyrocket climb. to bank in either direction, the vertical wing will A nose wheel helps preserve the prop from exert lift and return the ship to an even keel. In damage. Performing much like a high-pylon design, the plane climbs to the right and glides to the left.

156 POPULAR SCIENCE SEPTEMBER 1946

WHIRLIGIG By Roy L. Clough Jr.

Two views of the whirligig in actual flight. Note the flexing of the rotors under power.

EXPERIMENTING CAN BE FUN WITH THIS VERY SIMPLE HELICOPTER PROJECT

THIS direct-lift model utilizes a simple motor tube is 1 1/4" in diameter and is a little, then true up the shaft with the and foolproof counter-rotational system constructed of either balsa sheet or stiff tube. That is, make certain the motor based on the familiar principle of the drawing paper. The thrust bearing is tube and the hollow shaft rotate in the contest "whirligig." located at the bottom of the tube and same plane. The upper bearing is an odd Due to the nature of the rubber motor consists of a pin-washer-bead piece of aluminum tubing, 1/4" long, hook-up the two rotors are constantly arrangement. This bearing should rotate slipped over the hollow shaft and mounted and automatically in balance with each freely but should have very little in the 1/4" by 3/8" crosspiece in the top of other, effectually neutralizing the torque "play." Strive to get the bearing as close the fuselage. It simplifies matters to put element without gearing of any kind. to the dead center of former "C" as the crosspiece with the bearing in it on at This model is the 73d helicopter built by possible. The pin-shaft is bent at this this point, because it is impossible to the writer and experience gleaned from the point to keep it from falling inside the slide it on after the tube-shaft is flared to first 72 is incorporated in its construction. tube, but it is attached to its crosspiece take a bead bearing. Counter-rotation is considered the best only after the fuselage is completed. The lower rotor hub is mounted next. approach to the torque problem, due to Cement former "B" into the other end Drill the shaft hole a little undersize and the fact that as long as some power must of the tube leaving a 1/8" rim to force the hub on the tube. If it feels a be used to offset rotor torque that power accommodate "A." If you have chosen bit loose, wedge it tightly with short might just as well be turned to drawing paper for the construction of lengths of toothpick. Apply plenty of additional lift. The length of a rubber the motor tube, dope it now for cement, let the whole thing dry for a motor is in any case limited (barring additional strength. Allow plenty of couple of hours, and go over it with the use of gearing) in a model of this time for the dope to dry before cutting cement again. Hundreds of flights on type and it is therefore essential that the holes in it for access to the rubber motor. the original model failed to loose a hub best possible use be made of the power The shaft, which turns the lower rotor, is attached in this manner. that is available. made from either thin-wall brass or After the rear prop hub is well set, Two-bladed rotors were used on the aluminum tubing. 1/8" O.D. The tubing flare the end of the tube slightly to hold a original because they may be placed in is split two ways for about 1/2" and the glass bead, the thrust bearing for the line with the fuselage making the model a split ends flattened at right angles to the upper rotor. Insert the propshaft rather "flat package" and easily portable, a tube. Now "soak" the tubing for at least through one of the access holes cut in the somewhat important factor in cramped city five minutes in dope thinner to remove all motor tube (tweezers are a great help) quarters. Three-bladed rotors would grease and/or dirt. If this is done no and slide a bead and washer and the upper probably be okay if you wish to try difficulty will be experienced in making rotor hub over the shaft. Use your favorite them. More power would be needed and cement stick to it. Push the tube free-wheeler. slightly less pitch would doubtless through the hole in former "A" (it The rotor blades are cut from 1/20" increase the soaring qualities of the should fit snugly), coat liberally with sheet and sanded over a bottle to produce model. cement and push the whole assembly a slight camber. Note that the angle of Start construction with the coaxial down into the "cup" formed by former the lower rotor blades is slightly more unit. Study the plans until there is no "B" and the end of the motor tube. than that of the upper. This is done doubt as to the action of the unit. The Allow a few minutes for the glue to set because the upper blade "bites" into dead air and the air forced downward by the Power will vary according to the weight The center of lateral area should be high, lower blade is already in motion. A of the model. Start with a double loop of otherwise the flat fuselage sides will act higher blade angle on the lower blade, 1/8" flat brown (four strands) and build as a fin, causing the model to spill over in theory at least, prevents compression it up from there. The original model at the top of its flight and descend between the rotors, and consequent in- flew well on this power until stepped upon upside down. The center of gravity stability. and re-built, after which another loop had should be as low as possible for the same The fuselage of the helicopter model is to be added to take care of increased reason. About 75 percent of lateral area built up of 1/16" strip, and is quite weight. The tailskid, which is not shown in should be behind the axis of the rotors; conventional, except for the sharp curves the photograph, was added later to avoid otherwise the model may fly tail-first in in the forepart of the longerons. If the the necessity of holding the tail up in "forward" flight. longerons are soaked thoroughly in hot position in ROG flying. The model Stub-wings, elevators, flaps, and whatnot water before any attempt is made to should balance 1/4" ahead of the rotor are just so much junk on helicopters. Any bend them into place, no difficulty will axis for straight vertical flight. Hand unnecessary object sticking out into the be encountered. Because of the light nature launching is accomplished by letting the slipstream of the rotors is a good bid for of the construction it will be necessary to ship take off from the hand with the instability. install internal cross-braces at the points nose pointed slightly downward. This Do not expect a model helicopter to turn marked on the plans. Where the landing model can be made to fly forward as it in performance comparable to a gear legs are attached on the bottom of climbs by adding a small weight to the conventional model of similar weight. Don't the fuselage it is a good idea to cover in a nose. The free-wheeler is to let it down forget rubber length is limited and that the couple of sections with 1/32" sheet easy. lift of the model is produced entirely by balsa. Tail fin is of 1/32" sheet. The A few pertinent facts on model rotating vanes. Good performance, cabin section is cellophaned in before the helicopter design should be mentioned at however, can be had as a result of careful balance of the fuselage is covered. The this point. construction and half-minute flights should original was covered with orange tissue The first and holiest commandment of not be uncommon with this model. If the and water-shrunk, not doped. Weight is an model helicopter design is: Rotor blades free-wheeler works smoothly, a certain important factor in a model of this type; absolutely must balance. Lack of balance amount of soaring ability will be noticeable try to keep it down. The top section of induces vibration and loss of power. if the ship gets caught in a thermal. Use the fuselage should be left uncovered until Vibration induces instability and the fresh rubber, as the model is hand-wound, the coaxial unit is mounted. The bottom of average helicopter is, by reason of the or go us one better and figure out a way to the tube is anchored to a 1/8" crosspiece principles involved, not overly stable to use a winder on this ship. Making the and the upper crosspiece is mounted begin with. Rotor blades should have a bottom end of the coaxial tube and the directly into the fuselage. Check and certain amount of "flex" to them. bottom section of the fuselage under it, make certain that no part of the rotating Rigid blades and instability are, in removable, might do this. tube binds on the inside of the fuselage. models of this type at least, synonymous.

AIR TRAILS OCTOBER, 1946 does not exist; there is always some THE MODEL 'COPTER friction in the pivots and gimbals which tends to position the blades at 90 By ROY L. CLOUGH, JR. degrees to the mast, but this residual friction is seldom much in a model) Therefore, we must build in a small amount of friction, either by making the gimbal fittings a bit stiff to begin with, or by providing a drag of some sort, which can be adjusted. When this is done the model will fly forward by simply changing the C.G slightly, since the reaction of the rotor, in seeking to justify its position with respect to the angle of the mast and aerodynamic pressures, will result in cycling pitch. This is the simple way of doing it and it works quite well for models. By judicious use of a small weight arranged to slide fore and aft, the model will climb vertically or by forward at a fast clip in satisfactory fashion. By reference to the previous articles, note that sidewise flight can be obtained by raising or lowering the torque prop axis, or alternatively the weight can be attached to a wheel strut Keep this trick in mind, later, when building gas Roy's Little Infant job (AT Sept. '52) in flight. Damper fins have been removed and rudder turned over. Model will fly steadily forward, descends via auto-rotation pitch changes. models, you may wish to position the gas tank in such fashion that the attitude Roy's continued research into the whirlybirds has of the model changes in flight; as for produced some fine models including the first truly example, take-off directly into forward successful stable co-axial type. This is fascinating stuff, flight with the speed decreasing as fuel is consumed and with let-down in In our previous series of articles, reference point, ruling the me of autorotation vertical. ("What's the Score on Helicopters?") rotation of the rotor. Cyclic control of the rotor is a bit the writer tried to present a simple basic Thus it becomes quite simple to more complicated, but not greatly so, understanding of the major forces design a vertical-lofting or hovering and undoubtedly it will eventually involved in a rotary wing flying model, by simply arranging the rotor to replace C.G shift control except in the machine. feather along its longitudinal, or span simplest models. This is particularly We saw that the problem of flight wise axis and by hanging the hub in a true when we consider the advantages stability largely resolves into integrating gimbal which permits a seesawing of such a system in contest flying. the natural gyroscopic forces of a action, and positioning the blades by A cyclic control system means rotating system with its aerodynamic means of a flyweight or paddle bar so having a control which can be moved to characteristics in such fashion that a they will not roll over or develop flutter secure flight in any desired direction, reaction by either tends to maintain the in a chord-wise plane A rotor such as without changing ballast, by altering the positional integrity of the system with this is said to be independent, for if all pitch of the rotor blades for a segment respect to the rotor mast. bearings are free it will rotate in its own of their sweep around the circumference This, in the practical application, optimum plane regardless of the of the "disc " requires a certain amount of position of the fuselage, or mast. The type of cyclic control we are independence between mast and rotor in This is fine for an indoor model where interested in for model work is the so- order to prevent immediate gusts are not a factor, and when it is not called "indirect" or reactive control, in displacements from setting up a chain desired to obtain forward flight. which the linkage is not directly reaction of self-aggravated wobbling, However, the completely independent attached to the rotor, but to an and a certain amount of rotor is not desirable, even for model intermediary point from which the rotor interdependence in order that control work, because it has no reference point is controlled. If we tried to attach the may be effected, or imposed upon the from which control can be effected. (In cyclic mechanism directly to the blade rotor, and that the mast shall serve as a the practical sense it is well to point out roots, and connected the other end of it that a completely independent rotor to the fuselage, we would find that this

28 AIR TRAILS would freeze the system, resulting in a stiff rotor and destroying the stability we gained by freeing the rotor from the mast in the first place Therefore we must control the rotor from some point not rigidly attached to the fuselage. With the Bell system, this is the Young fly-bar control (see sketch). To work this connect the fly- bar to the longitudinal pivot with a jointed lever which can be cyclically pulled inward at the joint, thus changing the angle between the fly-bar and the blades, for a segment of each revolution The reaction of the blades to this deflection gives cyclic control. The Hiller Paddle system (see "Rotor-matic" sketch) uses two short wings set upon a cross-arm, which is attached to the central pivot. The angle of these wings or paddles may be changed through a simple scissors type linkage, which is attached to a swash Tandem rubber job. Rotors are Young fly-bar type; Power transmitted through bevel gears at plate. When the swash plate is tilted the each end of long motor which equalizes thrust. Brake on one rotor permits forward flight. angles of the paddles change in rhythmic cyclic fashion with each revolution, and the rotor blades' reaction to this produces a longitudinal rolling of the rotor, which results as cyclic pitch. This system is very simple, as is the Bell, but in both cases avoid any considerable play in the linkages since this may result in excessive wobbling and erratic control. However, for most small models this may not be critical because of the strong damping effect (scale effect) present in models. As a footnote to these two systems we can add that it isn't strictly necessary to duplicate the control systems of the originals in order to get satisfactory Co-ax close up. Dimensions not critical, but if large version is built top rotor should be performance. Here is a simple dodge, hung In gimbal since tension of heavy rubber motor may not allow sufficient see-saw. which judiciously applied works most effectively Build the rotor, with its In an effort to develop a system, be the first truly successful, inherently paddle beam or fly-bar in the simplest which would lend particular emphasis stable, co-axial rotor arrangement, fashion and simply stick a wire up from to the qualities desirable in model which positively controls the ancient the fuselage in such a way that the helicopter work, we have designed a problem of rotor clash cross-arm bumps it gently at the same two-part series of rotors, which we term The basic rotor and its derivations point every revolution Presto' The the "bungee-dynamic series." are shown in the drawings reaction gives you cyclic control. These rotors cover a wide field of accompanying this article We start with Remember, however, that this is application and include power delivered a two-bladed rotor (see sketch "Basic control by unstabling—the bumper wire at the hub and power applied at the tip, Rotor Design—Cyclic Control") which should be quite flexible or the fuselage which means the series covers rubber, is see-saw mounted in gimbals and free may sway excessively, and. while it internal combustion, rocket, pressure jet to pivot, within limits in a span wise sounds very simple, and it is, it can get and ducted fan configurations In the fashion This rotor is of the first part of out of hand by displacing the rotor too middle of the series is our special pride the series, which we term "locked " far if the jolts are too heavy. and joy—a system which we believe to

OCTOBER, I953 29 The upper rotor must be free to see-saw about ten degrees up and down, which allows plenty of leeway against clashing with moderate gap, and this may be accomplished, in a rubber model, by simply rounding the edges of the thrust button—the tension of the rubber motor being sufficient "bungee" action. If we build a gas model, with shafting, then of course the upper rotor must be mounted in a gimbal and snubbed with rubber bands, permitting damped motion between stops. Now with such an arrangement as this we secure forward flight by trimming slightly nose-heavy. No By this is meant that the pitch of the From this point of departure we other cyclic control is required. For rotor blades relative to each other is Axed proceed to multi-blade applications —we heading control a simple fin, as shown, at all times (as in the Hiller) except as may build a four bladed rotor simply by corrects for the downwash, which may subject to collective pitch control. The doubling up what has just been described, tend to rotate the fuselage the same way as blades are stabilized by means of dynamic except that of course only one mast the lower rotor. The sketch ("Basic weights, which protrude tangentially, attachment, or swash plate will be Coaxial 'Bungee' Dynamic"), incidentally, about one chord length ahead of the required. is all the plan needed by any reasonably Blades' leading edge. There is no fly-bar able builder to turn out his own machine in or paddle-beam; instead, we have a double horn to which are affixed two snubbers, or "bungees" which run to a swash plate which may be tilted to secure cyclic control. These elastic connectors replace the inertial damping forces of the fly-bar, or the aerodynamic damping of the paddle beam, and are simpler to work with than either of these. Because of the concentration of mass in the rotor tips we can use much lighter blades successfully— meaning balsa instead of birch or pine, and the corrective force is balanced at all times, exerting a positive, yet gentle steering action upon In order to build a stable co-axial short order. the system. This is the cyclic control machine, using rubber power as an One note on adjustment: The down version. example, we merely construct the lower wash’s tendency to rotate the fuselage is And if we desire extreme simplicity rotor attachment with span wise pivots and corrected by bending the fin. However, we just move the bungee connections 90 attach it rigidly, that is, without see-saw after doing so the machine may show a degrees, that is, amx them to the span wise gimbal to the drive tube with a bent wire tendency to drift sidewise. This is due to pivot to exert a continuous corrective force "lead-around" interconnecting the blades. the reaction of the air against the fin, so upon the seesaw axis, and the machine just move the rotor mast a trifle off-center becomes controllable through C.G. shift to correct it, countering the side thrust with a bit of off-center lift. The second part of the series includes the unlocked rotors. These rotors may be built in any number of blades, from one, with counterweight, through two, three, four, five, or as many as desired. In the unlocked blade series (final sketch) we run into "dynamic pitch." By this is meant that the blades have no particular fixed pitch relative to each other or the mast, but seek pitch angles individually according to the speed of rotation. This is

30 AIR TRAILS accomplished by positioning, the dynamic balances well below and ahead of the leading edge of the blades, which causes them to ride up under the action of centrifugal force until a balance is reached between the force exerted by the up-thrust of the counterweights and the aerodynamic pressure on the blades. It is important with this system to locate the hinge line knowingly to obtain high efficiency, but in the practical application we find it works well even with rough approximation of position. The hub attachment of this system to the mast may be quite varied, from a simple rubber disc which functions as a universal joint, to separate snubbers for each blade pivot. This system gives us a built-in and fully automatic cyclic and collective control. This machine believed to be fist truly successful stable co-axial type to solve problem of Auto-rotational letdown is fully automatic control by C. G. shift and eliminate problem of blade clash. Could be flown with bungee (with a simple ride-out dog release on the cyclic control to lower rotor only. Model has been kept simple, no collective pitch used; hence letdown must be under residual power. Dimensions: Disc: 24". Mean chord; 1½". mast) which solves a mechanical problem Tube: 7½" x 1" dia. (1/32" sheet). Fuselage: 3/32" sq. stock 18" long. Weight: 2 oz. that can be knotty, and cyclic control is Performance: Altitude: 20 ft. Forward flight: 25-30 ft. at 5-6 ft. altitude (Hand-wound). That's high performance on three loops of 3/16" flat!

revolutions in getting started. Rubber is a special case anyway, since the number of turns is always strictly limited by dimension, which isn't at all true in the case of jet or gas power. For rubber models the best bet is to skip autorotation and bring the model down under residual power, or if you are the ambitious type, fly with a locked rotor, which unlocks and de-pitches itself when the power is exhausted. Once again, we strongly recommend that the first model should be rubber power—it will give you a wonderful opportunity to get the "feel" of rotor wing merely a matter of shifting the C.G. on what you want to do with it, flying, without introducing a lot of There is just one precaution to be compared with its characteristics. For distracting complications. observed with this system in securing example, the unlocked bungee-dynamic (To be continued) forward flight by C.G. shift. It is better to rotor is perfect for jet power, quite good have the snubbers a bit too limp than a bit for gas engine, and a complete bust for too tight, and don't overdo the nose- rubber—because it wastes too many heaviness. The reason for this is that a condition of "over-cycling" will occur if the snubbers are too tight, that is, the blade pitch will adjust itself too rapidly, accelerating the cyclic action, meaning the model will nose down and dive into the ground. If the snubbers are too limp the worst that will happen is that the rotor will tilt backward and forward flight will proceed at a snail's pace. This adjustment is by no means highly critical—the admonition just given is of the same order as instructing a builder of conventional planes not to tilt up the leading edge of the stabilizer too far if he doesn't want the model to dive in. Whatever system you elect to use, try to make your selection knowingly, based

OCTOBER, 1953 31 Once the reader has flown a rubber job With full size choppers more and more in the news this successfully and wants to build a model capable of informative series will get you started off on the right really big performance, it will be necessary to switch to gas engine or jet power. Let's deal with foot in building your own model helicopter jets first. The Jetex motor is an excellent source of power for model helicopters; generally speaking two will be used, although it might prove practical to use up to four, although this complicates the problem or getting a number of motors ignited at the same time in order that the charges bum evenly to preserve the balance of the rotor. For that matter a one-bladed rotor, with the blade balanced by the motor, can be used very successfully—which I know sounds a bit contradictory, but the practical fact is that the burning charge getting out of balance in a one-bladed system is considerably less critical than, say, two or three charges consuming at an uneven rate in a multi-blade system. The reason for this seems to be that the thrust output of the Jetex varies according to the amount of fuel left at any given instant, and peaks at the last few seconds. Thus in a multi-bladed system we have several thrust peaks, and if they do not closely approximate each other the thrust load on each blade may vary widely, meaning considerable pitch variations in a dynamic pitch rotor. In a one-bladed, single-motor job, the thrust variation is inherently "in gear" with the single rotor blade. Unbalanced CLOUGH’S CONCLUDING COMMENTS centrifugal loads due to fuel, charge consumption result in a narrow period of oscillation of the rotor CONCERING 'COPTERS mast, but since this vibration lies in a span wise plane the practical effect is not serious—for a By ROY L. CLOUGH, JR. model. The jets replace the dynamic weights of the unlocked type rotor, being mounted below and ahead of the* rotor tips. The angle of thrust should be slightly downward, and it may be necessary to provide up-pitch limit stops to facilitate getting the rotor going. The balance of the rotor blade on its pivot should be slightly nose heavy with fuel charge aboard. Note this, because of the position and forces exerted in this type of rotor it is not necessary to use stable blade sections— use the highest lift cambered section you deem practical and don't worry about pitching moments; the orbiting of the tip weight clamps the blade firmly at whatever pitch the speed and dynamic settings call for, and transition into auto-rotation after burnout is smooth and easy with a good let-down. The adapting of a tiny internal combustion engine that screams out its very high power rating at speeds in excess of 10,000 rpm to rotors, which run under 2,000 rpm, offers an interesting challenge. This may be achieved in a number of ways. The classical method is to reduce the speed and increase the torque through reduction gears. These should be of at least 5-1 ratio and there must be some sort of clutching arrangement between the gears and the rotor, otherwise it may prove to be impossible to start the motor, or gear teeth will be stripped by the high starting loads. A clutch satisfactory for this purpose should en-

NOVEMBER, I953 25 gage smoothly and positively, and may be either of the manual engaging type, in which the release of a lever holding two faces apart permits them to be forced together under spring compression, or of the centrifugal type which engages automatically with an increase in speed. See center sketch on this page. Clutches require access to tools and a knowledge of machining operations, but this should not deter a really determined builder. The ideal thing, of course, will 1% for some hep manufacturer to read this and produce a small lightweight clutch-reduction-gear unit at a reasonable price. Experience in the model racecar field indicates this can be done. Reduction can be had by means of pulleys and belts, with a sliding engine mount serving as a "clutch," but belting is not the most satisfactory power transmission. I have flown a K&B .049 job with belt reduction, briefly. The belt begins to slip after a time and the model descends. For this job I used a round belt running over wood pulleys at 4.5:1 with a heavy application of a good belt dressing. The problem seems to be that the high speed of the engine pulley soon glazes the belt, causing excessive slippage. Howard G. McEntee has suggested using small Vee belts. This might work a lot better due to the better traction offered by such a belt, but obtaining Vee belts and pulleys small enough for the purpose has been a poser. When using belt drive with gas engines, great precautions must be taken to keep fuel spray 06 the belt and pulley. A baffle between the shaft and intake tube and exhaust ports is highly necessary, and frequent wiping of oozed oil from the end of the main bearing is a must. Another angle, which I’ve been experimenting with lately, is to use a torque converter between engine and rotor. A torque converter is simply a specialized type of fluid clutch and operates without any direct connection. I use a small high-speed rotor connected directly to the engine shaft, running inside a larger rotor, which is connected, to the helicopter end. The casing is filled with castor oil. This device, in bench tests, appears to transmit a fair amount of power—with redesigning and a bit of finagling it should be quite evident. However, I have had a lot of trouble due to overheating, which causes some of the oil to ooze out past the bearings, and that results in lowered efficiency of power transmitted. In any event power for the torque prop isn't hard to arrange. Turn this about two to three times as fast as the main rotor by means of a simple string belt running over sandpaper-faced pulleys. Remember that the torque prop should stop when the model goes into autorotation in order that it won't swing the tail around in a circle on the way down. Simply attach the driving pulley between the clutch and the ride-out dog of the rotor. We mentioned this before, the rotor release. Whether or not you plan for autorotation you must have a rotor release, which permits the rotor to override when the power quits. (Continued on page 66)

26 AIR TRAILS Clough on 'Copters affixed; second, torque effects may However, the oil sprayed by a (Continued from page 26) add a bit of complication. You can, 2-cycle engine tends to gum up the Otherwise the great amount of however, make such an works and mess up the blower kinetic energy stored in the arrangement work if you use my ducts. Tentatively I run my jobs spinning rotor may twist off a shaft rotor configuration, the unlocked that way anyhow and clean the or strip gears or even shatter the system, and play off torque and ducts after each flight with a wad blades if the system suddenly gyro effects against centrifugal of cotton tied on a string, which is freezes when the motor stops. This loads. Use very light driving props pulled through. Old-fashioned but unit can be incorporated in the of as high a pitch and small a effective. function of the clutch or may be a diameter as possible, and place the I have a grave suspicion, separate item in the rotor hub: I thrust line of the engine angled nevertheless, that the drag of the prefer it to be separate since this toward, or away from, the chord air against oil-coated tubes may simplifies the operation of parallel, depending upon which cancel out the gain produced by stopping the torque prop when the way you run the rotor; to help exhaust heat-gases. Have you, for motor quits. compensate for gyroscopic twist. example, ever noted the ripples Now, how about really simple In connection with this, note and ridges that develop on the gas motor hook-ups, requiring no that the props can be shrouded, surface of an oil-coated wing gears or clutches? converted into ducted fans, with exposed to prop blast? That means Sure, it is possible and stator vanes to eliminate torque quite a bit of drag, and it seems practical, and may be effects. This makes a neat looking logical to assume that the same accomplished in several ways. One job, but auto-rotation suffers condition obtains within the way is to use torque reaction heavily from any bulky pressure ducts of a blower jet drive—such as in the little Infant excrescence at the rotor tips. system. While it is true that a lot of powered job of the previous Another method of drive is to the oil is blown out with the air article. However, don't use the use a pressure-jet configuration. and by centrifugal force, a lot of it primitive semi-articulate rotor Mount the engine in the fuselage, still sticks to the inside. And that system of that model, but build or in the rotor, as a blower isn't so good. Probably, in the your rotor along the lines discussed supplying air under pressure to jet interests of tidiness, it might be in the previous issue for the rubber nozzle* in the tips of the blades. well to advise piping the exhaust co-axial job, except use unlocked This system isn’t terribly efficient, into the open, and eschew the blades on the big rotor to get a but the great power-to-weight ratio theoretical benefits in favor of the good auto-rotational descent, and of modem small engines will let practical considerations. locked, but feathering blades on you get away with it if you are I have tried to present as many the small rotor attached to the careful. This produces very dean applications, suggestions, and engine shaft, say in a rubber structures, smooth blades, and observations as space will allow, in mount, to permit a small amount of excellent auto-rotational and the belief that model builders win see-saw action. Because of the control characteristics—so in a find more of value in something strong downwash of the small rotor way it might be said that the like this than they would in an a brake or fin is required to prevent system is efficient after all. article which dealt with the fuselage rotation, but for simplicity There is one angle in designing construction of one particular this is hard to beat. pressure jet jobs, which I am not model and consisted largely of Propelling the rotors at the tips too happy about. From the instructions to glue stick A to stick by means of propellers has been standpoint of efficiency it is a fine B and so forth. This 2-part article, suggested many times by many thing to have the cylinder head and together with the previous series people. It seems simple, but it can exhaust opening inside the duct, covers, I fondly believe, enough of be very troublesome. The reason is that is, behind the fan, in order that the basics of helicopter principles two-fold. First, the props act as the motor may cool better, run to permit anybody to turn out a gyros running in a tight circle— faster from the supercharging very satisfactory job with a meaning the engine shaft tends to effect of air being rammed into the minimum experiment. Try it and twist upward or downward, intake, and the pressure augmented see for yourself! depending upon rotational by the heat of the cylinder and direction of the blade to which it is exhaust gas efflux.

AIR TRAILS NOVEMBER 1953 36 Air Trails, HOBBIES For Young Men

"This is one of my all-time bests," says the designer who has been acclaimed as one of the country's most original men of modeling. No fancy gimmicks here, no frills, just a little easy construction, and then lots of fascinating flying ahead

You'll stop the show when you put out at the end of 50 foot lines with any this spectacular rotary-wing job aloft. good .19, as high as you'd care to fly any In flight it looks just like a big tandem non-stunt type model of this weight, and rotor helicopter with lines reminiscent the wind bothers it less than fixed wing of the Piasecki and Bristol machines. models. There is a barely perceptible Although the appearance of the model cyclic slap from the rotors, but, far is very close to the double-ended heli- from being a nuisance, this gives the copter types it is really more closely re- "feel" of real rotary wing flying. You lated to the gyro-dyne family—rotary do not require any particular knowledge wing machines which may rise up vertic- of rotary-wing craft to build and fly it ally, like a helicopter, but which depend successfully. upon a propeller for forward motion. In Begin with the fuselage which consists The this respect it is somewhat similar to an of two 3/32" x 3" x 36" sheet sides cut autogyro. to shape. The bulkheads are 1/8" sheet To avoid mechanical complication our and the two rotor mast carrying bulk- model uses a short ground run instead of heads should be cut from very hard Control-Line vertical take-off. With this system it is stock, or else substitute plywood. You not necessary to power the rotors and will note that the fuselage follows very taking off with forward speed is more conventional construction lines for sheet practical in a controlled model because balsa building and requires little or no it keep the lines tight. explanation except at the front end. Gyro-Copter Okay, it sound great, but how does it This model differs from usual control- handle? Is it hard to fly? How does it liners in that the elevating surfaces are behave in a breeze? at the front end instead of the tail. The answers are that this model is Therefore study the control hook-up and By ROY L. CLOUGH, JR. actually easier to fly than the average be sure you understand it—the elevators sport job. The control response is very are depressed to raise the nose, and smooth and positive and it stays right lifted up to lower it, just the reverse of

SEPTEMBER. 1955 37

usual. The landing gear arrangement with rotors like this you can expect gear produces exceptionally good ground should be followed; if you use a radial cracked blades after the first flight and stability, but do not neglect the usual mount engine, for example, put in a ply- somewhere along about the third flight down-wind take-off precaution—you have wood floor to bolt the landing gear firmly you will get an interesting shower of two big rotors here, plus a propeller, in place. Note the L.G. wire should broken balsa as the rotors shatter under and if you flub a stall-off in a strong not be firmly attached to the elevator cyclic pounding. wind and the model rolls up in the lines cross-arm piece, but is held to it by rub- Clean metal and acid-core solder and it will take five years to untangle. ber bands which act as shock absorbers. an iron a bit hotter than necessary will After a couple of normal take-offs The motor mount depends upon the en- insure a good job. You do not have to under normal conditions you will learn gine. We used a McCoy Sportsman .19 use bottle caps of the exact size shown, the trick of yanking the nose up im- with rear rotor valving. This is about for anything similar which will fit is mediately after your helper releases the the top power which should be put in okay. Be sure to leave at least one inch model, and then letting it drop back. this model—in fact, if you go down to 35- of wire between the blade root and the This trick sets the rotors spinning very foot lines, a good hot .09 engine might hub for flexing. The cone angle should quickly and reduces an otherwise 15-20 prove quite adequate. be as shown; if no cone angle is used the feet take-off run by half. Spinning the The rotors are very simple to build, model will not fly well in level flight, rotors by hand before releasing the but a good touch with a soldering iron but will have to be nosed up, which is model does not work well and should be is necessary. These rotors are not rigid sloppy. Be sure the rotor masts tilt at the avoided. Near the end of the run, when as they may appear at a glance, but semi- correct angle; the rear rotor operates at the motor starts to sputter, bring the flexible, which takes the cyclic jar and a greater angle of attack than the front model down to five or six feet. When shock out and greatly increases the to compensate for downwash effects. This the motor dies bring it in gradually. operating life. We mention this so you will not make the model nose in. When will not substitute a heavier wire than you assemble the rotors to the mast make specified for the arms, or try to by-pass sure they rotate freely; there should Full-size plans for the Tan-Giro the soldering job by gluing up a solid not be any great difference in the ease are part of Group Plan #955 wood rotor head. A glued-up rotor head with which each bearing turns. Hobby Helpers, 770 Hunts Point seems simple and easy, and it is, but the Flying the model is not much different Ave., New York 59, N. Y. (50c). catch is that if you equip the model than flying any sport job. The four-wheel

A SURE FIRE

AUTOGIRO Autogiros are usually tricky, but this one IS a sure fire performer by ROY L. CLOUGH JR.

A DISTINCTLY rare item—the free flight model autogiro—has the reputation of being an extremely difficult thing to build and fly. Demonstrating that this reputation is quite undeserved, this model is simple enough to be knocked out in an evening and is no more difficult to fly than a conventional ship. In fact, it is not even necessary to set the rotor in motion before launching This model climbs at a steep angle and when power is exhausted floats gently back to earth on its spinning rotor, thus eliminating the chief cause of destruction of flying models—a head- on glide into a solid object Begin construction with the fuselage, which is built up from 1/32" medium sheet balsa. Stiffened are used at appropriate intervals and the thin covering is backed up with 1/16" sheet at the point where the landing gear is attached

Nose and tail plug openings are reinforced with strips of 1/16" x 1/8" stock. The bubble canopy is carved from a block of soft balsa Tail surfaces are 1/16" sheet and are cemented in place with no offsets of any kind Carve two end plugs; adapt one as a tail hook and the other as a thrust bearing for the propeller The prop may be sanded down from a purchased pre-sawed blank or built up as was the original. The prop should be of medium low pitch, and diameter should not exceed 9 inches Freewheeling would be of no particular advantage in this model Bend the landing gear from 1/20" steel wire and cement it to the reinforced underside of the fuselage Wheels are 1 1/4" in diameter and must be hardwood. The rotor and rotor mast, while quite simple, must be made exactly according to plan to obtain optimum performance. The mast is bent from a length of 1/20" steel wire and is anchored to a plate of 3/32" hard balsa which is cemented to -the top of the fuselage. A short length of drilled hardwood dowel is slipped over the mast and cemented to the plate for added strength. The rotor is acted upon by highly complex forces in flight and must be highly flexible to permit these forces to be damped out without upsetting the model The hub is a piece of dowel which is drilled to permit a loose fit on the mast The spars are 1/16" x 1/8" hardwood, pushed into slots in the hub at the angle shown on the plan, and cemented. Two short pieces of 1/16" x 1/8" balsa are cemented to the upper sides of the spars next to the hub. Rotor ribs are simply toothpicks. Cover the blade sections with a strip of smooth typing paper, 2 3/8" x 11" for each side. Note that the rotor has 0 degrees incidence and will spin in the proper direction regardless of the direction from which the relative wind comes. This is very important! Drill out two short pieces of dowel; slip one over the rotor mast, then put on the rotor, using the other bit of dowel to hold it in place. The proper height of the rotor above the fuselage is the shortest distance, which will give good propeller clearance. The retainers are cemented in place after testing. To test fly: install an 8-strand motor and balance the model at the rotor axis. Drop it from shoulder level a few times to make sure the rotor works well, then try short powered flights in calm air The model should climb without deviating right or left and is performing best when it gains a foot of altitude for every foot of forward flight Whatever minor adjustments may be required can be made by slightly bending the rotor mast

MODEL AIRPLANE NEWS MARCH 1948

BEFORE YOU conclude that this is a model of a helicopter, take another look. It's a model plane with a spinning wing, or rotor, that windmills in the slipstream of a conventional propeller to provide the lift necessary for flight. The rotor is self-spinning and that's where the autogiro or gyroplane, as it is now called, differs from the airplane and the helicopter in appearance, in flying characteristics and also in construction. And on the end of a control line it is a new experience for model-plane fans. Control-line gyros have been built, of course, and flown with fair success. But none could be Mount engine on the firewall with four small bolts, considered spectacular performers. Some showed using washers under left mounting to provide offset a persistent tendency to roll up in the control lines and some that performed satisfactorily otherwise developed an arm-shaking vibration. This appears to have been largely due to use of a rigid motor, which tended to develop a condition Remember the of unbalance while in flight. The rocker-type, or seesaw, rotor used in this model starts spinning quickly and easily and the gyro lifts off and flies smoothly without dipping, diving or rolling. It spinning-wing pulls hard, but not too hard, on the control lines and settles as lightly as an autumn leaf when the autogiro? motor fades. The fuselage is simply an elongated balsa box By ROY L. CLOUGH, JR. made mostly from 3/32-in. material except the bulkheads, A, B and C, and the stabilizer which are 1/8-in. stock. Although the over-all size at the center to permit a seesaw motion. Stops of the bulkhead, C, is given, you may have to on the hub pivot, limits vertical motion so that do some fitting of this member to assure a true the blades won't strike the tail. This type of fairing of the fuselage sides and top piece. The rotor mount allows the blades to rock without fuselage is fitted with a conventional engine, transferring motion to the fuselage, yet keeps propeller, landing gear and a standard control- the rotor tracking evenly. line elevator for controlling the gyro in flight. Give the model a coat or two of sealer before The rotor mast centers 4-1/4 in. from the applying pigmented dope. Make certain that forward end of the fuselage. In assembly it everything runs freely, and that the center of passes through the bottom of the fuselage, the gravity is either right on, or just ahead of the bend at the end being seated and cemented in a control crank or bell-crank axis. If the center of notch cut in the bottom of the fuselage. Note gravity (CG) is behind the control-crank axis, that it also passes through the control strut and the model may not pull hard enough on the lines the bell crank. Washers are soldered above to give good control. and below the crank, permitting the latter to After you get the feel of it, you can make jump swing freely on the mast. After installing the takeoffs by letting the model roll about 6 ft., controls and the reinforcing strips at the forward giving it full up and dumping the-elevator quickly end of the fuselage, cement the fuselage top to bring it into a normal flight attitude. pieces in place, then the pilot's head and the Incidentally, that machine-gun-like popping fairing. you hear in flight is common to all rotorcraft. Study the rotor drawing closely. Note that It's caused by the rotor blades running into their the blades operate at a negative pitch and that own tip vortices. the rotor, although stiff from tip to tip, is pivoted

POPULAR MECHANICS JULY, 1962

Torque Reaction Helicopter Models-further experiments By: Roy L. Clough Jr.

Thus far in discussions of model helicopters most pressure as they would be if the weight of the machine reports have stuck pretty closely to single rotor was being supported by them. As a result, control and machines, or those in which a rotor, or pair of rotors stabilizing reactions assume an altered aspect. The support the weight symmetrically. builder who does not understand this may find his However, for model work we find that duplicating model crashing repeatedly despite his efforts to re-rig the rotor arrangements of the big craft is not very it for normal flight, because the control reactions, in practical except in rubber or jet power configurations, most flight regimes, are actually reversed. If we build both types being unfortunately of short-lived duration. a very simple helicopter, with rigid, un-pivoted blades If we wish to use gas engine power, at this stage of the without tip weights and adjust it to fly forward we art, we must find some method of using a power plant, find that it starts to slide ahead, then noses upward which grinds out several thousand rpm without getting sharply, slides back and repeats the pattern with into too much complication. One method of doing this increasing amplitude until it crashes. The reason for is by designing our ships to the torque-reaction drive this is that the advancing blade produces a high lift specifics, the system whereby the engine torque spins force when it encounters the relative wind; this lift a large rotor in opposition to the rotation of a smaller processes 90 degrees forward tilting the nose up, prop on its shaft. (This, incidentally, should not be which kills forward speed, then the model slides back confused with true co-axial systems, which utilize with what was the retreating side of the rotor now equal-sized rotors turning in opposite directions.) producing a lift which will move 90 degrees, or to the Very good performance is possible with torque- tail, riding the tail up then sliding back, etc., etc. reaction drive although it has two major drawbacks: 1) So we now pivot the blades and fit them with it is not very efficient because of low mechanical dynamic balances. Now when the model moves ahead advantage; 2) the system does not behave in classical the air pressure on the front of the disc makes the fashion—that is, we have a new and different set of rotor blade twist its pitch angle upward, 90 degrees forces and reactions to deal with. Objection #2 is not ahead that is the retreating side, and downward, that is serious if we remember to keep the reactions of this 90 degrees behind on the advancing side. When this type isolated in our minds from the reactions of happens the change in pitch 90 degrees to the side standard types and not confuse them. produces a force that is moved another 90 degrees, so Torque-reaction drive helicopters are queer birds. that the rotor disk tends to tilt up at the rear and down They are almost as removed from conventional at the front. When the model is in a state of balance helicopters as, for example, an autogiro. The reason the forces cancel out and the machine flies forward for this is that torque-reaction drive helicopters split without riding up at the nose or going into a dive. This flight duties between a large, slow-moving rotor and a is due to the upward force of the relative wind striking prop attached to the engine shaft. The engine shaft the advancing blade being leveled out by the pre- prop is generally standard and it has one main cessive pitch shift in the blades produced by the function-it provides 99% of the lift. In some cases it pressure of the relative wind, which tends to nose the may be used to contribute to stability as well, but the rotor disk down. This is the way it should work, and primary function is to lift the machine. Its gyroscopic does work when the CG is properly located. However, effects are completely negated by the much larger if the CG is improperly located trouble develops, and mass of the engine and big rotor whirling around in this trouble is usually a dive. Why? the opposite direction underneath it. The function of Suppose the builder flies his model once or twice the large rotor is to provide a torque drag on the and it works quite well, moving forward steadily. He engine, a device with which to secure stability and then wishes to see it rise vertically. It would seem control, and finally, to serve as a parachute to let the reasonable then, to add a bit of ballast to the tail to kill machine down without damage when the power stops. off the forward motion? Unfortunately it does seem This division of labor produces an unusual very reasonable. We have the past precedent of fixed condition because, under power, the large rotor is wing models; we have the precedent of single rotor operating in a substantially unloaded condition. Its helicopters, which fly forward if the weight is moved blades are not damped by a strong aerodynamic forward and back if the weight is moved back. Seems reasonable. So weight is added to the tail, the model pronounced enough to permit flight in surprisingly rises up, starts forward faster than ever, noses down high winds and gusts without getting into trouble. and crashes. Why was this? However, if the CG is moved too far aft, the balance We just said that torque-reaction helicopters are a of forces is upset and the model will dive in. special case because of the unloaded condition of the Ordinarily the model D gives no trouble—except rotor, which does the controlling. Here is what where the builder has put on several heavy coats of happens: We have noted that air pressure on the rotor dope and has not re-checked his CG afterward. The results in a cyclic action which resolves to cancel the CG position shown on the plan, incidentally, is for nose up effects of that pressure, that is, relative wind absolute maximum top speed. To climb vertically it effects are self-nullifying. But, any force applied to must be moved ahead with ballast. the rotor reacts in cyclic control, the blades shift in an The other model, the TR, has four pivoted blades effort to nullify the applied force. and uses a swivel prop to provide a recovery couple. Now, when we add weight to the tail we are When the tilt is to the right, changing the lift vector, placing a steady pressure on each pivot blade as it which puts a side load on the rotor which induces a passes over the tail-the CG has shifted—and by cyclic shift which pushes the nose upward. This reference to gyroscopic precession laws we see that model has a tail rotor to control heading, and a few this force will result 90 degrees further on, or at the words on this: A rudder will not make a helicopter side. Thus the blade advancing tilts down and the turn. A positive side thrust is required; hence a tail blade which is retreating on the other side, tilts up. prop is needed to push the tail around or to hold it This tends to twist the rotor laterally, but again steady. A rudder will only crab the ship slightly while referring to gyroscopic rules we can see that this twist, it continues in substantially the same direction. moving 90 degrees, resolves to push the nose down! Another method of obtaining turn without a tail rotor Thus if we take a helicopter which is adjusted to rise is to tilt the rotor mast toward the side toward which vertically, and move the CG aft a little bit the model turn is desired. Don't get confused on this, the model will now fly forward—BUT if we move the CG too does not slide that way, but the downwash rebounds far aft the model will overdo it and dive into the from the side of the fuselage at a different angle, ground. This is because we have two cyclic instigators tending to roll the model over—but again by working, the CG imbalance, plus the normal cycling gyroscopic reference, the roll is resolved at 90 degrees produced by forward flight. into turn. A model of this sort therefore is fairly sensitive to There are many ways in which a torque-reaction CG location, too sensitive, as a matter of fact, so it is helicopter can be set up. One thing, which is quite customary to build in a safeguard which will allow a important, is to respect the fact that the fuselage lies in wider altitude of CG travel before diving or tail the downwash of the small prop, and exposed areas sliding occurs. A good example of this is the Berkeley should balance, or very nearly so or there may be kits, which use two different methods of obtaining the serious trouble. The use of small fins in the prop wash same result. In the D model we note that two of the to obtain turn, or to reflect the wash' backward for blades are fixed in pitch. Thus, as the model moves reactive forward propulsion meets with some success forward the lift build, caused by increased relative and one can use a twisted stabilizer which tends to put wind meeting the stiff blades tends to push the nose torsion on the fuselage with increased forward speed, up, while the cyclic action tends to push it down. to induce nose-up cycling, relative wind strikes the Since the up couple is a bit stronger we also have a prop edge it as a corrective force couple. drogue on this job, which increases the cyclic reaction When designing originals it is a very good idea to of the pivot blades, and, secondarily slows the model include always some governing factor on forward down. ' speed. Rig it either with a swivel prop, a stiff, Thus, within allowable CG travel the tilt angle of alternate set of blades, or torsion fins. Speed of the machine is self-governing. If it slows down the forward flight will vary with the design and power cycling action, which is fully automatic, tends to plant, and will not be as high as a fixed wing model— speed it up, if it goes faster, the stiff blades bring the a good fast walking pace is about right with present nose up, slowing it down. This governing action is designs. —ROY L. CLOUGH, JR.

THE USE OF TORSION FINS

"A" must clear rotor disk. Fins may be either horizontal or vertical. As forward speed builds up, fins tend to roll fuselage to right, which induces nose-up cycling moment.

FORCES ACTING ON TYPICAL HELICOPTER

Barred lines: drag of drogue tail produces down pressure on balance weight of pivoted blades which induces cycling action which tilts blade down at side and pushes nose down. Dash lines: fixed pitch of this blade encountering relative wind produces lift at side, but since rotor functions as a gyro the reaction moves 90 degrees, producing nose-up tendency. Solid line: wind pressure on pivot blades reacts at 90 degrees to make pitch change shown to hold nose down. Thus, if CG is too far aft it induces cycling in the pivoted blades which reinforces down control of drogue tail and wind impingement on pivoting blades and overrides nose-up tendency of fixed blades and the model will dive in. Centered CG has no cyclic effect and model will rise vertically. CG too far to front will cause model to back up or tail-slide. NOTE: CG is usually slightly aft of mast CL in order to balance fuselage effect and promote forward flight.

FORCES ACTING UPON TYPICAL SEE-SAW PROP HELICOPTER

A) CG rigged tail heavy induces cycling in pivoting blades which causes nose-down forward motion (barred lines). B) With CG centered, model rises vertically. C) Nose-heavy CG will cycle blades into backward flight (dash lines). Wind pressure on blades produces precessive pitch change at side position preventing nosing-up (solid lines). Role of the swivel prop: wind pressure on front of see-saw prop, by gyro precession, causes it to tilt to model's right, which angles lift vector to right. Side thrust on rotor system produces cycling which makes nose of model ride upward, thus limiting forward speed and preventing dive (assuming CG is correct). Seesaw prop must be mounted to rock freely for best results. (Seesaw prop can be eliminated if two opposite blades are fixed pitch with counterweights removed. Air Trails Model Annual - 1956 Snapper

By Roy L. Clough Jr

Ever since the first half-A engines appeared we've thought it would be a riot to stick one on a ten-inch wing and turn the contraption loose. We finally pared some wings down to mere stubs on an old free flighter and tried it. It was a riot . . . a short-lived one. of directional stability, wingspan, (B) limiting the motor, run After we swept up the balsa wood (2) a sharply limited reliably without a timer mechanism, (never leave the pieces in a hayfield—it's motor run, (3) no (C) making the model insensitive to bad for cows) and cleaned the turf out of tendency to climb or dive gusty weather, and (D) using the the engine we came to the conclusion that under slight variations in lightest and most simple geometry a free flight speed job would have to be a power output, and (4) be consistent with adequate strength. carefully tailored affair. The wild light and very rugged. "Snapper" is the answer. It is a corkscrew gilhooley and painful thump In order to obtain these reliable little ship. It will fly in calm of the clipped down free flighter had characteristics we must or windy weather with anything from given us a lot to think about. (A) find some way of a Cox .010 to an Atwood .049. With a A model intended to reach high speeds managing a whale of a good hot .049 it will hit close to in free flight must have (1) a high degree lot of torque with a small 100mph. Snapper is rakish, but, except for the cockpit, styling had nothing to do with its appearance. It's designed that way because that is the shape that will best do the job. Any built-in offsets in thrust line, wings or control surfaces are out. It doesn't take an engineering degree to figure out the reason. The model is light and it goes like a devil with his tail on fire. You'd never get a chance to balance off wing incidence by varying down thrust or to use any of the usual free flight adjustment tricks. The wings, stabilizers, fin and thrust line must be substantially parallel to each other. Dihedral angle raises the tips of the wings and this raises the center of resistance. We have to counter it by raising the thrust line a little above the wing. We Author Roy L. Clough Jr. wants you to admire that ultra simple, surge- require a special fuel tank and it has free, positive-duration fuel tank! Full size working (Continued on page 47) Drawings are on Hobby Helpers’ group plan #1162

American Modeler --November 1962 29 is started with a heavy prime and the first tankful is run out to warm it up. It doesn't seem to be practical to connect the open end of the coiled fuel line to a tank then detach it before flight. This changes the suction pattern and the needle valve, would be in need of adjustment before launching. With the arrangement shown the motor turns over for about 12 seconds. That gives you about 8 to be on the bottom of the plane. All that torque and no rudder? seconds to detach battery wires, This pretty clearly calls for an Just elevators? That's correct. straighten up your aching back and inverted engine mounting. So, we Because of the small span of the give the model a solid heave. start the motor with the plane held model the elevators act as ailerons. Plenty of time, once you get used upside down where we can check This means we correct for torque to it. The model will whizz for a the fuel flow. effect by giving the elevators a couple hundred feet before running Don't try to use a timer tank or differential twist. The left one out of juice. When it does it will fuel shut-off. This little job will slightly down, the right one slow up like it hit a brick wall and chew off about 100 feet of airspace slightly up. The less one has to roll to the right. Don't expect much a second when it gets rolling. That monkey with on a high-speed rig of a glide. means it could be well over a mile like Snapper the better. Pre-flight adjustments call for an away in less than a minute if you Cut off the needle valve about a arrow-straight "glide" with a fair forgot, or if something stuck. sixteenth of an inch outside the amount of roll to the right. Make Somebody is sure to ask why we needle valve body, file a slot in it your first test hops over deep grass included a landing gear on a hand- and do your adjusting-with a with low pitch props; step up the launched speed job that lands in screwdriver. If necessary, jam the pitch, and the speed as you – the grass. needle valve body a little out of become accustomed to the The answer is: it helps to keep round to get the necessary friction. adjustments. Snapper should fly 10 dirt out of the engine. But don't Needle valve settings (on the to 15 feet up, expect any wheels-on landings. Atwood) vary about half a turn No thermal worries here! around the "ideal" position. Model

47 American Modeler -- November 1962

Skyhook... lower end. The upper end rotates freely in a hole in the top of the fuselage with 1/8" clearance all around. Power absorption in one rotor is constantly balanced by that of the other and an unbalanced torque condition cannot occur. Elimination of torque is not enough, however, to obtain satisfactory flights in this type of model; hence the directional vane pointing rearward from the top of the fuselage. As the downwash of air leaves the lower rotor, it does so with a rotary motion and tends to impart this motion to the fuselage and cause it to revolve in the direction of rotation of the lower set of blades. To forestall this effect, the vane is attached at approximately the same angle as the upper rotor, and in this position acts to exert a push in the opposite direction and keep the fuselage pointed straight. The tips of the lower rotor are bent downward at a 30-deg. angle to give adequate air flow over the directional vane. A word of caution: A free-flight model helicopter is not an easy thing to build because of the number of "bugs" inherent in the helicopter idea. In fact, it might be said that if a model helicopter flies at all, it's good! Therefore, it is recommended that the plans be followed closely. Try to keep the weight down. Do not By ROY L. CLOUGH, JR. dope or add unnecessary detail to the model. Excessive weight means more power will N DRAWING boards and in secret test be required to fly it, and more power means O hangars of at least a dozen major more rubber, fewer winds, and more weight. companies and scores of smaller ones the This can develop into a vicious circle. helicopter of the near future is being evolved. Rotating-wing craft have caught the public fancy, and manufacturers are hurrying to perfect their direct-lift wares Notice mounting strip for the front wheel between the for the postwar market. Already at least bottom longerons of this unfinished fuselage. A cross three distinct types have flown brace midway at the rear adds strength. successfully. In the helicopter, torque effect is one of the major problems. If a single rotor were attached to a power source with no provision for this effect the entire fuselage would spin around and around. Two rotors revolving in opposite directions around a common center overcome this tendency. Counter rotation is employed in Skyhook, a model that flies straight up like the real thing and, when the power is expended, descends in a spiral and lands on its wheels. Skyhook is best flown indoors, but may be sent aloft outdoors on calm days. It will be noted that the motor tube, which also serves as a shaft for the lower rotor, is attached only by a simple bearing at the

148 A FLYING MODEL HELICOPTER It is best to form the motor tube of 1/20" medium-soft sheet balsa, but if this is not obtainable use 1/16" stock, well sanded. To avoid splitting, soak the wood in hot water before bending it around a circular form and wrapping in place with gauze. If a form of the size indicated is not available, the diameter of the tube may be safely altered, taut remember to change the hole in the motor guide plate accordingly to retain the 1/8" clearance. When the tube is thoroughly dry, slip it from the form and cement the edges together. Near one end of the tube cut two small holes in opposite sides for Two rotors revolving in opposite directions overcome torque. a short length of 1/8" dowel to hold the Build one side of the fuselage upon the other as in end of the rubber motor. Run a bead of cement a conventional model, using 3/32" square medium around the edges of these holes to prevent the wood balsa strip. Soak the upper longerons in hot water from splitting. before bending. Crosspieces are required at the points From 1/16" medium stock cut three disks to fit marked "X" in the plan, and another may be placed closely inside the tube. Cement one flush with the between the upper longerons near the rear for greater upper end of the tube and another about 1/8" inside strength. The floor the lower end. Keep the third for future use.

Motive parts include six rotor blades, motor tube, and top rotor hub. Note lower blades are cut shorter. plate shown in one photo is 3/32" by 2-1/4" down the tips as shown. Make certain that all by 2-3/4". Center a 1/32" by 1/4" strip be- blades balance and track evenly. tween the lower longerons from the floor plate Now bend a paper clip to the shape shown on to the nose to support the front wheel. the plan so that it will stand upright. Thrust Cover the windows with cellophane or light the stem through the third disk cut for the celluloid and place dark-blue tissue on the rest motor tube until the bent part rests flat against of the fuselage, except for the space occupied one side. Put plenty of cement into the recess at by the motor guide plate on top and the floor the lower end of the tube and push the disk with below. Water-shrink, but do not dope, the wire attached inside. covering. The lower bearing is a 1/2" length of 1/16" Form the landing gear from 1/32" hard balsa OD. brass tubing soldered into a 1/2" by 1/2" sheet, cement it to the lower longerons as piece of tin plate. Cement the latter to the center indicated, and mount 1-3/4" balsa or celluloid of the floor plate. wheels on its ends with pins. Attach the 1- Next cut the directional vane from 1/20" 1/2" front wheel with a wire strut. sheet and cement it to the motor plate at the Cut the six rotor blades from 1/20" balsa, point indicated on the plan. Wet the wood at well sanded. Notice that the plan below the thin part and twist until the vane has shows the top surface of the upper blades and approximately the same pitch in the same the bottom surface of the lower, since the direction as the upper rotor. upper rotor moves counter-clockwise and the Now install the rubber motor. About four lower clockwise when viewed from above. Also loops, or eight strands, of 1//8" flat rubber are notice the shape of the cross section. Do not required. Slip the tube through the motor guide dope these blades. plate and lower it into the fuselage. Poke the Carve the upper rotor hub from soft balsa and lower shaft through the bottom bearing. install the motor hook through a standard Solder a washer to the end to hold it, or thrust-plug and bearing as shown. The motor bend over the end of the shaft, and Skyhook is ring may be cut from 1/8" balsa, but two 1/16" ready for a trial flight. sheets glued together with the grain crosswise All take-offs should be from a level surface. have greater strength. Cement the ring to the Hold the circular lower rotor hub stationary motor tube about 1/2" from the upper end. and wind the upper blades. Set the model on Attach the upper blades to the rotor hub at a the ground with upper and lower rotors pitch of 25 deg., with a 2" dihedral under the between forked thumb and forefinger and tips. Mount the lower blades on release both simultaneously. the ring at 25 deg. but with no dihedral. Bend

150

Above: A shot of the full-scale Sikorsky S-51 helicopter in flight. About the only real difference between the real one and the model is that the aft rotor on the model does not turn. Instead, it is replaced by a celluloid disc that sup- plies ample stability to keep the model flying straight.

Left: A still shot of the model hanging from a string. The prop was held rigid for this shot so as not to tilt the model: The working prop is mounted so that it will swivel on the prop shaft, as shown on the plans. The ship is made of sheet balsa sides cemented to sheet balsa formers, with a simulated cockpit.

SIKORSKY S-51 by Roy L Clough, Jr.

In answer to many requests for a realistic helicopter that

actually flies, we offer this semi-scale Sikorsky.

• Probably the most famous design A good action shot showing the model in actual flight. Performance is realistic with no of pioneer helicopter builder Igor Si- danger of hard landings when the engine cuts as freewheeling vanes ease the model down. korsky, the S-51 helicopter has racked up an impressive record in life-saving and rescue operations, both at home and abroad. It is the standard unit of Los Angeles Airways, first airline with scheduled helicopter operation, and has been manufactured in England by Westland under license from the parent company. In addition to its perform- ance record, it is generally agreed to be the most beautiful rotary wing craft ever built, with clean flowing lines that adapt themselves readily to scale model practice. The big ship uses a three-bladed rotor of the type known in the trade as the "flapping blade" or articulated system. This rotor type has an extreme degree of maneuverability with rapid control reactions and is quite stable in normal cruising flight. The torque effect of the (Please turn to Page 34) FLYING MODELS FEBRUARY 1953 15

shaft should be quite clear from the plans. Note that the SIKORSKY landing gear struts have been omitted since we want a (Continued from Page 16) springy gear to absorb landing jars. Window details are rotor is nullified by a small rotor attached to the tail best painted on with a contrasting color—plastics do not boom which produces a counteractive side thrust and take kindly to the spray of fuel and oil from the engine is used as a heading control. (yes, you can use a 1/4" sheet profile fuselage if you want This arrangement is fine for a full-scale craft, but extreme simplicity—but move the CG ahead about 3/8" to the unstable hovering characteristics of an allow for altered fuselage effects). articulated rotor limits its usefulness to piloted craft— The rotor mechanism and engine hook-up is quite a it is not the best system to use on a model which simple affair, but study the plans carefully and make must fly independently and has no pilot aboard to certain you know how it works before tackling it. The hub correct disturbances due to gusts or roughness in the is tin-can stock, the blade arms 1/16" steel wire soldered air which are present under even the most ideal carefully in place. All bearings and bushings may be conditions. Therefore we must use a rotor, which has a made of brass tubing, or simply rolled around a music degree of automatic stability if we wish our model wire form with flat nose pliers, using thin brass or tin-can to fly for more than a few seconds without skating stock material. wildly in all directions and finally crashing. Make the rotor blades from a good tough variety of Our first S-51 model, therefore, used a 3/32" sheet balsa and be sure the rotor blades' tip dynamically stabilized rotor of the so-called weights (dynamic stabilizers) are securely cemented in "feathering" type. That is, the blades did not flap up place and bent to the proper angle. The amount of weight and down, but rotated within limits in a span-wise should be just enough on each blade so that the blade plane, allowing flight deflections to register as pitch will tip forward to maximum "down" pitch when at rest. changes instead of flapping movements. The pitch This weight will vary somewhat from model to model, but changes served to maintain the stability of the is not critical within wide limits as long as only a machine by adjusting the lift of the rotor from side- reasonable amount is used. to-side as required, since the blades were Understand how these weights operate—under independent of each other and, to a limited extent, of centrifugal force they ride up, increasing blade pitch, if the the rotor shaft. Pitch was determined by rotational model tilts they alter the blade pitch to provide a speed (centrifugal force) and the model used a rear corrective side thrust and, lastly, when the engine runs torque correcting propeller. out of fuel they govern collective pitch and throw the The power was rubber and thrust was rotor in auto-rotation to bring the machine down safely transmitted through a bevel gear drive to the main and slowly. rotor and by pulley to the tail rotor. This model flew The recommended engine for this model is the K&B very well, was stable and able to cope with rough air .049. It is recommended because of the ability of this without upsetting or going into a wild dance. engine, which has a longer stroke than some, to carry a However, the duration was very limited and the very large prop without killing out—a very important altitude attained was not very great, due to the consideration in torque-reaction-drive helicopter models. It complexity of the machinery required and the rather also has a very handy mount and the gas tank comes in sharply limited output of twisted rubber bands. the right place for this sort of model. Balance the cylinder We decided to scrap this design in favor of with a blob of solder on the blade holder arm opposite something that could be powered by a ½A engine, the tank. on the theory that builders would rather have a much The finished weight is of much greater importance in simpler model with greater performance, and would a helicopter than in any other type of model. This model be willing to sacrifice a bit of scale appearance to should weigh at least 4.5 ounces and less than 5.5 get it. ounces for best scale-type performance. If it is too light it By using the torque-reaction drive, we eliminated will zoom up much too rapidly to be properly enjoyed, gearing and clutches and the need for a torque and if it is too heavy it may be sluggish about rising— prop. The dynamic stabilizers, which govern particularly on hot days. individual blade pitch, were retained, giving a good, When the model is finished (up as far as the special positive and fully automatic auto-rotational let-down engine shaft rotor, and we're saving that to describe last when the motor quit—an important factor in models for a good reason), check it over for good blade tracking having any considerable weight and power. The and alignment. torque prop, an outstanding feature of the original, This model flies not only vertical, but forward as was replaced with a clear disk of plastic, which well. In order to get it to do this without incorporating a serves as a fin. The result is a model which is quite cyclic control mechanism we took advantage of the realistic in flight, more rugged in construction, and shape of the thing. actually much simpler to build than the original Forward flight is produced by the reaction of the rubber-powered version. downwash from the engine prop against the flat front Construction: The fuselage is a straightforward of the rotor pylon which creates a force which tends to semi-monocoque keel-type affair. Build one side over tilt the nose down, and the reaction to this tendency to the keel on a flat surface to insure good alignment, tilt by the main rotor blades results in an automatic then put on the half-bulkheads on the other side and shift of pitch which propels the model forward. finish the job. Attachment of the landing gear and rotor

34 FLYING MODELS FEBRUARY 1953 side, because when the blade pitch changes at one SIKORSKY spot—in this case the front of the model —the reaction (Continued from Page 34) comes 90° behind the alteration and the model tilts Now, when the model is finished up as far as sidewise and crashes (Factually there is a reverse the special see-saw engine rotor, it may be a reaction 90° ahead of the deflection in addition, since if strong temptation to stick a prop on it and turn it one side tilts down the other must tilt up). loose— just to see what will happen. If you try this Thus the solution of this knotty little problem calls, stunt be sure to have a dustpan with you in this case, for an automatically regulating counter- because you may need it. It it quite true that you reaction that will at all times interact with the forces of can fly the model this way, and if your balance is the main rotor to provide recovery couples. good you may get away with it for half a dozen We do this by installing on the engine shaft a special flights in dead air. But, just about as you are type of rotor or propeller which is pivoted to "see-saw" deciding that Clough is an overcautious old fuddy- gimbals. This isn't very difficult to build. Simply carve out duddy, your model may tilt over on its nose and end a prop to the dimensions shown and, instead of its career in one glorious full-throttle plunge into mounting it with a hole through the center, mount it in a the ground. U-shaped pivot bearing, using a length of 1/16" steel The reason for this happening (with a stiff wire for a pivot shaft, which runs through the side of center prop) is that the main rotor blades the prop. "feather" or adjust pitch angles relative to the air What have we here? Well, this prop has fixed pressure on them at any given rotational speed. pitch, it does not feather as does the big one beneath This is a condition of neutral stability which means it, but it can see-saw on its trunnions. When the motor that the model will fly stably unless disturbed by is running, it "planes" and runs flat and true. When the some external force—all things being equal. model starts to slide, this see-saw prop tilts back Unfortunately all things are not equal in opposite to the direction of sliding. This produces a actual practice. A gust may hit the model, or a complex of forces, but essentially it serves as a drag bubble in the feed line may make the motor kick -or in that the faster the model goes the more it tilts back, bump, which may set up a jiggle or tilt which will producing a counter-reaction and an opposing cause the rotor to shift its position. gyroscopic deflection that limits the speed of the slide Study the rotor a bit. Note that it functions as a to practically zero. gyroscope. If a condition of excessive forward speed The model, which was neutrally stable with a stiff or sidewise skid occurs, we have a strong pressure center prop, now becomes inherently stable with a see- upon the tip of the lead blade (the blade which at saw prop because a positive reaction is obtained which any given moment is perpendicular to airflow on the produces automatic correction. This means the model upwind side), and this pressure produces a will simply hover in one spot unless some other factor resultant force 90° behind the point of is added to make it fly forward, and the flat front impingement, which is the characteristic gyroscopic surface of the rotor pylon takes care of that. If you reaction. want more speed in forward flight, gradually shift the This force resolves into altered blade pitch as CG ahead a little at a time until you get what you want. the weight seeks to justify its inertial forces, and In our experience, few things offer the satisfaction this pitch alteration causes another reaction back and enjoyment of a good model helicopter. This model to the front of the rotor disk which pushes the nose is a good one. Build it carefully, according to plan, and of the model down into a dive. Since this condition it will give you performance you may have believed is self-propagating, there is no hope of recovery impossible, particularly if you have tried from such an attitude barring a miraculous gust of unsuccessfully in times past to adapt model engines wind or engine stoppage which, by pulling power to helicopter practice. from the rotor, kills off the precessive cycle allowing the nose to ride up again as the blade BILL OF MATERIALS (Balsa unless otherwise shifts into auto-rotation. specified) At this point somebody is sure to ask: why 3-3" x 1/32" x 36" (medium)………….Fuselage sides not add little dihedral sections to the tip of the rotor 1-3" x 1/16" x 36" (medium hard)..…..Fuselage keel ahead of the pivot line, so that air pressure in 1-5/8" x 7" x 1/8" (hardwood)…………..Prop blank forward (or any directional) flight will impinge upon 1-4 ¼" dia. .012 thick (plastic)……………………….Fin the tip of the leading blade, forcing it to assume a 12" length of soft iron wire 1/16" O.D.; clean dis- greater pitch and lifting it upward to return the carded tin can; loop of rosin core solder; 2, 1" dia. model to even keel? rubber wheels; 1, ¾" dia. rubber wheel; leather or It won't work that way. If we try it we find that fibre; small washers; dope, cement, fuel proofer and the model, instead of diving, now rolls over on its decorations; K&B .049 engine.

44 FLYING MODELS FEBRUARY 1953

This mini whirly-bird is a lot closer to scale con- figuration-wise than you'd think; big difference is way rotors are constructed and how they work.

Semi-Scale

Sikorsky R-6 One of history's most significant 'copters by one of modeling's most unorthodox designers; it's a mighty happy combo! In flight the model R-6 is a majestic sight. You'll really stop traffic with this one. Easy to build and a real thrill to fly as a free flight job. By ROY L. CLOUGH, JR. •The Sikorsky R-6 helicopter is historically For example: A rigid, non-feathering blade important for several reasons. As a design it marked produces a nose-up resultant in forward flight, it the beginning of a trend away from unlovely steel- does not autorotate; a Clough-type tip weighted tube box structures, demonstrating that a helicopter blade produces a nose-down resultant in forward could be beautiful as well as efficient. It was one of flight, and it autorotates beautifully; an angled hinge the first to be operationally fitted out as a flying blade will tend to adjust pitching motions, it ambulance— it could carry two external pods, each autorotates fairly well, but it is very critical in holding two stretchers on either side—and it took adjustment. In the multi-phase system we use the part in many early military experiments designed to rigid blade to counter the nose-down tendency of test the utility and application of rotary wing craft. the feathering blade (as in the Berkeley model D). The model R-6 follows in the historical tradition What does the angled hinge blade do? by introducing a new model helicopter rotor system, On this particular model we wanted to use a the "multi-phase rotor" which permits use of true manually set cyclic control, which flips the mechanical cyclic control in addition to the auto- feathering blade to produce forward flight by matic cyclic and collective pitch normally used in mechanical cycling, as in full scale, rather than by models. induced or C.G. shift cycling as is generally done in The "multi-phase" rotor system is based on the models. But, if we use a fixed cyclic deflection on idea that it is possible to build three distinct types of the feathering blade, in conjunction with a fixed rotors which occupy the same space at the same time, pitch stabilizing blade, we discover that as the speed so that the reactions of one rotor are modified by the of the model increases in forward flight we have two others, etc. This is an extension of the co-axial cyclic forces: first, the fixed mechanical cycling system previously published in which one rotor was a which will always be the same, and second, the rigid-feathering affair with the other a see-saw- dynamic cycling caused by air pressure on the feathering type, the interaction resulting in an entering edge of the rotor disk. This induced cycling automatically stable co-axial system. The multi- increases with forward speed at about the same rate phase system uses three rotor blades, each with a as the nose-up cycling effect produced by the fixed different characteristic dynamic reaction. Thus we pitch blade; therefore, if we add mechanical cycling include the desirable features of each blade type, to it we find that the model will accelerate and go while suppressing the undesirable reactions in the into a dive. We could prevent this by using larger composite meld. fixed blades operating at greater pitch—but this (The reader should be cautioned that simply tossing would spoil the autorotation. together a number of different types of blades in one So we add an angled hinge blade to the system. This rotor is no guarantee that the good features will will autorotate, and as forward speed increases the emerge and the bad features be suppressed—it can air pressure in front of the disk causes it to bend come out the other way around.) downward and increase its pitch on the advancing Air Trails Model Annual '55 47

side, and bend upward and decrease its pitch on the the works and check the blade balance next. It won't retreating side. Now we can pre-set the rotor system ordinarily happen, but it is possible that the rotor with a fixed amount of cyclic deflection on the feath- assembly may balance perfectly by accident due to ering blade and the model will accelerate up to the wood density variations. If this should happen, don't point where the induced reverse cycling of the angle- fly the model this way because a little extra mass is hinge blade cancels out both the pre-set and induced required on the tips of the fixed and angled hinge cycling in the feathering blade and will go no faster. blades—about equal to a dime. If in the balancing If air conditions, gusts, tend to speed up the model operation more weight is required on the feathering the rotor system increases it’s cycling momentarily to blade with the tip weight, add this extra weight on kill off the speed, then resumes normal operations. If, the hinge line, not on the counterweight arm. Do not in calm air, we launch the model sharply nose down, put the cyclic mechanism on yet. it slides forward, slows down, then finds its own opti- The original model used a Wasp with its fuel tank mum speed, and proceeds at that rate. modified as shown on the plans so it would operate When the power stops the model descends in auto- without throwing fuel out of the vents. rotation, the rate of descent being governed by the Let's fly it. Check the C.G. location by holding the fixed pitch blade, which acts as a governor upon the model sidewise by the engine shaft. If the tail dips two automatic blades. This incidentally does not pro- down it is tail heavy and may dive; the best trial duce a wobbling descent, provided any reasonable position is very slightly nose heavy or balanced on autorotational speed is maintained—90 rpm or a the mast axis. little better. Fire up the engine and make sure it is delivering Construction full power before releasing the model—a ragged 2-4 The model is a keel job; lay out and bulkhead in cycling engine is poison. Release the model from a the usual manner. Note how the landing gear struts level position and watch it! If you have followed di- are cemented in position between blocks. Make sure rections- closely the machine will rise up steadily, these are dry before covering. The rotor mast should move forward very slowly and will probably circle not be hard steel wire—use something fairly soft so rather tightly to the left—probably a bit tighter than it can be adjusted easily. The nose block goes on after you may desire, so bend the rotor mast slightly to the covering. The covering may be 1/32" sheet balsa, or model's right, which will make it fly straight, or turn fairly stiff double-calendered paper miking about to the right, depending upon degree of bend. This, by .008. If you use paper, start at the tail and work for- the way, is your combined rudder-aileron control on ward, lapping each joint 1/8" on the bulkheads. This this type model. paper covering trick produces an extremely smooth Fore and aft trim is accommodated by shifting the sheet-metal appearance and finishes with a minimum ballast—in reverse fashion, that is, more weight for- of doping, but it is slightly heavier. Whichever cover ward to kill off a dive, more weight aft to stop tail- is used, note that the top area between bulkhead C sliding. and B must be covered before the pylon is sheathed Once the trim settings are mastered the model can in. This provides a working base to which to trim the be flown that way if desired, but the cyclic control is pylon covering. Also be sure to cut a slot for the rear more fun since it allows a choice of vertical ascent or wheel strut. horizontal flight at the flip of a lever (or more ac- The tail rotor is simulated by a plastic disk. Edge curately, the bending of a wire!). Trim the model to it with a circle of rattan or reed to keep its shape. It rise vertically with a minimum of forward motion, functions purely as keel surface. Cabin detail is then install the cyclic control. Simply cement a length painted on in a contrasting color—silver blue makes of paper clip wire to the side of the pylon, as shown, a good "glass"—and the front of the machine may be and solder a short length of springy steel wire to the doped as much as desired since additional ballast will arm holding the feathering blade and blend it so the be needed in any event to balance the tail boom. blade is flipped gently each revolution. Vary the Before tangling with the rotor mechanism study position of the tripper by bending it up or down to the plan carefully. Sheet metal parts may be cut from regulate the cyclic deflection—not much is needed. tin can stock or secured from a Berkeley kit where Now, with this control, and by varying the rotor applicable. The big idea here is to have everything tilt you can make it climb straight, fly forward, tight that should be tight and freely-working on cruise in circles or any combination desired. Near- pivots and hinges. The rotor mast bearing should be hovering can be obtained by cutting the fuel with a very free, almost sloppy, but the pivots should work straight 3-1 mix of alky and castor oil. easily without any play for best results. The rotor blades are very simple, and while you're . Guide to Helicopter Adjustment at it make a couple of spares, just in case. Assemble Model helicopter flyers may find it easier to re- Sikorsky R-6 built in 1943 was the first military high-performance Glidden Doman of Doman Helicopters, Inc., used an R-6 to experi- helicopter. It would climb to 5000 ft. in 7 minutes, could carry bombs. ment with his dynamically balanced rotor system (no vibration).

Air Trails Model Annual '55 48 The cabin ol the R-6 was built of molded plastic impregnated Fiber- glass, probably the first use of this material in production aircraft.

member helicopter model adjustments by making an analogy to fixed wing practice, thus: Conventional Equivalent Helicopter Horizontal Stabilizer Fixed pitch rotor blade or See-saw engine prop or Torsion tail surf ace (s) Ailerons (wash-in—out) Lateral mast tilt Rudder Tail rotor, mast brake, downwash fins under mo- tor. Thrust Line Center of gravity location moving aft increases D.Th. Glide Angle Speed in Vertical FPM in Autorotation

Therefore we note that increasing the pitch of the fixed blade (s) reacts similarly to increasing the angle (negative) of a horizontal stabilizer, bringing the nose up under power, or, decreasing the gliding speed (rate of descent, power off). The rudder function, yaw, is obtained by a tail rotor, by a brake on the spinning main rotor, or by means of fins tending to promote or stop rotation of the fuselage in the slipstream. Aileron control, or bank-turn is by tilting the rotor laterally so the engine shaft inclines toward the desired direction, and altering the dynamic pressure on the feathering blades by moving the C.G. aft Full-size plans for the Sikorsky R-6 are part of (or forward) resolves out as down-thrust or up-thrust Group Plan # 55A from Hobby Helpers, 770 Hunts respectively. Point Ave., New York 59, N. Y. (50¢)

Air Trails Model Annual '55 49

30 YOUNG MEN

FLY THE ALL-ALUMINUM PLANE!

• Suzie looks like a rather complex bit of sheet metal work, but actually this gleaming aluminum beauty can be yours at a cost of so little time and effort that you won't believe it until you try. SHEET METAL The trick is the use of simple basic geometry which will distort naturally into the shape we desire. We squeeze the ends of a cylinder and there is our fuselage; we draw together the sides of a right angle and there is our wing sec- tion. By ROY L. CLOUGH, JR. The main disadvantage of sheet metal models SUSIE is the effect that high frequency engine vibration has upon metal-to-metal junctures. This punishing vibration will erode or fatigue the No hot fuel problems here; Susie's unique vibration toughest metal in a short time. Add to this the rough shocks of repeated landings and it is easy isolation assembly means a long-lasting model to understand why the operating life of MARCH, 1956 metal models of the past has been brief. the bulkhead in place in one end, mark up simply by twisting one way or the Suzie was designed with the elimina- and then remove the bulkhead, line up other, and when you are satisfied with tion of this weakness as a major point the cylinder, prick and drill and bolt the the alignment notch out the fuselage of effort. Note: there are no direct metal- edges together with ¼" round head 4-40 metal around the landing gear legs—this to-metal component junctures; no points bolts and nuts. (Riveting is okay if you will maintain the arrangement. You may where metal can chatter against metal, have the equipment.) wish to drill for the wood screws now and no points where heavy mass or Now observe the inside edge of the lap and put them in place temporarily. flight loads fall upon flat, or unsupported joint; this must come at the bottom right With a straightedge draw pencil lines sheet metal areas, in concentrated fa- (outside) fuselage. With this in mind down each side from the stabilizer cen- shion. Engine vibration is isolated and gently squeeze the tube into shape to ter to the centering marks on the bulk- absorbed by a wood bulkhead, which receive the tailpiece, the wood rudder, head. Balance the assembly between also takes landing shocks; the wings are and bolt this in place. Run a #3 drill fingertips and mark at this point. (This attached to a wooden spar, as are the tail through the sides, taking care to be will vary somewhat between the ultra- surfaces, the wood in turn being attached perpendicular to the rudder piece and light Cub .14 and something heavier, to the fuselage. The result of this type then carefully slit the fuselage as shown like an O&R .23). Do not make any al- of construction is a model which will and bend the resulting tab upward on lowances for missing elevators or prop, still be flying years from the time you each side. Drill and bolt the hardwood but cut for the spar at this point in build it—provided you don't run it into stabilizer to these tabs—a modicum of similar fashion as for the stabilizer-spar, stonewalls too often. bending is permissible if necessary for except that the tabs here are on the bot- How about the weight? good alignment. tom. Poke the wing spar into place, drill We won't kid you. Suzie is fabricated Set the fuselage aside and make up the and bolt temporarily. from .019 aluminum sheet and this stuff engine - mount - bulkhead - tank - landing Only at this time do we cut out the isn't microfilm. She squats on the take- gear assembly. This is a separate and in- cockpit. Use a coping saw and leave the edges rough, smear with Pliobond ce- off line with a full tank at 24 oz., and dependent unit and note that the engine ½ uses up one-third to half a circle to get shaft will be off-center to the left; re- ment, slit a 12 " length of heavy-wall airborne with a Cub .14—the smallest gardless of what engine you use, the black neoprene tubing and push it in engine you should use. Once aloft, how- shaft position will be dictated by having place as moulding around the cockpit ever, she flies as good as any sport-type just the glow plug tip project beyond the rim. model with an elevator response, climb fuselage side. This permits use of the (Continued on page 81) and dive, which belies its weight. When popular "flat-opposed" type of engine the engine quits Suzie whistles into a cowl. Next take the nose assembly and high-momentum glide as flat as a stick it into the open fuselage end—line Full-size plans for Sheet Metal Susie are tabletop and keeps pulling on the lines your assemblies up simply by twisting found on Group Plan #356 by Hobby until she stops rolling. You'll like her. one way or the other, and when you are Helpers, 770 Hunts Point Ave., New Construction: satisfied with the alignment notch out York 59, N. Y. (35c) Stop in at your local building material the fuselage end—line your assemblies outlet and ask for a couple feet of 24" aluminum flashing. This shouldn't cost over 75c. This stuff should mike about .019; don't get the heavy-duty .024 grade. Note that this material has a "grain," that is the long way and you'll get a better and easier job by observing the lay of the metal. Cut out a piece 18" x 10" and roll this into a cylinder, then get your perimeter dimension by setting

Sheet Metal Susie needle valve and lead this (Continued from page 31) through the cowling. Four nic- Now for the wings. These kel-plated wood screws hold FULL SIZE PLANS are simply cut out and bent to the whole front end together. YOUNG MEN & AIR TRAILS MODEL ANNUAL shape with the trailing edges The elevators are next. Use bolted or riveted together— a stitched bias tape hinge and Group No. 256 50¢ ENCLOSE COIN OR MONEY ORDER there is a little trick that makes roll an inter-connector of 1/16" "BUNKER BOAT" by Cal Smith and Frank Lashelt. The long awaited fishing boat model for electric power, can be radio it easier and more foolproof, wire into the flippers as controlled Scaled 5/16" to foot, 35¼" long, 6¾" beam First shown on June 1955 cover of ATHFYM however. Clamp the metal shown—it is fairly easy, but Group No. 356 35¢ along the leading edge line maybe you would like to ENCLOSE COIN OR MONEY ORDER "SHEET METAL SUSIE" by Roy L Clough, Jr. Aluminum between a couple of stout practice rolling a bit of scrap covered control line model that's easy to make and a snap to fly. Extremely durable model. Spans 27 Inches; overall length 21 sticks and bend it to 90 with wide flat nose pliers inches Uses 14 to 23 power plants degrees, then remove the sticks first. (This is a good trick to FOR SPECIAL HANDLING( Add 9¢ per plan—1st class ) and finish bending by hand to a know—once you learn it you'll of Plans Only ( Add 18* per plan — Air mall nice "natural" symmetrical never be caught short for a bit NEW 1956 CATALOG 12-5 section. Then hold the trailing of tubing for any purpose!) The 28 PAGE, FULLY ILLUSTRATED. SEND 10¢ TO COVER HANDLING. edges together with the sticks elevator horn is simply an while you drill and fasten them integral tab on the left side. together—this prevents a Make up the tailskid and bolt HOBBY HELPERS wavy edge from developing. this in place. We put the con- 770 HUNTS POINT AVENUE NEW YORK 59, N. Y Remove the spar bolt from one trol quadrant under the left side, slip the wing over the wing, pivoting on the inboard spar, spot the inboard hole and bolt for simplicity, but you the one near the end of the spar can pick up a little speed by and drill them. Dig up a couple putting it inside the fuselage, of "J" bolts and drill into the on the spar, if you wish to underside of the wing and the take the extra trouble. If an side of the fuselage and install external horn is used, make up a the "J" bolt with a fiber wire line-guide and bolt this in washer between wing root and place with the spar tip bolt. fuselage as shown on the plan The deep tail and the skid view. Do not omit this! places the model in proper Now do the other wing, take-off position, just let it spotting the "J" bolthole so as taxi—it’ll take off by itself as to provide a slight amount of the proper speed is reached. washout effect on the outboard Check all bolts for tightness wing. Next put in the balsa after the first flight and end caps, sticking them in place occasionally after that until with Plio-bond. The cowling is you are sure she has snugged simply a strip of aluminum down to business. Never wipe wrapped around the nose, sand or dirt away with a rag, slotted for the landing gear legs wash it off with kerosene to and the glow plug tip and held prevent scratching the metal. together with a couple of bolts or rivets at the bottom. You will find it easy to bump a nice edge on the cowl using an inkbottle form (one of the oval ones) and a plastic mallet. (From my experience I suggest you use an empty inkbottle!) Add an extension to the

By ROY L. CLOUGH, JR. Saturnian

SPACE SKIMMER

• This ultra-weird and flashy, U-control looks like it just zoomed out of the pages of a science-fiction magazine. A start- ling eye-catcher, our vane-winged dreamboat has a lot to recommend it besides its unusual looks It is easy to build, easy to fly and never breaks a prop. Odd as it may seem, lift is excellent despite the unusual fore and aft arrangement of the lifting surfaces This permits a very good glide and nice handling charactestics. The huge dorsal and ventral fins which flare forth so rakishly are not just decorative, they're functional. They provide lift to hold the model out when flown near the vertical, an idea we may see adapted to future stunt jobs The construction, although specialized to fit the unusual geometry, is quite ordinary in method. Start with the cabin or pod.

which is built up on the plywood cross beam. This may be covered with 1/32" sheet balsa, or stiff tag stock Take particular care with the engine installation since the thrust and surface incident lines must be parallel. We used a Space Bug Jr. running backwards. A left-hand Wasp would also do the trick, or the ambitious could carve a left-hand prop for any .049. Regardless of the engine used, note that the tank, if integral, must be arranged so the fuel will feed properly. Generally this will mean running the engine on its side with plastic lines attached to the filler and vent and brought above fuel level. Make up the wing vanes, joined at the rear with the stabilizer and elevator and stiffened with the long fins. Note how the joint goes together between the cross beam and the wing vanes, stiffened by the projection of the long fins. Use plenty of cement and give it plenty of time to dry. Check the thrust line against the wing plane and add the struts next. Tie control system hardly requires explanation, except to note that unlike most models, your Skimmer has no lead-out wire. The control lines attach directly to the control quadrant. A wheel landing gear may be added if desired, We built one into the original in order to locate the correct placement for those who wanted a wheel. However, there is a lot to be said in favor of flying the model hand-launched or with a U-Reely, and it looks even more "unearthly" without it. Much of the charm of this model is its color scheme, the flasher, the better.

Modeling a rotor sailing ship

By ROY L. CLOUGH, JR

Anton flettner's famous rotor ship Buckau which also provides rotary shaft power to spin was propelled by spinning drums upon which an underwater propeller. It's actually a the wind acted to produce thrust. While it Magnus windmill that will spin regardless of required a small motor to spin these rotors, the the wind direction. main source of power was the wind harnessed The thrust produced by the rotor is in direct through the Magnus effect—if a drum is set to proportion to the speed at which it turns. How- spinning in a wind, a thrust vector is produced ever, you will note that this rotor has been at 90 deg. from wind impingement. loaded with a rather large propeller which Unlike the original rotor ship, this little holds down its speed, since the propeller model uses an un-powered modified rotor thrust must be greater than the rotor thrust. The reason for this is actually quite simple. When the model has the wind on its port beam, the thrust of the clockwise rotor is dead ahead, but when the wind is on the starboard beam, the rotor thrust is toward the rear of the ship. In the first instance, the rotor thrust is added to the propeller thrust, but in the second it is subtracted. Thus, the greater prop thrust makes it possible for the model to tack either way. The graceful little hull will go together as easily as a box if you allow the cement to dry well between assembly steps, Solder the shaft-log bearing into a bit of tin-can stock and The two sides should be attached at the stem and stern block, and then sprung apart so that the cement it into the hull. The deep keel (pine) bulkheads may be inserted. Pin the guide strip to the should be cemented and nailed to the hail. keel so that different sections of the bottom planking Drill an. undersized lead hole in this and drive may be aligned easily in the 1/8" wire mast. Ballast can be a length of old shafting, solder, Babbitt or type metal, soak the balsa. To shape the vanes of the rotor, soak the balsa until it's pliable, and then bind the two sheets around a 2-1/4" mailing tube which you have covered with wax paper. When dry, you can make minor dimensional corrections by springing them slightly during assembly. Next, roil up a tube of stiff paper, soak it well in model airplane dope and mount it between the rotor end disks on locating plugs. Finally, glue the curved vanes in place. A rotor sailor makes the best speed when the wind is on It's particularly important that the gearing the port beam. At varying angles in front of the wind the and shaft in the power tram work freely, speed will vary with the thrust vector resultant flattened egg-beater gears were used in the model illustrated, but many similar gears would have worked just as well. Be careful to align the cross member which supports the upper part of the propeller shaft. This should mesh perfectly with the gears. You can adjust the location of the rotor gear by slipping washers or bits of tubing over the rotor mast so that this gear engages the prop shaft gear favorably. The shaft-log bearing may be very loose and still not leak water, since a couple of drops of lubricating oil will be enough to keep the water from entering. Gears which link the rotor to the propeller may be salvaged from any clockwork mechanism. However, be sure to mount them so they mesh perfectly and work easily

Roy Clough PDF files (Rock collection)

Air Car Saturian Basic Design Problems of Model Helicopters Sheet Metal Susie Blow-Bug Sikorsky R-6 Build Your Own FLYING SAUCER Sikorsky S-51 Channel Winger Slat Wing Cloud-Copter TR Snapper CLOUD-COPTER-D Spinning Disc Saucer CLOUD-COPTER-TR Spinning-Wing Clough Helicopter From Toys and Games Sure Fire Clough autobiography Tan-Giro FULL Expansion Engines Tan-Giro Tiled Gyro Kite The Model Copter Hoopskirt The Whirligig Hover Bug TRIAD Hydro jet Powers Little Speedster Try a Turbine LITTLE DRAGON b Typhoon Engine LITTLE DRAGON original Venusian Scout Martian Space Ship Water Bug More on Helicopters What's the score on helicopters? New Model Helicopter WhirliC02pter Original Channel Winger Whirly Bird Kite b Parasol Plane Yankee Flea Peter 0'Dactyl Build it... and watch it soar 1,000 feet in the sky:

New Model Helicopter:

By Roy L. Clough Jr.

designs to succeed really well. EVER since the first helicopter got off the Its secret? Most early models were such ground, model-makers have been trying to complicated contraptions that they sometimes design a miniature version that would do the worked-but more often didn't. The new one is same. Here's one of the first model-helicopter ingeniously simple in construction, yet makes

"HERE'S a radically new free-flight helicopter,” says noted model-airplane authority Howard G. McEntee, shown at left flight- testing the model for POPULAR SCIENCE. "Its ingenious engine-on-rotor-blade design is the first such I know of. It gives the model a stable, soaring flight, uncomplicated by the many problems that have plagued other copter designers for so long." Why It Flies

use of half a dozen complex principles of Poke at the rim of a spinning gyroscope flight. The result is a fascinating study of 1and it immediately tilts. But not aerodynamic problems that have plagued where you touch it—instead at point designers of both real and model copters 90 degrees past where you touch it. Scientists call this "precession." In the for years. PS helicopter, the whirling rotor acts The power plant is a glow-plug engine. like a horizontal gyroscope and the propeller blade a vertical gyroscope.

To keep a copter level, rotor blades must Whirling blade-tip weights react 90 degrees 2decrease pitch on forward stroke to balance 3later to the force at the tail by twisting reduced lift of rearward stroke—called "cyclic blades down on copter's right side. This re- pitch." This is done by weighting the model duces lift as blades advance into the wind. tail-heavy so it pulls down on the blades at At same time, air pressure against the down- the rear—like pushing on rim of a gyroscope. tilted blades exerts a new force on the rotor.

Blade tips, again acting as a gyroscope, Blades spring back up on left side to take 4react 90 degrees later to force of air on 5full bite of air. Since lift is less on rearward the right side by tilting down in front. This stroke away from the wind, the full-pitched tips the nose down so the copter, while tail- blades now balance reduced-pitch blades on heavy, tilts forward for straight-ahead flight. opposite side, and the copter flies level. CONTINUED 147 How you can build the gas-model helicopter

like that used in most model planes. But instead of being mounted inside the fuselage, the engine is attached directly to one of the copter's three rotor blades. In most conventional copters, both real and model, the engine drives the rotor from a central shaft. In turning the rotor forward, it "braces its feet" against the fuselage and also pushes backward. This backward torque keeps attempting to spin the fuselage in the opposite direction from the rotor. In full-size copters, torque must be offset by a Underside of rotor hub shows how spider forces two non- separate stabilizing tail rotor or other special powered blades to tilt at the same angle as powered devices to keep the craft flying straight. In the blade. Wire blade stems are bent at right angles to engage holes in spider plate. Solder parts with hub held model shown here, the blade-mounted engine flat, upside down, to insure uniform alignment of the pulls the rotor around instead of pushing it. It blades. creates no torque and thus needs nothing to counteract it. 148 POPULAR SCIENCE MAY 1962 The model is a whopper, too—nearly 4' across the rotor tips. Yet, despite its size, it's so efficient that it flies on a tiny .020 Cox engine— one of the smallest made. Designed for free flight, it has hit altitudes of 1,000 feet on two minutes of fuel, giving it a rate of climb of 500 feet a minute. Earlier models have required much bigger engines to achieve the same lifting power. How the model flies. The three rotor blades are pivoted loosely at the hub, leaving them free to tilt up or down like the elevator on an airplane. The blades are also linked together at the hub by a bell-crank mechanism so that whatever one blade does, the other two do likewise. Unlike a conventional helicopter, however, no special controls are needed to tilt the blades up or down for takeoff or landing, or to provide complicated changes, known as cyclic pitch, during flight. They're automatic. The trick is based on the fact that the whirling rotor and the spinning propeller [Continued on page 186]

How the model climbs

Whirling propeller acts like a gyroscope in the same way as the rotor, but this time in a vertical plane. It reacts at 90 degrees to the sideward twist on it by tilting upward. This tilts up the rotor blade (and the other two blades linked to it), giving the helicopter lift for climbing.

How the model lands When the engine quits, the upward gyroscopic twist on the rotor blades also stops, and they pivot freely. Upward air pressure on the trailing edges forces the blades to tilt down, and the helicopter glides slowly to earth.

New Model Helicopter: Why It Flies [Continued from page 149] attached to the rotor both act like When the plate is twisted by the stem on gyroscopes. As the drawings show, a the power blade, it in turn twists the stems gyroscope reacts to a force placed on it by on the other two blades to a like angle. tilting at 90 degrees, or sideways, to the The U-shaped stop bracket should limit original point of force. This is used in the plate's movement to provide a several ways to provide stable flight. maximum of 12 degrees upward blade pitch The upward gyroscopic twist of the pro- for climbing. Downward or negative peller tilts the rotor blades up to give the pitch should be set as shallow as possible copter lift for taking off and climbing. A for a slow, leisurely descent. similar gyroscopic reaction is given to the Note that the engine is mounted at an rotor by weighting the copter tail-heavy. angle on the rotor blade, rather than This causes weights fastened to the leading straight-ahead. This puts its thrust line at edges of the blades to twist the blades a tangent to its circle of rotation. If it downward and reduce lift as they advance pointed straight ahead, it would exert a into the air stream—just like the cyclic- side thrust on the rotor as it whirled around. pitch mechanism on big copters. Note, too, that it is turned partially on its An additional gyroscopic reaction in the side, with its cylinder tilted inward toward rotor forces it to tilt downward at the nose the rotor hub. This puts its fuel reservoir to keep the model flying forward. Earlier in line with centrifugal force so the gravity attempts to make a model copter fly feed will continue to operate even though forward by simply weighting it nose-heavy the engine is being slung around sideways proved disastrous. The rotor, pulled down by the rotor. at the front, reacted like a gyroscope and The engine must also be tilted slightly flipped over, on its side, sending the craft downward to minimize the force of its crashing to the ground upside down. slipstream. The slipstream tends to turn the Earlier models had another fault: Blade copter's fuselage to the right, but is offset pitch was fixed at an upward angle for by the rotor's downwash and bearing climbing. To provide the downward pitch friction, which tend to swing the fuselage for landing, the rotor had to come to a to the left. stop, then reverse its direction. This time The engine can be mounted on the metal lag caused the copter to drop a long bracket shown in the construction drawing distance before the reversed rotor got up or, for a neater appearance, can be faired enough speed to break its fall. In the new into the rotor blade with a shaped balsa design, the pivoted rotor blades continue block, as shown in the photos. If a larger to turn in the same direction, but engine than the .020 Cox is used, it will automatically tilt downward when the require additional counter weighting of the engine stops to let the model glide gently rotor blades. In this case, add the extra to earth. weight to the tips of the blades themselves, Only the rotor is tricky, the copter's not to the tip weights, which must remain fuselage is a simple sheet-balsa job. But the same. the rotor, the heart of the craft, must be Flight-testing the copter. An ROG (rise- carefully balanced to provide correct blade off-ground) takeoff is slower but safer at pitch and avoid vibration. The blade-tip the start since you can see what's weights are blobs of solder, each equal to happening. When all adjustments are the weight of three nickels. They are used perfect, you can go to the faster hand- only on the two non-powered blades as the launch. engine supplies the weight on the third Begin with a 6"-diarneter, 3"-pitch blade. After the weights are mounted, plastic prop and trim it a little at a time gradually shave off bits of solder until the until the engine reaches maximum r.p.m. rotor remains balanced in any position. Hold the ship by the tail until the rotor Weight the fuselage with clay until it gains speed, and duck out of the way. The balances at a point 1/2" behind the rotor's model should rise slowly, then tuck its nose axis. This will make the ship slightly tail- down and climb in a right-hand spiral of heavy as required for proper flight. 20' to 30' in diameter. During trials and on Blade pitch is controlled by a spider- windy days, let some of the fuel flow/ shaped plate on the underside of the hub. through before letting go—or you may wish This works like a three-way bell crank. the copter didn't fly so well. •

(86 POPULAR SCIENCE MAY 1962

....MORE ON

HELICOPTERS by R. L. CLOUGH JR.

Twin spool drive of tail prop is used on this model Coaxial rotors eliminate torque propeller

THE design of a helicopter poses otherwise very satisfactory once the fuselage now possesses a stronger many problems which often cannot be proper relationship has been worked out. relative wind; it is in effect flying into solved by analogy to fixed-wing Rotor speed should be high enough to the wind at the speed of the wind, but practice. provide a good slipstream over the vane with the important difference that no In "Basic Design Problems of the Model and slow enough to permit a fair momentum is produced as a result of this Helicopter" (M.A.N. Sept. 1945), the duration. Theoretically the rotor forward flight. Therefore, it may be writer endeavored to present briefly, and should be as small as possible and of seen that "groundspeed" is an important in general terms, several types of flying very low pitch. It is necessary to factor in reckoning performance model helicopter arrangements together incorporate a cyclic pitch mechanism if characteristics of helicopters. with their characteristics. forward flight is desired. The CG should If a helicopter is hovering into a stiff Since that time two new types of come slightly forward of the rotor axis breeze and that breeze suddenly ceases, helicopters have appeared, both of in order to balance the drag of the vane. the machine is apt to drop to the ground which offer interesting possibilities to the To understand thoroughly the (such accidents have occurred) But, if model experimenter. Also during this difference between helicopters and the machine is flying forward at a good interval, the writer found time to conduct conventional aircraft—and this rate of speed into the wind and the wind further investigation into the subject and understanding is the difference between ceases, the momentum of the mass will has reached a few conclusions, which success and failure—it must be realized accelerate it as the air resistance drops should be illuminating. Many incidental that, unlike the airplane, the helicopter is a and "carry over" loss of altitude will be mechanisms were tried, many discarded machine of variables. By way of negligible. and a few retained. illustration let us consider a conventional The effects of this differential of inertias Fig. 1 represents the dual rotor inter- model plane. The performance of such a are quite marked in helicopters and in meshing machines. The Kellett and machine is fixed and does not vary; thus some maneuvers can become very com- Flettner helicopters utilize this form of at a certain speed a certain amount of lift plex. In the practical application to our torque nullification. On full scale is produced. The fundamental problem of designing stable model machines the rotors are meshed by performance is the same whether the helicopters it serves to remind us that it gearing, but in models it is possible to machine is under power or gliding; this is not wise to go overboard on the construct the rotors in such fashion that is because the machine is one distinct matter of "pendulum stability." Too they mesh of themselves. Use of piano mass in motion. great a distance between rotors and wire sections near the hubs is a fairly Now, in the helicopter we have the fuselage is likely to accentuate swinging good substitute for gearing as well as rather paradoxical situation of part of moments rather than minimize them. providing a desirable degree of blade an airborne mass being exposed to a Relative wind differentials must be articulation. Both rubber motors relative wind (the rotors); and part of borne in mind as well when designing should be of the same tension, and the mass (fuselage) having no relative rotary wing craft. When the fact that winding is best accomplished from the wind or greatly varying degrees of the relative wind over the rotors and over underside. Rotors must be of equal relative wind depending on the velocity the fuselage have different effects, is degree of pitch and very well balanced for of the mechanism as a whole through thoroughly digested, many seemingly good results. the air. baffling problems are made clear at one Fig. 2 is a single rotor helicopter with Let us repeat the above, substituting stroke. torque effect compensation obtained by "kinetic energy" for relative wind. The Power, the degree of power that is, is means of an airfoil shaped tail vane, kinetic energy of a flying machine is the another important factor. A rubber band which is provided with an adjustable flap. product of its speed times its mass, minus motor's output varies with every This type is particularly well adapted air friction or drag. Thus a helicopter in revolution of whatever mechanism it to models and will probably be the hovering flight, in calm air, has a relative drives. This humpbacked power curve of favorite in future duration contests. It wind over the rotors, a much smaller rubber has considerable influence upon has amount over the fuselage, and no kinetic the design of models so propelled. the disadvantage of over-correcting for energy of the mass as a whole. When Often it is torque when fully wound and under- hovering into a strong breeze the above correcting when nearly exhausted, but is factors are the same, except that the

MODEL AIRPLANE NEWS May, 1947 39 necessary to alter a design to a methods of obtaining freewheeling by nately the solution is not that simple. considerable degree from what it reversing direction of rotation are shown Picture a two-blade rotor spinning in a "should" be in order that stable flight in Fig. 4. Both these methods are horizontal plane. When hovering, the lift be obtained through all phases of the adaptable to various types of rotor of each blade is equal that is each blade power curve. arrangements. Of the two, the coil spring is moving a similar mass of air The over-powered model helicopter is is the most positive, but in some situations downward. Let's assign an arbitrary tip lifted rapidly and stops climbing very the friction disk setup is more practical. speed to the rotor of, say 100 mph. Now, suddenly—with the effect that inertia may Friction disks should be alternately inner by shifting the CG of the rotor we carry the machine a bit higher after lift tube rubber and coarse emery cloth or cause it to move forward at 50 mph. ceases, permitting the machine to fall sandpaper. What happens? The blade advancing free until it attains sufficient velocity for In the previous helicopter article the into the slipstream encounters a relative the fuselage area to act as fin surface and writer laid great stress on the necessity wind of 150 mph, its own speed, plus the invert the model. for well-articulated rotor blades to speed of forward motion; the blade The properly powered model rises more minimize forces set up by gyroscopic receding from the slipstream encounters a slowly, perhaps to a slightly lower action. At this point something called relative wind of 50 mph, its own speed, altitude, and performs the transition "cyclic pitch" should be explored in minus forward speed. Such a difference from climb to controlled descent without some detail. in lift makes the arrangement un- the weight of the machine being Cyclic pitch means independent flyable; it simply wouldn't remain right removed from the rotors and transferred control of the pitch of individual rotor side up. to the fuselage at any time. blades at various positions as the rotor Therefore, in order to make a single It may be stated that the ideal power turns. By means of cyclic pitch rotor stable in forward flight it is neces- loading for any given model helicopter mechanisms the angle of any blade may be sary to incorporate a mechanism that is the highest which can be achieved increased or decreased as it passes will decrease the pitch of the advancing without sacrificing desired flight through any segment of the rotor disk. blade and increase the pitch of the characteristics. More simply: use the Thus it is possible to increase the lift receding blade to an extent which will smallest possible amount of rubber. produced by the rotor on one side and equalize the all-over lift of the rotor disk. There are several types of flight decrease it on the other. This causes the A mechanism for producing cyclic performance possible: (1) power climb, rotor to tilt toward the side on which lift pitch in models is shown in Fig. 5. This power braked descent; (2) power climb, is decreased. Increasing the lift of each is quite simple and produces less friction free-fall descent; (3) power climb, blade as it passes through the rear of the than some methods that have been reverse free-wheeling descent; (4) power disk causes the machine to move forward; suggested. The rotor hub is thin brass climb, over-riding freewheeling descent: increased lift at the front causes it to tubing through which is slid the blade (5) horizontal flight, landing being move backward. Thus the force which holder before the blades are affixed. accomplished while the machine is still is applied to single rotor helicopters to Cyclic control is obtained by means of an under power, (It is almost impossible to secure forward flight is not a constant eccentric mounted disk, which may be secure hovering flight in rubber powered thrust as in the case of propeller driven shifted about and pinned to secure helicopters without using a very tricky planes but is like a series of "jiggles" horizontal flight in all directions. This automatic pitch rotor head.) which nudge the machine along. This disk controls the movements of a small Of these types No. 4 is the most accounts for much of the vibration wheel or roller, which in turn transmits its desirable, and often No. 1 is the most incident to machines of this type. movements to the rotor by means of a practical. Fig. 3 shows a method of Now it would seem that forward flight simple linkage. It is desirable to have a obtaining overriding free wheeling (and, could be attained as easily by shifting the pin and hole setup in the plate upon incidentally, automatic pitch). This center of gravity in relation to the rotor which the cam is mounted in order to method can be adapted to either co-axial axis, as is done in many co-axial prevent it from shifting while the model or single rotor designs, and produces machines, and avoid the vibration caused is in flight. A light coil spring between the very realistic nights. by cyclic pitch. To a casual observer this roller arm and rotor shaft is necessary to If greater simplicity is desired, two appears to be quite logical, but unfortu- prevent (Turn to page 64)

40 MODEL AIRPLANE NEWS . Moy, 1947 ... More on Helicopters (Continued from page 40) "floating." Sometimes, depending on the vertical and forward flight by flying forward flight characteristics. At any size of the rotor, static balance weights with or without various small weights. rate either one appears to be better than ahead of each blade will give a smoother A slightly more complicated method is a perfectly flat disk, and the writer performance. shown in Fig. 7. With this setup the suggests that builders try both and de- The rotor head of the model with tail motor tube is moved fore and aft cide for themselves. Much can be prop illustrated herewith is an attempt to along an arc by means of a movable said in favor of either. secure fully automatic cycling. This guide plate and pivoted thrust bearing. Sometimes, after carefully designing model is flown forward by adding a A friction holder is required on the and building a helicopter of his own de- small weight to the nose, the angle of the movable plate to prevent shifting in sign, the experimenter finds that blades on each side of the rotor being flight. When laying out a model of this despite all his efforts the machine will controlled by air pressure on them. type, be sure to allow ample not perform as intended. What is This method shows promise, although clearance for the rotors at both wrong? the-writer has had only indifferent extremes of movement so they won't First, check the model for gyro effect. success with it to date. The crux of hit fuselage or tail surfaces. The procedure is relative in nature and the matter seems to be obtaining the Slipstream controls may be used to must be learned but is not difficult. proper static balance. turn the nose of the model right or left Wind up the rotors and hold the Now the question is sure to be raised: (or correct turning tendencies), secure machine nose down. Releasing the "Is it possible to obtain forward flight in forward flight, or may be used in con- rotors but not the fuselage, move the machines of this type without using junction with CG shift to obtain ex- machine around in various directions cyclic pitch?" The answer is "Yes," but tremely accurate trim. Several types of about its longitudinal axis. If there is in a rather weak voice. If the rotor slipstream controls are shown in Fig. 8. considerable resistance to such speed is high enough and the forward Control surfaces of this type on a heli- movements, the chances are that the speed of the machine slow enough, a copter differ in function from that of a blades are gyroscoping. This calls for fairly decent horizontal flight can be conventional plane, and it is important more sandpapering to add flexibility or obtained—but the rotor must be highly that this difference be understood. easing up of the articulation system if articulated. If the speed increases above In a conventional plane, control sur- the rotor is of that type. a certain critical point, however, the faces are used to set up or arrest If the machine rises but shows a ten- model will tilt and begin to fly sideways turning moments around one or dency to oscillate, the trouble may be at the same time, which condition will several axes. (Flaps and slots are no caused by an unintentional pitch differ- soon resolve itself into the helicopter's exception; neither are they true ential between two or more blades of the equivalent of a nose dive. controls.) In the helicopter, only one same rotor. Check the pitch carefully, Several methods of transmitting power control surface effects a turning using a template to insure uniformity. to. the torque prop are shown in Fig. 6. moment, that is the heading surface Plain and simple wobbling is usually "A" is the common sandpaper-faced pul- which points the machine in the desired caused by unbalanced blades or uneven ley and string belt arrangement, "B" is direction. The other surfaces are not as tracking. Another type of wobble diffi- the flexible shaft drive which uses alu- much control surfaces as they are sec- cult to correct is caused by "puffs" of air minum and neoprene tubing and a fric- ondary propelling surfaces and act by striking the top of the fuselage aft of the tion roller at the rotor head; and "C" is reaction to direct slipstream in a direc- rotor axis and ahead -of it at different the wind-up, wind-down string and spool tion opposite to that in which forward times. This effect is most often system in which the string winds both motion is desired. This is the function of noticed in machines employing a ways at once and rewinds itself auto- the "elevator" shown in Fig. 8, as should three-blade rotor. For this reason the matically as the main rotor is turned. In be quite clear from the drawing. writer recommends that rotors having any case the blades of the torque prop It. must be noted that the resistance of two or four blades be used. This may should be adjustable. these control surfaces at a distance from sound like a small thing, but in In dealing with the problems of con- the rotor axis has a tendency to helicopters it is often the small things trol of co-axial model helicopters we produce a condition similar to that of that count. find there are several methods that give CG shift, and this effect must be taken The helicopter experimenter should good results. Because there are two into consideration when designing this never take it for granted that something rotors turning in opposite directions in type of model. which is good practice in airplanes will co-axial machines, it is possible to A question, not covered work equally well on rotary wing craft. make these fly forward by adding exhaustively in the previous article, is Usually it will not. However, if there is weight to the nose or by shifting the that of "coning angle." Coning angle is ever any theoretical doubt as to angle of the rotor axis. In models there the helicopter's dihedral angle. It is_ the whether or not a thing will work, try it! are two good methods of obtaining angle of "dish," positive or negative, of a Some of the most important inventions forward flight by CG shift: the simplest spinning rotor. From the writer's have been accidental discoveries. Such is to add weights to a hook in the nose. experience it seems difficult to lay discoveries are the rewards of This works well on experimental down any hard and fast rule regarding providence to an inquiring mind—and machines and is very convenient. A it. Apparently it is wise to use positive certainly nothing to be ashamed of. model using this method should be cone on single rotor and dual rotor Good luck! slightly, tail heavy without weights machines. With co-axial machines making it possible to obtain reverse, negative cone seems to give the best 64 MODEL AIRPLANE NEWS . May, 1947 Conventional model-plane power plant pushes little niques are used to build the craft from balsa. The craft over water, and standard model-plane tech- nacelle accepts most .020-049 radial-mount engines. MODEL HYDROPLANE Skims Pusher prop spun by model-plane and control systems to keep them at proper depth. Surface-piercing foils au- engine gives high performance. tomatically adjust for depth—but they Construction is easy and fast also have a tendency to create air bub- bles that reduce lift. The PS model uses a foil design that minimizes this unde- By ROY L. CLOUGH JR. sirable side effect. Instabilities can develop in either type of foil. This is particularly true of mod- els. Simply put, the angle necessary to ydrofoils have been around for some make the foils "fly" at low speed can also timeH , but even so, nothing on the boating make them hop out of the water at high scene draws every eye like a hydroplane speed and spill the boat. The model has lifting out of the water as it gains speed. a designed-in, relatively steep foil inci- Even the U.S. Navy has been attracted dence and a high thrust line to minimize to foils, and has tested them on its fast the possibility of this happening. PT boats. Building the model. Typical model- The PS model shown here can be com- plane construction techniques are used. pleted in a couple of work sessions. Sur- But keep in mind two important con- face-piercing foils and air-prop drive give struction hints: Cut all parts very ac- it speed and stability with minimum com- curately. Use ordinary pins to hold the plexity. Construction is far simpler than components while the glue dries. you'd guess from the performance. Build the cabin first, complete with Basically, these craft deliver greater tail boom and rear foils. Cover the lower speed because resistance against several half of the cabin with lightweight model small areas (foils) is considerably lower tissue before doping, for a smooth and than against a complete, submerged hull. watertight finish. The windows are sim- Resistance declines as the craft rises. ply clear plastic (I cut mine from bubble- Completely submerged foils are the type packaging). most efficient, but they require sensing Next, make up the front foils, floats, 140 POPULAR SCIENCE the Water and crossbeam as a unit, and cut them into the cabin floor at the correct angle. Shape and fasten the mo- tor-mount nacelle; the one shown on the blueprint will accept most .020-.049 ra- dial-mount engines. To be safe, check your engine be- fore shaping the part. A large lake or a broad river will serve as a suitable playground for Mount the engine to the the model. Run it on a tether around your boat, or turn it loose for plywood firewall during as- a "free flight" if there's enough water area to do so safely. sembly; epoxy cement is best here and a good-size dab on the nuts holding the mounting control heading and raise or lower the screws is recommended. nose, much like the elevators on an air- The pusher engine. If you use a reed- plane. valve type you can use a standard prop- For your shakedown cruise, bend the but be sure to put it on backward. If trim tabs up at the rear edge until the your engine has a rotary valve, use a model rises up on its foils and scoots. left-hand pusher prop of the type used To get maximum speed, bend the tabs for air-drive model race cars. upward to the minimum that will make Important: The model should balance the craft "fly." Direction is controlled by when fingertip-held between the points differential bending of the tabs. shown on the blueprint. Though a little I flew the model on a large lake, chas- tail heaviness is allowable, a nose-heavy ing it with a boat. But you might also fly model puts you out of business. it on a tether around a boat. Double-check all foil angles before making a test run. The rear, inverted-V foil is fitted with bendable tabs, which Turn the page for PS lie-flat blueprint MAY 1969 141

LITTLE

DRAGON

Part One

by ROY L CLOUGH, JR.

HE Little Dragon glow engine is a project any amateur Tmachinist can tackle with full confidence of good results. It does not require any special tools, special talents, or extreme Little Dragon all ready to roar! This engine is really "on the square" precision. A large part of the total time spent in developing the design was devoted to eliminating awkward machining jobs, plified construction considerably and is one of the reasons you delicate operations, and tricky assemblies. If the reader owns will find dimensions indicated in 32nds of an inch instead of a small lathe and can center a piece of stock with 1/64", he thousandths. (Editors note: Cad drawing in thousandths.) need have no qualms about being able to turn out the job. On However, those who wish to build the engine to conform to the other hand, the skilled builder who has a good "touch" for AMA 1/2A regulation can use a 1/2" O.D. cylinder liner instead this sort of thing will discover he has an engine, which requires of the 9/16" specified on the plans. This will bring the dis- absolutely no apologies on the score of being homemade. placement down to about .049, safely within the rules for The motor is a basic design, as old-engine hands will recog- engines of .05 or less. This will require slight alterations in nize by the drawings. It has great amounts of leeway at every the width of the con rod for adequate clearance, and of course step of construction. This means there is plenty of room for the liner hole, piston size and head are changed accordingly. the correction of errors, which should appeal to the amateur, Conversely, a skillful builder can increase the displacement to and equally of importance, it allows the experienced motor more than .070 if he desires. builder to "soup-up" the design as he sees fit. For example, To those who think an elaborate machine outlay is required the weight of the original came out at 2 oz., complete with in order to build engines, a glance through the list of tools plug and prop. Skillful shaving-down by experienced machin- used to make the original should prove refreshing. These were: ists can reduce this figure greatly, but this has nothing to do small lathe, hack saw, hand drill, two files, two taps, one die, with the operating characteristics. Port areas and valve timing and a pocket scale graduated in 64ths. A micrometer was used are laid out with an eye to obtaining maximum start ability to check sizes, but actually could have been dispensed with. and a good rate of speed with average construction and And the big news, of course, is that no milling operations are internal fits, but the experienced worker who is capable of required. doing very good work will find it possible to increase the The Little Dragon employs what is known as the "sleeve-in- porting and degree of valve opening to obtain an extremely block" style of construction. Instead of having separate cylinder hot engine. and crankcase, one blends into the other, eliminating cylinder The original Little Dragon was turning the plastic prop tie downs, heat dams, and two more places for errors to shown in the photo at 8,000 rpm, 5 minutes after it was accumulate. The engine block serves the same purpose as the assembled. It did this on a break-in mix of 3 parts O & R "keel" frequently used in model airplane construction, being a No. 2 and 1 part castor oil. This is the performance the basic member, which when laid out correctly serves as an average builder can reasonably expect. For experts, and with accurate basis for the remainder of the construction. The block one of the hot Francisco Lab fuels, 10,000 rpm is a reasonably is the easiest part to make, in terms of tolerances, and serves conservative estimate. the amateur builder the purpose of getting his hand in as he The mounting of any engine uses up time and energy and goes along. Once the block is made the rest of the engine falls in too many cases is finicky and bothersome. We have tried to right into line. get around this and come up with something that is simple, Cut off about 1-7/8" of 3/4" sq. hard aluminum alloy bar quick, and practical. The two-stud mount is our answer. stock, center it accurately in the four-jaw and face off the Simply press the studs against a piece of plywood to mark it end. This gives a plane surface to set against the chuck face. for drilling, set the engine in place and run on a couple of Remove the piece, re-center, and face it down to the proper nuts. No muss, no fuss, and no bother. size. Next, outline the cylinder block. Here is a good rule to A bore of approximately 7/16" with a 3/8" stroke fixes the remember: always keep as much stock between the end of the displacement at about .06. By selecting these dimensions, it piece and the chuck as possible; in other words, make the first was possible to take advantage of material sizes which sim- cuts out near the end to leave a maximum diameter of support- ing metal. By this rule, we see that the fins are machined first. If your lathe is a light one, use the back gears and feed the finning tool in slowly, particularly at the start of each cut where it is chopping at the square corners of the stock. The first fin is extra heavy because this must carry the screws, which will hold the head in place. If you have cut the piece a bit short by accident, you may take the error out of the first fin. For example, if the piece is 1/32" shorter than it should be, the first fin would be 3/32" deep instead of 1/8". This is all right, but don't make it any thinner. There are three fins below this, each 1/32" deep with a 1/16" gap between all fins. Since the lowest fin must come in exactly the right posi- tion because of the exhaust port, cut this one after you have made the top fin. If your finning tool isn't quite the correct width, split the difference to fix the location of the middle two fins. Do not cut the fins too deeply and weaken the block. A fin depth of 1/32" measured from the flat of the stock is entirely adequate. Turn down the "barrel" and buff it with a crocus cloth. A good shine here increases (Turn to page 48) An ordinary book of matches dwarfs our tiny engine

MODEL AIRPLANE NEWS • October, 1950 23 Little Dragon simply a threaded disc. The writer has used threaded (Continued from page 23) the eye appeal; rough tool drive washers on a number of engines with good results marks give the engine the appearance of having been and why no commercial engine uses them is something of whittled out of a stove bolt with a cold chisel! a mystery since it is certainly easier than milling splines or The block is drilled out to an I.D. of a shy 9/16" and grinding flats. brought up to size with a boring tool, or reamer. Getting Now, remove the piece and put on the four-jaw. Chuck the correct depth is important, not because it will prevent up the shaft by the journal and off-center the piece 3/16" the engine from running, but because you will have to go by adjusting the jaws. It is possible to hold the piece over the whole thing changing other dimensions to make it adequately without marring the journal, but the cautious come out right. Note how a shoulder is left to support the may wish to push the shaft into a length of brass tubing liner. This liner must fit closely in order to prevent blow- and squeeze the jaws down on this. If this is done, be sure by around the exhaust port and at the head. This does not to use only a gentle tapping to put it in place, because the mean a piston-type fit by any means, but it should be journal must be knocked out again afterward. The whole tight enough so that it is just about possible to pull the secret of turning off-centers is setting the lathe tool on piece out with the fingers. A dummy sleeve cut from the center, feeding in slowly, and using power feed to drag the steel tube stock is a great help here. If by some mischance tool along the work. In addition, be willing to take a little the hole is oversize, don't scrap the job, just tin the sleeve time to do the job. The pin should be brought to a good and resize it to fit the hole. (But you won't be able to surface finish. The crank disc may be ground or filed away harden the sleeve if you do this, and then you will have as indicated by the dotted lines on the plan for a sort of to use an aluminum or cast iron piston.) counterbalance effect, but this is not critical. Remove the piece and re-chuck it in order to bore out The rotor comes next. Most people seem to have the the front of the case. Open this up part way with a drill opinion that disc valves must be tricky since they come and bring to final size with a boring tool. The inside rear in the more expensive engines, so we'll give a little must be faced off smoothly because the rotor valve will background on this. When the original Little Dragon was ride against it. The rotor pin hole is drilled out by holding being laid out, a great deal of consideration was given to a 3/32" drill in the tailstock. At this point lay the piece the induction method. It had to be very simple and very aside and make up the crankcase front section. Do a effective. Three-port induction seemed simple, but it good job here and no gasket will be needed; in any case a meant tapping into the block and cutting another hole in short piece of thread wrapped around the plug portion of the liner. Besides this it did not allow much leeway for this part will serve very well as a gasket. If the inside error and would not produce the best power output. Shaft end is turned first and fitted to the block, the job is rotary looked good at first glance, but this would mean easier, as this leaves something to chuck with. Next, less than optimum strength for the crankshaft, chances for reverse the piece and bore out to 3/16" I.D. and bring the errors in both the port hole and the hollow shaft, and the outside down to size. No bearing is used other than the added difficulty of setting the intake tube into the front metal itself. If you want to be ritzy about it, the hole can case. So that was out. Next we toyed with the idea of be bored oversize and bronze, or Oilite bearing material flutter valve induction; these arrangements are simple, and pressed in. In practice, the writer has found aluminum to since they work on crankcase pressure, very effective. serve very well, but the coefficient of friction of Oilite However, a speck of dirt, or oil hardening in the valve material is undoubtedly more favorable if the end in view makes them inoperable with a vengeance. Further difficulty is extreme performance. For that matter, ball bearings was foreseen due to the great powers of fuel meniscus in these small enough to be used in this engine can be obtained, small sizes. Fuel meniscus? That did it! So we used a disc and we are indebted to Malcolm D. Whitman, Jr., of rotor and made it free-floating. Five minutes after assembly Carmel, Calif., for that information. If you use ball we knew we had it. Only two smooth faces are needed, and bearings, the crankshaft diameter must be reduced or the one of them is already inside the crankcase. Best of all the outboard end of the bearing increased to accommodate the intake hole can be spotted easily, and if missed, it can be ball race, should double ball suspension be desired. tried again with a new rotor. In addition to all these The crankshaft belongs to a breed of cats that seems advantages, the thickness of the rotor is not critical and this able to scare a lot of people. Don't worry about it. Put gives the amateur machinist another place to pick up and the three-jaw chuck on your lathe and insert the piece of correct accumulated error. 9/16" drill rod. Bring this down to size with light cuts and Chuck up the 5/8" aluminum rod and turn down the power feed. Finish the journal with a fine file, crocus cloth rotor shaft to fit the hole in the rear of the engine block. and common sense. If you happen to have a tool post This should not be a tight fit, but smooth running and a bit grinder, by all means use it. Custom fit the shaft to the loose if anything. Bring the O.D. of the rotor down to size crankcase front section, double checking to be certain the and face it with a gentle cut, making certain there is no thrust washer clearance is adequate, then mark the spot shoulder next to the shaft as this will prevent seating. and turn down to the size you have selected for the Cutting loose from the stock should be halted about halfway threaded portion. We call for an 8-32 thread, but this is a through and all sharp edges broken, then complete the matter of choice and whatever die you have handy. The severance. Locate and drill the drive hole. This should be a threads may be cut on the lathe, but some will find it less bit oversize, but do not drill all the way through the disc, trouble to back off the tail stock and use an ordinary die. just enough for good clearance. Mark the outline of the port Be sure to start it straight; back the die off every half turn and file away the indicated area. The rotor may be held to break the chips and insure a good thread. A few drops between two thin bits of wood or fibre in a vise for this of light oil makes the cut easier. Near the end of the cut it operation. Break any edges that develop. Now, take up the is a good idea to reverse the die in order to cut the block and put the rotor shaft into the hole from the outside threads up close to the journal. The thrust washer is rear of the case and scratch the outline of the round portion as shown on the plan. Split the difference between this line (Next month we'll bring you the concluding part of the and the edge of the shaft hole and drill a 1/8" hole along the Little Dragon construction article, giving instructions for con diagonal. The intake tube is a 'length of 5/32" thin wall rod, cylinder head, and the amazingly simple sleeve and brass tube. Taper one end slightly (this taper is emphasized piston arrangement which eliminates the need of on the drawings) and press the tube firmly into the case. The conventional milled or cast-in by-pass. Details of fuel, needle valve assembly may be from a Baby Spitfire or other starting and running will also be covered.) small engine. BILL OF MATERIALS (for entire engine) The crankcase front section must now be drilled; set it in 8" of 3/4" sq. hard aluminum alloy rod the engine block and spot the holes for drilling. These 2" of 5/8" round hard aluminum alloy rod holes are drilled and tapped 2-56. The original engine used 3- 3" of 1/2" round 17ST rod 48 screws throughout, but the larger size is not needed. 3" of 9/16" seamless steel tubing However, it may be comforting to know that if you ruin 3" of 9/16" drill rod the No. 2 hole you can always re-tap it for 3-48. Tapping is 1" of 1/8" O.D. heavy wall brass tube easier if the holes are first filled with kerosene and the tap 1" of 5/32" O.D. thin wall brass tube backed off at frequent intervals. Tap in the mounting studs Scrap of 1/8" thick dural sheet (hard) for con rod next. 2—3-48 studs 5/8" long At this point, clean up all the parts and make a trial 8—2-56 or 3-48 screws, fillister head, 3/8" long assembly to be sure everything fits smoothly and turns freely. 2—No. 4 hole washers If the rotor valve shows a tendency to creep forward on the 2—3-48 nuts pin, don't worry about it—it won't when the engine is l"-sq. thin gasket material running. The important thing is that it seats well and does 1 Baby Spitfire needle valve assembly not bind at any point. 1 McCoy Hot Point Plug

MODEL AIRPLANE NEWS • October, 1950 49 little

dragon

part two

by ROY L. CLOUGH JR.

Here are details for finishing testing, and troubleshooting; let us know your results with this simple but efficient power plant THE Little Dragon shapes up rapidly once the block and lower versed and driven through the right way. Always drive it in assemblies are completed. The cylinder liner is made from a from the lower end of the liner and turn the piston slightly length of 9/16" seamless steel tubing which has a wall thickness from its last position. Use plenty of castor oil and keep the of about 1/16". Use great care in cutting it to size. Hold it by piston wiped clean. After a time it will be found possible to means of a leather strap in a vise and use a fine hack saw blade rotate the piston without a great deal of resistance and a fairly (put in the frame backwards). Take light strokes. The final good fit will have been established. sizing is done in the lathe three-jaw chuck. Once again The conn rod is worked up from 1/8" hard dural stock. Check please note, here is an opportunity to adjust for previous error. with the plans against what you have built, before drilling the The internal finish of cold drawn tubing is quite good to begin rod holes. The piston skirt must not hit on the front case plug with. It can be brought to a fair running finish by means of at bottom stroke. If you require a longer rod due to small lapping. If the builder has access to a hone, so much the better; errors, make it longer—you can take the difference out of the if not, make up a brass lap and polish out the inside of the tube. head. The wrist pin is simply a short length of 1/8" heavy-wall This can be done easily by holding the sleeve in the three-jaw brass tube. chuck, running the lathe slowly and working the lap back and Assemble the engine, using light oil on all bearing surfaces, forth evenly. Always run the lap into the sleeve from the same and turn it over by hand. The piston will (or should) have end; it is a good idea to daub a bit of red dope on this end to quite a bit of resistance, but no real "sticks" should develop keep track of it. This will be the lower end of the sleeve. When anywhere. If they do, correct them. Check the position of the the lapping has been finished, clean all traces of lapping com- piston relative to the liner at top and bottom center. If these pound from the liner. positions are within 1/64" of the positions shown on the plan, At this stage of the construction it may be helpful to read congratulate yourself on a job well done. If not, you will have over either of the two previously published engine articles, the to make allowances for the liner ports. Simplex 25 (M. A. N. March and April, 1947,) and "Build Your The exhaust port and intake by-pass are cut into the liner Own Diesel" (M. A. N. May and June, 1948,) on the subject of with a small, medium-fine file. Support the liner endwise be- piston and cylinder fits. This ground has been covered very tween two thin pieces of wood in the jaws of a vise. This opera- thoroughly. The state of the fit, the material and degree of tion is very simple as can be seen by the plan, but care and hardness of the piston, have great bearing upon the life of your accuracy can return big dividends here. Carefully remove any motor, and to a lesser degree, its original performance. The best burrs that develop. The piston deflector is now filed on. Check piston as far as wearing qualities are concerned is hardened and this against both the plan and the liner. The exhaust port must centerless-ground steel. The next best is cast iron ground on open first, and leads the intake port by 1/32" of piston travel. centers. Both of these methods offer difficulties to the File through the barrel of the engine block below the last homebuilder, but there is no question of their excellence. If fin, put the liner in place and check the alignment. The block either of these two methods is elected, there is little, if slot should be slightly larger than the liner slot, but no smaller. anything, the writer can add, as the Little Dragon piston design Take a scribe and mark the portion of the liner supporting rim is about as straightforward as they come, and requires no below the by-pass slot, remove the liner and cut away this por- special instructions. tion of the rim with a fine metal chisel or hand grinder. This If, on the other hand, the reader is anxious to get his motor licks the by-pass problem. running and wants a method of fitting a piston that will produce The cylinder head is of the "plug" variety and also has a quick results, although it will not last as long, he can make up slight gasket-retaining groove. The combination makes it leak- a hard aluminum piston in very short order by means of the proof even with very indifferent machining. Ideally, the plug "cold broach" method. If the internal liner surface is in good should be a smooth push fit into the liner. The plug portion is condition to begin with, aluminum pistons sometimes last for a extra long to facilitate final assembly. Tap a 1/4" x 32 hole into surprisingly long time, and several commercially produced the head for the glow plug. The head is mounted the same way engines have used aluminum pistons with good results. as the front case section, that is, drill the head holes first and Here is the method: chuck up a piece of 1/2" 17ST, about 3" use these as guides for drilling the holes in the engine block. long in the three-jaw. Do not support the tail end. Using power These are tapped 2-56 all the way through the first fin. feed and very light cuts, bring the O.D. down so that the piece Clean up everything, wipe castor oil on all contacting sur- will barely fit in the lower end of the liner. Because of the faces and assemble the engine except for the head. Put a prop length of the piece and its unsupported condition the finest on the shaft and turn it over a few times. There will probably cuts that can be managed will still produce a slight taper. The be quite a bit of piston resistance, but this is all right. The thing surface must be very bright and free of tool marks. Bore out the to watch out for is jamming, though this is not likely to occur piston, cut it loose, and drill the wrist-pin holes. We now have due to the general design of the engine. If it should happen, the following condition: the skirt of the piston will go into the take the engine apart and look for surfaces that appear un- lower end of the liner about 1/8". This is backward from the naturally bright, or scored-looking. Fix them up. The internal way it will run. Set the liner on a block of wood, dip the piston clearance between rotor, rod and crankshaft need be no more in castor oil, set it into the liner, and making certain it is square, than 1/32". If the clearance is as much as 1/16 the meniscus take a drift and drive it right through. After a couple of trips effect will be lost on the rotor plate. This will not prevent through the cylinder liner backwards, the piston can be re- running, but it will make starting a bit harder. 30 MODEL AIRPLANE NEWS • November, 1950 a half dozen bursts, the parts will "find" and the motor will run out the fuel. Don't hook it up to a tank and lean it out until it has run off a few minutes of four-cycling. The fuel you will use depends to a great extent upon the piston fit. It is loose, more oil will be required, but if very good it can be run on straight O & R No. 2. Don't jump to con- clusions about the compression ratio if it doesn't run correctly. Try altering the fuel mixture (oil ratio) because it may be a case of poor piston fit. If you're certain the piston fit is good, then increase the ratio by deepening the gasket groove. This engine has quite a wide range of glow C.R. because of good thermal characteristics and will operate well between 7- and 10-1, with 8 being about optimum. Once the engine is running properly don't take it apart unless absolutely necessary, as this disturbs the run-in. This is particularly true if the alumi- num piston is used. The Little Dragon is the result of about three months of design consideration by the writer, in an effort to obtain a layout in the ½A size, which could be, quite literally, all things to all men. A basically simple construction which could return good results to the beginner, yet give the old motor hand a design which would permit him full exercise of his skill and require no apologies for the fact of being homemade. If you like it, let's hear about it. If you run into difficulties, don't hesitate to write the author. Good luck. GLOW PLUG DIAGNOSTICS Set the head in place (without glow plug) and turn the piston up to top center, and see how much the head lifts off. SYMPTOM: Starts readily, revs up well, rpm drops off when Then rechuck the head and face off the plug portion enough to plug wire is removed. Indication: Compression ratio is too allow 1/32" clearance between it and the piston, at top dead low. center. Don't break the sharp edge of the cut—it's too handy Cure: Add oil and/or nitrate to fuel, deepen gasket groove to to cut holes in gaskets with. Use it now to cut a gasket, and trim decrease head space. around the edges enough to allow the head screws to go SYMPTOM: Starts very hard with much flashback, but runs through. Dip the gasket in castor oil and assemble the head to well once started. the engine. Pull the screws down "cross corner" fashion, a little Indication: Exhaust port not opening soon enough before intake at a time. They should be snug and fairly tight, but don't strip transfer. the threads out of the block. Cure: Check liner slots against plan, file more "lead" into Mount the engine on a piece of wood, which can be screwed exhaust. down to something solid, and put on a four- or five-inch length SYMPTOM: Must be flooded to start and will run only on rich of fuel line. Turn the engine over by hand for a few minutes mixture. and get used to its grunts and groans. Don't put the glow plug Indication: Cylinder head, or glow plug gasket is leaking. in yet. Get to know the various wheezes and pops and what Cure: Replace gaskets, check surfaces for damage. they mean. Note the soft "tunk!" made by the intake port open- SYMPTOM: Kicks violently, runs in short high speed bursts, ing into the cylinder, the gurgle of the intake rotor. These kicks off prop, stops suddenly. Indication: Compression ratio is sounds are usually masked by the louder pop of released com- too high. pression when the motor is flipped over. Cure: Reduce compression ratio by shaving down inserted Turn the motor over slowly several times and the intake "plug" portion of cylinder head, or try high compression fuels port noise may disappear. This means the rotor has ridden off its seat. A quick flip backward reseats it. Repeat this trick with with a cold glow plug. the glow plug in place (McCoy Hot Point plug is recom- SYMPTOM: Starts easily, holds up speed when wire is re- mended). When the rotor unseats there will seem to be a loss moved, leans out well, then gradually dies out. Indication: of compression. Again flip the prop backwards and the "com- Motor is not yet broken-in, probably overheating. Cure: Use pression" reappears. Unless you are familiar with this stunt, heavy, low pitch prop and run motor as rich as it will take you may think the head gasket has blown, or there is dirt under for ten to fifteen minutes, then try it again. General: Watch the rotor, and tear the motor down to find the "trouble." for the usual bugs, clogged fuel line or needle, tanks not vented Mix up a break-in mix of three parts O & R No. 2 and one correctly, loose prop, bad plug, loose wires, insecure mounting, part castor oil. Fill the fuel line and squirt a couple of drops evaporation weakened fuel. Use a port prime to start engine. into the exhaust port. Hook up the wires and give it a flip. After

MODEL AIRPLANE NEWS • November, 1950 31

LITTLE

DRAGON

Part One

by ROY L CLOUGH, JR.

HE Little Dragon glow engine is a project any amateur Tmachinist can tackle with full confidence of good results. It does not require any special tools, special talents, or extreme Little Dragon all ready to roar! This engine is really "on the square" precision. A large part of the total time spent in developing the design was devoted to eliminating awkward machining jobs, plified construction considerably and is one of the reasons you delicate operations, and tricky assemblies. If the reader owns will find dimensions indicated in 32nds of an inch instead of a small lathe and can center a piece of stock with 1/64", he thousandths. (Editors note: Cad drawing in thousandths.) need have no qualms about being able to turn out the job. On However, those who wish to build the engine to conform to the other hand, the skilled builder who has a good "touch" for AMA 1/2A regulation can use a 1/2" O.D. cylinder liner instead this sort of thing will discover he has an engine, which requires of the 9/16" specified on the plans. This will bring the dis- absolutely no apologies on the score of being homemade. placement down to about .049, safely within the rules for The motor is a basic design, as old-engine hands will recog- engines of .05 or less. This will require slight alterations in nize by the drawings. It has great amounts of leeway at every the width of the con rod for adequate clearance, and of course step of construction. This means there is plenty of room for the liner hole, piston size and head are changed accordingly. the correction of errors, which should appeal to the amateur, Conversely, a skillful builder can increase the displacement to and equally of importance, it allows the experienced motor more than .070 if he desires. builder to "soup-up" the design as he sees fit. For example, To those who think an elaborate machine outlay is required the weight of the original came out at 2 oz., complete with in order to build engines, a glance through the list of tools plug and prop. Skillful shaving-down by experienced machin- used to make the original should prove refreshing. These were: ists can reduce this figure greatly, but this has nothing to do small lathe, hack saw, hand drill, two files, two taps, one die, with the operating characteristics. Port areas and valve timing and a pocket scale graduated in 64ths. A micrometer was used are laid out with an eye to obtaining maximum start ability to check sizes, but actually could have been dispensed with. and a good rate of speed with average construction and And the big news, of course, is that no milling operations are internal fits, but the experienced worker who is capable of required. doing very good work will find it possible to increase the The Little Dragon employs what is known as the "sleeve-in- porting and degree of valve opening to obtain an extremely block" style of construction. Instead of having separate cylinder hot engine. and crankcase, one blends into the other, eliminating cylinder The original Little Dragon was turning the plastic prop tie downs, heat dams, and two more places for errors to shown in the photo at 8,000 rpm, 5 minutes after it was accumulate. The engine block serves the same purpose as the assembled. It did this on a break-in mix of 3 parts O & R "keel" frequently used in model airplane construction, being a No. 2 and 1 part castor oil. This is the performance the basic member, which when laid out correctly serves as an average builder can reasonably expect. For experts, and with accurate basis for the remainder of the construction. The block one of the hot Francisco Lab fuels, 10,000 rpm is a reasonably is the easiest part to make, in terms of tolerances, and serves conservative estimate. the amateur builder the purpose of getting his hand in as he The mounting of any engine uses up time and energy and goes along. Once the block is made the rest of the engine falls in too many cases is finicky and bothersome. We have tried to right into line. get around this and come up with something that is simple, Cut off about 1-7/8" of 3/4" sq. hard aluminum alloy bar quick, and practical. The two-stud mount is our answer. stock, center it accurately in the four-jaw and face off the Simply press the studs against a piece of plywood to mark it end. This gives a plane surface to set against the chuck face. for drilling, set the engine in place and run on a couple of Remove the piece, re-center, and face it down to the proper nuts. No muss, no fuss, and no bother. size. Next, outline the cylinder block. Here is a good rule to A bore of approximately 7/16" with a 3/8" stroke fixes the remember: always keep as much stock between the end of the displacement at about .06. By selecting these dimensions, it piece and the chuck as possible; in other words, make the first was possible to take advantage of material sizes which sim- cuts out near the end to leave a maximum diameter of support- ing metal. By this rule, we see that the fins are machined first. If your lathe is a light one, use the back gears and feed the finning tool in slowly, particularly at the start of each cut where it is chopping at the square corners of the stock. The first fin is extra heavy because this must carry the screws, which will hold the head in place. If you have cut the piece a bit short by accident, you may take the error out of the first fin. For example, if the piece is 1/32" shorter than it should be, the first fin would be 3/32" deep instead of 1/8". This is all right, but don't make it any thinner. There are three fins below this, each 1/32" deep with a 1/16" gap between all fins. Since the lowest fin must come in exactly the right posi- tion because of the exhaust port, cut this one after you have made the top fin. If your finning tool isn't quite the correct width, split the difference to fix the location of the middle two fins. Do not cut the fins too deeply and weaken the block. A fin depth of 1/32" measured from the flat of the stock is entirely adequate. Turn down the "barrel" and buff it with a crocus cloth. A good shine here increases (Turn to page 48) An ordinary book of matches dwarfs our tiny engine

MODEL AIRPLANE NEWS • October, 1950 23 Little Dragon simply a threaded disc. The writer has used threaded (Continued from page 23) the eye appeal; rough tool drive washers on a number of engines with good results marks give the engine the appearance of having been and why no commercial engine uses them is something of whittled out of a stove bolt with a cold chisel! a mystery since it is certainly easier than milling splines or The block is drilled out to an I.D. of a shy 9/16" and grinding flats. brought up to size with a boring tool, or reamer. Getting Now, remove the piece and put on the four-jaw. Chuck the correct depth is important, not because it will prevent up the shaft by the journal and off-center the piece 3/16" the engine from running, but because you will have to go by adjusting the jaws. It is possible to hold the piece over the whole thing changing other dimensions to make it adequately without marring the journal, but the cautious come out right. Note how a shoulder is left to support the may wish to push the shaft into a length of brass tubing liner. This liner must fit closely in order to prevent blow- and squeeze the jaws down on this. If this is done, be sure by around the exhaust port and at the head. This does not to use only a gentle tapping to put it in place, because the mean a piston-type fit by any means, but it should be journal must be knocked out again afterward. The whole tight enough so that it is just about possible to pull the secret of turning off-centers is setting the lathe tool on piece out with the fingers. A dummy sleeve cut from the center, feeding in slowly, and using power feed to drag the steel tube stock is a great help here. If by some mischance tool along the work. In addition, be willing to take a little the hole is oversize, don't scrap the job, just tin the sleeve time to do the job. The pin should be brought to a good and resize it to fit the hole. (But you won't be able to surface finish. The crank disc may be ground or filed away harden the sleeve if you do this, and then you will have as indicated by the dotted lines on the plan for a sort of to use an aluminum or cast iron piston.) counterbalance effect, but this is not critical. Remove the piece and re-chuck it in order to bore out The rotor comes next. Most people seem to have the the front of the case. Open this up part way with a drill opinion that disc valves must be tricky since they come and bring to final size with a boring tool. The inside rear in the more expensive engines, so we'll give a little must be faced off smoothly because the rotor valve will background on this. When the original Little Dragon was ride against it. The rotor pin hole is drilled out by holding being laid out, a great deal of consideration was given to a 3/32" drill in the tailstock. At this point lay the piece the induction method. It had to be very simple and very aside and make up the crankcase front section. Do a effective. Three-port induction seemed simple, but it good job here and no gasket will be needed; in any case a meant tapping into the block and cutting another hole in short piece of thread wrapped around the plug portion of the liner. Besides this it did not allow much leeway for this part will serve very well as a gasket. If the inside error and would not produce the best power output. Shaft end is turned first and fitted to the block, the job is rotary looked good at first glance, but this would mean easier, as this leaves something to chuck with. Next, less than optimum strength for the crankshaft, chances for reverse the piece and bore out to 3/16" I.D. and bring the errors in both the port hole and the hollow shaft, and the outside down to size. No bearing is used other than the added difficulty of setting the intake tube into the front metal itself. If you want to be ritzy about it, the hole can case. So that was out. Next we toyed with the idea of be bored oversize and bronze, or Oilite bearing material flutter valve induction; these arrangements are simple, and pressed in. In practice, the writer has found aluminum to since they work on crankcase pressure, very effective. serve very well, but the coefficient of friction of Oilite However, a speck of dirt, or oil hardening in the valve material is undoubtedly more favorable if the end in view makes them inoperable with a vengeance. Further difficulty is extreme performance. For that matter, ball bearings was foreseen due to the great powers of fuel meniscus in these small enough to be used in this engine can be obtained, small sizes. Fuel meniscus? That did it! So we used a disc and we are indebted to Malcolm D. Whitman, Jr., of rotor and made it free-floating. Five minutes after assembly Carmel, Calif., for that information. If you use ball we knew we had it. Only two smooth faces are needed, and bearings, the crankshaft diameter must be reduced or the one of them is already inside the crankcase. Best of all the outboard end of the bearing increased to accommodate the intake hole can be spotted easily, and if missed, it can be ball race, should double ball suspension be desired. tried again with a new rotor. In addition to all these The crankshaft belongs to a breed of cats that seems advantages, the thickness of the rotor is not critical and this able to scare a lot of people. Don't worry about it. Put gives the amateur machinist another place to pick up and the three-jaw chuck on your lathe and insert the piece of correct accumulated error. 9/16" drill rod. Bring this down to size with light cuts and Chuck up the 5/8" aluminum rod and turn down the power feed. Finish the journal with a fine file, crocus cloth rotor shaft to fit the hole in the rear of the engine block. and common sense. If you happen to have a tool post This should not be a tight fit, but smooth running and a bit grinder, by all means use it. Custom fit the shaft to the loose if anything. Bring the O.D. of the rotor down to size crankcase front section, double checking to be certain the and face it with a gentle cut, making certain there is no thrust washer clearance is adequate, then mark the spot shoulder next to the shaft as this will prevent seating. and turn down to the size you have selected for the Cutting loose from the stock should be halted about halfway threaded portion. We call for an 8-32 thread, but this is a through and all sharp edges broken, then complete the matter of choice and whatever die you have handy. The severance. Locate and drill the drive hole. This should be a threads may be cut on the lathe, but some will find it less bit oversize, but do not drill all the way through the disc, trouble to back off the tail stock and use an ordinary die. just enough for good clearance. Mark the outline of the port Be sure to start it straight; back the die off every half turn and file away the indicated area. The rotor may be held to break the chips and insure a good thread. A few drops between two thin bits of wood or fibre in a vise for this of light oil makes the cut easier. Near the end of the cut it operation. Break any edges that develop. Now, take up the is a good idea to reverse the die in order to cut the block and put the rotor shaft into the hole from the outside threads up close to the journal. The thrust washer is rear of the case and scratch the outline of the round portion as shown on the plan. Split the difference between this line (Next month we'll bring you the concluding part of the and the edge of the shaft hole and drill a 1/8" hole along the Little Dragon construction article, giving instructions for con diagonal. The intake tube is a 'length of 5/32" thin wall rod, cylinder head, and the amazingly simple sleeve and brass tube. Taper one end slightly (this taper is emphasized piston arrangement which eliminates the need of on the drawings) and press the tube firmly into the case. The conventional milled or cast-in by-pass. Details of fuel, needle valve assembly may be from a Baby Spitfire or other starting and running will also be covered.) small engine. BILL OF MATERIALS (for entire engine) The crankcase front section must now be drilled; set it in 8" of 3/4" sq. hard aluminum alloy rod the engine block and spot the holes for drilling. These 2" of 5/8" round hard aluminum alloy rod holes are drilled and tapped 2-56. The original engine used 3- 3" of 1/2" round 17ST rod 48 screws throughout, but the larger size is not needed. 3" of 9/16" seamless steel tubing However, it may be comforting to know that if you ruin 3" of 9/16" drill rod the No. 2 hole you can always re-tap it for 3-48. Tapping is 1" of 1/8" O.D. heavy wall brass tube easier if the holes are first filled with kerosene and the tap 1" of 5/32" O.D. thin wall brass tube backed off at frequent intervals. Tap in the mounting studs Scrap of 1/8" thick dural sheet (hard) for con rod next. 2—3-48 studs 5/8" long At this point, clean up all the parts and make a trial 8—2-56 or 3-48 screws, fillister head, 3/8" long assembly to be sure everything fits smoothly and turns freely. 2—No. 4 hole washers If the rotor valve shows a tendency to creep forward on the 2—3-48 nuts pin, don't worry about it—it won't when the engine is l"-sq. thin gasket material running. The important thing is that it seats well and does 1 Baby Spitfire needle valve assembly not bind at any point. 1 McCoy Hot Point Plug

MODEL AIRPLANE NEWS • October, 1950 49 little

dragon

part two

by ROY L. CLOUGH JR.

Here are details for finishing testing, and troubleshooting; let us know your results with this simple but efficient power plant THE Little Dragon shapes up rapidly once the block and lower versed and driven through the right way. Always drive it in assemblies are completed. The cylinder liner is made from a from the lower end of the liner and turn the piston slightly length of 9/16" seamless steel tubing which has a wall thickness from its last position. Use plenty of castor oil and keep the of about 1/16". Use great care in cutting it to size. Hold it by piston wiped clean. After a time it will be found possible to means of a leather strap in a vise and use a fine hack saw blade rotate the piston without a great deal of resistance and a fairly (put in the frame backwards). Take light strokes. The final good fit will have been established. sizing is done in the lathe three-jaw chuck. Once again The conn rod is worked up from 1/8" hard dural stock. Check please note, here is an opportunity to adjust for previous error. with the plans against what you have built, before drilling the The internal finish of cold drawn tubing is quite good to begin rod holes. The piston skirt must not hit on the front case plug with. It can be brought to a fair running finish by means of at bottom stroke. If you require a longer rod due to small lapping. If the builder has access to a hone, so much the better; errors, make it longer—you can take the difference out of the if not, make up a brass lap and polish out the inside of the tube. head. The wrist pin is simply a short length of 1/8" heavy-wall This can be done easily by holding the sleeve in the three-jaw brass tube. chuck, running the lathe slowly and working the lap back and Assemble the engine, using light oil on all bearing surfaces, forth evenly. Always run the lap into the sleeve from the same and turn it over by hand. The piston will (or should) have end; it is a good idea to daub a bit of red dope on this end to quite a bit of resistance, but no real "sticks" should develop keep track of it. This will be the lower end of the sleeve. When anywhere. If they do, correct them. Check the position of the the lapping has been finished, clean all traces of lapping com- piston relative to the liner at top and bottom center. If these pound from the liner. positions are within 1/64" of the positions shown on the plan, At this stage of the construction it may be helpful to read congratulate yourself on a job well done. If not, you will have over either of the two previously published engine articles, the to make allowances for the liner ports. Simplex 25 (M. A. N. March and April, 1947,) and "Build Your The exhaust port and intake by-pass are cut into the liner Own Diesel" (M. A. N. May and June, 1948,) on the subject of with a small, medium-fine file. Support the liner endwise be- piston and cylinder fits. This ground has been covered very tween two thin pieces of wood in the jaws of a vise. This opera- thoroughly. The state of the fit, the material and degree of tion is very simple as can be seen by the plan, but care and hardness of the piston, have great bearing upon the life of your accuracy can return big dividends here. Carefully remove any motor, and to a lesser degree, its original performance. The best burrs that develop. The piston deflector is now filed on. Check piston as far as wearing qualities are concerned is hardened and this against both the plan and the liner. The exhaust port must centerless-ground steel. The next best is cast iron ground on open first, and leads the intake port by 1/32" of piston travel. centers. Both of these methods offer difficulties to the File through the barrel of the engine block below the last homebuilder, but there is no question of their excellence. If fin, put the liner in place and check the alignment. The block either of these two methods is elected, there is little, if slot should be slightly larger than the liner slot, but no smaller. anything, the writer can add, as the Little Dragon piston design Take a scribe and mark the portion of the liner supporting rim is about as straightforward as they come, and requires no below the by-pass slot, remove the liner and cut away this por- special instructions. tion of the rim with a fine metal chisel or hand grinder. This If, on the other hand, the reader is anxious to get his motor licks the by-pass problem. running and wants a method of fitting a piston that will produce The cylinder head is of the "plug" variety and also has a quick results, although it will not last as long, he can make up slight gasket-retaining groove. The combination makes it leak- a hard aluminum piston in very short order by means of the proof even with very indifferent machining. Ideally, the plug "cold broach" method. If the internal liner surface is in good should be a smooth push fit into the liner. The plug portion is condition to begin with, aluminum pistons sometimes last for a extra long to facilitate final assembly. Tap a 1/4" x 32 hole into surprisingly long time, and several commercially produced the head for the glow plug. The head is mounted the same way engines have used aluminum pistons with good results. as the front case section, that is, drill the head holes first and Here is the method: chuck up a piece of 1/2" 17ST, about 3" use these as guides for drilling the holes in the engine block. long in the three-jaw. Do not support the tail end. Using power These are tapped 2-56 all the way through the first fin. feed and very light cuts, bring the O.D. down so that the piece Clean up everything, wipe castor oil on all contacting sur- will barely fit in the lower end of the liner. Because of the faces and assemble the engine except for the head. Put a prop length of the piece and its unsupported condition the finest on the shaft and turn it over a few times. There will probably cuts that can be managed will still produce a slight taper. The be quite a bit of piston resistance, but this is all right. The thing surface must be very bright and free of tool marks. Bore out the to watch out for is jamming, though this is not likely to occur piston, cut it loose, and drill the wrist-pin holes. We now have due to the general design of the engine. If it should happen, the following condition: the skirt of the piston will go into the take the engine apart and look for surfaces that appear un- lower end of the liner about 1/8". This is backward from the naturally bright, or scored-looking. Fix them up. The internal way it will run. Set the liner on a block of wood, dip the piston clearance between rotor, rod and crankshaft need be no more in castor oil, set it into the liner, and making certain it is square, than 1/32". If the clearance is as much as 1/16 the meniscus take a drift and drive it right through. After a couple of trips effect will be lost on the rotor plate. This will not prevent through the cylinder liner backwards, the piston can be re- running, but it will make starting a bit harder. 30 MODEL AIRPLANE NEWS • November, 1950 a half dozen bursts, the parts will "find" and the motor will run out the fuel. Don't hook it up to a tank and lean it out until it has run off a few minutes of four-cycling. The fuel you will use depends to a great extent upon the piston fit. It is loose, more oil will be required, but if very good it can be run on straight O & R No. 2. Don't jump to con- clusions about the compression ratio if it doesn't run correctly. Try altering the fuel mixture (oil ratio) because it may be a case of poor piston fit. If you're certain the piston fit is good, then increase the ratio by deepening the gasket groove. This engine has quite a wide range of glow C.R. because of good thermal characteristics and will operate well between 7- and 10-1, with 8 being about optimum. Once the engine is running properly don't take it apart unless absolutely necessary, as this disturbs the run-in. This is particularly true if the alumi- num piston is used. The Little Dragon is the result of about three months of design consideration by the writer, in an effort to obtain a layout in the ½A size, which could be, quite literally, all things to all men. A basically simple construction which could return good results to the beginner, yet give the old motor hand a design which would permit him full exercise of his skill and require no apologies for the fact of being homemade. If you like it, let's hear about it. If you run into difficulties, don't hesitate to write the author. Good luck. GLOW PLUG DIAGNOSTICS Set the head in place (without glow plug) and turn the piston up to top center, and see how much the head lifts off. SYMPTOM: Starts readily, revs up well, rpm drops off when Then rechuck the head and face off the plug portion enough to plug wire is removed. Indication: Compression ratio is too allow 1/32" clearance between it and the piston, at top dead low. center. Don't break the sharp edge of the cut—it's too handy Cure: Add oil and/or nitrate to fuel, deepen gasket groove to to cut holes in gaskets with. Use it now to cut a gasket, and trim decrease head space. around the edges enough to allow the head screws to go SYMPTOM: Starts very hard with much flashback, but runs through. Dip the gasket in castor oil and assemble the head to well once started. the engine. Pull the screws down "cross corner" fashion, a little Indication: Exhaust port not opening soon enough before intake at a time. They should be snug and fairly tight, but don't strip transfer. the threads out of the block. Cure: Check liner slots against plan, file more "lead" into Mount the engine on a piece of wood, which can be screwed exhaust. down to something solid, and put on a four- or five-inch length SYMPTOM: Must be flooded to start and will run only on rich of fuel line. Turn the engine over by hand for a few minutes mixture. and get used to its grunts and groans. Don't put the glow plug Indication: Cylinder head, or glow plug gasket is leaking. in yet. Get to know the various wheezes and pops and what Cure: Replace gaskets, check surfaces for damage. they mean. Note the soft "tunk!" made by the intake port open- SYMPTOM: Kicks violently, runs in short high speed bursts, ing into the cylinder, the gurgle of the intake rotor. These kicks off prop, stops suddenly. Indication: Compression ratio is sounds are usually masked by the louder pop of released com- too high. pression when the motor is flipped over. Cure: Reduce compression ratio by shaving down inserted Turn the motor over slowly several times and the intake "plug" portion of cylinder head, or try high compression fuels port noise may disappear. This means the rotor has ridden off its seat. A quick flip backward reseats it. Repeat this trick with with a cold glow plug. the glow plug in place (McCoy Hot Point plug is recom- SYMPTOM: Starts easily, holds up speed when wire is re- mended). When the rotor unseats there will seem to be a loss moved, leans out well, then gradually dies out. Indication: of compression. Again flip the prop backwards and the "com- Motor is not yet broken-in, probably overheating. Cure: Use pression" reappears. Unless you are familiar with this stunt, heavy, low pitch prop and run motor as rich as it will take you may think the head gasket has blown, or there is dirt under for ten to fifteen minutes, then try it again. General: Watch the rotor, and tear the motor down to find the "trouble." for the usual bugs, clogged fuel line or needle, tanks not vented Mix up a break-in mix of three parts O & R No. 2 and one correctly, loose prop, bad plug, loose wires, insecure mounting, part castor oil. Fill the fuel line and squirt a couple of drops evaporation weakened fuel. Use a port prime to start engine. into the exhaust port. Hook up the wires and give it a flip. After

MODEL AIRPLANE NEWS • November, 1950 31 Hydrojet Powers Little Newest thing in nautical propulsion, this clever midget boat has no weed-snagging paddles or prop—won't nip unwary fingers.

By Roy Clough it at the stern. Housed in a casing between them is a rotary pump, which draws in ERE'S a little boat that skims over the water and kicks it backward at high speed. Hwater like a speedy sea sled, riding Reaction to this stream drives the boat. high on two rocket-like chine planes. Yet The hull. Use 1/8" sheet balsa for the when you pick it up you'll find no finger- sides, bulkhead, transom (stern), pilot's- nipping propeller underneath. The only clue head support and chine planes. Thinner to its hidden power is the intake port on the balsa serves for the bottom, deck and gun- bottom, and an exhaust port directly behind wales. Before decking in the bow be sure to

170 POPULAR SCIENCE Speedster

cement a couple of ounces of ballast to the front of the bulkhead. A ping-pong ball forms the pilot's head, and the windshield is a scrap of acetate sheeting edged with tin. To finish off the hull, sand down the assembly and cover it with model tissue, then paint with hot-fuel-proof dope. Pump and housing. Before building an engine mount, the driving unit should be

OFF TO A FLYING START, the hydrojet speed- ster is already climbing. Top and side ele - vations on opposite page are half size for a boat powered by an .047 displacement engine. The upper detail drawing at left indicates the planing angle; the exploded section below it, the pump-housing pat- tern and impeller-and-shaft assembly. AUGUST 1954 171 Before mounting the blade in the hous- ing, solder a short arm, or "dog," to the top of the impeller shaft. Then tin both the slotted end of the shaft and the blade, scraping off just enough solder to let the notch slip firmly over the center of the blade. To mount, turn the housing upside down and press the shaft through the bear- ing from below. Drop a small washer through the water-intake hole and over the notched shaft end. Slip the blade through the nozzle with tweezers and press it onto the shaft. Rotate the shaft to make sure the blade doesn't scrape against the housing, then solder it in position. Engine. The power plant is a miniature gas engine, suspended in a U frame of /s" OPENING AT BOTTOM OF PUMP HOUSING takes in water, which is kicked back through rec- sheet balsa directly above the impeller shaft. tangular port at the stern. The planing angle For the slightly angled coupling between of the hull eliminates need for a water scoop. the engine and shaft, a pin on a flywheel engages the shaft dog. The flywheel is a assembled and placed in the hull. The large iron washer backed up by a small V- pump housing is made from a single piece of groove pulley turned from hardwood. tin-can stock (see detail drawing). Dotted Mount the fuel tank on one side of the lines are right-angle bends, and the tab cockpit floor and connect it to the engine extension between the pear-shaped bottom with plastic hose. and top sections is curved around the rotor Operation. The hydrojet boat is started end to form a continuation of the sides. by winding a number of turns of string Butting edges are soldered, starting at the around the grooved pulley and then hauling nozzle to insure good alignment. Make sure the twine sharply back through the engine that the bearing hole is centered with the frame. larger water-intake hole. A short piece of If you don't want to chase the craft tubing should be soldered over the bearing with a rowboat, tether it to a line from five hole to keep the impeller shaft aligned. to six feet long. One end of the line is This impeller shaft has a slot sawed in one attached to an upright post, the other to the end to receive the blade, which is a strip of side of the bull nearest the fuel tank. Other- thin brass stock curved in the form of a wise centrifugal force would starve the shallow S. engine. END

172 POPULAR SCIENCE The control surface is next. For the lower spar, which is also the wheel axle, use a length of 1/8" sq. basswood or very hard balsa, as this piece must sustain landing shocks. Tissue cover and pin flat when shrinking. A small hardwood block is fastened to the center of this piece with a liberal quantity of cement. (See detail sketches.) This block is pierced with a pin and linked to a similar block cemented to a length of 1/16" hardwood dowel. Attach the control surface to the rotor base plate with cloth hinges as shown. A small block of soft balsa is drilled to fit the 1/16" dowel tightly; it is then slid over the dowel and cemented to the fuselage. The control is adjusted by sliding the dowel fore or aft and the control surface should depart 45° from the vertical in either direction. Use pin axles to attach two hardwood wheels to the ends of the control vane. Cementing together two more wheels of the same size and attaching them to the nose block by means of a wire yoke make the front wheel. The rotor tube is formed from a 6" length of 1/16" medium soft balsa sheet, soaked in hot water, wrapped around a dowel, and held in place with gauze. Permit it to dry thoroughly before removing and cementing up the seam. The upper end of the tube is plugged with a disk of 1/8" hard balsa drilled to accommodate a standard hardwood thrust button. Cut out and reinforce two notches in the lower end of the tube to hold the lower rubber anchor, which is a short length of hardwood dowel. Center a pin or piece of wire in another disk of 1/8" hard balsa, cement firmly in place and attach the disk to the bottom of the tube. Next cut four rotor blades from 1/16" medium sheet and sand them over a bottle to produce a slight camber. The lower rotor blades are cemented directly to the motor tube at a pitch of 30° and with a slight negative coning (or dihedral) angle. Don't spare the cement on this assembly. The unit just by ROY L. CLOUGH. JR. assembled is tested for balance separately. This stable model gives true helicopter performance Build up the top rotor by cementing the two blades over the 1/4" sq. hard balsa hub DESIGNED to fly vertically, forward or back, that it is more effective if built flat; therefore it piece at an angle of 35°. A wire hook, washer this rubber powered helicopter is easy to is recommended that it be made this way. A and thrust plug complete the assembly. Six build and certain to give good results. simple push-rod linkage is used to hold it in strands of 1/8" flat rubber comprise the motor. Instead of individual rotor blade articulation, any desired position. Drop the completed motor tube into place in which is usually necessary to secure steady A word of caution: It is frequently desirable the fuselage, poking the pin-axle of the tube flight, the entire rotor mechanism of this to enlarge plans of conventional model planes through the reinforcing washer in the machine is permitted relatively free motion about above the size recommended by the designer mounting plate and bending it over to hold in its point of attachment. This motion must be and this is often done with good results. But place. limited in order to obtain forward flight; this procedure or any other alteration of the plans Since there is no freewheeling device, this therefore there is only 1/8" clearance between the must be discouraged by the writer as regards to model is flown under power at all times, using rotor tube and the fore and aft cross-members. Hoverbug because, to do so, may result in an un- residual power to brake its descent. It is best Side motion is permitted up to the width of the flyable machine. This is because weight flown indoors and first hops should be of short fuselage, about 1/2 in each direction. distribution, articulation problems, and power duration. Balance should come just ahead of the A long fuselage is used on this model to requirements may be greatly modified by a size rotor tube axis, but to secure maximum distance spread its mass over a large area, thus increase. in forward flight it may be necessary to minimizing disturbing effects, which may occur Begin construction with the fuselage, which is make the machine slightly nose-heavy. For in the rotor. A high tail fin performs the function built on the plans (presented full size). The forward flight slant the control surface rearward, of maintaining proper heading and brings the structure is strictly conventional except that it just the reverse to fly backward. Experiment CLA into a favorable position relative to CG. becomes tri-angular aft of the rotor tube with varying degrees of power for best results. Despite appearances, the vertical control surface location. For outdoor flying greater duration can be employed on this model does not create an The fin may be integral or built separately. obtained by using considerably more rubber and untoward amount of drag in forward flight. Use 1/16" hard balsa strip for all members. incorporating one of the reversing free-wheelers This is because the actual relative wind is The rotor tube mounting plate is a bit of sheet described in the writer's previous helicopter largely downward in the immediate vicinity of balsa to which a reinforcing washer has been article in the May issue. the ship. As shown in the photographs this centered and cemented. Cover windows with MODEL AIRPLANE NEWS surface is cambered, but further experiments cellophane, and balance of the fuselage with September. 1947 made after the pictures were taken indicate tissue. Water shrink but do not dope.

airplane models

For a real eye- stopper, build "Hoopskirt"

By ROY L. CLOUGH, JR.

Flying barrels have been in the air since Bleriot, but this model proves they can still turn in a top performance

TROT THIS MODEL out on the field at your next meet move a lot of air relatively slowly than a small amount at and watch the eyes bug. If anybody snickers, put 'em in high speed. (It's rather like matching impedances.) The their place by reminding them that the annular wing is annular wing with a propeller ahead of it functions as an a very old aeronautical principle. Then launch your effective aspirator to increase the amount of air thrust Hoopskirt. If its tradition hasn't impressed them, its per- backward. formance is certain to! Such a wing has more lift than you might think. The At least a half-dozen full-scale planes (plus innumerable closed-circuit nature of the airfoil eliminates wing-tip kites and gliders) have been built on the "flying barrel" vortices. Theoretically, a hoop-wing plane shouldn't have design. One of the initial aircraft made by Ellehammer— to bank in order to turn. This model does, however, the first Dane to fly—took this form. Louis Bleriot, the because of the vertical stabilizing fin at the top of the daring Frenchman who was the first to fly the English wing. This was added to produce an effect comparable to Channel, perched one on floats and tried, with indifferent dihedral. success, to get it off the water. The French are still at it; The Hoopskirt is an extremely stable flying machine. It'll their latest attempt at annular-winged aircraft is a tail teach you a lot about this offbeat configuration. Don't let sitting jet. the circular wing scare you—it's quite easy to build. Any One of the big advantages of this design is its propulsive cylinder with a diameter of about 10 in. (a half inch efficiency. Efficiency in a flying system is highest when either way won't hurt) can serve as a mold for the two the velocity of the discharged air is almost as great as spars. I used a straight-sided layer-cake pan. The the forward speed of the plane. This means that it's spars can be of any lightwood that bends easily when better to soaked in hot water. Bind these

46 around the mold with a strip of rag. When dry, trim the have no adjustments, and are simply cemented to the ends in long, matching bevels to form the lap shown in sides of the booms after the tail plane is in place. the sketch; cement and bind with sewing thread. The engine-pilot nacelle is given a coat of pigmented You can trace the wing-rib pattern directly onto your dope after the motor is fastened on its plywood mount. balsa, stacking blanks to cut as many at once as you The color scheme of the model shown is: red nacelle, can manage. The slots in each end are 3/32 in. wide and rudders and fin: natural white wing; silver booms, strut 1/4 in. deep. The width should provide a snug fit over the and tail plane—a highly visible combination against a spars. When these hoops are seated in the notches, blue sky. their outer edges will protrude 1/16 in. for rounding off. For best performance, be sure the model balances at a An easy way to space the ribs accurately is to set the point about 1-1/4-in. ahead of the trailing edge of the spar-mold cylinder on a piece of cardboard and scribe wing. An easy way to balance the plane is to stick straight around it to produce a circle the same diameter as the pins into both booms 1-1/4-in. ahead of the trailing spars. Mark off sixteen rib positions by means of radius edges. Support the plane on these pins between two stacks lines and assemble the wing vertically over this pattern. of books, and add weight—in the form of bits of clay, Cover the frame one section at a time with light small pieces of lead, etc.—to either the nose or the tail model-plane tissue. Sections into which the strut, fin until the plane is suspended between the books in a level or booms will pass can be left uncovered until assembly flight position. is completed—or you can cover the entire wing and Hand launch the model over tall grass until, by bending then slit the paper the elevators up a little at a time, you get a flat glide. As a of these sections when you install parts that must be check on these adjustments try a flight with the motor cemented to the ribs. Water-shrink the paper; when dry, running rich, then lean it out and watch your model give it a coat of clear dope. zoom. Careful alignment of all balsa parts pays off in good This is a free-flying model, and has not been adapted for performance. Don't diminish the strength of the rock- control-line operation. It is a stable flyer, and when out of hard-balsa booms by sanding off the corners—leave fuel, it will glide gracefully to a landing if you balanced them square. it carefully. The tail plane has a deeply notched trailing edge, backed If you're flying it in a limited space, it's a good idea to up with parallel pieces of soft wire cemented to the wood. burn off some of the fuel before turning it loose, These wires—which can be snipped from a paper clip— because the model travels at a good clip. will hold any flight-adjustment bends you may give the In any event, you'll draw a good many curious glances— two elevator sections after trial runs. An annular wing and perhaps a few snorts of derision —when you take operates at zero incidence, so you'll have to bend the Hoopskirt out for its first flight. Any snickers in your elevators up two or three degrees to get an angle of direction, though, will quickly change to whistles of attack for climb. Bending one elevator up more than the admiration when onlookers see the stability of the "flying other makes the model turn in that direction. The rudders barrel," one of the earliest of all aircraft designs.

47 POPULAR MECHANICS APRIL, 1963

Fig. 1 V-4 motor with gas generator was made in Japan Fig. 2 Compressed air plant offered clean, quiet power but took lots of pumping Expansion Engines

By ROY L. CLOUGH JR.

The author feels these power units have been neglected--get busy, experimenters!

THE re-introduction and acceptance of expansion engines as model airplane power plants must bring a definite "I told you so" grin to the faces of old- timers. For here is a category of prime mover sadly neglected up to now by builders and manufacturers alike, yet which is in many ways more suited to free and controlled flight than the presently popular gas and diesel engines. At this writing there are 2 expansion engines on the market, both CO2 powered. Their quiet operation, nonexistent starting troubles, reliability and cleanliness are appealing to many. Expansion engines are those in which the gases which drive the piston are brought in from an outside source instead of being generated in the cylinder. Engines of this type were the first dynamic power plants used in model planes. They fall into 2 main categories: reservoir and generator engines. Reservoir engines operate from a tank or cartridge of compressed gas; generator engines from a generator or boiler, which produces the energizing gas. The small CO2 engines available today are reservoir engines. The performance of this type is similar to a rubber, or spring motor, the greatest thrust being exerted as soon as the propeller comes up to speed, with output continuously dropping off as the energy (temperature and pressure) of the gas decreases. Fig. 3 Business end of successful steam-powered controlliner There are at present no generator engines on the market. An olden example of this type is shown in Fig. 1—the Imp Tornado, offered by International Models during the 30's. It was produced in 2 models, of 2 and 4 cylinders. One of the most powerful pre-gasoline power plants, the Imp gave many a good flight to those who could find a convenient source of the dry ice propellant. The engine in the picture is the 4-cylinder model. The cylinders are arranged in "Vee," 2 cylinders to a bank, with a slide valve for each bank, which operates from a throw at the rear of the crankshaft. The engine is very lightly built of soft brass and light sheet steel stampings, soft soldered and bolted together. The pistons are a good fit and the crankshaft is a very neat job of precision bending. Provision is made to oil the slide valves through screw caps on each bank and the crankcase holds 1/2 oz. of 3 in 1 or mineral oil for lubrication. The gas generator at the right is an ingenious mechanism. It requires small lumps of dry ice and carbide plus water to operate. It is designed to be removed from the plane for loading and cleaning and the feed line detaches from the tank for this purpose. Here there is some leakage in evidence. The inside of the tank is compartmented to hold the 3 requisite fuels. Water is used to heat up the dry ice to Fig. 4 The author's version of a "hot" compressed air engine.

MODEL AIRPLANE NEWS. June. 1948 13 cause it to evolve into gas, and the heat developed by the carbide we obtained flights of 1000 feet and up, with 20 to 30 strokes of a tire added to the water prevents the water from, freezing in the process. A pump. A relatively constant pressure supply to the engine was established dumping lever is used to bring the components together, after which the by use of an Austin flight timer connected to gradually open the feed valve gas is produced very rapidly. as the tank pressure lessened. We found best results came when the engine Frankly, we never start this thing up without a bit of fear and trembling was made to carry as much propeller as possible, smaller props at high because we have heard of similar mechanisms exploding violently when speed resulting only in a needless waste of pressure. overloaded. However, it does have ample power to fly a 6-foot model and is One of the most interesting expansion engine experiments made by the reliable and consistent in operation when one can obtain the all-essential writer is shown in Fig. 3, a steam engine control line plane. The engine, dry ice. boiler and burner are built as an integral unit, which bolts to the front of The compressed air unit shown in Fig. 2 is typical of the engines of the plane. About 4 min. is required to get up steam after which the burner this type offered during the late 20's and early 30's. The tank is is doused, refueled and relit for flight. This engine has never been checked (apparently) phosphor bronze about .005" thick, and wrapped with .010" with a Strobotac but the best estimate of its rpm would not be over 2000 on steel wire for extra strength. The ends are closed with .012" spun brass the ground. Thus the trick is to get it airborne, which requires a smooth caps and a standard tire valve is used for inflation. takeoff surface and a bit of leading. Once in the air, however, the engine The motor, of the rotary valve type, is mounted to the tank with soft picks up and puts out enough power to fly the ship at about 40 mph on 20 solder. This part of the unit is rather poorly constructed; a three-cylinder ft. lines, without whipping. This is because of the small size of the burner affairs, the crankcase is of spun brass, cylinders of brass tubing, slotted and boiler, which requires a considerable blast of air into the intake scoop to aluminum pistons with leather compression rings and the connecting rods build up a good pressure. With naptha fuel the engine has quite a bit more are merely hard copper. The crankshaft is a 2-piece assembly with a pep, but since this soots up badly in the burner employed we have had to machine screw crankpin. The fit between crankshaft and main bearing, stick to denatured alcohol, which burns cleanly. which forms the rotary valve intake and exhaust arrangement, is very poor The engine is an inverted oscillating cylinder type with a 1/2" bore and and leaks badly. Soft solder is used as an assembly medium throughout. 3/4" stroke. It swings an 11 dia. 9" pitch balsa, or an 8-8 Pawlownia The tank, we discovered accidentally, will hold 100 Ibs. pressure prop with about equal thrust output. A fairly heavy counterweight is used safely—how much more is problematical. At this pressure the motor will which makes operation nearly vibration-free. Weight (fueled and watered) swing a 12D 10P Pawlownia prop for 45 sec. The first burst of power is a shade over 8 oz. The boiler, incidentally, is stuffed with copper wool to when the valve is opened is rather surprising, but within 15 sec. the prevent sloshing and improve thermal efficiency. A molded asbestos cap, thrust begins to fall off rapidly. After 30 sec. the thrust is negligible. The removed for the picture, keeps the slipstream from hitting the cylinder in efficiency of this engine is very low due to excessive leakage of the flight; otherwise condensation of the steam would lower efficiency. rotary valve; with the prop held still and the admission valve open a full Fig. 4 illustrates an interesting but rather impractical experiment—a "hot" tank of air will leak out in just under a minute! expansion motor, sort of a "McCoy" among compressed air engines. This In order to evaluate properly the worth of compressed air in an efficient develops more power than any of the other engines shown. It has 1/2" engine we built a single cylinder, poppet-valve motor of .20 cu. in. bore, 7/16" stroke and is constructed of hard brass tubing, except for the displacement and with the above tank obtained runs of over a minute and a crankshaft, which is steel. The piston is hand-lapped to fit and connects to half with power output equal to the 3 cylinder engine originally supplied the connecting rod with a ball and socket joint. Full counter- (Turn to page with the tank. With this arrangement mounted in a 48" span free flight job 38)

Fig. 5 Below are shown six different valve mechanisms, applicable to various types of expansion engines

14 MODEL AIRPLANE NEWS • June 1948 Expansion Engines (F) the ball valve requires no external quite cheaply are light, strong, and would serve (Continued from page 14) drive, seats well and gives little trouble. this purpose well. —Ed.) weighting is used and a splash oiler with However, this type of admission works well at The gas generator engine offers literally breather vent provides lubrication. high speeds and pressures only. Because of the dozen of methods of securing pressure. Dry At bottom, of the stroke, air is exhausted great amount of "lead" (gas enters the cylinder ice can be heated in a tank by means of a tiny, not only through the very large port but also before the piston reaches top dead-center) a well shielded alcohol flame; CO2-evolving through a pressure release slot in the rotary considerable amount of flywheel effect is chemicals can be mixed with a small quantity valve. This motor turns up 10,000 rpm with a necessary. If this is not supplied the engine may of water, and a small quantity of air and 2 oz. flywheel at 90 Ibs. pressure, but refuse to start, or may oscillate back and forth gasoline exploded by an electric spark into a consumption of air is terrific. We loaned it to a without turning a full revolution. This is larger amount of dry air will produce instan- friend who tried it at 200 Ibs. pressure on a probably the best type for high pressure CO2 taneous pressure. However, do not attempt any factory airline, and he gave a speed estimate of work and both present day CO2 engines use of these methods without using a reliable 20,000 rpm, which seems a bit overenthusiastic. this principle, but we do not recommend it safety-valve, and in particular do not try the After about 2 hours running time (much for low pressure or steam engines. gasoline exploding stunt without first of it spent in getting it synchronized with an Efficient exhaust porting, of expansion calculating very carefully the proportions of electric motor—so we could put a revolution engines offers a special problem. Usually it is the generator. If you don't know how, don't counter on the motor and see what speed we not enough merely to cut a hole in the try it! were getting), the motor shows considerable cylinder as is done in 2 cycle engines where Steam is probably the safest thing to wear of piston and cylinder and the rotary the piston itself acts as an exhaust valve* generate and the easiest to handle. The boiler valve no longer fits as snugly as it should. This is because the cylinder will exhaust only should be strongly constructed of non-corroding However, at lower speeds and particularly with down to atmospheric pressure, the portion of metals, and baffles of some sort are needed to steam we have found brass to be quite a gases remaining offering considerable prevent sloshing around in flight. The steam satisfactory material. resistance to the piston on the way up again. line should be attached to the tank in such All expansion engines have 2 main re- Drag of this sort can absorb a high proportion of fashion that it cannot pick up water if the plane quirements: a good smooth valve action, and a the potential power of a low-pressure engine. should bank sharply. The burner is best fueled source of pressure. There are many types of *Although this practice is permissible with alcohol. The safest type we have found is valve gear, which give good results, and a few, where very high pressures are employed, simply a pad of asbestos wicking soaked in with appropriate comments included here, are such as in the popular CO2 engines with their fuel. This removes practically all fire hazards shown in Fig. 5. four large ports, and in some types of annular since the fuel stays put and there are no feed (A) The first is the oscillating cylinder valve, ported steam engines where the sudden drop lines to overheat, fracture, or otherwise cause which is adaptable to steam, compressed air or in pressure causes "condensation vacuum." the model to ignite. Air scoops can be used to other pressure. This is about the simplest and To obtain optimum efficiency the exhaust increase the heat of the burner and, by strategic most positive valve gear since it requires no valve should operate from the head of the placement, carry away all heat, which might cams, cranks or levers and wear tends to cylinder and remain open until the piston is be transmitted to the plane's framework. improve the seal. Since much of the operating nearly at top of the stroke, closing before or if A carefully designed steam plane is stress of the engine comes upon the cylinder possible at the same instant the inlet valve is perfectly safe for free flight since it will not stud it is essential that this part be well opened. descend until the burner goes out. Smooth anchored. This engine may be reversed by Thus far we have not mentioned double operation makes it possible to use lighter simply switching the intake line from one acting engines; a word about them is in order. construction to improve soaring qualities. tube to the other. A double acting engine is one in which the The possibilities of steam have never been (B) is the rotary valve. This, too, is a very operating gases push the piston both ways by fully realized. In view of the results obtained simple form of valve and operates with means of a duplication of valves at lower end of with comparatively crude constructions we minimum drag. However, a rotary valve is the cylinder. This necessitates some sort of venture to suggest that if somebody with the subject to leakage with wear, is limited to packing gland around the connecting rod, a time, money and ambition put as much relatively low pressures and is not particularly heavier structure and complication of the valve engineering effort into developing a good suited to steam. If carefully made it is a fair gear. It is, in effect, a 2-cylinder engine in 1 airplane model steam engine, as has been put compressed air valve, but its efficiency is not cylinder. On the basis of our experiments we do into development of present day gasoline en- as high as the more positively sealing types. not recommend this type for aircraft use, gines, the steam engine would give internal^ (C) the piston valve is very positive in although it may be advantageous for model combustion a good run for its money. action but has the disadvantage of requiring a automotive and marine installations. Instead we There are many sound reasons for this separate linkage to operate, and it does put suggest the use of multiple cylinders, 3 being premise. First, there is absolutely no some extra load on the engine since the valve ideal, since there is no "dead center." In radial question of whether or not it will run. If closes against line pressure. It is however "ex-pension engines, any number of cylinders you can scratch a match you can start a steam practically leak-proof if well made, and this may be employed, odd or even, with the power engine. Second, there are no electrical feature alone makes it worthwhile. output becoming smoother as the number of problems, no wiring, and no switches. Third, (D) the slide valve is perhaps the most cylinders is increased. steam is quieter, cleaner, and generally easier to widely employed expansion engine gear. It Now, how can we obtain pressure? There handle than internal combustion with its special wears well, seats without leakage and offers a are several methods of storing gas under fuel mixtures, variable compression (in the comparatively minor drag on the engine. It is pressure to drive an expansion engine. The case of diesels) point clearances, cowling equally good for steam, air, or CO2, but should simplest, oldest and in many ways most problems, and oil-throwing disposition. have some provision for lubrication if the latter satisfactory method is to compress air in a But is steam capable of offering as much 2 "dry" gases are used. Leakage is apt to occur light tank by means of a and pump. For those power? around the gland where the activating rod who dislike pumping operations the tank may We think it is, and with weights comparing enters the pressure chest. be filled from a seltzer cartridge by means of a favorably with internal combustion. The (E) poppet valves offer fast action with little gadget used to secure emergency inflation reasons are: minimum leakage and good wearing of bike tires. We once used an old high-pressure Although the steam power plant is not as characteristics. Excellent for steam or truck tire, inflated to 80 Ibs. at a local service efficient—interims of B.T.U. converted to compressed air, they may tend to stick if station; rolled to the flying site it provided, by mechanical energy—as the internal high-pressure CO2 is used, due to the great means of a detachable air-chuck, about a dozen combustion engine, it can quantitively convert refrigerating quality of this gas. flights. (Surplus oxygen tanks now available more fuel into mechanical effort for any given displacement. pressure over the piston is limited only by subject—what are the possibilities of using tiny Thus, if a gasoline engine of .299 cu. in. how much heat is being applied to the bottom of impact turbines and driving the prop at a displacement, obtains a thermal efficiency of the boiler. We can raise this limit by raising lower speed through a magnetic slip clutch? 25%, and a steam engine of the same size has an the burner temperature; that is, by forcing To sum it up, it is the writer's conclusion that efficiency of only 10%, this does not more air and fuel into the firebox. there has never been a fair test of basic worth necessarily mean the gasoline engine is more Another angle: in order to get any sort of between the expansion engine' and gasoline powerful even though it is 2-1/2 times as power output from internal combustion engines power plants for model plane use. There is, efficient. We can burn 5 times as much fuel they must turn over at very high speeds, speeds today, a need for a good reliable compressed in the steam engine and raise its power which it has been demonstrated are not the air motor for free flight which can be filled with output to twice that of its rival. The amount most efficient propeller wise. To permit high a few strokes of a tire pump. The whole thing of fuel, which can be burned in an internal engine speeds and lower and more efficient should not be over 24" in length and should combustion engine, is strictly limited by its propeller speeds, the use of some sort of be manufactured to tolerances comparing with displacement. Therefore, for each revolution it reduction gearing is mandatory, bringing added those used for gasoline engines. In steam, there is practical to convert to heat only as much fuel weight and frictional losses. However, with the are boundless opportunities for both control as will give the greatest expansion of gases; steam engine it is possible to hold the speed and free flight. The application of cartridge additional fuel will not give additional power down with a larger propeller, of higher pitch, gas (CO2 etc.) to model prime movers has only but will simply be wasted. The maximum gas and let the increase in boiler pressure carry the been briefly exploited. pressure over the piston for any given stroke is load. What should we be able to do with In short, the expansion engine field is one, limited strictly to the maximum pressure it is props of 20" pitch, 3 to 4 times the area of which has been but lightly and sketchily possible to obtain by burning a given quantity today's racing toothpicks? touched, with no real effort to extract the of gasoline and air. And—just in passing, because we have done utmost performance from the basic idea. This does not hold true for steam. Here, the but a sketchy amount of work on the Now, who is going to do something about it?

MODEL AIRPLANE NEWS • June 1948

I Fly a Control-Line

Trainer It looks like a refugee from a Venetian-blind factory, but it flies fine—and it won't stall.

By James Webb The prop is spun . . . the engine roars . . . must remember . . . pull back on stick. Then ease off . . . in the air now . . . everything's going by so fast . . . trees . . . ski . . . water . . . trees . . . a blur . . . beginning to feel dizzy . . . nose down again . . . must pull stick back . . . there's the sun . . . dazzling . . . can't see very well. . . she's stalling . . . Crash! I'd cracked up on my first solo flight.

F COURSE I could walk away from Oit—you always can; that's a big advantage in flying control-line models over the real thing. But the crash discouraged me from getting a model for the kids. Now, here was Roy Clough Jr., whose model I'd cracked up, with another plane, a funny-looking one. The wing was a series of slats with air spaces between. And there was a big cardboard disk in front of the prop. "What have you got there?" I asked. Roy had been mighty nice about his plane—explained that lots of beginners cracked up control-line jobs because they are so fast and so easy to stall if you freeze on the controls. Then he grinned. "This," he explained, "is a control-line model designed especially for beginners —a basic trainer. She's slow and she won't stall. Swell for kids to learn with. Why,

AUGUST 1955 189

After a flight checkout ...... away she goes

I bet even you will be able to fly her." Air compressed under the wing by the I was in no position to resent that. In- forward motion is squirted through the stead, I asked for a demonstration. spaces and over the slats to provide the The little plane took off slow and easy lift. and went around the circle with a lazy "And notice the low angle of that front lope like a tired hound-dog. Then Roy strip," he went on. "That's what keeps stuck her nose up and held it there. In- her from stalling even when the nose stead of stalling and crashing, she kept is way up." mushing around, nose in the air, even I took the controls, and Roy was right. slower—walking speed. Even I could fly this job, and I could Roy wasn't kidding. This little job turn her over to small fry with little risk was as different from the model I'd flown of a discouraging crack-up on the first before as a cub trainer is from a Shooting try. What was equally important, I found Star. "What's the secret?" I asked. I could build a trainer model for the kids He pointed to the slat wing and the myself. So can you. Here's how to go prop disk. "The disk spoils the air stream about it. from the prop so that the plane travels Fuselage. Trace the fuselage outline slowly. And she gets the lift to keep go- on a sheet of 1/4" balsa and cut it out ing at low speeds from this fancy wing. with a razor or a modeler's knife. Cement a 1-3/8"-diameter disk of 1/4" plywood WING SLATS set at varying angles, ranging to the nose for the engine mount. Then from negative (downward) angle at leading edge of wing to positive (upward) angle at add two half-round blocks of balsa, trailing edge, give lift at low speeds. The faired from the disk to the fuselage, to tail surfaees are hinged with cloth tabs. reinforce the engine mount and hold the mounting nuts and landing gear in place. Cement the cloth-hinged tail surfaces in place and brace them with two wooden toothpicks. Bend a tailskid from soft wire, press it into the fuselage, and secure it with cement. Wing. Cut the slats for the Venetian- blind wing from 1/8" balsa and cement them to tip racks made from scraps of 1/4" balsa left over from the fuselage. These tip racks must be stepped or

190 POPULAR SCIENCE

climbing high ...... into the sky notched exactly like the fuselage for good alignment. Add 1/16" tip plates to the wing and cement to the fuselage. Coat the model with fuel proof dope to protect it from the engine fuel. Controls. Cut a T-shaped bell crank from tin can stock and pivot it on a nail pressed into the fuselage. Link the con- trol crank to the elevator horn with a length of 1/32" music wire. Support the wire at its center by a piece of plastic- soda straw cemented to the side of the fuselage. Tie and cement a 25' length of light fishing line to each leg of the bell What a show! crank and pass the lines through the wire loop on the wing tip. Trim the free ends from the fuel is clogging the tank and to exactly the same length and attach feed line. They can be cleaned with lac- them to the control handle. quer thinner. But a word of caution. Engine. Almost any small half-A en- Even a tiny half-A engine has nasty ex- gine can be fitted to the mounting disk. haust fumes; spend the evening in your Just be sure the engine shaft is mounted shop turning her over and you'll end up at a slight downward angle for good low- with a bad headache. Have plenty of speed behavior. Fit it with a 6" propeller ventilation, or better still, do your tuning- and kill its efficiency by fastening a 3" up outdoors. Fueling. Your fuel comes ready-mixed disk of cardboard in front of it. Operation. As soon as the trainer was —a typical formula has castor oil plus finished, the kids and I took her out to methanol plus nitro-paraffins—in half- the empty lot next door. With Roy along pint cans that cost about 55 cents. This to give us some expert advice, we quickly may seem pretty high on a gallon basis— got the hang of it and could walk her $8.80-but you'll find it's only slightly over a penny a flight. You can fill the tiny around the circle without any trouble. Engine tune-up. After you've been fly- tank with an eyedropper, but it's a lot ing a while, you may find your engine easier and safer to use a miniature pump getting cranky and hard to start. This that any model-supply store carries. Starting. Prime the engine first until probably means that a gummy deposit it slops over—don't try to be neat if yon

AUGUST 1955 191 want easy starting. Then hook on the bat- prop, one at the controls. If there is no teries—a couple of 1-1/2 volt jobs wired in bare earth or pavement handy for the parallel. These supply the juice to heat take-off run, the prop handler will have the glow plug that ignites the fuel inside to hold the plane in the air and give her the cylinder. One contact goes to the a little toss forward; she won't take off glow plug, the other to the engine frame. from grass. The take-off run should last You can make your own connecting 10 or 15 feet. Level off after a slow climb. wires, but again it's easier to use a ready- Gentle the controls; the plane responds made wire with a neat double tip that readily as she picks up speed. fits exactly and costs only 35 cents. Of If you freeze onto the controls with course, you disconnect the batteries as the nose up, the trainer will just mush soon as the engine catches. around instead of stalling. But don't get Before spinning the prop, set the fuel- in the habit if you plan to fly conven- air-mix screw at the point recommended tional models. by the manufacturer—usually three to You may think the fuel supply is very five turns open. If the engine catches small; later you can add auxiliary tanks readily but then dies, your mixture is too for longer flights. Actually, however, lean. If it does this even with a rich mix- you'll find at first you can get pretty ture, your fuel line is probably clogged. dizzy even with a short flight. Once the engine catches, the engine Props. You can vary the speed con- will sputter and spit, so lean the mixture siderably with different combinations of until it roars smoothly (it will really roar, props and spoiler disks. Those recom- too). mended for the plane fly her about as Controls. Be careful when you unwind slowly as she'll go and still take off. the reel not to cross the control lines. You'll soon find props are expendable, Operation is simple. Hold the reel verti- so take along half a dozen spares. cally, with the end upward that is con- Beware the wind. Because the trainer nected to the up action of the elevator. flies so slowly, she develops very little (Mark this end with a red dot on the centrifugal force to keep her out at the reel.) Then you pull the top of the reel end of the control lines. Even a slight back to make the plane rise; the bottom breeze may blow her toward you as she to make it dip. flies crosswind—and if the lines slacken, Flying. It takes two people to handle your control is lost. If necessary, keep any control-line plane: one to spin the lines taut by running downwind. - END

A TIN CRANK transmits your pull on control The plane climbs when you tilt the stick back, lines to elevator. Lines are attached to a dives when you ease it forward. Cabin windows control stick hand-held in vertical position. are painted on the fuselage.

164 TOYS AND GAMES Try a Real Challenge-Build Free-Flying Powered

HELICOPTER

High-flying helicopter takes off ver- tically, and solves control problems of gyroscopic forces and torque

By ROY L CLOUGH JR.

Taking off vertically and flying at reduced speed forward allows you to experiment with the helicopter a model helicopter involves some complex dy- in reduced flying areas without it disappearing. namic problems. Flight stability has been a big stumbling block, as early models either crashed within seconds after take-off or rose drunkenly Craft Print Project No. 202 into the air before tipping over to one side and plummeting downward. Helicopters gained the THERE'S little chance you'll lose this helicop- reputation of being tricky, hard-to-control, and ter in a free-flight, as it takes off vertically, requiring an expert's patience to adjust all the flies forward at reduced speeds, and slowly factors that would keep it in the air for a few floats down when the gas runs out. You can minutes. fly it in a limited space with less danger of Actually the trouble was not with the helicopter cracking it up. And it will teach you about idea, but with the approach to the problem. A rotary-wing aircraft and their problems. rotating wing observes not only aerodynamic With all the advantages of helicopter flying- laws, but also the laws which govern gyro- why haven't we seen more of them? Controlling scopics. Rotors behave in much the same fash- ion as a toy gyro top. Applying a force at one point on the rim tilts the rotor, not at that point, but 90 degrees from that point. This is a basic law of gyroscopic action. A rotor that is rigid and stiff, as most of the early rotors were, would react at 90° to any deflection in flight. If a wind struck the front of the rotor, for example, it

Counter-rotating props solve torque problem as small blade attaches to engine output shaft while main rotating wings are fastened to engine frame.

TOYS AND GAMES 165

automatically, small flyweights are attached to the blade tips to integrate the gyroscopic forces with the aerodynamic forces. When the rotor encounters a tilting force it tilted on its side. Then, if the reacts at 90°, causing the tip Helicopter Adjustments Made Easy same wind struck the side (due to weights to bob up or down. FIRST, remember that the spinning rotor is essentially a These weights change the angle the slip induced by the first gyroscope. Since the large rotor has the most mass, it displacement), the rotor would rules the system in this type of model. A gyro reacts of attack of that particular pitch fore and aft. The net result to an adjustment or disturbance at 90 degrees from blade. Since this reaction where the disturbance takes place. Thus it might be occurs at 90° from the was a wild series of dips and said that we adjust model helicopters "around the rolls of increasing amplitude corner." For example, if the center of gravity is in the original displacement, the con- ending in a crash. These correct position and the model tends to nose up, we trol reaction, which also moves correct this by bending the rotor mast so that the rotor 90°, travels back to the original reactions happen so rapidly that mechanism tilts slightly to the left. If the model tends it appeared the model simply to dive, then we tilt the mast somewhat to the right. By point of displacement to cancel varying the sidewise tilt of the rotor mechanism we can out of the disturbance. 'went crazy' and crashed. Solving make the model fly forward to right or left or rise The flyweight solution also this stability problem calls for vertically. provides automatic auto- freeing the rotor blades so they On the other hand, suppose we load the model tail heavy. This puts a side load on the rotor, which is rotation when the motor stops. can tilt, increasing or decreasing processed (moved 90 degrees) by the stabilizing tip Otherwise the rotor would their pitch angle according to the weights and changes the pitch (cycles the blades) and produces FORWARD flight. If we load the model nose slow down and stop, then aerodynamic load upon them. To heavy it will tend to back up, but due to the keel start to spin backwards, which obtain this motion surface it will swing around quickly at high speed nine times out of and may dive because of sudden change in altitude. 166 TOYS AND GAMES

with this system's mechanical simplicity is its more dynamic complexity. The small rotor does the major lifting task while the large rotor takes care of the stability and auto- rotation. The fuselage is a good place to begin construction. Bulkheads slip on a simple keel and the resulting frame is covered with stiff construction paper. The rotor mast and the landing gear legs must be ruggedly attached. Cabin windows are painted on with hot fuel-proof dope in a contrasting color. The tail surfaces are fixed, as it is not necessary to adjust them (we'll explain this later). The rotor unit, the heart of the helicopter, begins with two small can covers—we used caps MATERIALS LIST—HELICOPTER from baby food jars. These should be about 1-1/4 All Dimensions in Inches in. diameter and no larger than 2 in. diameter No. Size and Material 1 1/8 x 3 x 18 balsa Clean out the seal or cardboard and accurately 1 1/16x 3 x 36 balsa (spare blade allowance) center a hole to fit the rotor mast in each. The 1/4 sheet balsa, approximately 1-1/2 x 3 (mast fairing) 1 10 x 12 stiff paper for fuselage covering blade arms are 1/16 in. diameter music wire. 2 small jar covers (press-on type) Bend to shape (Fig. 4) and solder in place inside 3 paper clips 4 3/32 hole washers one of the caps. Good balance and accurate layout 1 length 1/16 piano wire, 36 long are important here. 5 5-in lengths soft iron wire, 1/16 diameter 20 sq in tin can stock Next drill holes for the engine mount, taking 2 1-diameter wheels care to center the engine exactly. Solder the 5 2/56 x % nuts and bolts mounting nuts in place over the holes. 1 1/8 leather washer or equivalent 1 Wasp. .049 or Atwood .049 model engine The blade clips are bent from tin can stock. 1 2 or 3 pitch prop 5 to 7 diameter for engine Brass or copper tubing forms the pivots on two of Misc. colored fuel proof dope, cement, solder, etc. them (Fig. 4) while the third is soldered directly to the blade arm at a slight positive angle. A #3-48 or #2-56 nut and bolt holds the blades in place. With ten would tumble the model into a crash, to say the rotor stems in place, take the other jar cap, nothing of presenting a very sloppy performance butt it up against the first (which has the hardware having little in common with full-scale machines. in it) and run a bead of solder around the seam. While our helicopter appears to be, and actually This makes a very light and friction-free rotor is, an extremely simple design, the design bearing. Hold it to the fuselage mast with a considerations behind it are based on a working washer soldered to the mast. Make up the rotor knowledge of some rather complex factors, so don't blades now. The woodwork is identical for all alter the plans if you want the best performance. three; simply sand them to a 'glider wing' section While everybody likes to make minor changes here and dope. Two of the blades are fitted with tip and there, you'll find it to your advantage to build this weights (Fig. 4). The third blade is assembled model exactly as shown. Later on, with more without weights and goes in the fixed holder. experience and the understanding of gyro forces The only weight we put on this is whatever is learned from this model, plus actual flying required to balance the engine cylinder. experience and observation, you can design an Assemble the whole works and check for bal- original. Understanding of what goes on is the ance. Then make up the pivot prop and put it keynote to success with helicopters. on the engine (Fig. 3). Use a small wood block Our helicopter uses a 'torque reaction drive', to provide take-up for the shaft nut. which bypasses all problems of clutches and gearing. You're now ready to test fly it. Check the Two rotors supply lift—a small one attached to the balance of the fuselage. The center of gravity engine's output shaft and a large one, which spins in should lie about 1/8 in. behind the vertical axis the opposite direction. Along of the rotor. This is why: In order for the TOYS AND GAMES 167

helicopter to fly forward while it is rising we must bending the wire slightly and bend the have some force that makes it do so. The flyweights on the other two blades down a bit design of the fuselage causes it to present further so that when they ride up under more resistance to the high-speed downwash of centrifugal force the pitch on these blades will the small rotor in the direction in which we 'seek' about the same angle as the fixed wish it to travel. This means the fuselage blade. Since the feathering (or pivoted) will tend to tilt down unless we move the CG blades automatically tip up when the engine aft to compensate for the downwash effect. In stops, the fixed pitch blade does not interfere flight the fuselage will tilt forward only slightly, with auto-rotation. because the reaction to this tilting force is The function of the special stabilizer precessed gyroscopically to the blades, which arrangement, which tends to twist the shift position slightly and propel the model fuselage to the right if the forward speed forward. becomes high, is to lift the nose and slow the Start the engine and run it up to top speed model down. This feature makes the model with the mixture set a bit on the rich side to easier to handle, acting as a sort of built-in compensate for the centrifugal force on the 'governor.' For this reason it may be flown at tank. Allow the main rotor to come up to its considerably higher forward speed than the maximum speed, and then allow the model to usual run of model helicopters. Do not reduce rise under its own power from your hand. the size of this set of surfaces, and in Be sure it is level and never throw it. The stubborn cases (if, for example, your model is machine should rise up steadily and when very heavy) it may be necessary to increase the about 10 feet up it should start to move size slightly. The recommended engines for forward, flying in a large circle to the left, and this model are the Wasp .049 or the Atwood gaining altitude until the engine stops, when it .049. Use either STA dopes or Aerogloss will drop vertically on its spinning rotor. finishes throughout. Bending rotor shaft to left, forward or to right controls direction of flight. • Craft Print No. 202, in enlarged size for building the Powered Helicopter is available at $1. SPECIAL This model has one fixed blade on the rotor, QUANTITY DISCOUNT! If you order two or more which is used to control forward speed and craft prints (this or any other print), you may eliminate diving tendencies. The fixed pitch deduct 25 Ë from the regular price of each print. angle should be about the same as the Hence, for two prints, deduct 50Ë; three prints, normal angle of the feathering blades, deduct 75Ë, etc. Order by print number. To avoid otherwise the model may 'walk' a bit as it possible loss of coin or currency in the mails, we suggest you remit by check or money order (no flies. If your model refuses to fly forward, C.O.D.'s or stamps) to Craft Print Dept. 5561, decrease the pitch of the fixed blade, and at Science and Mechanics, 450 East Ohio Street, the same time bend the flyweights up on the Chicago 11, Illinois. See coupon on page 192. Now other two blades so they rotate at the same available, our new illustrated catalog of "186 Do It average pitch. Yourself Plans," 10Ë. Please allow three to four If, on the other hand, your model tends to weeks for delivery dive, increase the pitch of this fixed blade by

Scanned in from: Toys and Games You Can Make

Science and Mechanics Handbook Annual No. 6, 1958—No. 556

Autobiography of ROY L. CLOUGH, Jr. Modeler, Author, Novelist, Magazine Contributor, Designer, AMA Hall of Fame Life Member Modeler since 1931 Birth Date: November 18, 1921 AMA: 3254 Written & Submitted by RLC; Updated 7/02 Transcribed by NR (5/97) Edited by SS (2002)

Career: ● Designed the Berkeley “Cloud Copters” ● Designed the first ground effect vehicle in late 1930s ● Built successful rubber powered helicopters and gas powered versions in the 1950's ● Built ducted fan delta in late 1940s ● Was an early builder of reso-jets ● Designed and built glow and diesel engines ● Built a steam-powered control liner ● Designed the original free flight version of the Martian Spaceship ● Have built and flown Flettner-type rotor planes as early as the late 1950's ● Originated the slotted flying saucer design made popular by Fran McElwee ● Built and flown several types of autogyro ● In 1948, built a liquid fuel rocket with compressed air oxidizer ● 22 years as Chief Eng. of high tech firm ● Four years as an Ind. Consultant ● Worked as reporter/writer/editor New Haven Journal-Courier, Eastern Pilot ● At present a freelance writer/designer, author of four books, including 1930s period novel: A Brief History of the Ashmont Town Team etc. ● Long time C&W musician, pedal steel, Dobro. Designer and builder of many instruments Honors: ● 1999 – AMA Hall of Fame

I was about 10-years-old when I built my first flying model out of pine sticks, gray building paper and inner-tube rubber. It flew about 25 feet and I was hooked.

My first kit was a Guillow 10-cent Spad, given to me by a little girl who drew my name in a school Christmas party. Spad wound up as a midwing that would not fly. Early inspiration to design my own sparked by Gordon Light's Wakefield winner. It proved a good pattern.

I have built models with all sorts of power including rubber, compressed air, steam, rocket, park ignition, glow engines and electric motors. One early model, best forgotten, even had a clock spring motor. .

I developed an early interest in unusual, unorthodox, new types etc., and in early 1940's built successful rubber powered helicopters and gas powered versions in the 1950's. Both types were widely copied.

I got into magazine projects by accident when Popular Science's Workshop Editor, the late Harry Clough Page 2 of 3

Walton, was told by his secretary, Ria Nichol, that during a visit to my wife and I in Now Haven she had seen me repeatedly fly a model helicopter from one table top to another. When I discovered I could get paid for this stuff I published a lot of it in MAN, FM, Pop Science, Air Trails, Science & Mechanics, Popular Mechanics and Mechanix Illustrated. I also designed the Berkely “Cloud Copters.” My rotor system was widely copied, including by Cox Manufacturing who never acknowledged or paid for it. Considering the job they did on Jim Walker I figured I lacked the resources to buck them. Later involvement with Big John Elliot and Larry Renger was pleasant and productive, but they fared no better at the hands of Cox management.

I had a lot of firsts including perhaps the first ground effect vehicle. It was a small gas engine powered model about three feet long. It worked great, but all the dirt, grass and twigs it threw up convinced me the idea was practically useless. Talk about blowing it!! I could have had a basic patent. Later on I built a .049 powered model for Popular Mechanics, which they reprinted in one of their workshop books.

I built several early ducted fans, maybe the first to achieve worthwhile thrust. I was flying Free Flight versions when Bill Effinger and Don McGovern could not get their Control Liners off the ground, but what they told me was helpful to my later designs. Also I built two or three pressure Jets. Only one of these was published but I might get back to the idea. Jets published in Air Trails & Popular Science. I was an early builder of reso-jets; the smallest had 7/16 diameter and a tailpipe made from telescoping tubing sections from a golf club. I slid sections back and forth like a trombone to locate the proper resonant frequency. I designed and built glow and diesel engines. Little Dragon, published in Model Airplane News is the best known. I converted an OK C02 motor to run very poorly as a diesel. I also built a small steam boat and a steam race car for Popular Science. I built a steam-powered Control Liner that blew up on take-off.

I designed a gas helicopter with 48" self-powered rotor that flew well on Cox .02. Pop Science.

Originated the slotted flying saucer design, (Air Trails,) but it was made popular by Fran McElwee who carried the design forward. Much later I published a couple of versions in Model Builder.

While I designed the original Free Flight version of the Martian Spaceship, (Air Trails,) Skip Ruff should get the lion's share of the credit for the bigger radio control versions that have made such a hit on the West Coast.

I built and flew Flettner-type rotor planes as early as the late 1950's. Model Aviation News, Popular Science, latest “Rotorplane!” in MAN. (*)See bibliography

Built and flown several types of autogiro. MAN. Autogyro kites for PS and S~&M. Built early but not greatly successful electric in the 50's.

In 1948 I built a liquid fuel rocket with compressed air oxidizer that blew up with a very satisfactory bang. Clough Page 3 of 3

Despite early AMA membership have, until recently usually been a loner. Now, in the springtime of my senility have joined up with the Winnipesaukee Radio Controllers, and acquired a great bunch of flying buddies. I'm likely to try any construct that gets my interest. As a result of this I know more things that won't work than anybody.

Background includes: 22 years as Chief Eng. of high tech firm, Four years as an Ind. Consult. Worked as reporter/writer/editor New Haven.Journal-Courier & Eastern Pilot. Co-authored a McGraw-Hill text on Industrial Psych.

At present a freelance writer/designer, novelist and semi-pro C&W musician: pedal steel/ Dobro/ keyboards. Have worked with Paul Main, Hank Thompson, Dick Curless, and ran my own “Stateliners” for a few years, but enforcement of tough driving and drinking laws has wreaked havoc on the cabaret scene.

Although I believe I am widely known as a designer of “weirdos,” I wonder what these same readers would think if they had seen some of the stuff I tried but did not publish. Reason? It has always been my policy to publish only those things that were easy to build, were not dangerous and would work on the first try for anybody. This ruled out my regen engine that developed so much ungovernable power it kept blowing up; my fuelless flying machine that would have to dump energy continuously to avoid melt-down, and a new system of propulsion that pilot and passengers probably could not live with. Fun stuff, but practically just curiosities.

Currently I have a couple of dozen hot model projects in the works, which, now being retired, I'll finish doing whenever so will not interfere with goofing-off.

Bibilography: MAN= Model Airplane News AT= Air Trails AM= American Modeler FM=Flying Model PM= Popular Mechanics PS= Popular Science AST= Astounding Science Fiction AZ= Amazing Stories SM= Science & Mechanics BL= Boy's Life MODAV= AMA'S Model Aviation Magazine AP= Airports Magazine CL= Car Life MN=Merchandising News MI= Mechanix Illustrated RTV= S&M's RAD.TV.EXP. PMA= PM Shop Man

Date Magazine Title, Subject or Content June 1945 Hunt. Fish Several Hum. Verses anent H&F Sept. 1945 Bas. Des. Problems of Model Helis Oct. 1945 AP Dear Mr. Small Operator Clough Page 4 of 4

Oct. 1945 Sky Raiders Is German.Sec. Weapon a Rocket Plane? Oct. 1945 PS Skyhook Coax Helicopter Jan. 1946 PS Air Freighter of the Future? Jan. 1946 MAN SOS to Model Manufacturer March 1946 MAN Unorthodox Design April 1946 PS “Naclio” Steamboat Model Summer 1946 ? PS Roadable Plane Model Sept. 1946 PS Triad (Radial Wing FF Model) Sept. 1946 MAN Speed Made Easy Oct. 1946 AT Cage Drive Rubber Co-Ax Helicopter March 1947 PS Steam Powered Model Race Car May 1947 MAN More About Model Helicopters May 1947 PS Stressed Paper U-Control (Atom .05) Car and Plane in Home Workshop Annual for 1950 Aug. 1947 AT Evolution of the Model Plane Sept. 1947 MAN Hoverbug Rubber Powered Helicopter Feb. 1948 MAN Improving CO2 Performance – Wat. Jack. Jan. 1948 MAN Autogiro Theory March 1948 MAN Autogiro Free Flight Rubber Job April 1948 PS WHIZZER CO2 Racing Boat Model June 1948 MAN Experiments with Expansion Engines Aug. 1948 MAN English Gyro to Clough Specs Nov. 1948 AT Beginners’ Goat (Still Flying, March 1990) May 1949 MAN Theory of Rotor Planes Aug. & Sept. MAN Reworking Old Engines 1949 April 1950 MAN WhirliCO2pter Mo.? 1950 AZ Social Obligation – STF Mo.? 1950 AZ How the Saucers Fly Sept. 1950 MAN Flying Saucer Design Oct. 1950 MAN Little Dragon Glow Engine Nov. 1950 MAN Part 2 Mo.? 1950 AZ Micrometer in Your Brain April 1951 PS Why Shacks Come Apart (Foundations) June 1951 AST Bait (Picked up for Anth. Space Police) Aug. 1951 FM Try a Helicopter Aug. 1951 MAN Why Models Land in Trees (Prof. Tate) Mo.? 1951 MAN Flying Barrel – Description and pictures only July 1952 MN Small Dealers on the Carpet Aug. 1952 AT Build Flying Saucer (Famous slot job) Sept. & Oct. AT What’s the Score on Helicopters? 1952 Dec. 1952 PS Fly a Plane in the Living Room Feb. 1953 FM Sikorsky S51 TR Helicopter Clough Page 5 of 5

July 1953 AT Tubine (Duct. Fan.) Jets for Models Aug. 1953 AT Below Bug Pressure Jet Model Sept/ 1953 PS Jetex Driven Turbie – FF Model Nov. 1953 AT Two-Part Helicopter Design Dope Aug. 1954 PS Hydrojet Powers Tiny Boat June 1954 SM TR Helicopter .049 Mo. ? 1954 ? Reprinted Model Craft V3, 1954 Not. Pub. PS to BERK Oil Can Reso-Jet Pub. 54-55 AT Doggerel Verse Fillers April 1954 AT Martian Spaceship July 1954 AT Typhoon Expansion Engine Nov. 1954 AST It Didn’t Come From Mars Aug. 1954 FM Stunt Goat CL Model Annual 1955 AT Sikorsky R-6 Helicopter TR Mo. ? 1954 PS Co-axial Autogiro Kite Mo.? 1954 PS More Fillers per Request July 1954 PS Fourth of July Noisemakers July 1954 AT Channel Wing Control Line Plane Mo.? 1954 AT Tri-Yi Rubber Model Sept. 1954 AT January Alouette’ .049 Duct Fan – Ukie Oct. 1954 AT Wind Wagon Air Drive Race Car JORA 1954 S BL Mille Diesel Endurance – Ukie Dec. 1954 PS Ceiling Repair Fillers Dec. 1954 PS Uses for umbrella ribs Jan. 1955 PS Electric Shop Heater from Oil Can Mo.? 1954-55 PS Things to do with Coffee Cans Mo.? 1954-55 PS Turbine Jet Race Car Model Feb. 1955 PS Model Submarine Bautilus March 1955 AT Venusian Scout Aug. 1955 AT Saturanian Space Skimmer Aug. 1955 PM Slat Wing Control Line Trainer Sept.1955 AT TanGiro Twin – CL Autogiro Oct. 1955 AT Teenie Genie Oct. 1955 AT Tri-Yil Dec. 1955 PS Aerial Tramway Dec. 1955 AT (YM) TEE JAY’Super Delta Ducted Fan Mo.? 1955 CL Phantom of the Turnpike Dec. 1955 SM Rebec Medieval Three String Violin March 1956 AT Sheet Metal Susie June 1956 MAN Lil’ Dragon Used as School Project June 1956 AT (YM) Cement Drives Crazy Water Gadgets Pub. 1956 AT Ann Special Case of TR Helicopters March 1957 AM Tumblewing CL Flettner Rotor Plane Dec. 1957 AM Famous Firsts (Yet to be Made) Clough Page 6 of 6

July 1960 PS Rebuild of Cecil Peoli Twin Pusher Sept. 1960 AM Typhoon’s Expansion Engine Feb. 1961 SM Two String Splinter Bass June 1961 SM Triple Neck Steel Guitar June 1961 PS Tethered Ducted Fan Jet Plane Sept. 1961 PS Boat that Flips to Go (Porp. Tail Dr) Nov. 1961 SM Reader Report on Guitar Projects Jan. 1962 PM Ground Effect Vehicle Air Car Annual 1963 PMSHOP Reprint GEV Sept. 1962 PS Platter Plane-Non-Slot Saucer Sept. 1962 PM Old Mill Waterwheel Table Centerpiece Mo.? 1961-62 MAN Model Helicopter Dynamics Feb. 1962 A.E. Esty Machine and Tool Employees Manual March 1962 MAN Nervous Nellie .05 Stunt Job May 1962 PS Self-Powered Rotor Helicopter July 1962 PM Remember the Spinning Wing Autogiro? Aug. 1962 AM Spinning Disk Model Ven. Scout Sold Aug. 1962 PM Control Line Kite Nov. 1962 SM Whirlybird Co-Axial Autogiro Kite Nov. 1962 AM Snapper .49 FF Speed Job 1962 Crestwood Please Shake Carefully (Humor) Sold Dec. 1962 PM (Pub?) Tetra Four Radial Wings Ukie (X-Wing) Dec. 1962 MI String Phones Deluxe Dec. 1962 AM Peter O’Dactyl Mo.? 1962 SM Homemade Vernier Dials Mo.? 1962 PM Vapor Pressure Drivers Model Boat Pub. 1962-63 Sam Bierman How to Open Anything (Humor) Jan. – Feb. 1963 AM Yankee Flea Tandem March 1963 MI Darkroom Light Box March 1963 PM Mystery Moving Box and Kite, p. 164 March 1963 PS Styrofoam Model Oos on Cox .010 April 1963 PM Hoopskirt Annular Wing FF June 1963 AM Turkey Buzzard Flying Plank Type June 1963 PM Water Skating Model Boat Aug. 1963 PM Wind Rotor Drives Boat Propeller Fall 1963 SMRTVEXP Speaker Box Does Everything Fall 1963 SMRTVEXP Electric Amp for Banjo Nov. 1963 SM Moon Scout Nov. 1963 PM Electric Centrifugal Cannon Mo.? 1963 PM Harlequin Stressed Paper Glider Mo.? 1963 PM Control Line Stunt Kite

Clough Page 7 of 7

As a result of being bugged by Skip Ruff and Bill Northrop in 1990. First published was in MAN, July 1992 a review of “Modelcad.” Then “Multiwiz” in August 1992 in MAN. More articles are due in MAN, FM and MB.

Date Magazine Title, Subject or Content July 1992 MAN CAD for Your Model Designs Aug. 1992 MAN Multiwiz Model 2-Channel From 1 Servo June 1993 MB Pushcart .049 RC Pusher July 1993 MAN Rotorplane! Flettner Wing-Rotor Oct. 1993 MB Saucer Mania Two Slot Saucers Feb. 1994 MB Ment. RLC Award Winner May 1994 FM Morles 1915 .049 FMBD RC May 1994 MB Pix Reader Built Zoomslot July 1994 MB Ment. Adv. For Martian SS July 1994 FM Ment. FM Helic. Of August 1951 Aug. 1994 MB Mention Nov. 1994 MB Traysvite May 1995 FM Ment. Page 7 and Class, Gas and Jazz June 1995 MAN Ment. Page 28 and 57 Martian Spaceship July 1995 MAN Ment. Hal DeBolt’s Col. On Early RC Aug. 1995 MAN Stringer Wing-Warp Control 02 RC Oct. 1995 MAN Designed 2D 6.0 Critique Nov. 1995 MB R.K. Hicks FF Electric Dec. 1995 MAN Air Age RC Book Chapter “Mindset” Dec. 1996 MAN Ringer Annular Wing .049 RC Dec. 1996 FM Faux Fighter FMBD ‘Pilchard’ Dec. 1996 MODAV Aileron Trainer Dec. 1996 FM Materia Aeronautica Modela

The following list of articles are missing from my files and have incomplete information.

Date Magazine Title, Subject or Content Early 1960s AT or MAN Flying Barrel Early 1960s PS Gyro Glider Kite Sold April 1967 PM Foilplane, Flying Body Aircraft Early 1960s Lost by AT Maple Seed Jetex Powered One-Bladed Helicopter

Other Projects

● Constructed the steam-powered race car model made for Minimax importer ● Cloud Copters Designed for Berkley Models ● Hummingbird Helicopter Design for Hamp. Research Foundation] ● Helicopter engine design with K & B ● Helicopter blade system for Sikorsky Aircraft Patent Inter. Clough Page 8 of 8

● Co-authored text on Ind. Psych. With Dr. Brian Kay, McGraw-Hill ● Wrote novel: “A Brief History of the Ashmont Town Team vs Equestrian Statue.” (Amazon.com Barnesandnoble.com)

(signed) Roy Clough, Jr. Updated July 15, 2002

- End -

BASIC DESIGN PROBLEMS OF MODEL HELICOPTERS by R. L. CLOUGH JR.

A timely, interesting Article on a subject that has been stumping the experts for years

EXPERIMENTERS in the model helicopter field soon discover they are working with a tricky breed in which instability is inherent and where such terms as "balance," "keel surface" and "power transmission" take on a deeper and at times maddening significance. If one approaches the holy trio—dihedral, down thrust and balance—with the proper degree of reverence in designing a fixed-wing model, it is a fairly simple task to plan a ship that will fly and fly well However, this is not so with helicopters. In the model helicopter, and we are speaking of those intended to represent the real thing and not the familiar whirligig of the "freak" contest, one soon discovers dihedral, or coning angle of the blades, does not assure stability; that balance may be a variable due to gyroscopic action when "stiff" rotor blades are used; and that "down-thrust" has no true counterpart. Unlike most scale models, the fact that a full size machine has flown does not necessarily mean a model helicopter built to the same pattern will be successful. This discrepancy is due in part to what is commonly called "scale effect," and because in a larger machine there is a pilot along to constantly correct flight aberrations as they appear. In power transmission, friction losses in a model run far higher in direct proportion than in full-scale machines. Torque effect is also more pronounced because more power is needed proportionately to fly a model. Therefore, in order to secure successful flights, the modeler must design his little ship in such a manner as to insure inherent stability—something which makers of full-scale machines have not been too successful in to date. The greatest single problem in helicopter design is: What to do with torque? Shall we concentrate on using it, nullifying it, or plot such a design wherein it may be successfully ignored? Since this article is dealing primarily with rubber powered helicopter models we shall concentrate on the first two; either to nullify torque or use it. The latter method of plotting a design wherein torque may be ignored involves self-motivated rotors, propelled by jets at their tips, and confronts the modeler with many mechanical difficulties. Perhaps we speak rather loosely of "using torque." What is meant is that torque is being "used" in a model when the method of eliminating it contributes to the overall lift. When this equalization does not contribute to the lift it is considered nullification, Gyroscopic action is another bugbear. It will always be present to a certain extent, but evidence at hand indicates it is not an insurmountable problem. 14 MODEL AIRPLANE NEWS • September, 1945 Flexible blades and articulated rotor hubs do much to alleviate this effect Proof of the power of this effect was made quite apparent to the writer in an early model design. This model was of the single-rotor and torque prop design and featured a heavy, non-flexible main rotor. It was discovered that when the model was hand launched it would maintain the position in which it took the air until the motor had wound down enough to permit the weight of the machine to overcome the gyro action and return to an even keel This effect was so pronounced that the model would fly on edge for several seconds before leveling off when launched in that position Subsequent experiments with a flexible main rotor definitely laid the blame for this condition at demon gyro's door When choosing the type of design to work with, the experimenter should make UP his mind to stick to that type until he is thoroughly familiar with its intricacies There are five basic types of helicopters and many modifications of each. There are certain disadvantages to each type and all lack the simplicity of rigid wing aircraft Probably the most familiar is the Sikorsky type which corrects for torque by means of a smaller rotor at right angles to the larger in such ratio as to amply compensate for torque at all speeds Second is the contra rotating, in which two main rotors revolve in opposite directions around a common center The De Bothezat, Hiller-copter and Bleriot machines are good representative types Third is the twin-rotored helicopter utilizing two main rotors of opposite rotation extended on booms from the side of the aircraft A variation of this principle is to put the rotors at opposite ends of the fuselage, thus doing away with the booms. The Landgraf, Platt-LePage and German Foeke-Achgelis are examples of this trend of thought. This type is probably the oldest. Fourth is a fairly recent innovation control could be effected through the works best and with the power and the writer has been unable to large single rotor which would being applied to the tip of the rotor secure information as to .whether the undoubtedly throw dangerous instead of the hub the mechanical machine has actually been built or stresses onto the smaller rotors. This advantage is much greater, permitting was merely proposed Three rotors type is definitely not recommended concentration of thrust where drag is are employed, a large main rotor in for model experimentation. heaviest and allowing rotor structures the middle and two smaller ones on The fifth type is the newest and has to be lighter booms, rotating in opposition from the received quite a bit of attention. In As far as model helicopters are main rotor to counterbalance its this type there is but one main rotor, concerned, however, this method torque. From casual inspection it which is activated by jets located in offers many difficulties The writer has would seem the gearing necessary to the tips. Thus thrust is contained succeeded in making a compressed accomplish this would result in within the rotor and, acting directly air jet powered rotor lift its own weight something of a plumber's nightmare, upon it, automatically eliminates (and no more) under 90 Ibs pressure, with more power being absorbed by torque effect. and a steam jet rotor lift its own gear boxes than by the rotors. It is interesting to note in relation to boiler—but not its heat source Control, too, would offer quite a full sized ships that this idea appears Powder rockets will supply enough problem. Either all three rotors must basically sound for two very good thrust and are not overly heavy, but be controllable entailing a great deal of reasons. Tip speeds approach their extremely short duration is weight and machinery, or possibly velocities at which jet propulsion discouraging Therefore the remainder of this enables them to bounce and helps to mass of lateral area must be well back article will deal with the first three destroy the aforementioned gyro of the rotor axis to keep it headed right. types Power utilized for these effect. However, this brings in another factor: experiments is rubber, chiefly because This model is described first to top-of-fuselage area. Since with this of the simplicity of hookup and the high point out the effect of keel surface type there is more area on top of the power-to-weight ratio Helicopter gas upon the flying qualities of the fuselage exposed to the downwash of models will probably be built, but for helicopter. Note the very narrow rear the rotors, behind the rotor axis, if the the present it is undoubtedly best to section and pointed nose. This is model balances directly on the rotor leave out the added complexities of because when displaced air axis the down wash will force the tail internal combustion until familiarity produced by the upper rotor strikes down and give the model all the with the stability problem is gained. the fuselage it has a marked tendency symptoms of tail-heaviness. This is A gas engine would produce a fine to rotate it in the direction of the rotors best counteracted by balancing the steady source of power, but would movement. Therefore, the larger the model slightly ahead of the center of also mean slip-clutches and gearing. keel-surface, the greater the turning lift. Unless one has access to a machine moment. A friction brake on the lower The upper rotor should be shop these items are rather difficult to prop is, in theory, the best way to equipped with a freewheeling device produce counteract this effect. In practice, for easy descents, and it has been The design of the model helicopter however, it proves tricky to adjust. A found that best results are obtained if poses the question- "Straight up, or felt washer on the lower prop will the lower rotor has a slightly greater straight ahead9" If the model is, often turn the trick, but a fin hinged pitch—about 2°. The climbing ability of designed to fly vertically and attain on a fore and aft axis works better. this type apparently exceeds that of all the greatest possible elevation it This same effect is why pylon gas others. This is probably due to the seldom can be adjusted for "cross jobs turn to the right under full power, direct utilization of available thrust country" flights of any great duration when one might be inclined to think where it will do the most good with a One exception to this rule is the they should swing to the left because minimum of fuselage or deflection contra rotating type with a free- of the torque. interference. wheeler which may be adjusted to One tricky phase of keel-surface, or Fig. 3 illustrates the dual rotor move forward as it climbs by adding lateral area, should be mentioned helicopter. Principal problem here is weight to the nose It will continue to before going any further. In fixed-wing to equalize the thrust of the two move forward during its free-wheeling models one usually attempts to get rotors. The simplest and most positive descent but "glide" ratio will be small the center of lateral area as low as way to accomplish this is by an Since model helicopters are designed possible. The reverse of this equalizer beam. Hook-up should be primarily to fly vertically, the ordinarily good rule is true in model clear from the sketch. In this model it is experimenter would do well to helicopters for this reason: highly important to keep the center of concentrate upon arriving at a design At the top of the flight the rotors lateral area as high as possible and capable of a steady climb and slow come to a stop, then reverse for a to make the two rotors as nearly descent with good stability throughout freewheeling descent. The rudder identical as possible. This helicopter is the flight Then, and only then, effect of the fuselage side area is very the simplest to adjust for forward should he attempt "cross country" pronounced at this moment, and if the flight as it climbs. Simply add a bit flights. area below the center of gravity of weight to the nose. The following sketches are exceeds that above it the model will flip Fig. 4 of the Platt-LePage pattern is presented primarily to stimulate the over on its back and descend inverted. basically the same idea as Fig. 3. imagination of model experimenters; Therefore, in designing a model Power transmission of some sort is however, if the general proportions helicopter one must work out a good needed for this type; therefore it are followed throughout these models compromise with sufficient area above requires a lot of work in building and will fly well, though in no case is any the center of gravity to permit a right- excellent balance for good results. sketch intended to represent a side-up descent and sufficient area Pulley and belt, of the kind described completely "perfect" solution. below the c. g. to permit a stable in Fig. 5, seems to work better than the Fig. 1 is perhaps the simplest climb. About 60% above and 40% connecting-rod type of transmission. possible form. It is a direct takeoff on below is about right, although on some Bevel gearing might be the ideal the familiar contest whirligig and is the types it is advisable to have as much solution if a set of the same, light easiest to build and fly. Directional as 75% of the lateral area above the c. enough for practicality, could be stability is only fair, but "glide" is quite g. obtained. A horizontal stabilizer good if a free-wheeler is employed. Fig. 2 is the contra rotating type. Two seems to be necessary on this model The long nose-wheel strut protects rotors of equal diameter revolve in and a rudder often helps. The best the lower prop and brings the center of opposed directions. Hook-up is simple way of winding is by a small crank in gravity forward. Rubber hook-up is but care must be exercised in building the nose section as shown on simple and contra-rotation is the "cage," and all bearings must be sketch. automatic. true. Balance of all moving parts is the Fig. 5 is based on the Sikorsky In this, as in all types of model keynote to success with this model. design. This is the model shown in the helicopters, too much emphasis Directional stability is very good and accompanying photograph. Power cannot be laid upon the importance of this sketch points up another phase of transmission to the rear prop was a making the rotor blades flexible. For helicopter design. In this model, great problem in designing the original. every foot of radius the blade should forward flight may be secured by After numerous experiments the have a "spring" of at least 1-1/2". This adding weight to the nose, and the pulley and belt system was adopted as the most simple and efficient. One interesting fact about the anti- Once adjusted this type will stay Ordinarily one might think such an torque propeller was discovered: It adjusted. Varying power used will arrangement would result in slippages does not need to produce a thrust not upset the ratio between the two so great as to obviate the possibility of anywhere near equal to the torque rotors. any constant ratio between the main reaction produced by the main rotor It is a good idea for the serious rotor and torque propeller. This in order to hold the ship steady. This experimenter to keep a record of his problem, however, was solved very is probably due to a keel-surface experiments for future reference. nicely by facing the pulleys with a fine effect produced by the spilling of air Patience is the keynote to success. grade of sandpaper. The belt is from the tips of the main rotor Do not give up any design type until common twine, tied snugly in place against the apparent disk of the anti- you are certain you have tried and shrunk with water. torque propeller, which would of everything that can be done with it. A four bladed rotor is used to course tend to push the boom in the Often a very simple "bug" will prevent absorb as much thrust as possible direction of the main rotor. a model helicopter from performing within a small area to keep the anti- Adjusting this model so that torque well. Once this is located the model torque rotor boom as short as is evenly balanced is quite simple. will often turn in a surprising possible. The main disadvantage of With a pulley ratio of 3-1 start with the performance. Remember that in these this type is the short rubber length, blade area of the little prop equal to little jobs a somewhat different set of but due to the proportionately slow % the area of the main rotor. This conditions holds sway from those of revolutions of the main rotor, longer will cause a slight over-correction conventional models. Respect those flights than one might be inclined to and cause the boom to swing conditions and success will be yours. think possible may be had. around in the direction of the big VICTORY This model works best under power prop. Then trim the small rotor, a dropping quite rapidly after achieving little at a time until it balances. This is maximum altitude. It is presented here considered the best way, even if it chiefly as an experiment in power amounts to cut and try, because it has transmission. The model will fly well been found that a difference in only if weight is kept down. This bearings and pulley alignment is method of nullifying torque rather than peculiar to each builder, with a natural "using" it does not seem to be very slight difference in results. If the efficient, more rubber being required blades are over-trimmed, add a small proportionately to fly this type of fin to the boom in the slipstream of model than one featuring dual, or the larger prop and trim it to fit. contra rotating props.