JANUARY 25, 1940.

Equipment and Tactics for DIVE-BOMBING Specialised : Diving Brakes : Heavy Bombs : The Human Element By H. F. KING NTEREST aroused by an article 's Dive Bombers appearing in Flight of September 28 last year I suggested a review of international practice in this form 01 attack with reference to the specialised aircraft required and the problems presented. Both the Spanisn and the Polish struggles demonstrated that dive-bombing has a very definite place in modern warfare. They established that diving attacks made with specially designed aircraft will give excellent results not only against small individual targets on land (e.g., build- ings, cross roads, railway junctions and " pill boxes ") but against moving objects like ships, tanks and mechanised columns. Previously dive-bombing with heavy projectiles, par- ticularly as fostered in America, was regarded as being chiefly of use against ships and it is significant that, despite the fact that several squadrons of the are equipped with and Henschel Hs 123 dive- bombers, the great majority of American, British and French machines designed primarily for diving attacks operate from the decks of airciaft carriers. Reference has already been made in Flight to the exten- sive and successful employment of Ju 87s in Spain. They were introduced into the conflict early in 1938 and were used on the drive to the Mediterranean coast, during the fighting on the Ebro front and on the Catalonian offensive. They met with particular success in the final phase of the Spanish war when they bombed ports and ships on the Mediterranean coast. The havoc wrought in Valencia, A German Henschel Hs 123 single-seater dive-bomber Taragona and Barcelona was due chiefly to their activities. releases a salvo of four 50 kg. bombs One pilot is said to have accounted, single-handed, for three large steamers off Taragona, each time securing a Dive-bombing as we shall consider it entails the release direct hit. of a bomb or bombs while an aircraft is diving steeply to- In Poland, German dive-bombers, particularly the Hen- wards a target. Obviously there is only one point of re- schel Hs 123 single-seater , were used in close sup- lease for a given dive, for after leaving the aircraft the port of the infantry. As already inferred, such aircraft bomb will not follow a straight path. Special sights to give good results against tanks and other obstacles to facilitate aiming have been evolved but it is believed that ground forces. these are not in general use. The speed of the dive increases the vertical velocity of the bomb so that its penetration is equivalent to that of A study of the German Junkers Ju 87 two-seater dive-bomber a similar projectile released in level flight at a greater showing how the single large bomb carried beneath the altitude. Although dive-bombing with bombs of 500 or radiator is swung outboard before release. There are diving- brakes under the wings.

'.}?? JANUARY 25, 1940.

(Left) An American bomb-displacing gear shown diagrammatically. It is believed that this is essentially simi- 6000-70O0FT. lar to the type used by the U.S. Navy.

anti-aircraft defences. Converging tactics may also be profitably used by formations, while single machines 2000-3000 FT may adopt evasive measures before their final aiming dive. It is reported that Japanese tactical dive-bombers approach obliquely at 2,500-3,500ft., then turn sharply through 35-40 deg. before diving on the target at 60-70 deg., recovering at 1,300ft. With present machines the From left to right the diagrams above \ speed rises from 90-200 m.p.h. The illustrate possible dive-bombing approaches in (i) clear weather, (2) when there are escape is made in a turn. some clouds, and (3) when there is an un- Apart from keeping his machine on broken layer of cloud. the target the pilot of a dive-bomber must allow for wind which will tend to cause the bomb to 1,000 lb. would give good results against destroyers, light fall short on up-wind approaches, wide on cross-wind cruisers and fairly heavily armoured cruisers (e.g. the attacks and over the target on down-wind dives. pocket battleships), its effectiveness against very large capi- On its final aiming dive a dive-bomber is an excellent tal ships is often questioned, for the thicker the bomb target for anti-aircraft gunners on the ground and may casing (necessary to ensure penetration) the smaller the be subjected to all kinds of " hate " in the form of shrap- explosive charge. nel, multiple pom-pom shells and large and small-bore As an interesting sidelight we may recall that it is neces- machine gun bullets. The French expert, Rougeron, sary to dig down through four feet of solid earth to retrieve recommends the use of shrapnel against dive-bombers, a small practice bomb after a diving release. each 10 cm. shell containing about 240 bullets. These are The tactics of dive-bombing vary considerably according expelled inside a relatively small cone and at a distance of to the nature of the target and efficiency of its defences, about 100 yd. from the burst one bullet may be expected the state of the weather and the type of aircraft employed. per square yard, whilst at 650 yd. the proportion is one Diagrammatic representations of attacks under various bullet to about 3 sq. yd. Even should the bullets be conditions of weather are given on this page. It is advis- met at an appreciable distance from the point of burst able where possible to attack out of the sun to handicap the impact velocity, due to the high speed of the diving aircraft, will accentuate the damage. Precise details of the tactics used by Royal Air Force and Fleet Air Arm units are, for obvious reasons, not available for publication. A Continental author- ity, however, has set out the following stages of a modern dive-bombing attack. Phase 1 is a spiral from 10,000 m. down to 1,500 m., the time being about 90 sec. if a speed of 120 m./sec is assumed. In Phase 2 the horizontal speed is reduced to 40 m./sec. while getting into position for the attack. The course during this phase is usually at 30 to 40 deg. to the direction of the final dive and the time is 10 seconds. Phase 3 is the actual dive at about 70 deg. on to the target and lasts 7 seconds. At the beginning

The highly efficient flaps on the Blackburn Skua fleet fighter dive-bomber which not only improve take-off and landing quali- ties, but restrict the diving speed. JANUARY 25, 1940. of the dive the target is 1,500 m. away and at the end only 600 m. The release of the bomb and the pull-out (Phase 4) is said to occupy 2 sec. and the spiral get-away and gradual climb (Phase 5) 90 seconds. It is considered that during Phases 1 and 5 the dive- bomber has complete manoeuvrability and is therefore diffi- cult to hit with anti-aircraft guns. The sudden reduction in speed in the second phase is also disconcerting to the artillery. It is in Phase 3, when the flight path of the dive-bomber must necessarily almost coincide with the tra- jectory of the bullets and shells, that the chances of its being hit are greatest. Phase 4 is said to be too short for consideration by the anti-aircraft artillery. Testing in America Dive-bombing and the pilots who do it have been heavily over-drarnatised by pen and camera, mainly because the 9-G '' pull-outs required until fairly recently of prototypes for the U.S. Navy sometimes subjected test pilots to rather unpleasant strains. Referring to this test a writer in an American contemporary once said: '' We are told that in one of these sharp pull-outs from a terminal velocity dive to meet the current rigid Navy requirements the pilot is absolutely without control as to the amount of force of pull-out he puts on a ship, as the only physical or mental reaction possible under these circumstances is to decide The Fokker G. 1 multiple-purpose machine can be fitted with when he is going to pull out, pray, pull like hell, pass out, diving brakes shown above in their "normal flight" and and hope that when he does come to he and the airplane "diving" positions. will still be intact." To minimise the effects of sharp pull-outs American test It is said that German dive-bombing pilots used to adopt pilots sometimes gird themselves with a corset-like belt a crouching position to minimise the effect of " G " during and tie a scarf tightly round their throats. There is a the pull-out, a special sighting window being fitted in the natural desire to yell during the dive and this is also bottom of the . Certainly this position enables a considered beneficial. man to withstand a greater acceleration, but it is not so An American Service pilot, discussing dive-bombing, efficient as the prone position. writes: '' The average pilot is uncomfortable only in pro- longed dives from extremely high altitudes ; under io,oooft. Design Difficulties the sensation is exhilarating, even in a terminal velocity Design requirements as affecting dive-bombers are often dive. No other sport offers such a feeling of projection, very difficult, for, apart from considerations of structure, for the very attitude of your 'plane, which becomes only an aerodynamics and view, it is often necessary to limit extension of yourself, is the factor which determines your dimensions and landing speeds to such figures as can be accuracy." He goes on to say: "A lot of bilge has been tolerated for carrier operation and to provide for folding written about the tremendous bodily stresses that pilots wings and alternative loadings. undergo in this work, but the fact is that the human body A dive-bomber must be strong enough to withstand can be subjected to stresses that will wrench the wings off sharp pull-outs ; manoeuvrable enough to keep enemy A.A. the sturdiest airplane." gunners guessing; the pilot's view over the nose must be especially good ; and provision must be made, if the machine is a single- engined type and the bomb is carried beneath the fuselage, for the projectile to be guided clear of the airscrew. The twin-engined layout not only gives the pilot a better outlook forward, but facilitates bomb displacement. Diving brakes, typical examples of which will be discussed later, are

On the left is the Douglas (Northrop) DB-19 dive-bomber which, like the Brewster XSBA-i shown below, has " double-split " trailing edge flaps for restricting its speed. The Brewster has internal stowage for a single 500-lb. bomb. a JANUARY 25, 1940.

71702' only do these drawings offer a comparison in the design of representative dive- DIVE-BOMBERS •*• * bombers but they indicate the relative sizes of the projectiles carried. The loadings shown for the Skua, Henley and P.4/34 are necessarily conjectural. Internal stowage COMPARED is provided on certain types, including the Brewster and the Savoia Marchetti.

FAIREY P434 ;&eal Briia.nj A Ian Itghl bomber smaller than (he taJlle f 1L WILi; (Wolf) (Poland! Desioned al a t'9ri'« di»e bomber lor tr.e Poluli

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K>KKER Cl iHoUarid; A var^an! crl a muto. purp«te LOISE NIEUPOST IN 40 (France. In let-tice wnh French Nevy

SAVOIA MASCHfTTI SM8S (Half) In lervce vitri !l.;n» Air Force JANUARY 25, 1940. 79 Dive-Bombing This experimental Great Lakes dive- bomber was of special interest because it carried its bomb internally and, although a biplane, had a retractable undercarriage. incorporated in certain machines which would otherwise attain too high a speed for the pilot to take accurate aim. Special reversible-pitch air- screws have also been tried with the same end in view. Under high-speed diving conditions the airscrew—if it is of the fixed-pitch type—will "windmill" the crank- shaft round far beyond the approved r.p.m. and will result in a relative increase in the dynamic loadings and stresses of various Brewster XSBA-i mid-wing monoplane. One version of vital components of, perhaps, more than 70 per cent. this has been released for export and another is being built Fortunately, airscrew design has made exceptional pro- at the Naval Aircraft Factory, Philadelphia. The bomb gress during the past few years. Not long ago a Curtiss is stowed internally and the speed-reducing flaps are of machine attained a speed of 575 m.p.h. in a 9,000ft. dive, unusual design as shown in our photograph on page c. but, being fitted with one of the new electrical automatic Vought dive-bombers include and the SBU constant-speed airscrews, the engine at no time exceeded series of monoplanes, the latter being capable of handling 2,550 r.p.m., its rated figure for normal level flight. a 500- or a 1,000-lb. bomb. As countries have their own pet ideas on the design of As long ago as 1935 Hawkers produced their P.V.4 dive-bombers, let us examine selected types according to Pegasus-engined dive-bomber, which looked like a large nationality. Pegasus-Hart and which was the first British bomber to Although America can in no sense be considered to have be evolved specifically for diving attacks with a 1,000-lb. "invented" dive-bombing, this country has done more to bomb load. Notwithstanding its great strength the struc- develop specialised equipment than any other, and will ture weight was only 27J per cent, of the gross weight. accordingly take pride of place in this survey. The best current example of a specialised British dive- It was ten or eleven years ago that the Martin 125 and bomber is the Blackburn Skua, which has special diving- original Curtiss Helldiver marked the rise of interest brake flaps with a combined area of 18.5 sq. ft. These are in the technique of dive-bombing with comparative heavy metal-covered and are normally stowed flush with the lower loads. The Martin was the larger machine and was capable surface of the wing, being inset from the trailing edge. of carrying a 1,000-lb. bomb in a terminal velocity dive They limit the diving speed to about 220 knots. Like and of recovering without dropping the bomb. The t.v. the Swordfish and Shark TSRs, the new Fairey Albacore speed was about 260 m.p.h., and the makers were very deck-landing biplane is capable of delivering diving attacks proud of the fact that, even with the bomb in position, with a heavy bomb-load. The pilot, being situated in the 125 was capable of all normal aerobatics, including front of the wings, has an excellent view over the nose. loops, rolls and inverted flying. Dive-bombing is practised by squadrons of the R.A.F. equipped with the Fairey Battle Merlin-engined monoplane: Modern Helldiver This machine carries its bombs on hydraulic jacks which To-day the Curtiss Company still has a Helldiver, though are normally retracted into the wing, though for dive- this bears not the slightest resemblance to its forerunner. bombing they are lowered beneath the wing surface. The Actually the name is applied to an export version of the normal bomb-load is stated by the Fairey Company to be SBC series (Marks 1-4) as used in large numbers by the 1,000 lb. External stowage can be provided for the U.S. Navy's aircraft carriers. The machine is an excep- following U.S. pattern bombs: Ten 120-lb.; three 285-lb.; tionally clean biplane, with heavily staggered wings and two 625-lb., or one i,ioo-lb. Diving brakes are not fitted, single interplane struts. The undercarriage retracts into but the machine has frequently demonstrated in public its the sides of the fuselage behind the Cyclone engine. A single ability to make diving attacks. large bomb is carried externally beneath the fuselage and smaller projectiles can be slung beneath the wings. The fuselage bomb is provided with displacement gear, precise Qertnan Practice details of which have not been released. It may well be Apart from the small single-seater Henschel Hs 123, that this resembles the gear patented by Messrs. Schuyler Germany uses large numbers of Junkers Ju 87 single- and Miles (United States Navy) and D. A. Chadwick, This engined two-seater dive-bombers. The Ju 87 has a cranked comprises a shaft secured to the fuselage with two dis- wing which carries diving brakes in the form of slats placing members, each capable of revolving separately upon mounted just aft of the leading edge on each side. These the shaft and having a limited lateral motion in respect to are adjusted edge-on to the air stream for dive-bombing the aircraft. A spring-backed swivelled fork member is operations. Without them the T.V. speed is 430 m.p.h. mounted at the end of each displacing member, the forks It is possible to cam- a single 550-lb. or 1,100-lb. bomb being adapted to engage lugs fitted on the bomb. Elastic beneath the fuselage, and there are external wing racks for cords are fixed to each displacing member, the other end four bombs of no lb. each. Diving brakes somewhat of the cords being secured either to the bomb rack or to the similar to those on the Ju 87 are fitted to the Fokker Gi. structure oi the aircraft. It is believed, incidentally, that Germany's new high- On the lower tvings of this unusual Curtiss biplane are speed twin-engined bomber, the , is stressed '' double-split'' flaps which open like the leaves of a book for delivering diving attacks at a comparatively shallow to retard the speed in a bombing dive. A constant-speed angle. This form of attack obviously lacks certain advan- airscrew keeps engine r.p.ni. within desired limits. tages given by the vertical or nearly vertical dive. The Douglas concern, apart from its TBD-i torpedo- Apart from some old Gourdou-Leseurre single-seater bomber monoplane which is used for dive-bombing, has parasol monoplane dive-bombers, the French Navy has a two types (actually Northrop designs) in service with the number of Loire-Nieuport 40 cranked-wing monoplanes U.S. Navy. In appearance these resemble the Northrop with Hispano 690 h.p. engines. These are single-seaters: attack machines and Bristol's flying test bed for the A number of Vought monoplanes has also been acquired. Hercules, but are specially stressed for dive-bombing and One of the most modern dive-bombers in the world is have split trailing edge flaps which, incidentally, are per- Italy's Savoia Marchetti S.M.85 twin-engined high-wing forated as on other modern Northrop designs. monoplane. The trailing edge flaps on this mach" ae hinge One of the most interesting American designs is the through 90 deg. to act as diving brakes.