The bomber - from piston engine to jet
Ever since the appearance of the Handley Page V-1500 in 1918, the four-engined bomber has kept reappearing throughout the years whenever the gain in performance and power has seemed worth the extra complication and the inevitable drain on engine supply. The first serious attempt to evolve a really heavy bomber was the British Air Ministry B12/36 Specification for a monoplane with four 1,500 h.p. radial engines. This specification was intended to be backed by another for a large twin-engined type to be powered by the new Rolls-Royce Vulture X-type, liquid-cooled engine. A heavy defensive armament in power-operated turrets was a feature of both specifications.
By a curious set of circumstances both specifications resulted eventually in four-engined bombers and the twin-engined specification led to the best of the three types built, the Avro Lancaster. But perhaps the fairest way to tell the story is to take the events chronologically.
Short Brothers of Rochester, designers of the Empire Boat and the Sunderland, tendered successfully for the B12/36 contract and produced the Stirling with four Bristol Hercules engines. Sir Arthur Gouge, the designer, used what was practically an Empire Boat wing to which he added a lanky, almost untapered fuselage. Because of the large Gouge extension flaps, the Stirling had a very tall undercarriage to give a steep ground angle. The geometry of the legs was extraordinary; with a queer bedstead affair at the top that collapsed forward as the wheel came up backward to lie snugly in the engine nacelle. The tail shape followed closely that of the flying-boats, with a large metal single fin and fabric-covered controls with inset hinge balances.
The Stirling is a good example of the weight-lifting ideas of the late thirties; a wing of about one hundred feet span, considerable thickness, and moderate aspect ratio—factors which made the design of a strong, stiff structure comparatively simple. Pre-war ideas on bombs and bomb aiming were based on dropping a large number of moderate-sized bombs in the hope that some might hit the target. Although a 2,000 lb. bomb existed, the 1,000 lb. and 500 lb. ones, particularly the latter, were those most considered. Because of this, the 42 ft. 7 in. long bomb bay in the bottom of the Stirling's fuselage was divided into three longitudinal cells and there were further bomb cells in the wing inboard of the inner engines. The use of two beams to support the bombs in the bay greatly stiffened the fuselage, but later was to impede the carrying of larger bombs. The maximum bomb load was 18,000 lb.—a hitherto unheard-of figure. The long straight bomb bay, coupled with the nose and tail turrets, gave the designer little chance to emulate with this fuselage the grace of his flying-boat hulls.
Originally it was planned to have a retractable "dustbin" power-operated twin-gun turret, but this was discarded because of its weight, the fact that its extension reduced speed at a critical moment and because the four tail guns were thought to be adequate. Later a small hand-operated, twin-gun under position was installed and a power-operated, twin-gun dorsal turret was also added. The front turret had two guns.
Because of its advanced design, the Stirling was first flown as a model. This was an aerodynamically similar half-scale monoplane fitted with four 130 h.p. Pobjoy radial engines.
Much was learned from this model and the first Stirling went into service with Bomber Command late in 1940. Because of its capacity for carrying very large numbers of the smaller bombs, the Stirling was used for attacking targets that were not susceptible to damage by the large blast bombs. Some unpleasant tasks fell to the Stirling, of which daylight raids on U-boat pens at Brest and La Pallice, and on flying bomb sights in the Pas de Calais were examples. Again, because of its ability to carry a large load in small packages, the Stirling was used for glider towing and supply dropping with the Airborne Forces, a particularly gallant episode in its career being the supplying of the beleaguered troops at Arnhem.
Two bombers to the B13/36 Specification were started and their history is curious indeed—a very revealing example of the mind changing that goes on whenever a new aeroplane is being designed. Originally these bombers were to have been about 27,000 lb. in weight, but trouble was being experienced with the Vulture engine and so the Handley Page design was altered to take four Merlins—and the all-up weight was raised, on paper, to 40,000 lb. By the time the prototype Halifax, as it was called, flew first in October 1939 the gross weight had grown to 55,000 lb. A year later the production Mark I could lift 60,000 lb. and in the latter part of the War, when fitted with 1,600 h.p. Bristol Hercules radials, the normal all-up weight became 65,000 lb. Meanwhile, Avros built and flew their version of B13/36, the Manchester, just before the War in July 1939, and it was in action eighteen months later. By the middle of 1940, flight trials had shown that there was little future in the Vulture engine and that even when its teething troubles were cured, the power would be low for the loads now to be carried, so it was decided to try four Merlins. Using as much as 75 per cent of Manchester parts, with a new centre section having the necessary four engine mountings, a first prototype was built. Flight trials were promising, so another, incorporating several detail structural changes and replacing the Manchester's triple fins by the familiar two tall "shields" of the Lancaster, was built. In this devious fashion the best heavy bomber of the War was born, the aeroplane which from the beginning of 1942 was to be the spearhead of Bomber Command. Very different in appearance from the Stirling, the Lancaster and Halifax also show how varied can be the ideas of different designers on the same subject.
Roy Chadwick managed the almost impossible feat of building a measure of grace into the Lancaster despite the handicaps of bomb bay and turrets. By choosing just the right fuselage length and depth to combine with gentle curves to the turrets at nose and tail an excellent fuselage shape was achieved. The wing plan, the attractive tail shape, and the neat cowlings of the Merlin "standard" power plants added to the generally good appearance and helped materially toward the all-round high performance, which included a top speed of 275 m.p.h.
Like so many good aeroplanes, the essence of the Lancaster was its simplicity. As with the aerodynamic shape, so the neatness rather than the originality of the structure was the reason for its success. For instance, the main wheel units consisted of two shock-absorber legs braced by backwardly inclined folding struts—just a large version of what had been used on smaller « aeroplanes. As a small comment on the Lancaster's cleanness, its large tail wheel was never retracted, since the saving in drag was not worth the weight and complication of the hydraulics. The Lancaster handled well, and even though crews are notoriously loyal to their aircraft, it was very popular. The long raised enclosure for the pilots, navigator and radio operator with a station for the fighting controller close behind the pilot * was eminently practical. The fighting controller was introduced after a disastrous encounter, early in the War, between a formation of Wellingtons and Me 110s. All gunners fired on one
flight of attackers, with the result that the formation was decimated by machines from the other side. Thereafter the fighting controller acted as a lookout, told the gunners where to fire and also told the pilot when to "weave". The Lancaster's hydraulically operated turrets, two-gun in the nose and on top, four-gun in the tail gave the same fire-power as the Stirling, the guns being .303 Brownings. It is not generally known that the tail guns are fed from ammunition boxes amidships, the belts travelling along chutes to the rear turret. This Heath Robinson arrangement is necessary to avoid excessive c.g. changes as the ammunition is used.
Above all, the Lancaster was a bomber and carried out its work to perfection. The bomb bay was shorter than that of the Stirling, being 33 ft. in length, but it was wider and had two large doors, so that the inside was entirely unobstructed. The Lancaster was highly adaptable and could carry 14,000 lb. for 1,000 miles, or 18,000 lb. for a shorter range. Fitted with bulged bomb doors, it could carry the 12,000 lb. "Tallboy" and without doors the 22,000 lb. "Grand Slam", the supersonic, highaltitude , deep-striking bombs invented by Barnes Neville Wallis, co-designer of the Wellington. It was the Lancaster, also, that was chosen for the "Dam Busters", when they breached the Mohne and Eder dams with another child of Wallis's fertile brain, the still secret spinning bomb. With the "Tallboy" the Tirpitz was sunk in Alten Fjord.
The Lancaster was undoubtedly a magnificent bomber and without it the Battle of the Ruhr would have been a longer and harder struggle than it was, while with it Berlin first felt the might and power of Bomber Command. It is significant that during its three years of action there were virtually only two marks of Lancaster; the Mark I with four 1,280 h.p. Merlins, and the Mark II with 1,600 h.p. Hercules. The latter was only made as a precaution against a shortage of Merlins, and it was not a success, since the Lancaster did not need the extra power, so that the bigger drag and higher fuel consumption that went with it were a handicap. Other Lancaster marks were introduced for other causes than alterations to the airframe : the Mark III introduced Packard-built Merlins and the X was a Canadian-built version.
The Lancaster was used by the master bombers, as well as the main force, in major saturation attacks. These leading aeroplanes had special radio equipment and carried H2S, a radar blind-bombing aid distinguished by a scanner in a large streamlined blister under the rear fuselage. Later, as supplies became available, this blister was a familiar sight on nearly all large bombers.
The quality of the Lancaster can be well judged from the empty weight of 37,000 lb. related to the normal all-up of 68,000 lb. With the 22,000 lb. bomb, the gross weight was double the tare figure, a remarkable achievement in an aeroplane stressed for combat. The Avro Lancaster must be numbered among the great aeroplanes of history and was certainly the outstanding bomber of the Second World War.
Britain's third "heavy", the Halifax, lacked the advantages to be gained from flying models. Undoubtedly, the flying of the half-scale Stirling and of the Manchester proved exceptionally valuable in the clearing up of teething troubles. The Halifax did not have either advantage and when it went into service it ran into many unforeseen difficulties. Rather bulkier than the Lancaster, the Halifax had a deeper fuselage limned by straight lines rather than curves. The bomb bay was wide and unobstructed by beams, but only 22 ft. long, there being further cells in the centre section to bring the total capacity up to 14,500 lb. The cockpit was flush with the top of the fuselage, which reduced drag (and view) and there were the usual nose and tail turrets, later supplemented by a four-gun dorsal turret. Fat nacelles of Handley Page design and not the slim, RollsRoyce designed standard power plants were used. These had a higher drag, but they were later to prove valuable, since they were readily adaptable to the larger Hercules radial engines.
Originally the Halifax had a smaller span than the other two heavies, because, like the Hampden, its square-cut wings were to have been fitted with automatic slats as well as slotted flaps. This combination would have given a higher lift coefficient than flaps alone and so the wing area could be reduced. However, before the Halifax went into service the Air Ministry introduced balloon barrage cable-cutters as a standard fitment. These consisted of small cartridge-operated, chisel-and-anvil units in the leading edge of the wing. In order that the cable would slide along the wing until it lodged in a cutter and was severed, a hardened steel leading edge was necessary. The slats prevented installation of the steel strip and cutters, so the slats had to go.
In service the early Halifaxes proved to be underpowered for their drag and there was a whole series of modifications to reduce both weight and drag. First the nose turret was removed and faired over, then a Hampden-type glazed nose was fitted carrying a single hand-operated .303 gun. The original bulbous upper turret was replaced by the smaller Defiant type with four guns. The engine nacelles, flame dampers, astro-dome and many detailed parts were reduced in size or altered in shape, the tail wheel was made retractable and even a special smoothfinish paint was adopted to reduce drag. Then came the Halifax III, the first version with Bristol Hercules air-cooled radials and on this variant rounded wingtips were added to increase the wing area and improve the ceiling. Later, the 1,800 h.p. Hercules 100 was fitted in the Mark VI, which was the finally developed bomber version. The extra power of the Bristol engines restored the performance and allowed a higher all-up weight—most of which was absorbed by the larger fuel supply needed.
One trouble with the Halifax introduced a rare aerodynamic problem and, as such, is of considerable historical interest. At one period there were several unexplained crashes in which the aeroplane got into an inverted dive. The trouble was difficult to trace because attempts to reproduce identical conditions failed to get the effect. Eventually pilots of the R.A.F. Aircraft and Armament Experimental Establishment at Boscombe Down traced it to rudder stalling. When the Halifax was designed , end-plate fins were in the fashion. These had the advantage of increasing the effectiveness of the tail plane, so that it could be smaller, and of being in the airscrew slipstream where the rudders were most powerful. In the original Halifax, the fin in front of the rectangular rudder was triangular and under certain conditions the fin stalled and turbulent air, passing between the gap between fin and rudder, locked the latter hard over. The trouble was cured by fitting the large rectangular fin that became the Halifax recognition "trade mark".
Toward the end of the War many Halifaxes were diverted to support the airborne forces. Some were used, with little modification, for towing the Hamilcar tank-carrying gliders. There was, too, the C Mark VIII, in which a huge stores pannier could be slung under the bomb bay. There was also provision for carrying troops and parachuting. After the War this variant was converted into the Halton freighter, which helped to fill Europe's desperate initial shortage of civil transports. The American outlook on heavy bombers was an extraordinary one. As early as 1934 the specification for a fourengined , fast, high-flying monoplane bomber was issued and a prototype, the Boeing XB-17, flew on July 28, 1935. Delivery
to the Army Air Corps of a trial series, the Y1B-17, started in March 1937, but it was the success of the first Y1B-17A with exhaust turbo-superchargers in January 1939 which decided the production of the type. As an aeroplane the original "Flying Fortress" was beautiful, as a weapon it was ridiculous. The design was based on a large, well-proportioned wing of rather deep section at the root, which was blended to a wellstreamlined fuselage. A large graceful tail with a single fin and rudder completed the attractiveness of the design and ensured good control. The engines were four 1,000 h.p. radials. The cockpit was built up from the circular fuselage and, in addition to the glazed nose for the bomb-aimer there were numerous glazed streamline blisters for hand-operated .303 in. machineguns . At the intersection of wing and fuselage there was a small internal bomb bay capable of taking a maximum of 6,000 lb.—with the largest bomb only 2,000 lb.
The theory behind the Fortress was that it should fly at 25,000 ft. where it would be largely immune from fighters and guns. A few of the B-17C version, with 1,200 h.p. Wright Cyclones and a total of seven rifle-calibre guns, were sent to the R.A.F. in 1941 under Lease-Lend. These were almost immediately used to try and sink enemy warships in Brest harbour, ., the Scharnhorst and Gneisenau, which had proved an almost impossibly heavily defended target—obscured by smoke •screens for good measure. It was thought that a daylight attack (on July 24th, 1941) with the Fortresses might succeed, but all the action proved was that the hand-operated guns were a hopelessly inadequate defence.
The Americans learned by our mistake and the first version they sent into action was the redesigned B-17E. Aesthetically this aeroplane was a retrograde step, but militarily it was a success. Electrically operated twin-gun top and ventral ball turrets, hand-operated nose, beam and tail guns, all .50 calibre, gave a terrific defensive firepower. To overcome the air flow disturbances of guns and turrets the tail size was greatly increased and a very long dorsal fin was added to ensure directional stability. Crew stations were heavily armoured. i In its final and most used form, the B-17G (or Fortress II in the R.A.F.) there was a crew of ten and no less than thirteen .50 in. machine-guns; twin-gun chin turret, two "cheek" guns in the nose, twin top turret, single top gun ahead of the fin, twin ball turret, two beam guns and twin tail guns. The crew was also provided with personal body armour. All-in-all, it is scarcely surprising that the bomb load was not raised other than an abortive attempt to carry two 4,000 lb. bombs under the wing instead of the internal load.
The Fortresses of the U.S. Eighth Air Force played a decisive part in the latter stage of the War by their daylight raids which, apart from the actual damage done, kept the German defences from resting. Despite the terrific fire power of the large close formations and huge fighter escorts losses were very heavy. It was also necessary to use a large number of aircraft to achieve a heavy raid—and, even so, no large blast bombs could be used. Certainly one cause of heavy casualties was that the special high-altitude bomb sight meant a long, straight bombing run of several miles and since only certain "lead" planes carried bomb-aimers a whole formation was committed to a steady course for some minutes, so making it a perfect anti-aircraft gun target.
A little-known activity of the Fortress was its use in Bomber Command's night mass attacks. Fitted with special radar, these heavily armed aeroplanes were used as decoys to destroy enemy night fighters and also for dropping "window" to confuse the defences.
America's other "heavy", the Consolidated B-24 Liberator, was conceived in 1939 and was a very adaptable aeroplane— though its internal bomb load was still a mere 8,000 lb. Because of a special high aspect-ratio, low-drag wing the Liberator was an excellent long-range performer and was chosen by R.A.F. Coastal Command for long overseas reconnaissance. Some 19,000 Liberators were built, which gives some idea of how widely it was used. A high-wing monoplane, the deep fuselage with nose and tail turrets, reminiscent of the Halifax, led to its being adapted as a commodious transport—the Prime Minister, Mr. Winston Churchill, was particularly fond of his personal Liberator. As in the Fortress, the engines were radials, four 1,200 h.p. Pratt and Whitney Wasps.
Characteristically, the Liberator's offensive capacity suffered from the bomb bay being designed so that it was incapable of enlargement. It was in the fuselage under the wing and was divided into front and rear compartments for bombs to be stowed vertically. The two compartments were further divided by a central catwalk, which was also the beam acting as a keel to the fuselage. The most interesting feature lay in the bomb doors, which slid up the sides of the fuselage like a rolltop desk.
There was little to choose in speed between these very varied four-engined types. The ranges, too, were about the same, with the Liberator rather better than the others. The American types could operate 5,000 ft. higher, thanks to the turbo-superchargers, but the British aeroplanes carried far greater bomb loads. It is worth emphasizing that the British types were designed for the express purpose of bombing Germany, while the Americans must have had only the vaguest idea of their possible targets, but, living in a continent bordered by two vast oceans, long range was obviously an important factor to them.
Toward the end of the War, the Allies put two larger bombers into service, the Boeing B-29 and the Avro Lincoln. Design of the B-29 Superfortress started in 1940, it first went into action on June 5th, 1944, and it finished the War by dropping the first atom bomb on August 6th, 1945. A logical development of the B-17 conception, the B-29 was an entirely different approach to its fulfilment. First of all, a worthwhile * bomb load was specified, crew efficiency was improved by pressurization, and when Japan materialized as the real enemy the design was enlarged to increase range. To achieve these ends a high aspect-ratio wing of low induced drag, four 2,200 h.p. engines and a clean fuselage with the minimum drag were essential.
With the long ranges envisaged (a radius of up to 1,500 miles), there could be no fighter escort so it was a choice between night flying over enemy territory or very heavy defensive armament. The decision was made to have a large crew (ten to fourteen) and five electrically-operated twin .5 in. gun positions. Instead of turrets the guns were in almost flush barbettes and were aimed with computing sights by remote control from blisters in the fuselage. The tail position was reminiscent of that on the B-17, save that it was a tiny pressure cabin, and instead of two .5 in. guns two 20 mm. cannon were sometimes fitted. The pilot was "submerged" in the long glazed nose—a feature which makes the Superfortress unpleasant to fly at night. Because of the explosive effect of puncturing a pressurized cabin, the outgoing blast of air will suck a man through a broken window, both the main and tail compartments « were deflated before combat.
The Superfortress operated at the same height as its predecessor , but was faster and more manoeuvrable. It was, however , a very large aeroplane, twice the weight of the other "heavies", requiring many more manhours in its construction. It was, in fact, the first step along the expensive road we are now pursuing. The generally clean, stick-like shape, as opposed
to a streamline is worth noting, such a form is suited to the low indicated air speeds at great heights and has become increasingly common.
The British contribution to the Japanese campaign was the Avro Lincoln, which never saw action because of the sudden end of the War. Originally known as the Lancaster IV and V, the first prototypes were made to fulfil a new specification, B14/43, specially drawn up to meet the long distances of the Pacific War. Eighteen feet were added to the span and about six feet to the middle of the fuselage. Two-stage supercharged 1,600 h.p. Merlins were fitted to overcome the added weight and drag and four-bladed airscrews were used to give extra thrust at the cruising height of 20,000 ft. The maximum bomb load was 22,000 lb. for 1,150 miles and 14,000 lb. could be carried 3,250 miles. In fact, the Lincoln was no mean performer, but it was hard work for the crew flying for ten hours or so at 20,000 ft. without pressurization.
The Lincoln, which is still in service with the R.A.F. in 1953, lacks the grace of the Lancaster because of its lengthening treatment and also because of the circular Rolls-Royce "universal " power plants, but its performance does not compare unfavourably with the far more powerful Superfortress. Armament , as befits a night bomber, was less, although more powerful than on other British types, a twin .5 in. barbette in the nose, upper twin 20 mm. turret, twin .5 in. tail turret with a radar gunsight. To sum up, for an all-up weight of 82,000 lb. the Lincoln came surprisingly close to the 140,000 lb. Superfortress. The Germans and the Russians contributed virtually nothing to heavy bomber development. Both countries believed in air power as tactical support for the army and they wanted versatile aeroplanes of moderate range that could be switched to different targets in advance of the Panzer columns of the Blitzkrieg. When halted by the Channel, the Luftwaffe had to attack by day with medium bombers, since crews were not trained for night work. Fighter Command's complete victory by daylight resulted in an enforced switch to night attacks, still using the twin-engined types. The several efforts to make heavier aeroplanes, one was even by joining two He 11 1s together as a twin-fuselage machine, were clumsy and are of only passing interest.
The Russians made one large bomber, the TB-7, in small numbers, with which they raided Berlin. This was a clumsy aeroplane, something like the B-17 in general outline but much
larger and fitted with liquid-cooled engines, and it can scarcely be taken as a stage in evolution. The curious thing is that between the Wars the Red Air Force had been the solitary protagonist of the large four-engined bomber monoplane. In the fighting between Germany and Russia there were several reasons why large bombers would have been a waste of effort. In the first place, at least three times the labour would have been absorbed in manufacture and Soviet industry, evacuated en masse to the Urals, was already strained to the uttermost. The campaign was a classic war of movement over vast areas of land and medium bombers were much more adaptable for bringing up near the front where they were required. Thirdly, and equally important, the Germans were being heavily pounded night and day by the R.A.F. and the U.S.A.A.F.
As exponents of medium bomber design, the Germans were probably supreme. The He 11 1 "mail plane" was adapted in its final form as one of the three principal bomber types. Roughly equivalent in size and performance to the Wellington, it could carry a maximum of about 6,000 lb. of bombs, suspended vertically in the fuselage bomb bay or in external wing racks. With the army support role uppermost in their minds the Germans reduced drag by submerging the pilot's seat in all but the earlier models and this reduced its efficiency at night. The glazed nose contained a hand-operated gun mounting and bomb-aimer's station, on top of the fuselage there was an open gun cockpit, and a "foot bath" below the fuselage contained another manual gun position.
The slender Do 17 went through a process of power and weight increase that kept it in action throughout the War, still recognizable if somewhat grotesquely distorted, under the numbers Do 215 and Do 217. This aeroplane was an example of the German belief in close-grouping the crew to ensure fighting efficiency and mutual moral support. The sleek nose first used was changed, even before the War, to a curiously ugly excrescence manifestly designed as an operational unit with little attention to aerodynamic refinement. The cockpit roof was raised and fully glazed to give the pilot a better allround view and was continued aft to house the radio-operator and rear gunner. The nose, containing the bomb aimer's station, was fully glazed with a series of small flat panels. The under part of the nose was bulged to give a rear gun position. The losses of the Battle of Britain showed the Luftwaffe the complete inadequacy of their bombers' light defensive armament . At first the Dornier types were given extra "flexible" guns mounted in universal joints inserted in side and front windows. Later, when an electric turret had been developed, this was added at the rear of the canopy. In one version, the Do 217K, there were four fixed guns in the tail cone.
As first planned, the Do 17 was intended to be easily fitted with different engines, both liquid and air cooled, and this adaptability was maintained right up to the final Do 217M version. This flexibility, achieved also with the Ju 88 and its derivatives, but never equalled by the Allies, must have eased German production organization considerably. The first Do 17s had 770 h.p. BMW liquid-cooled vee engines as a temporary measure until the thousand horsepower DB 600 inverted-vee liquid and BMW 800 air-cooled radial engines had been developed in preparation for the War. In the versions evolved during the War the power was eventually increased to 1,750 h.p.
As an airframe the Dornier bomber changed but little, the span was increased by three feet and the length by rather more, depending upon the duties. The triangular-section belly of the fuselage was deepened considerably to increase the bomb capacity to 5,500 lb. On most types two 550 lb. bombs could also be carried under the wing. Throughout its career this aeroplane had slotted ailerons, but the original slotted flaps were replaced by split ones. Dive brakes were added, either of the "grid" type under the wing or in the tail, where panels opened like an umbrella. There was also a high-altitude version, the Do 217K, with wing span extended to 80 ft.
Equally important in the German offensive scheme was the Junkers Ju 88 and Ju 188 series of bombers. First flown in 1936, the first Ju 88s reached the Luftwaffe early in 1939 and they were used extensively in the Battle of Britain. The layout was again based on close-grouping of the crew and interchangeable power plants. There was also the thin rear fuselage—intended to give a good field of fire for upper and lower guns—and the bomb bay was of negligible size, suitable only for flares or small bombs. The main bomb load was carried on four streamlined external racks under the centre section.
Most of the early versions had 1,200 h.p. Junkers Jumo 211 liquid-cooled engines in curious circular cowlings with nose radiators—as on the Ta 154. Later, power was added by fitting 1,700 h.p. BMW 801 radials that were difficult to distinguish from the earlier power plants. The 1,750 h.p. Jumo 213 was also fitted.
Although a speed of nearly 300 m.p.h. was attributed to the Ju 88, it must have been very much slower while the external bombs were actually on board. When the more powerful engines were introduced the aeroplane was cleaned up by removing the under gun blister and by giving it a dome-shaped nose in place of the "beetle's eye" of optically flat panels, which together brought the speed up to the 350 m.p.h. range at 20,000 ft.
About the middle of the War a general re-design was undertaken, which emerged as the Ju 188 with the higher powered engines. Wingtip extensions increased the span by a little over six feet and the nose was re-modelled to a much cleaner globular shape. In this rather cramped, extensively glazed cabin were the crew of four, a 20 mm. fixed front cannon, a 20 mm. top turret, a 13 mm. top hand-operated, and single or twin 7.9 mm. under guns. There also had to be space for piloting, navigating, bomb-aiming and radio stations. In a final series, the Ju 388, the design was developed for high-altitude operation in night fighter, bomber and reconnaissance forms. The cockpit "bulb" was pressurized and reduced in size, details were cleaned up and more powerful engines were fitted. A bulged bomb bay enabled the load to be carried internally and armament was restricted to a remotecontrol tail barbette. With Jumo 222E engines of 2,500 h.p. a maximum speed of 432 m.p.h. at 37,700 ft., with a cruising range of 1,130 miles was claimed.
This German predilection for developing existing bomber types was, of course, because of their concentration on mass production. The authorities were afraid to disturb manufacture by turning over to new types while a modification of an existing aeroplane might be used. This policy also suited the large industrialists, who stood to profit most by long production runs, without re-tooling.
The R.A.F. heavy bomber night attacks proved to be so successful that little was done to develop the twin-engined medium bomber, so that the Blenheim became virtually the end of a line. The reasons for this were partly strategic. In the first place, operating from the British Isles there were few targets for light or small bombers, which are primarily army support aircraft—that is, long range artillery. The fighter sweeps, with "Hurribombers", were adequate for molesting the coastal areas of Europe. Army activities were confined to North Africa and, although Blenheims and Wellingtons were largely used there, the problems of reinforcement from Britain were acute. In this theatre, reliance was placed largely on supplies from America, which could be shipped across the U-boat free Southern Atlantic, and so these forces used the American light bombers.
There were six American light bombers: the Douglas Boston, Martin Maryland, Baltimore and Marauder, the North American Mitchell, and the Douglas Invader, to put them in chronological order.
The first two were in the Blenheim class—1,000 h.p. radials, 1,250 lb. bombs, 300 m.p.h., and crew of three—but in both cases the fuselage was narrow, so that there was no intercommunication. The Boston (A-20) was developed to 1,700 h.p. engines and 2,000 lb. of bombs with little change in appearance. As a bomber armament was light, but as a ground attack bomber or intruder, several fixed guns were mounted. In its final forms, Boston IV and V (A-20 J and K), a twin .50 in. turret was fitted. The Boston was a handsome aeroplane, pleasant to fly, but not a very powerful weapon. It was the first military aeroplane with a tricycle undercarriage.
The Maryland and Baltimore—the one was directly evolved from the oth/s.—suffered from crew segregation and, like the Boston, this meant that if the pilot were injured neither of the other occupants could reach the controls. Successor, late in the War, of these light bombers, or ground attack, aeroplanes was the Douglas A-26 Invader. Generally similar to the Boston, only larger, and heavier, the Invader had a wider fuselage giving space for communication and upper and lower twin .50 in. barbettes. Engines gave 2,000 h.p., bomb load was increased and the speed was nearly 350 m.p.h. Somewhat similar, but for its twin rudders, was the North American B-25, the Mitchell. This was possibly the best all-round light bomber of the War. With an internal bomb load of 3,000 lb., and the same amount externally for short ranges, the Mitchell also had a heavy gun armament, including a twin .50 in. turret. It was a docile and adaptable aeroplane and was fitted for many duties. Another variation of this theme was the Martin B-26, the Marauder. With an almost perfectly streamlined circular fuselage and two 2,000 h.p. radials, the good looks of this aeroplane were largely spurious. Structural weight was high and speed, heavy armament , and bomb load (4,000 lb.) were badly compromised, so that wing loading was too high and the maximum speed low.
It was the unarmed de Havilland Mosquito that really altered the conception of the bomber. As finally developed, it could carry 4,000 lb. of bombs faster, farther and higher than any other aeroplane of the War—with wing bombs the load was 5,000 lb. The performance of the Mosquito was achieved by concentration on one idea, the substitution of speed for defensive armament and because of this it was the forerunner of the modern bomber. Sheer aerodynamic cleanness gave it a higher speed than contemporary fighters and even the gradual increase of load from the original 1,000 lb. was more than met by higher-powered engines. The ultimate version, the B Mk. 35, with Rolls-Royce Merlin 113/114, two-speed, two-stage supercharged engines of 1,750 h.p., had a maximum speed of 422 m.p.h. at 30,000 ft. and at that height could take its 4,000 lb. bomb 1,750 miles at 310 m.p.h.
It was a bold stroke to drop all armament, but the results were excellent, not only operationally, but in the saving of manufacturing effort and number of air crew required. Contributory to the success of the Mosquito were its outstanding handling qualities. Even the later marks, with high wing loadings and stalling speeds of 118 m.p.h., were pleasant to fly and land.
In Germany, an attempt was made to emulate the Mosquito with the Messerschmitt Me 210 and the similar but more powerful Me 410. These fast, twin-engined fighter-bombers were of an unadaptable design and yet their authors had lacked the courage to go all out for any one feature. Tandem seating was used to keep down frontal area, but the fitting of rear armament in special side barbettes showed a lack of faith in performance. The pilot aimed the bombs through glazed floor panels and the bombs themselves were carried in a small bay under the cockpit. Although two 1,700 h.p. liquid-cooled engines gave the Me 410 a speed of 390 m.p.h. at 22,000 ft. it was an expensive way of carrying 1,100 lb. of bombs—2,200 lb. as overload—and the fixed forward armament was no heavier than that of a single-seater fighter. The ground attack role resulted in half a ton of armour having to be carried.
One of the duties of the Me 410 was to take over dive bombing from the notorious Stuka, the Ju 87. Evolved mainly as a result of the work of the Swedish Junkers company, the Ju 87 was, in 1938, a modern application of the dive bomber mooted a decade earlier by the Americans. This was, in a sense, the German equivalent of the Battle, but specially designed to help advancing troops. Rugged in appearance and construction , the undercarriage was fixed, the fuselage had a rising
line with pilot and radio-operator/gunner close together under a small canopy. The Junkers corrugated skin was dropped, but the "double wing" was retained. Under the wing were divebrake slats. Normally there were two front and two rear guns, but for ground attack extra guns could be mounted under the wings. The main bomb (up to 4,000 lb.) was carried under the fuselage on a special carrier that swung it clear of the airscrew before release. With loads of smaller bombs wing racks could also be used. In the advances on Poland, the Low Countries and France, the Stuka proved a supreme weapon, particularly for causing panic by attacking roads packed with refugees or undefended towns—anywhere where there were no fighters. When used against Channel convoys the Ju 87s were severely mauled by R.A.F. fighters and when they attempted one raid on Croydon the whole force was destroyed. It was fairly conclusive that the Stuka was a telling weapon only where there were no opposing fighters or a supporting fighter screen. The Russians evolved a similar type, the 11-2, and later the Il-1o, which was very heavily armoured and, armed with rockets, was a good ground support aeroplane. Apart from a few abortive American dive bombers this seemed to be the end of this line of thought.
After the War, money for bombers was very scarce in Europe, but the Americans continued with their global bomber policy, the logical development of the B-29. This took the form of the modified, higher-powered, heavier, but generally similar Boeing B-50 and the new Convair B-36. The latter, global policy or not, must be attributed primarily to the innate American predilection for size. It is a huge aeroplane, with a span of 230 ft., length 162 ft., gross weight, fully developed, 358,000 lb.—almost 160 tons. The designed bomb load was 10,000 lb. for 10,000 miles—alternatively a maximum of 84,000 lb. can be carried for short distances.
To achieve these requirements, the fuselage is a long cylinder, with large bomb bays, pressurized crew compartments and six retractable remotely controlled 20 mm. barbettes, two hand-operated 20 mm. cannon in the nose and twin 20 mm. tail cannon. To lift all this, and also to provide fuel tankage, there is a huge, thick wing, its leading edge swept back to accommodate variations of c.g. Originally, six Pratt and Whitney R-4360 engines of 3,000 h.p. each were fitted and these were later replaced by 3,500 h.p. and then 3,800 h.p. versions. The engines have, of course, turbo-superchargers and they were installed as pushers to improve air flow over the wing. As a means of boosting speed two twin-jet pods with 5,200 lb. static thrust J-47 engines were fitted, so that speed over the target can be as high as 435 m.p.h.
A huge tail rising nearly forty-seven feet in the air is necessary to control this vast aeroplane. Runway loads, too, posed a problem and the usual two main wheels have been replaced by two four-wheel bogie units. It is not always realized that a large aeroplane causes very high ground loads and it is now general practice to spread the weight over as many wheels as possible. It is also easier to stow a unit of several small wheels rather than one very large one.
Although not very fast, the B-36 has proved that it can fly so high that it is very difficult to intercept. In particular, the heavily loaded American jet fighter has trouble in manoeuvring at 35,000 ft., where the B-36 flies—although the MiG-15 is still operating well at that height. The original idea of the B-36 was that it could attack Europe or Asia from home bases, but now it is based in Britain and other "fringe" countries from which it could reach almost any part of the U.S.S.R. The turbo-jet engine completely revolutionized the bomber. At first, the high fuel consumption appalled designers, and then they realized that by flying high and fast "miles per gallon" could be increased. Yet, paradoxically, the first jet bomber, the Arado Ar 234, was used for low-level attacks in the winter of 1944-45. The aeroplane itself was simply a well-shaped fuselage, with submerged cockpit, a thin high wing with ^ underslung nacelles, an angular high aspect ratio tail and an undercarriage retracting into the fuselage. As an aeroplane, the Ar 234 was not striking, but it had some special features of future significance: a tail parachute was used to pull it up after landing; and the Ar 234A version had only skids under fuselage and nacelles for landing, a jettisonable trolley being used for take-offs. Two Jumo 004 engines gave a speed of 470 m.p.h. at 20,000 ft. Although the Ar 234B essentially relied on speed, and was therefore in the Mosquito tradition, some had two 20 mm. fixed rearward-fixing cannon sighted by periscope. A version, the Ar 234C had four engines in double nacelles, giving a speed of 546 m.p.h. at 20,000 ft.—with only 40 minutes' endurance at full power. The fuselage in this bomber, apart from the cockpit and the wheel stowage, was a fuel tank, the 4,400 lb. bomb load had to be mounted externally.
There were numerous German projects for bombers at the end of the War. Many of these were of very advanced design, particularly tailless and delta configurations, but the only one to be completed was the Junkers Ju 287. This was a 47,500 lb. aeroplane designed for two 6,000 lb. thrust jet units, but the prototype was flown with four Jumo 004 engines mounted under the wing and alongside the nose. The fuselage of this aeroplane resembled that of the B-29 and it had a pressure cabin. The interest of the Ju 287 lay in its thin, forward-swept wing. This gave the same advantages as sweepback but was not subject to tip stalling. The mounting of the engines was also novel, since they were in pods held clear of the wing and fuselage respectively. Because of the low-thrust engines on the prototype auxiliary rockets were used for take-off.
In 1947 four American jet bombers came on the scene. Three of these were conventional adaptations of piston engine ideas, using thin, straight, high aspect ratio wings, sleek * fuselages and single-fin tails. The engines were in underslung nacelles and totalled about 20,000 lb. thrust, for aeroplanes the size of the Lancaster, but with the load and weight of the Lincoln. Speed was only about 500 m.p.h. and they were of little practical use.
The fourth prototype was the Boeing XB-47, now in . service with the U.S.A.F. as the B-47 Stratojet. This aeroplane was of radical design, with 35 degree wing sweep based on German research. The design was established on a thin wing of very high aspect ratio, thereby ensuring low drag, but incurring the penalties of high wing loading, extreme flexibility (the tips rise over six feet in flight), and lack of internal stowage space. The use of the thin, flexible wing meant having a large fuselage capable of housing bombs, fuel, and the main wheels of the "bicycle" undercarriage. Since the wing was too thin for the engines to be buried, they were slung under the wing in pods as a precaution against fire. They were also mounted along the span to assist the flexible wing with relieving moments, that is to say, by hanging the weight along the span it is distributed without too much concentration.
The bicycle landing gear introduces a handling peculiarity. Landing and take-off must be made at a precise angle so that the wheels touch and leave the runway together, otherwise there is a tendency to porpoise. To achieve the simultaneous touch down of both sets of wheels the B-47 nas to be landed within 2 m.p.h. of the speed calculated for its all-up weight at the time of landing.
The six General Electric J-47 engines give 5,800 lb. static
thrust each, but because of the very high weight, 185,000 lb., auxiliary take-off rockets, totalling 20,000 lb. thrust, are mounted in the sides of the rear fuselage. The B-47 can carry a bomb load of 20,000 lb., at a speed of over 600 m.p.h. The range has not been revealed, but it can be extended by carrying two huge 1,780 U.S. gallon drop tanks at mid-span. Under an arbitrary ruling of the Pentagon a "medium" bomber was denned in 1950 as one with a still-air range of about 5,000 miles, and the B-47 *s known as a medium bomber although it carries the load of the largest wartime "heavies" and has a longer range. There is no doubt of the B-47's performance , but its very high wing loading gives food for thought as to whether it will be able to reach 50,000 ft., the recognized best cruising height, and as to how it would be handled in wartime, when the necessary 3,000 yard runways would be subject to bombing.
In 1952 an even larger jet bomber, the B-52 Stratofortress, flew and showed that it was a logical scaling-up of the B-47. Design principles are similar: high wing loading to reduce drag by keeping wing size down, extremely elastic wing structure requiring external engine pods and a huge fuselage containing fuel, bombs and undercarriage.
At the time of writing, the B-52 is very much "Restricted", only the main dimensions may be quoted, but the eight engines give a total static thrust of some 80,000 lb. The main undercarriage consists of four twin-wheel units, actually the same ones that are on the B-47, which fold into the fuselage. Lateral balance is preserved by small wheels nearer the wingtips than those on the B-47, which are mounted in the twin nacelles. Because of the great flexibility of the wing the normal ailerons have been replaced by special spoilers. These are plates that are raised on one wing to spoil the lift and thereby impart a rolling motion.
There are two ways of supporting a heavy load on a wing: one is to make the structure very stiff, the other is to make it very flexible. The latter is the only choice with a thin, high aspect ratio wing if a reasonable weight is to be achieved. In the flexible wing the elastic deformation relieves the loads—on the B-47 the wings can be seen gently flapping in flight. Structurally this theory is excellent, but it poses severe control problems. When the ailerons are deflected, instead of rolling the aeroplane they twist the wing, so causing control reversal. The Boeing solution to this problem is to use lift spoilers, small flaps like air brakes that are raised only on the wing
that is to go down. These spoilers are fitted inboard (to prevent their causing tip stalling and spinning) and to give the pilot "feel" they operate in conjunction with small ailerons, also at mid-span. The other U.S. heavy bomber is the Convair YB-60, an adaptation of the B-36 that incorporates the sweepback and engine pods of the Boeing designs. A modified B-36 fuselage is used, with a similar tricycle undercarriage. The wing is much thicker, less flexible and so contains fuel and is stiff enough to support the loads of conventional ailerons. After the War, the R.A.F. had to economize and no money was forthcoming for Lincoln replacements. About 1946 the Air Council began to formulate ideas for very advanced jet
bombers of about the Superfortress weight. The emphasis was, once again, on restricted wing loading, so that the bombers would be able to fly and manoeuvre freely at very great heights and would be able to use normal aerodromes. This basic requirement had a profound effect on design and all three types evolved were fundamentally different from the Americans.
The British designers abandoned the temptations of low * cruising drag offered by high aspect ratio and, instead, used a large wing area to obtain a low thickness-chord ratio with considerable physical thickness, so giving a good structural depth for strength and ample stowage volume. Here it is worth recalling that an important difference between piston and turbine-engined long-range aeroplanes is the difference in the ratio of empty to all-up weight. In the first place, despite higher speeds causing higher stresses, the structure is lighter because the engines themselves weigh far less, there are no airscrews, and the lack of vibration means that much of the structure can be lightened. On the other hand, fuel consumption is higher because of the great power needed to cruise near the speed of sound. All this means that the jet bomber may well carry its own weight—possibly even more—at take-off, but after it has used its fuel and dropped its bombs, its wing-loading will be almost halved. Now the effects of this are two-fold: as fuel is consumed the manoeuvrability and ceiling are constantly improving and what was a heavily loaded aeroplane at the start becomes more nimble the deeper it penetrates enemy territory; while on the return to base wing loading will be so much reduced that the landing speed will have become very moderate indeed. With the British formula, this aspect is felt much more than with the American one.
Of course, there has also been a fundamental alteration of the British strategic outlook on bombers. In the twenties no definite enemy was in view and, therefore, the policy on range was very vague, but when the Nazis came to power the Air Council awoke to the fact that the Hun was still the potential foe. This fact set the range pattern for the bomber specifications until the middle of the War, when the Lincoln was ordered with a view to bombing Japan from bases in New Guinea, Malaya or Polynesia. As the post-War political situation resolved itself, it became obvious that the U.S.S.R. was the only likely enemy. The vast areas of this land, with distances increased by the shield of the satellite countries, meant very long-range bombers capable of a 2,000 mile radius of action. (Contrariwise, the Soviet Air Force can operate from bases far ahead of its own industry and so long-range bombers are of relatively little interest to the Russians.) Despite the fact that the new British bombers of the 1946 specifications are much larger than the wartime "heavies", they are designated "medium bombers" in concurrence with the Pentagon definition. Apparently the most conventional of the three British bombers, the Vickers Valiant, was the first to fly, on May 18th, 1951. This very beautiful design of George Edwards will be the first to go into squadron service. Although smaller than the B-47 it is known to have a better range and ceiling, speed and load being similar.
The sleek fuselage embodies the needs of today, for it is a streamlined container for the operational equipment. The diameter is much greater than that of earlier bombers because fuel as well as bombs have to be housed in it. The crew is grouped in a pressurized cabin in the nose, for there is no armament. The rear fuselage is but a streamlined fairing carrying the tail unit.
The most interesting feature of the Valiant is the patented compound-sweep wing, which has both aerodynamic and structural advantages. By sweeping the root forward, not only is the chord reduced, but the angle of sweepback is increased. Both these factors mean that the wing can be thickened considerably without reducing the critical Mach number. In this thick centre-section the four Rolls-Royce Avon engines can be almost completely submerged, so reducing their drag to a negligible quantity. Such installations do, of course, bring with them their own problems, particularly in ducting, as the entirely different intakes on the first and second Valiant 1 prototypes reveal. The outer part of the wing has much less sweep and, in consequence, is considerably reduced in thickness, which means that it has to be flexible. The problem of aileron reversal is overcome by a very ingenious subterfuge. The outer part of the wing is flexible, but it has been made very resistant to twisting—the main cause of reversal. Between the wing root and the outer plane there is the undercarriage bay which, because of the large opening in its lower skin, does not resist twisting, although its strong spars are stiff against bending. This combination forms a structural "hinge", so that when the wing is heavily loaded at high speed, deflexion does not reduce incidence, neither does aileron movement lead to reversal. If this "judo" behaviour of the wing is hard to understand it may be some consolation to know that one of the most revered structural pundits in this country publicly stated that it was impossible!
The tail of the Valiant is a simple swept unit of low aspect ratio. The tail plane is set high to clear the wing wake and its juncture with the fin has no bullet fairing. The control surfaces have aerodynamic balances and extensive tabs. The scoop on the fin is an air intake for a combustion heater used • for de-icing the tail surfaces.
On August 30th, 1952, the second British bomber, the Avro Vulcan, flew. This delta-wing aeroplane is of very advanced design and was preceded by a lengthy and careful programme with three one-third scale models, the Avro 707s. The arguments for and against the delta configuration are fully set out in Chapter XIII, so I will simply give the bomber side of the story here.
Faced with a very severe specification the Avro designer, S. D. Davies, investigated the possibilities of the very large wing area presented by the delta. German research had shown that high-speed characteristics were, theoretically, very
promising, although there was considerable doubt about low-speed behaviour. From the bomber viewpoint the vast internal volume was alone a temptation. The project started with a setback, the early loss of the first 707 model in a lowspeed crash of the type predicted by the doubters. Undeterred, the company pursued its studies, although it was almost a year before the second machine was airborne. A careful research programme overcame the difficulties and low-speed behaviour is now so good that the Vulcan, once trimmed into its gliding angle, can be landed hands off. Despite the proven virtues of these Avro deltas, a considerable amount of effort had to be exerted to overcome prejudice against such unconventional aeroplanes and ones that landed at such a queer angle.
The Vulcan is, of course, a "flying wing", the fuselage being reduced to a minimum. The nose contains the pressure cabin and a radome for electronic equipment—bombing from above 40,000 ft. is almost impossible visually and special radar is required. The wing has a root chord of some 70 ft. with a maximum thickness of six feet, which gives ample volume for engines, undercarriage, fuel and bombs, without a single excrescence. The wing loading is low enough to dispense with flaps (a considerable saving in weight), which would also have required a tail plane to trim out their nose-down effect, and tail parachutes are used to pull up on landing.
The Avro Vulcan is not only a beautiful aeroplane, it gives every promise of being a superlative weapon, a design for a purpose—though one hopes this may never be put to the test. Third of the bombers is the Handley Page Victor, which has a crescent wing based on research work initiated in 1944 by Arado. The aerodynamic theory here is similar to that of
the Vickers compound-sweep, the critical Mach number is maintained constant along the span by varying the thickness ratio and sweepback. Heavily swept inner portions allow sufficient depth for engines and undercarriage, while the tip has so little sweep that tip stalling is greatly reduced. Unfortunately, the tip is so thin that leading-edge flaps are necessary to increase the camber, so introducing another complication. Theoretically the crescent wing has advantages in high-speed flight, but these may be outweighed, literally, by complications in the structure—with details shrouded by security there is no way to judge. The fuselage of the Victor is scarcely pleasing to the eye. With the cabin submerged into the top line, the nose has a supersonic look that has been rather spoiled by the "chin" caused by the necessary lowering of the radar equipment. The
rather abrupt tapering of the rear fuselage would, one imagines, tend to cause directional instability—it usually has in the past.
An event that may well have been decisive in formulating the British policy of low wing loading was the flight of the English Electric Canberra on May 13th, 1949. This was originally a private venture project by W. E. W. Petter, but the Air Ministry was impressed and wrote a specification round the design. The Canberra has been the subject for much scathing comment: it has been called a "scaled-up Meteor"; its speed has been criticized; its bomb load called negligible; its range considered useless. Yet in May 1953 it was the only jet bomber operating with the N.A.T.O. forces and the only jet aeroplane to have flown the Atlantic direct—and the only aeroplane to make the double crossing in one day. It has flown to South America, East Africa and Australia, as well as to many intermediate points in record time. Although performance is secret, these several flights reveal a cruising speed of about 500 m.p.h. A telling point in the Canberra story is that it was chosen for manufacture under licence in the U.S.A.
Fundamentally, the Canberra is simply a very clean aeroplane with a large, low aspect ratio wing. The large wing area gives a high ceiling, while the low aspect ratio allows a fairly small thickness chord ratio. Without sweepback, the Canberra has not a very high critical Mach number, but its low wing loading gives it far better manoeuvrability above 40,000 ft. than that of any contemporary fighter. When attacked, a Canberra turns and the fighter that tries to follow it stalls and spins.'
Symmetry is a design feature of the Canberra; both the fuselage and the nacelles are placed on the wing centreline, so reducing interference to the minimum. The crew of three is in a pressure cabin in the nose, where they have ejector seats and jettisonable canopy and hatches. The bomb bay is below the wing. Fuel is carried in wing and fuselage and wingtip tanks may be fitted. The low aspect ratio tail unit is, in effect, swept back because of the sharp leading-edge taper. It is generally considered best to sweep the tail even with a straight wing because the latter's passage speeds up the air flow and, without precautions, the tail will have a lower critical Mach number.
Briefly, mention may be made of three bombers in the' Canberra class, but based on opposite principles. The Martin XB-51, which flew a few months after the Canberra, was somewhat in the tradition of the Ju 287. A huge fuselage houses crew, bicycle undercarriage, fuel, bombs and one engine in the tail, two more being mounted in pods by the nose. The thin swept wing has variable-incidence and slats as well as full-span flaps, with spoilers instead of ailerons. Original in conception, the XB-51 gives the impression of being rather too ambitious. It is significant that the Martinbuilt Canberra should be a ground-attack version, the same specific duty as the company's own XB-51.
In France Pierre Satre, Chief Designer of the S.N.C.A. du Sud-Est, had an original thought for an attack bomber on somewhat similar fines. Work on this was started quite soon after the liberation of France and the first prototype of the * Grognard flew on April 30th, 1950. This design incorporates several unique features. The apparently bulky fuselage actually houses two Nene engines, one above, and ahead of, the other, with a single dorsal intake. The wing is thin and swept, leadingedge flaps being fitted, so that the fuselage is once again a hold-all for the fuel and undercarriage. The low-set tail plane, a position usually avoided because of the chance of ground damage, is a feature that is becoming of increasing interest for high-speed aeroplanes, since it is clear of the wing wake without the weight and structural complication of the high position on the fin. The tail plane, which has a dihedral angle to increase ground clearance is fitted with variable incidence gear.
The S.N.C.A. du Sud-Ouest SO-4000 is also a twin-engined bomber of unusual configuration. Preparation for this aeroplane was very careful, with first a glider and then a half-scale model to investigate behaviour in flight. The all-embracing fuselage in this case has two Nenes side by side. The wing area is fairly large, so that loading is reasonable. The performance, however, is not very high, which must be attributed to duct losses and the rather low thrust of 10,000 lb. A most ingenious alighting gear is fitted, a nose wheel and four main wheels under the wing which give a rather narrow track. On the SO-4000 a low tail plane has been used, made possible by the high midwing position.
Such, then, are the bomber designs of 1953. Which will prove most successful, which are the links with the future are almost anybody's guess. Able minds, both strategic and technical, have reached diverse conclusions on the same subjects and it would be presumption to attempt to forecast the most likely lines of future development. It may well be that the bomber has no future in that it will be supplanted entirely by the long-range guided missile and the even greater horrors of push-button warfare.