The Dive Bomber

Design, Development and Application of Fighter Divers and Four-engined "Heavies"

Not to define it too academically, dive bombing is a form of attack in which the bomb is released from an aircraft diving in the direction of its target. Unless the dive is truly vertical (which, as precise control is not possible, is rarely the case) allowances must be made for gravitational pull on the bomb and for air resistance. This is usually achieved by release at a previously determined point on the pull-out radius; alternatively, compensation for the "lag" of the bomb may be effected by its release while the aircraft is being aimed at a point beyond the target. In either case wind must be taken into account.

Thus the conditions governing dive bombing are essentially those of fixed gunnery, in which the pilot must contend with the "drop" of the projectile.

Obviously the bombing dive should be as steep as possible consistent with good handling qualities of the aircraft, for the greater the angle the less will be the allowance for the curve of the bomb trajectory.

Specialized aircraft in use today can attain angles of 80° and more, but somewhat shallower angles (50°-70°) are more common. The steep aiming dive, particularly if it follows carefully planned evasive action during the approach to the target area, lessens the chances of AA defenses.

Provided accuracy is not to be prejudiced by releasing the bomb at too great a height, a steep dive will entail a sharp pull-out; this has necessitated the development of aerodynamic brakes, which are now standard equipment on all types of dive bombers.

Degree Of Accuracy

The main advantages offered by dive bombing are a higher degree of accuracy than can be guaranteed with high- or medium-altitude ("precision") bombing and greater penetration than is possible with low-level bombing. The possibility of the bomb "bouncing" over its objective as in low-level bombing is eliminated.

In true dive bombing as at present practiced, it is the pilot of the aircraft who is responsible for releasing the bombs.

Dive bombing tactics vary greatly according to the type of aircraft, the size of the attacking formation, and the weather. Advantage is taken of clouds to confuse AA defenses, and the dive may be made in several "steps," with periodic changes of direction. This calls for good aileron and elevator control, and in consequence the specially developed dive bomber is usually an agreeable aircraft to handle.

It is noteworthy that recent criticisms have been directed not so much at the theory or practice of dive bombing as a method of attack (it having been demonstrated by the enemy that a very high degree of accuracy is attainable) as at the vulnerability and limited usefulness of what is generally visualized as a typical dive bombing aircraft. The machine in question — the Ju-87 Stuka (sturzkampflugzeug) — has, since the beginning of the war, been in action in such quantities that a great deal of information is now available relative to its capabilities and shortcomings. Nobody with a knowledge of the facts will dispute that, in combat with a modern single-seat fighter, one of these elderly Stukas is at an almost pitiable disadvantage. It must, however, be recorded that the Russians, who have had unique opportunities of studying the Ju-87 in action, are more restrained in their criticisms than British commentators.

Dive Or Attack Bombers?

Condemnation of the Ju-87 on specific technical grounds usually concerns its obviously poor defensive armament by comparison with the American-style "attack bombers"; these latter are twin-engined aircraft of higher power and of much more modern design, but more difficult and costly to build and incapable of delivering the steep diving attacks which alone permit something approaching pin-point accuracy to be combined with high penetration.

Dogmatic criticism of the dive bomber's inadaptability is ill-founded; this will be gathered from the subsequent descriptions of types which are of much higher performance than the old Junkers and are suitable for tactical reconnaissance work and even, in certain cases, as heavy fighters. In the latter role their dive-brakes — indispensable accessories on all modern dive bombers — might prove to be of great advantage at night to prevent overshooting the target. The finest example of such an aircraft is the Me-210 now coming into service in the German Air Force.

Much has been said of the vulnerability of dive bombers to small-arms and light AA fire during the final stages of their aiming dive and during the ensuing getaway. Here, again, the student of the facts will not dispute that extensive destruction has been wrought among the Ju-87s and Ju-88s by resolute ground fire and by other measures intended primarily for defense against low-flying aircraft. Nevertheless, it has not been proved that losses have been disproportionate to the results obtained (particularly against marine targets) nor to the losses incurred in other forms of attack entailing low flying.

Physical Aspects

It is not denied that, for the manning of dive bombers, personnel of high courage and of great physical endurance are essential; but of courage there is a limitless supply, and concerning physical endurance, it may be said that the alarming distortions to which the human frame is shown to be subjected in popular films of test diving are not normally encountered in modern dive bombing.

When undergoing contractor's trials a dive bomber prototype may be subjected to an acceleration of 9 G, but this is not approached on operations or during training. A value of 3.5-5 G is comparatively common and can be endured for a short time by a person of normal physique without "blacking out." The latter phenomenon, which results in temporary loss of vision, is caused by the blood being drawn from the head during the pull-out. The effect of the dive itself is a minor one, resulting only from the rapid change of air pressure.

A modern dive bomber pilot must, nevertheless, possess an astute brain, not only to decide rapidly on the tactics to be adopted against a particular target, but to perform during the heat of an action a number of operations necessary for the safety of his aircraft. Devices have been evolved to relieve him of certain responsibilities, but these are found mainly on the multi-engined types, such as the Ju-88.

On a typical single-engined dive bomber it is necessary, before starting the dive, to adjust the blower change and airscrew pitch levers; to close the radiator or cowling flaps; throttle back; operate levers to apply the dive brakes and trim tabs; and possibly to restrict the movement of the control column to avoid undue application of "G" during the pull-out. Although the mere pressing of a button on the control column may release the bomb (or bombs if a salvo has previously been selected on the bomb distributor) and set the elevator tab to the pull-out position, this must be followed by the retraction of the dive brakes, the release of the control column to give full range of movement, and by the readjustment of the cooling system to prevent overheating.

Bomb Penetration

Here a word may be said in reply to the allegation that the penetration of a bomb released from a dive bomber is less than that of a similar projectile dropped with the aid of a precision sight in level flight at a great altitude. The obvious answer is that this is offset by the greater accuracy obtainable with dive bombing, but an even stronger argument is possible now that rocket-propelled bombs have been introduced. The design of such bombs is particularly favorable to their employment from dive bombers. The Russians use them against tanks from specially armored aircraft which are not equipped with dive brakes.

By land the dive bomber has, up to the present, been utilized mainly as an army-support weapon for the reduction of strong points, the disruption of lines of communication and defense, and the destruction of bodies of troops, transports, gun emplacements, headquarters and similar targets. Long range is not generally required, except for reinforcement purposes, and the army-support dive bomber of today is typically a single-engined, two-seater monoplane of very sturdy construction, capable, by virtue of having special aerodynamic dive brakes, of attacking at angles up to, and including, the vertical and of being brought out of the dive in a small radius and consequently at a low altitude. Fitted with supplementary fuel tanks and carrying a reduced bomb load, it may, under certain conditions, present a serious menace to strategical targets such as docks, railway stations and other vital installations. Operations against these targets will usually demand a strong fighter escort, but this seems to have become a normal requirement of any bomber force operating in daylight over territory defended by fighters.

It would appear that the single-engined arrangement will remain in favor for close-support dive bombers, but it is probable that the twin-engined layout will also be adopted, though on a more limited scale, use being made of two power units of moderate output. An aircraft on the lines of the German HS-129 ground-attack machine suggests itself.

The twin-engined dive bomber offers a much improved View for the approach and final aim, and there is the incidental possibility of survival on one engine — a consideration of some importance, as the power plant of a dive bomber is the most vulnerable item during the dive. Simplification of bomb-ejection problems (there being no airscrew to clear, provided the bombs are carried in, or under, the fuselage) is another benefit to be derived from this arrangement.

For marine use, other than coast defense, the dive bomber is likely to remain a fairly small, single-engined type, as it must operate from, and be stowed in, an aircraft carrier. Except for the provision of arrester and flotation gear and of wing folding, there is no reason why the deck- landing dive bomber should not resemble the single-engined, land-based, army-support type. In this connection mention may be made of the Brewster Bermuda, which, ordered by the RAF for land operation, is identical in basic design with a carrier-borne aircraft adopted by the US Navy.

It is, perhaps, not generally appreciated that the two-engined, carrier-based dive bomber is by no means beyond the bounds of technical possibility, and it has even been reported that Japan has for some time been endeavoring to evolve an aircraft of this class. The main factors governing the operation of such a type are the strength of the carrier's deck and the minimum dimensions for stowage.

Although reference has been made to the potentialities of the single-engined dive bomber for attacking strategical and commercial targets, this work is normally assigned to larger twin-engine types which, although not suitable for such steep dives as the smaller models, can handle loads two or three times as heavy. Their drawbacks of a comparatively shallow permissible diving angle and greater pull-out height can largely be nullified by the use of special sights and computers which are not available on the smaller single-engined machines; even so, it is frequently contended that such types as the German Ju-88 and Do-217 cannot strictly be categorized as dive bombers because they are not suitable for vertical diving. This denotes ignorance of modern technique, for the normal angle is only 65°.

The development as dive bombers of much larger aircraft than the Ju-88 (particularly the He-177) is reported to be proceeding in Germany, if not in other countries. Dive bombing, even at 45°, by an aircraft carrying a projectile load of six or seven tons, calls for meditation on the part of naval authorities.

The problems associated with the design of dive bombers, particularly of the size of the He-177, are varied and complex. This will be understood when it is realized that until a few years ago steep dives were maintained only for a few hundred feet and were regarded as aerobatic and fighting maneuvers to be undertaken solely by small aircraft. Consequently, development has in the main been undertaken by a comparatively few specialist firms.

From the structural viewpoint the first requirement for dive bombing is great strength to withstand the strain of the pull-out and of evasive maneuvers. This alone results in a poorer disposable load than would be obtainable were the aircraft not designed specifically for steep diving.

Additional weight results from the dive brakes themselves, and from the design of the structure to which the brake loads are transmitted. Aerodynamic design may suffer in the attainment of a good view from the pilot's position, and it may be considered necessary to fit a transparent panel in the floor for the observation of the target during the approach.

Control surfaces must be particularly strong and provide adequate power of maneuver for aim adjustment in the dive.

On a conventional single-engined design strong points must be provided for anchoring the ejector arms which guide the bomb clear of the airscrew.

The design of dive brakes presents special difficulties; they must not create violent eddies and thus cause tail buffeting or wing flutter, nor must they affect aileron control. The control surfaces must be of ample area and, if a device for initiating the pull-out is fitted, elevator tabs must be designed accordingly. With Allied and Axis belligerents solving all of these problems, it is obvious that the dive bomber is far from "through." Only the Stuka is taking a back seat.

This article was originally published in the August, 1943, issue of Air News magazine, vol 5, no 2, pp 14-15, 38.
The original article includes 2 photos and 10 diagrams.
Photos credited to Brewster, Flight magazine.