FLIGHT, Jti'y 10th, 11741. a

The Brewster Bermuda two-seater dive-bomber now in production m America for the R.A.F. and F.A.A. DIVE BOMBING Factors Affecting Pilot and Machine IVE bombing may be defined as is aimed at the target and descends for an effect of " 5g " while holding the release of bombs when com- rapidly towards it. For maximum the same speed of 340 m.p.h. right D ing out of a dive at a target. accuracy, the bomb should not be re round the curve. That is to say, the There is only one exact position for leased in the straight dive, but its pilot's effective weight on the seat at release of the bomb because, unless instant of release should be timed to the bottom of the pull-out curve is the dive is at 90 deg. to the ground, occur just after the start of the pull- five times what it is in straight and the bomb does not travel in a straight out, so that the curvature of the unaccelerated flight. For such a path after it leaves the aeroplane. bomb's path will bring it right on to factor, the descent is 1,300ft after Although, as is obvious, different air the target. starting the pull-out. Of course, if craft will dive at different speeds, it During the pull-out the aeroplane the diving speed is lower, the loss of is generally assumed that the addi- travels round the arc of a circle until height in recovery from the dive is tional velocity imparted to the bomb it is again climbing, and after that very much reduced, and a Ju 87 is equal to dropping the same bomb makes good its escape. Its path in Stuka diving at 240 m.p.h. at 70 deg. in level flight 4,000ft. higher. This the pull-out is circular if the control would only require 620ft. of vertical figure is, of course, for dive bombing column and throttle are worked to air space in which to pull out, with from the usual heights. If the bomb- maintain a constant speed ; naturally the same "g effect." ing were to take place from such a the radius of the circle can be in- Four pull-out curves are also shown height that the terminal velocity of creased or decreased by moving the for different values of the "g effect." the bomb was reached, it would make stick forward or back as the pilot de- In addition to the 5g curve, one of no diflerence whether dive bombing or cides. Such movement of the stick larger radius and two of smaller radii level bombing was employed. varies the load factor, commonly re- are shown. These curves are arcs of Modern dive bombers are going to ferred to as the " g effect," which the circles with centres at the points A, descend faster than the 240 m.p.h. of pilot feels. With the stick farther B, C, D. From centre B, for the " 5g the Stuka, probably 100 m.p.h. back, the radius of the circle is effect," the circle has a radius of faster, and this speed of 340 m.p.h smaller and the • . and an angle of 70 deg. have been " g effect " selected as the initial conditions in our greater. The diagrams. In the dive the aeroplane curve shown is

In this diagram is shown the paths of the aircraft and the A graph showing the height loss and the " g effect' bomb in a 340 m.p.h. 70-degree dive with a 5g. pull-out. experienced in pull-outs of different radii. FLIGHT JULY IOTH, 1941.

DIVE BOMBING

Excessive speed in the dive is pressure, increasing their capacity, prevented by the use of diving and those above the heart contract. brakes ; these are flaps under the In the organs from which the blood wings made to project into the has drained away owing to this circu- wind and so cause resistance. lation breakdown there is a deficiency The Skua's diving brakes are of oxygen normally carried by the " solid " ; the Ju. 88 has brakes blood-stream. The brain and the eyes of parallel slats with spaces be- are obviously the organs affected tween them, and the Brewster most; darkening of vision occurs, and Bermuda has fretted plates. The even unconsciousness if the accelera- effect sought after in the two tions continue. When accelerations, latter types is to " smooth '' the or " g," ease off, the eyes resume their air resistance of the brake and function almost immediately, but un- prevent it setting up large aero- consciousness persists — hence the dynamic vibrations. reason for the automatic pull-out. It is quite obvious that if the blood- vessels were inelastic, like metal pipes, ij Blacking-out and could not distend or collapse, the circulation would be unaffected be- A pull-out with a very small cause the blood could not drain away descent is desired so that the from any part of the body. It is im- may go as low as possible to support each vein separ- possible before releasing the ately, but a certain amount can be bomb, which, of course, helps done by wearing bandages and belts. accuracy. But a sudden pull- Any way of bolstering up internal out means a high value of the load factor and this may break the aeroplane or the pilot. A "g effect" of about 10 would pull the wings off the bomber and would also probably seriously injure the internal structure of the pilot by tearing the lungs and other soft parts away from the bony structure of the body. So there are defi- nite limits to the '' g effect'' in the pull-out, and probably five is about the maximum that, could be used. At higher values than this the "blacking-out" of the pilot's sight would prob- ' "' ably be so severe that he would The Junkers Ju 87 (Stuka) going be unable to continue flying. down at a steep angle. An ejector The effect on the pilot of pull- arm throws the bomb clear of the airscrew. ing out of a dive at, say, 5g, is to force the blood down the 1,960ft. The vertical descent is, of blood-vessels towards the feet, as course, less than this figure because of if it weighed five times its normal the initial inclination of the straight weight, with the consequent draining dive. If the dive were vertical the from the regions above the heart. In favourable weather conditions, the descent in the pull-out would be equal The blood-vessels being elastic, those attack should be made out of the sun to the radius of curvature. below the heart swell under the extra and into cloud for getaway.

Diagrammatic illustrations of the use of varying cloud cover. On the left is broken cloud. The machine moves from one cloud to another, making the final dive between two clouds. A continuous layer is shown on the right. The machine comes out for short intervals to get its bearings before making the actual attack. JULY IOTH, 1941. FLIGHT

DIVE BOMBING pressure is effective. For instance, can be more or less ignored. more " g " can be borne after a meal A dive bomber is no different when the stomach is full. from any other military vehicle Altering the attitude of the pilot can and must be able to reach its have a considerable effect on the " g " target, do its job and return to which can be borne without ill effect. its base. As with other military It is inconvenient, to say the least, to vehicles, there is a choice of depart from sitting as the standard three elements in making the position of the air crew. Standing up- approach and get-away reason right gives the maximum effect. Sit- ably possible. Cover by the ting with the legs level or above the skilful use of clouds, the sun and hips improves matters considerably, aerial manoeuvre is the first aid while in the horizontal position a large to the dive bomber. Speed may proportion of pilots could put up with be used to avoid interception by as much as 10 or more "g" without enemy fighters on the way to losing consciousness. This, however, and from the target, and is, of would be of little use, since the course, a useful adjunct against machine would probably break under ground defences. Finally, there the stress. The time element also is the time-honoured military enters into consideration but, gener- system of fitting sufficient arma- ally speaking, the dive bomber pull- ment and armouring to enable out is of such short duration that it the craft to fight its way to the target and out again. Weather conditions are out of the hands of man, and the use of clouds or other natural cover is a question of training crews to make the best use of the conditions pre- vailing at the time.

Aircraft Type The other two elements must be taken into account in evolv- ing what is considered the most suitable craft. Range, quality of opposing air force, money available, are but three of the many considerations which have to be taken into account when Designed for shipboard work, the working out the compromise. has folding wings Speed is expensive, and life in and the diving brakes are " solid." the German Army is cheap. Hence the Ju 87 has neither speed nor defensive armament, nor armour plate to protect the pilot, and better defensive armament and but we have never had the requisite is, therefore, a much more formidable If the wind is in the wrong direction number of fighters available to give machine when used for attacking the reverse procedure can be made. them & really severe mauling and so special targets. The Brewstei Ber- Use the cloud for cover and the the type has served its purpose. The muda, which is now in production in blinding effect of the sun for getaway. Ju 88 has speed and armour-plating America for the R.A.F. and F.A.A.,

The effect of wind and movement of the target is shown here with the right and wrong methods of approach. (Left) Out-of-wind or against-target movement will steepen the dive to a dangerous degree. (Right) Into-wind or with-target movement will lessen the angle of dive and is easily allowed for. FLIGHT JULY IOTH, 1941.

DIVE BOMBING strikes midway between these two and The time element enters largely into should be very useful for general use. the approach problem, and every The Vultee Vengeance, of which but moment spent near the target means little information has been announced, extra risk from A.A. fire. Height is seems to be a fighter-dive bomber with also a consideration. Nine thousand really high speed in addition to a feet gives reasonable security from heavy battery of machine-guns. light A.A. fire, but for the heavier Whether the attack is to be made guns at least 20,000ft. is necessary. by a single machine with a special On arrival at the scene of operations target or by a large formation with several factors have to be taken into fighter protection, the actual attack account. Wind speed and direction ; becomes an individual operation. At absence or otherwise of cloud cover; this late stage the ground defences angle of sun to target and cloud cover ; constitute the most formidable speed and direction of target; these obstacle and, while the taking of ex- are all factors in consideration of treme care in the aim must be a first which the resulting dive is a com- consideration, every manoeuvre and promise. No hard-and-fast rules can bit of cloud cover available should be be laid down ; the attacker must make put to good use. the best use of prevailing circum- stances. Wind measurements can be taken while on the approach in order further to reduce the time spent actu- ally over the target. Theoretically, the vertical nose dive in still air should produce 100 per cent, bull's-eyes, and should also give the Without diving brakes the Junkeis> bomb the maximum velocity. In Ju -88—which is used for both level practice, of course, " still air " seldom and dive bombing—has a maximum happens. The natural endeavour by diving speed of 419 m.p.h. a pilot in a vertical dive with wind drift On is to keep his nose on the ward-firing guns, and it is ordinary target. This leads to his machine get- practice to paint marks on the cock- ting beyond the vertical and makes pit windscreens in order that the it impossible to pull out of the dive proper angle to the ground can be before impact with the ground. With checked off against the horizon. A this in mind it is easy to realise that dive is never as steep as it feels. A the 90 deg. dive requires the bombs truly vertical dive gives the feeling to be released from a greater altitude, of being well over on the back. The and this nullifies any advantage customary method of approach is to gained. aim slightly behind or on the lee side of the target in order that the target Angle of Attack may be kept in view the whole time Dives at 45 deg. to 70 deg. are and not hidden by the engine or other coming to be the accepted angles of cowling. Release of the bomb is then attack. Between these two figures made as the target appears to come simplicity of aiming still obtains gently downward through the sights. without putting too great a strain on The attack having been made, it the air crews or the machines ; neither is up to the pilot to make himself 13 it necessary to fit the bomb on an scarce as soon as possible. If there ejector arm to miss the airscrew. is backward-firing armament this may It is desirable to make the attack be used to quieten the ground de- into wind and in the direction in which fences, but accurate shooting is im- the target is moving, for the very good possible of achievement until after the reason that the effect of both can '' g effect'' of the pull-out from the easily be corrected during the final dive has passed off. There are two stages of the dive. The reverse direc- means of evasion commonly used. tion would have the effect of steepen- The first is to keep low and zigzag ing the dive to a dangerous angle. or crazy-fly the aircraft. This makes Nevertheless, if the target is large and the pull-out a good deal gentler and well defended, the use of the blinding puts the heavier A.A. guns off their effect of the sun and available cloud mark. The second evasive action is cover will over-ride considerations of to fly up into the nearest cloud or to- wind direction. Aiming is much the ward the sun, according to their actual same as that employed for fixed for- position in relation to the getaway.

ELEVATOR TRIMMING .TAB

ELECTRIC QUICK RELEASE HYDRAULIC If neither cloud nor sun is available CYLINDER to cloak the approach, aerobatics to put the ground gunners off their aim Diagram of automatic pull-out mechanism. Hydraulic pressure is applied to a piston is the only subterfuge left to the which moves the servo tab to the dive position. Release of the bomb also releases dive-bombing pilot. the pressure and the spring operates the tab in the opposite direction. FLIGHT FEBRUARY 26TH, 1942

Twenty-seventh of the Second Series FRIEND or FOE ? Fleet Dive-bomber and the American Trainer : Blackburn Skua and the Harvard

HE skua has been defined as a sea-bird which lives chiefly on T offal, so the species provides a very appropriate name for a dive-bomber. The Blackburn

Skua and the North American Har­ vard trainer provide another example of two aircraft which greatly resemble each other except for their tail units. Their overall dimensions are reason­ ably close to each other, and the gen­ eral outlines of fuselage with radial engines, low wings and tandem cock­ pits under similar styles of '' glass­ house '' all follow pretty much the same layout. But when one's eye reaches the tail of the Skua it will at once spot a distinctive characteristic which this machine shares only with its sister craft, the Blackburn Roc. The Roc (floatplane version), readers will remember, was dealt with in the 24th article of this present series, in Flight of February 5th, and a comparison between the illustra­ tions of the Skua on this page and those of the Roc will show that the fins and rudders., set well forward in rela­ tion to the tailplane, are identical on both machines. The plan and mount­ The Harvard tailplane has a pro- ing of their respective tailplanes are Qounced backsweep to its leading-edge also the same, the only small differ­ and gracefully curved elevators with ence in the complete tail assembly small, rounded tips. In plan view the lying in the fact that the Skua, with its trailing-edge shows the conventional fixed tail wheel, has a smaller stabilis­ '' bite '' in the centre to allow rudder ing fin beneath the stern of the fuse movement. The tail wheel is non- lage. retractable. The Harvard I has a straight slope Although not strictly to the leading-edge of the fin and a within the scope of this projecting rudder extended right down series, it is worth repeat­ to the bottom line of the fuselage. The ing that a useful charac­ trailing-edge rises vertically from the teristic of the Skua is its heel but curves in to the small round turned-up wing-tips. HARVARD: Conventional apex. Incidentally, the rudder of the fin and rudder, with Harvard II differs from that of the Next week :—Brewster straight slope to leading- Harvard I in that its trailing-edge Buffalo and Grumman edge, small apex and makes practically a straight slope be­ Martlet. curved trailing-edge. Tail- plane has pronounced tween apex and heel, giving a triangu­ backsweep to leading-edge lar effect very similar to that of the and curving elevators and Defiant tips. Fixed tail wheel. FLIGHT Thirty-seventh of the New Recognition Series Aircraft Types and BLACKBURN ROC NE ot the only two single-engined fighters to be turally similar except for the gun-turret, is quoted as 225 equipped with a power-operated , the Roc m.p.h. at 6,500ft., its cruising speed only 187 m.p.h. at O appeared in 1939 as a development of the Skua, 15,000ft., and service ceiling 20,200ft. which it greatly resembles. The power is supplied by a Bristol Perseus XII nine- ' Its intended mission in life was the role of Fleet fighter cylinder, sleeve-valve, air-cooled of 905 h.p. and it could be equipped either with a wheel undercarriage within a long-chord cowling having a leading-edge exhaust .(outwardly retracting) for operation from aircraft carriers, collector ring and trailing-edge cooling gills. An interesting or as a floatplane as illustrated in the sketch below. Since feature about the all-metal circular monocoque fuselage is the drag of a gun-turret would obviously be a serious speed- that it has watertight compartments capable of keeping reducer to a single-engined machine of this size, and since the aircraft afloat for long periods even if the two cockpits a retractable turret was also out of the question for the are flooded—a very useful asset in an aircraft intended for same considerations of aircraft size, retractable fairings operations over the sea. were provided fore and ait of the turret. These materially The wings, which fold, as on all carrier-borne aircraft, reduce "form drag" when raised, and allow complete differ from those of the Skua in that they lack the turned-up traverse when lowered, nevertheless the top speed of the tips which characterise the latter machine ; they also have a Roc, like that of the Skua, was scarcely up to modern much more pronounced dihedral angle from the narrow, operational fighter requirements. No official figures have flat centre-section. This and the presence or otherwise of ever been issued of the Roc's performance, although it the Boulton Paul four-gun power-operated turret provide has long since ceased to be on the secret list, but the top almost the only visible recognition features as between the speed of the Skua, which has the same engine and is struc- two aircraft. The distinctive tail unit applies to both.

Top speed : About 225 m.p.h.

ROUNDED TIPS

DISTINCTIVE TAIL UNIT BLUNT NOSE

SQUARE CENTRE SECTION DIMENSIONS OF ROC Span 46ft. Oin. Length 35ft. 7in. Height /2ft. I in. Wing area .. .. 310 sq.ft.