The Rotary Is Here And

THE ROTARY (S HERE NOAND W

By Patrick Frers (EAA 16476) may lead you to seek a more comprehensive insight into 108 Guatay Ave. this marvelous powerplant through available litera- Chula Vista. CA 92011 ture. A CONDENSED HISTORY OF THE WANKEL It all started with some very old basic concepts pre- O'N, E THING THAT has kept me puzzled is the fact viously used in the development of the rotary valve sys- that our community of aircraft homebuilders has not tem and the positive displacement pump. On February 1, as yet "discovered" the Wankel rotary engine, with its 1957 Dr. Felix Wankel succeeded in test running a many extraordinary advantages over the type of recipro- "motorized" version of these systems, the culmination cating engines commonly favored for aircraft use. of a research program supported by N.S.U. in Germany. Alternatives to certified aircraft engines are being This rudimentary but ingenious machine, vaguely re- used in increasing numbers, but their selection seems sembling today's successful rotary engine at least proved to be based on whether they "look" like the typical air- for the first time the feasibility of an engine with the craft engine rather than on the basis of dependability, simplicity of a valveless two-stroke without its draw- endurance, simplicity and economy of overhaul — char- backs, promising the realization of a dream of a futuris- acteristics of the rotary that cannot be touched by more tic powerplant with a minimum of moving parts and ex- "conventional" engines. treme reliability. It was a beautiful dream . . . and the The neglect of the rotary can no longer be laid to most beautiful part is that today it is a total reality!! availability . . . new and used automotive units can be Shortly after the initiation of work with develop- bought almost anywhere in the country. Replacement mental models, another inspired scientist made an im- parts are as close as the nearest auto dealerships. Cost portant contribution to the study. Professor Othmar is not a valid argument against the Wankel as it is now Baier of the Technical College of Stuttgart demonstrat- more or less competitive with other mass produced en- ed theoretically that the shape of the new engine's com- gines of roughly the same horsepower. Maintenance bustion chamber, arrived at empirically by Dr. Wankel, and overhaul costs can't be factors either because with was in effect and epitrochoid. This paved the way to mathe- its fewer internal parts, the Wankel is cheaper to bring matical analysis for the development of the engine. Dr. back to "like new" condition than other types. Wankel started off working on the assumption that rather than in a reciprocating piston, it was in the THE INERTIA EFFECT smoother and more "logical" motion of a "rotating piston" turning within an epitrochoid envelope that the Perhaps one of the probable causes keeping us from promise of a realistic combination of displacement and "discovering" the rotary engine is that well known "in- useful compression ratios existed for an engine for the ertia" effect (something between "persistence of set" future. and "functional fixedness", as known in human psy- After several developmental changes, the engine chology). As applied in this case . . . we continue using as we know it today, began to take shape and by as late something just because we've been doing it for so long as 1960 one of the models successfully endured a 1000 before, or simply "because it's commonly used", thus ig- hour test at N.S.U.; and then another 1400 hour test noring possible better alternatives. in 1963. As the many problems were inexorably con- We may even "know" that there is something better, quered, one after the other, finally the most persistent but when the time to make a decision arrives, we seem of all — apex seal durability — was solved, too. Proto- to be "conditioned" to choose the "common, usual" choice type engines ran routine tests of 1000 hours without as long as it seems adequate . . . not necessarily the best. problems, and consumption came down to rates com- The fostering of progress has always been out of the parable to those of reciprocating four-stroke engines reach of those who do not dare to be different, be them- (0.57 Ib./hr./hp at 5000 rpm and 0.5 at 2000 rpm in 1964 selves, think for themselves. tests). This "inertia" effect is a fact in human psychology, In the meantime, of all the firms holding a license and it often takes independent thinking to break away agreement, Toyo Kogyo of Hiroshima, Japan (Mazda) from it ... and, of course, the information and knowl- proved to be one of the most impressively active and edge to found the break upon. successful by developing a highly remarkable version But most "home-builders" are "home-builders" pre- of the Wankel rotary combustion engine in a relatively cisely because of their individualistic independence of short time. Ironically, they had initially been very coldly thinking and acting. Therefore, it could very well be received by N.S.U. and, in fact, had achieved a license that lack of familiarity with the Wankel is what is keep- only through the friendly mediation of the then Ambas- ing us from its advantages. sador of the Republic of West Germany to Japan, Dr. Then, perhaps, the brief information presented here Wilhelm Haas. This was in 1961 — only two years after SPORT AVIATION 59 engines. (The single rotor N.S.U. Spider had been in- troduced in 1964 as an exploratory move but was dis- continued in 1967.) It was not until 1969 that the first Wankel cars ap- peared on the American market in quantity with the introduction of the Mazda 100. Today, the dual ignition Mazdas still are the only rotaries widely available, but after 7 years we have a reasonable abundance of engines in the used market — the internal combustion engine of the future ready to power our airplanes now with greater dependability and financial economy than can be offered by any reciprocating piston engine in the moderate power category. A sad and ironic commentary on the American industrial picture is the fact that the very first Wankel licensing agreement was issued to the Curtiss Wright Corporation in 1958. This company developed its own versions of the engine, the two rotor RC2-60 of 180 hp for automotive use and a more sophisticated aircraft en-

OIL PUMP , , gine. Although possessed of definite and proven advan-

(O.u l.ur.0 01.... t <.!»•») k,C3T__J ] tages over conventional engines, none have been put into production. In 1970 General Motors reluctantly en- tered as a "late comer" in the Wankel race and, as of this writing, is still thinking about the possible use of the engine. However, if figures published in 1972 are any indication, GM's cast iron engines will be of little A Wankel Engine Longitudinal Section use to homebuilders — a 160 hp engine (at 6500 rpm) (Two-Rotor Mazda) weighing 350 pounds and a 200 hp engine weighing 440 pounds. (By comparison, the good old aluminum block Olds V-8 215 weighs about 315 pounds and produces 185 hp.) So what's new in Detroit? The emphasis, as always, seems to be on cheapness. They may still manage to turn an inherently light, reliable and efficient engine into a heavy, reliable, clumsy one. When they will ever learn the lesson of lightness from foreign industry is anyone's guess.

OPERATION The Wankel rotary combustion engine utilizes the same principle of internal combustion as demonstrated by Dr. Nicholas Otto in 1878 with his first working model ofa reciprocating engine . . . the well known "Otto Cycle", intake, compression, combustion and exhaust. There the similarity with the reciprocating engine ends. While in the reciprocating engine the combustion ac- celerates the piston in one direction at an average speed of 3000 ft. per minute, only to stop at the end of the few inches of the "stroke" run, and reverse its motion in the opposite direction, then stop again and reverse, and so on, several thousands times per minute ... in the ro- A Wankel Engine Cross-Section tary engine the so-called "piston" is rather a rotor that (Two-Rotor Mazda) doesn't waste the energy of its inertia constantly revers- ing its motion. Instead it "rotates", propelled by the news of the Wankel had reached Hiroshima. expanding gases of the combustion, always in the same Mr. Tsuneji Matsuda, president of Toyo Kogyo, made direction. Mr. Kenichi Yamamoto manager of the Rotary Engine The fundamentals of this operation can be better Development Division and in record time one of the most understood by observing Figure 1. modern and computerized development laboratory plants Since the relative position of the rotor within its was working at an extremely accelerated development housing opens and closes the intake and exhaust ports, effort. the rotor and its housing by themselves become their By 1964 Toyo Kogyo was ready to show two of its own "positive" valve system with a precise and invariable versions of the Wankel, a two rotor and a four rotor, at timing, better even than that ofa four stroke engine with the llth Tokyo Motor Show. Their first production car, its elaboration and power robbing friction. The rotor the Cosmo Sport 110-S, was completed that year and was is always timed, it doesn't burn or have to be main- shown to the public for the first time at the 1966 Tokyo tained or replaced. It also eliminates the inadequacies Motor Show. It had a two-rotor engine that produced of the absence of valves as in the two-stroke engine. 110 hp at 7000 rpm and rotor seals good for 80,000 miles. The centerline of the rotor, mounted on a "lobe" of It delivered 24 miles per gallon at 70 mph. the engine shaft, does not coincide concentrically with Then, in 1967 both N.S.U. and Toyo Kogyo put the the axis of this shaft. So, when the rotor turns, its cen- first rotary engined cars on the market, the N.S.U. Ro. ter goes around the shaft axis as in a planetary motion 80 and the Mazda Cosmo Sport 110-S. Both had two rotor ( . . . just as a "hula-hoop" around the waist of the play- 60 APRIL 1976 AIR-COOLED FAMILY Model RC]-60 RC2-60 RC4-60 RC2-90 RC3-90 RC4-90 RC5-90 RC6-90 HP (aircraft T/O) 103 206 412 310 465 620 775 930 RPM (aircraft T/O) 6,000 6,000 6,000 6,000 6,000 6.000 6,000 6,000 HP (surface equip.) 80 160 320 240 360 480 600 720 RPM (surface equip.) 5,000 5,000 5,000 5,000 5.000 5,000 5,000 5,000 Dry weight—lbs. 192 266 417 317 410 510 605 710 Specific weight—lbs./hp. 1.96 1.29 1.01 1.02 0.882 0.882 0.781 0.764 Length—in. 24.4 29.4 39.4 32.4 38.9 45.4 51.9 58.4 Width—in. 20.7 20.7 27.3 20.7 22.0 23.3 25.2 27.2 Height—in. 18.0 18.0 18.0 18.0 18.5 19.9 21.0 22.0 Volume—cu. ft. S. 26 6.35 8.5 7.0 9.06 12.2 15.9 20.2 Specific volume—cu. ft./hp. 0.052 0.031 0.021 0.023 0.020 0.020 0.020 0.022

LIQUID-COOLED FAMILY Model RC2-90 RC3-90 RC4-90 RC 5-90 RC6-90 HP (w/o fan) 285 428 570 713 855 HP (w/fan) 276 414 552 690 828 RPM 5,000 5,000 5,000 5,000 5,000 Dry weight—lbs. 345 480 613 740 860 Specific weight—lbs./hp. 1.21 1.12 1.08 1.04 1.01 Length—in. 28 34.5 41 47.5 54.0 Width—in. 23.8 23.8 23.8 23.8 23.8 Height—in. 22.0 22.0 22.0 22.0 22.0 Volume—cu. ft. 8.5 10.5 12.4 14.4 16.4 Specific \olumc— cu. ft./hp. 0.030 0.025 0.022 0.020 0.019

_ ^ ,\ ' I \

FIGURE 2: Phasing Gears FIGURE 3: Counterweights

course, for the gear arrangement for the distributors, oil pump and accessories. The small eccentricity of the rotation of the rotor is perfectly balanced by small counterweights, one in the flywheel and the other at the opposite end of the shaft. (Figure 3) Since, therefore, there are no unbalanced FIGURE 1: Wankel Operating "Phases" forces like in any reciprocating engine, the rotary is al- (Equivalent to "strokes") most vibrationless, like a turbine.

SEALING er). Thus, the rotation of the rotor is transmitted to the Gas sealing of the rotating variable shape chamber shaft through the lobe on which this rotor is mounted. formed by the cavity between the rotor faces and the A simple arrangement of two intermeshing gears, housing, is provided by side seals peripherically ar- one fixed to the center of the rotor and the other to the ranged along the "edges" of the rotor and another set side wall of the housing, governs and insures the cor- of two "corner" seals and one "apex" seal on each of rect motion of the rotor, establishing a precise angular three "tips" of the curvy-sided triangular rotor (Figure relationship between its rotation and that of the shaft, 4). so that for each complete revolution of the rotor, the These apex seals — which were the critical ones dur- shaft has accomplished three, (more about this later.) ing development — now insure a long between-overhaul Figure 2. time. (Mazda dealers dare claim they remain efficient These two parts, the rotor and the shaft, are the two for 100,000 miles, which is roughly the equivalent of basic moving parts in the Wankel. So, i.e., a two-rotor 2500 hours at medium rpm. Being conservative, I would Wankel engine would have only three basic moving stipulate for our purposes a somewhat lesser time at parts: the two rotors and the common shaft (in the ro- higher cruising engine rpm, and this still would com- tary nomenclature called the "eccentric"), except, of pare well with most other engines at those higher rpm.) SPORT AVIATION 61 ure 6). Also, the Mazda engine uses a little pump driven by the distributor gear to meter a very minute amount of the same lubricating oil and introduce it into the fuel before this is atomized. This insures further lubrication for the seals, as well as additional cooling. The small size of the radiators makes it easy to lo- cate them advantageously inside a small, well streamlined fuselage ( . . . imagine a fighter replica powered by a rotary. It would make a P-51 hundreds of pounds lighter all around and with a planetary type reduction gear easily obtainable, would fit ideally in a radial engine type fighter replica.)

OPERATIONAL CHARACTERISTICS SIDE SEALSPRIKOS Having three faces, the rotor accomplishes three com- FIGURE 4: Seals plete (all four "phases"; phases being the counterpart of "strokes") combustion processes during each one of its revolutions. Since the shaft has gone in the meantime through three revolutions, it means that there is one power "phase" per each shaft revolution. Also, it completes each of the "phases" with each turn of 90 degrees, that is, while the shaft has turned 270 degrees. This interesting feature accounts for several of its remarkable advantages too, i.e., the change from minimum to maximum volume in its working chamber takes place during 270° or shaft revolution, and this results in a greatly increased "breathing" (some esti- mate up to 50'? ). Consequently, a higher volumetric efficiency is encouraged compared with the intake stroke of 90" in the reciprocating engine — and this without considering the efficiency in expulsing the burned gases with the "free" aid of the centrifugal forces, also through 270° "=• _-re7). FIGURE 5: Dual Ignition System (Mazda)

O ANGLE OF CRANKSHAFT ROTATION FIGURE 6: Oil System Torque Overlapping . . . Performance Curves IGNITION In the Mazdas (which are the only rotaries regularly available in the USA, while the Canadians have the option of the excellent Audi N.S.U. Ro-80), we have the big plus of a dual ignition system with two spark plugs

firing into each rotor for better combustion and a more Aflfir of roiftiion ol stable one, especially at low rpm (Figure 5). The N.S.U. ihe Output Jitwti Ro-80 has single ignition, but compensates by having the benefits of a C.D. system.

COOLING .if roiBiun of Cooling is by both water and recirculating lubrica- ' ihr Ou.p..- Shaft tion oil. The water cooling system is of the sealed type (another plus for us) with an expansion chamber and small aluminum radiator. The oil, besides lubricating, cools the rotor and side walls of the housing. It is, in FIGURE 8: FIGURE 9: turn, cooled by being circulated through a radiator (Fig- 62 APRIL 1976 FRONT In-Lme. 4 Cylinder Another important factor is the smoothness of the Recrprocatmg Engine rotary's torque output. Each one of its impulses are ap- 5^v-. •'•' \ plied during three-quarters of a shaft revolution with £;f:l ,_•,*• i an overlap of one-quarter of a revolution over the next K' torque impulse (in a two rotor Wankel). The reciprocating engine necessitates at least six cylinders in order to achieve a similar proportional overlap (Figure 8: "K" - "coefficient" indicating smoothness in the "Torque Variation" and reflecting this relationship . . . this also shows why, among other factors, those little "four cylinder" engines are excellent "vibration machines".) The operational smoothness of the Wankel, to which this makes another contribution, results in such benefit to In-Lme 6 Cylinder Reciprocating Engine 2 Rotor Rotary Engine the structural integrity of the vehicle in which it's FIGURE 11 mounted, that would not be wise to fail considering . . . manufacturer's rated displacement per rotor and multi- also, adds to a rather "flat" torque curve, with little drop ply it times two, and the result times the number of after maximum (Figure 9). rotors in the engine in question. Thus, a two-rotor Maz- Then, of course, this also contributes to the rotary da RX-2 rated by the manufacturer as displacing 35 cu. ability for high rpm operation while maintaining a rea- in. per rotor, as per the above "standard" formula would sonable "apex" velocity. have an "equivalent displacement" of: A look at the sketch showing the operation of the 35 cu. in. x 2 x 2 rotors = 140 cu. in. Wankel (Figure 1), shows it can achieve high compres- And even this figure doesn't really look any greater sion ratios, which is the key to efficiency in burning considering the 130 hp it can develop, when compared the mixture. While the reciprocating engine also can with most "stock" reciprocating engines . . . (The U. S. obtain high compression ratios, the marvelous thing in "smog system" radically reduces the engine's output, the Wankel is that it does it without increasing the oc- but this doesn't concern us since in flying configuration tane requirement!! In fact, the Mazda can be fed with it operates without that burden.) the cheapest gas despite a 9.4:1 ratio. Therefore, a judgment with any degree of validity should be made on the basis of power output, that is ... FUEL CONSUMPTION the root of the concept of "specific fuel consumption". During the latest "stage hit" on the national scene, Let us think of a small block 1972 V-8 of 130 hp dis- dubiously called "The Energy Crisis" for the benefit of placing 307 CID; or a Buick Special V-6 rated at 135 hp the average taxpayer, voices (mostly from persons unin- and 198 CID; or a 1970 Ford 6 Inline of 120 hp with a 200 formed in any reasonable degree about the Wankel) CID. Now, if it could rightfully be said that the rotary raised the claim that the rotary "consumed too much burns more gas than these engines, then the claim of fuel". We should ask by what standards those persons "high consumption" could begin to appear having some arrived at such a judgment. Certainly to appraise its truth in it. But certainly, the rotary consumption is consumption by its displacement as expressed in the better than most of these engines when a relationship case of a Wankel, for example, would be quite fallacious. between their power output is established. Although while in terms of maximum volume of On the other hand, anyone who attempts to com- chamber, its displacement can be expressed in ways no pare the two-rotor Wankel consumption with that of different to that of the reciprocating engine, functionally those so-called little "economy" engines like the many its significance is entirely different. Let us not forget, meager four-cylinder vibrators would show the same there are three firings of correspondingly three admit- logic in comparing the food consumption of an elephant ted (intake) and compressed charges for each revolu- with that of a mouse . . . and attempting to hold valid tion of the rotor, deriving power from their combustion the conclusion that the elephant "just eats too much!" every 270" of shaft revolution. Displacement rating for A two-rotor Wankel has never been a cheap "economy" a rotary is therefore merely an expression of maximum engine, but a "high performance" one. It is interesting volume per rotor, but it could obviously not be equated to note that some small four-cylinder "high-performers" with that of a reciprocating engine either in terms re- in sport cars will consume just as much as the two-rotor flecting power or consumption. It is for this that the In- Wankel, yet yielding less horsepower, i.e., Volvo B-18's ternational Automobile Federation, the recognized sanc- (1800 series — they are good — I had one). tioning body for international auto racing, had to arrive The specific fuel consumption of the rotary is in the at a practical formula (not necessarily scientific) for same class as that of four-stroke reciprocating engines. an interpretation of the Wankel CID that could be "cor- We mentioned already that way back in 1963, develop- related" to that of the reciprocating engine . . . the man- mental engines at N.S.U. were yielding a S.F.C. of around ner on which they agreed to do just this is to take the the 0.5 figure, and in 1966 the Mazda Cosmo yielded 24 mph at a fast 70 mph. The specific fuel consumption of the Curtiss-Wright RC2-60 U10, shows in their graphs 0.5 even at 5000 rpm . . . and that's better than many of Detroit's products . . . and these, rather than judgments or rumors, are documented facts. Notorious, however, is the voracious specific fuel consumption of the two-stroke reciprocating engine, FIGURE 10 now so popular in boating and snowmobiles and even in some homebuilts.

WEIGHT After reliability, almost no maintenance and great endurance, "specific weight" (lbs./hp) is another in- stance in which the rotary moves ahead of any reciprocating four-stroke engine, whether automotive or the SPORT AVIATION 63 good old faithful aircraft certified type (with the excep- tion of some of the higher hp Continental Tiara series and some others in the highest power categories of aircraft engines, which come very close to the heaviest WANKEL R.C.) Figure 10 shows the position of the rotary type engines in specific weight versus hp rating. Their superi- ority is readily obvious. The higher hp versions are found in direct competition with the turbo-shafts, but, of course, without their thirst for fuel. The only reciprocating piston engines (not shown in the graph) that are in the same class of specific weight with the rotaries are some of the two-stroke type, like those found in the outboard industry and some snowmobiles. Unfortunately, their fuel consumption rate is very high — which is typical of this type. Also, they are not generally available in powers higher than 150 hp and their applicability to power homebuilts offers some very delicate problems. There are some basic factors that put the rotary engine ahead of most any other engines that the home- builder has to choose among, either automotive or older design aircraft types. While even an inline six or a V-12 reciprocating engine cannot balance the secondary forces originated in We could briefly add that the rings, also subject to the asymmetry of the swinging motion of the rods in this insane up-and-down action will develop flutter at their crankpins (their primary can be balanced by coun- extreme shaft rpm, while the valve system, under the tering the motion of one piston with that of the other), same alternating inertia forces, will eventually be un- the rotary by contrast, is free of all these sources of des- able to follow the movement of the cams and its timing tructive vibration. In addition, the cranking motion of becomes disordered (the condition known as "surging"). the crankshaft requires both a heavy construction and In the rotary, the seals (counterpart of the rings) slide balancing. Conversely, the small eccentricity of the ro- always in the same direction. It has no valves to burn or tor rotation can be easily and perfectly balanced by light damage or in which to waste power, and its intake/ex- counterweights. Furthermore, even the rotor itself can haust timing is always positive, precise and invariable. be constructed lighter since its motion is strictly rotary Over-reving or abusing a piston engine can result in and not subject to the severe reversal of inertia stresses broken pistons, connecting rods or crankshaft, bent or as is the piston and other parts in the reciprocating en- burned valves, broken lifters or pierced rocker arms, etc. gine. These stresses dictate that the letter's parts be In the rotary there are no such parts (except for the "ec- stronger and be made heavier . . . which closes a vicious centric", the crankshaft counterpart, but never so much circle as this tends to increase their inertia. Thus, a stressed), and in fact there isn't much to burn or break. solid limit to the recips' rpm becomes firmly established, Over-reving a Wankel is free of all these disasters and beyond which only disastrous effects could be expected. would mostly lead to an excessive rate of wear and oil As a result, the lighter piston engine will weigh at consumption. Broken seals and chatter marks in the ro- least 2 lbs. per hp, and the average can be found close or tary's chamber would result in a loss of compression and above a ridiculous 3 lbs. per hp. Most Volkswagen en- power to a varying degree, but not likely to a catastrophic gines are around or above the first figure, and the other breakdown. Most loose fragments from the seals should is the trademark of most V-8's. (The only popular excep- be expelled right through the exhaust by the centrifu- tion given to us by Detroit years back was the aluminum gal forces. block V-8 powering the Olds' F'85's and Buick Specials.) The dependability characteristics of the Wankel The Mazda, not being one of the top examples of the ro- should therefore be a factor of paramount interest to tary's virtues in weight-to-power ratio since it was us, even if all other advantages should be ignored. originally expected to power automobiles, beats most (Caution: this should give no cause to abuse even a automotive and aircraft engines with a figure slightly rotary engine. No conscientious and intelligent operator over 1.5. would exceed engine limitations.) Specific weights here noted do not assume any "hot- rodding" modification . . . which, if applied to aircraft adaptation, could be the fastest and most effective method of inviting tragedy for a visit. Also, it applies to the hp range that most of us would consider for our projects ADAPTING THE WANKEL TO AIRCRAFT POWER (there are some automotive racing engines in the very Adapting one of the rotaries available to us today high power ranges that, if you can afford them, will should definitely be not any more involved than any of give you a lot of muscle at a low rate of weight: Chevro- the other automotive choices. In many cases even less. let L-88 and the 426 Hemi-Dodge are examples). With the Mazda rotary engine we already have the benefit of dual ignition, and a very compact size which, along with the fact that it is water cooled, should permit a very well streamlined cowling, with the resulting ad- DEPENDABILITY vantages in looks and performance (Figure 11). In many cases, the rotary could be used in an aircraft The extraordinary degree of dependability of the ro- just as is, with only the addition of a simple reduction tary is built into its own intrinsic simplicity, the very arrangement whose parts are easily obtainable. This limited number of moving parts and the absence of re- should be mounted on the flywheel end. versing inertia stresses. We already have discussed Figure 12 shows a tentative adaptation carried some most of the highlights about this. steps further. Should a very slim cowling be desired, 64 APRIL 1976 the oil filter and the carburetor have been repositioned to predict. But, no doubt, it still will see many more to further lower the profile. improvements. Should it be desired, the change to a diaphragm type Also, no doubt, the reciprocating engine will die aviation carburetor could be studied, which would in- hard and will be around for some time more. There are volve a minor modification in order to introduce the always those who keep pace with progress and those minute amount of oil metered by the engine into the who prefer to stick to the old things. Still today you'll fuel. find some who'll argue that the "stick shift" is better No modification to the engine itself should either be than the automatic transmission or that the "conven- necessary or advisable. It would be difficult to improve tional landing gear" is superior to the "tri-cycle" (other on it anyway. than in economics or drag). The demise of the reciprocating engine will probably be a matter of industrial re-tooling, "corporate" economics, market readiness, energy resources and environ- CONCLUSION mental pollution. And all of these are considerations In the world of the internal combustion engine, the that will find their way into different solutions of vary- Wankel is ahead of most all others in specific weight — ing effectiveness in a not-so-far future. except for the turbo-shafts. Together with this, it offers In the meantime, the chance to further progress is an attractive rate of specific fuel consumption in a class here for a few individualists, unsatisfied with what is with the four-stroke reciprocating engine. abundant all around, and on the alert for what it may Nevertheless, to judge or discuss the rotary engine be a step forward. only on the basis of its lightweight and comparable fuel The EAA community, with its talents and the com- consumption would be like judging Raquel Welch by parative freedom in designing and building we enjoy, stopping at her facial features and beautiful hair . . . has become the recognized spearhead of progress in sport well, it just couldn't be done! and personal aircraft development. It is a true "reserve The value of its great dependability, easy mainte- bank" of inspiring ideas and the natural breeding ground nance, total economy and adaptability is also a very of constant improvement, to be carried out by a cast of important part of the picture. "explorers" with a foot in the present and the other in While the reciprocating engine has enjoyed the bene- the future to find there the better things waiting to be fit of about three-quarters of a century of development discovered and brought right into our "now". and improvement, the rotary has been around for only In keeping with this, perhaps we should look some about ten years after an accelerated gestation of another more into the rotary. I have. I am working on it. I have ten before being born into the market. Despite this, to- chosen it for my project. Perhaps, some of you should day it is already superior to most reciprocating engines too. by any standard except popularity . . . but this will be The rotary is "here and now". so only until people start looking at it twice. Given the (Note: Those interested in this subject wishing to chance of even further development, how much better write me may do so to the address listed at the begin- something already good can become would be difficult ning of this article.)

For all you homebuilders who ing edge back to the 35c/< chord. LOWER have built designs that incorporate The result is no increase in drag at the NACA 64/2-212 or most of the cruise speed, reduced pitching mo- other laminar flow airfoils and are ment and, most important, a 30% THOSE STALL not happy with your high stall increase in lift. speeds, help is here. This upper surface contour change I'm sure all of you know the var- could easily be accomplished with ious STOL kits available for various foam and fiber-glass. For those of SPEEDS Cessna and Piper aircraft but don't you who might be interested, the re- know where to get the data for such sults of the wind tunnel tests, the a modification. Most of the STOL aerodynamic data and airfoil coor- conversions utilize a drooped, en- dinates are contained in NASA By Don Thomas larged radius leading edge. This Technical Memorandum "NASA 3843 Wynnwood Dr. method works, but as NASA has TMX-3293" dated September 1975 Macon, GA 31206 found, it has the disadvantage of and titled "Effects of Forward Con- increasing drag and pitching mo- tour Modifications on the Aerody- ment, which requires a larger hori- namic Characteristics of the NACA (From: The Slipstream, Newsletter zontal stabilizer and/or elevator and 64/2-212 Airfoil Section." This re- of Chapter 38, Macon, Ga.) reduces cruise speed. port can be obtained from the Na- NASA has developed an alterna- tional Technical Information Ser- tive design involving a change to the vice, Springfield, Virginia 22161. upper surface contour from the lead- The price is $4.75.

SPORT AVIATION 65