England having come rather abruptly, for reasons best known to the RAF, to a more than academic interest in heavy, long range bombers, there is naturally some speculation on this side of the water over the home-grown British models, the Handley-Page Halifax and Short Stirling.
As the long range, high altitude, bomber was pioneered in this country, among the questions foremost in American minds is, how do the new British bombers stack up against the Flying Fortress, a type originally developed by the Boeing Airplane Co for our Air Corps in the early 30s?
Details released by the Air Ministry on the Halifax and Stirling are confined mainly to physical descriptions; performance figures are kept secret, although a number of Halifaxes have been brought down over enemy territory. The Stirling, which is somewhat the larger of the two, weighing about 65,000 lb gross, has a wing span of 99', length of 87' 3", and a height of 22' 9". Fortresses, weighing 47,500 lb gross and 31,160 lb empty, have a greater wing span, 103', but overall length is considerably less, approximately 68'. So the Stirling, built like a flying box car, must be capable of carrying a bigger bundle of bombs to Berlin, something like 6-7,000 lb. The Fortress Model C carries about 4,800 lb. in bombs.
Power for the Stirling comes from either four Bristol Hercules 14-cylinder air-cooled radials of 1,600 hp each, or four double-row 1,600-hp Wright Cyclone 14s. Boeings are powered by Cyclone 9s.
The Halifax is approximately the same size as the Boeings, although it is greater in height by some feet span is 99', length 70', and height 22' but unlike any other British or American heavy bombers, it is powered by liquid-cooled engines, four Rolls- Royce Merlins rated at about 1,050 hp each at 18,500 ft. Both the Halifax and the Stirling are midwing monoplanes, but whereas the former has twin fins and rudders, the Stirling has a single tail structure. The Halifax is reported to have good controllability. Stalled in a demonstration flight last Sept 12, the motors are said to have picked up again with little loss of altitude. Takeoff was quite short and with the Handley-Page slotted flaps fully depressed, landing was said to be both slow and reasonably short.
Three-bladed Rotol constant speed, full feathering propellers are used, and the Merlins are housed in nacelles which are level with the upper surfaces of the wings. Two glycol radiators and an oil cooler are carried together in a duct under the crankcase. Exhausts are single jet, flame damping types.
Of all metal construction, the Halifax is said to have been designed for rapid production, although as both bombers were just being built when the war started it is probable large numbers have not yet been produced. Each part is divided into sections small enough for easy transportation from shadow factories to final assembly points, and each section is in turn subdivided to obtain maximum economy of manpower.
The wings are of sweep-back design with square-cut tips, affording the pilot and bomb-aimer a lateral view extending abaft of the beam. For some reason the wings are not provided with de-icers, although the tail is. The Stirling seems to be similarly equipped.
Landing gear on the Halifax is a remarkably sturdy-looking fork-type, which is a single magnesium casting, having telescopic action capable of more than 12 inches travel. Retraction is backwards into the inboard nacelles. The Halifax's tail wheel is fixed, but the interesting double tail wheel on the Stirling, installed undoubtedly because of the great loads carried, is retractable, as is also the main landing gear.
Bomb compartments take up most of the fuselage below the wing in these planes triple bomb racks extend almost 2/3 the length of the Stirling's 87' fuselage, starting from beneath the pi1ots' cockpit in the nose and armament is reported to be very heavy. On the Halifax a 4-gun Boulton Paul power turret is installed in the rear tail position and a 2-gun turret in the nose, which in both bombers, especially the Stirling, juts far out beyond the leading edge of the wings. The Stirling is apparently armed in like manner, with further armaments on either unrevealed. Armament on the Boeing B-17E is also heavy, with a power turret "stinger" in the tail and another in the fuselage, in addition to the belly guns.
Neither the Halifax nor the Stirling were in service until some time after the present dispute with Germany started it is reported that last winter not more than two squadrons of Stirlings were in operation at any one time. A perhaps significant revelation concerning the Halifax, in lieu of performance figures, is the admission that "several have been lost", whereas up to this time there has been no confirmed loss of a Flying Fortress. Undoubtedly, no Boeings have been lost because they can reach altitudes in excess of effective ground fire, and, although Me-109Fs have engaged the Fortresses in combat at 30,000 ft, the Nazi fighters find it difficult to maneuver at that altitude.
British pilots, not the magazine writers, are credited with saying that at high altitudes the Boeing was definitely better than the Stirling or Halifax, and that at 25,000 ft they found it to be even faster than the Spitfire or Hurricane.
Thus, any shortcomings in the defensive armament of the Boeings, so often complained of by British aviation journals, is more than made up by their ability to climb far above the effective ceilings of aircraft attempting to intercept them. In fact, the ceiling of the Boeing Fortress is not actually known, for it will still climb above 40,000 ft, where atmospheric pressure is about 1/5 what it is at sea level (14.7 lb/in²), beyond which human endurance and ingenuity at present fails. Even the older models, which the British Purchasing Commission rejected early in 1940, had ceilings labeled 40,000 plus, for no one then, as now, knew how much higher they could go.
The reason for the exceptionally high ceiling for the Boeings is, of course, the turbosupercharger developed by General Electric, which at altitudes above 20,000 ft is superior to the mechanical type supercharger favored by the British. Moreover, although the average European bomber is not steady enough to drop bombs accurately at 20,000 ft, being confined to "regional bombing", our own Air Corps is said to have placed several bombs within a 25-ft circle on the ground from a Fortress at that altitude. This stability, according to Eddie Allen, Boeing's flight engineer and a former Associate Editor of Aviation, is entirely a matter of designing a bomber's tail surfaces.
Regarding the turbosupercharger, it is interesting to note that the Stirling has an alternative power installation of Cyclone 14s which could be fitted with the General Electric turbosupercharger, thus giving the British bomber a higher ceiling than it otherwise could attain. However, installation of the Cyclones may be merely because the British have not yet got into quantity production on such air-cooled radials, and need to augment their supply.
At any rate, whichever the case, it is unlikely the Stirling, with its greater weight and shorter wing span, could fly at the heights the Fortress will.
Needless to say, a cabin-heating arrangement has been incorporated in the British bombers, for at altitudes above 35,000 ft the temperature is about 67° below zero. The crew, also, quite likely wear electrically heated suits in case a shell fragment should let in the numbing cold of the substratosphere.
Judging from available reports, it would seem that the new British bombers have exceptional load-carrying capacity; greater, in the case of the Stirling, than that of the Fortresses now in service abroad, but having lower ceilings than the present Boeings. Lord Beaverbrook is quoted as saying that the "Flying Fortress is the most valuable and useful of all bombers with all respect to the Stirlings, Halifaxes and Manchesters." Fortresses won't carry so heavy at load as some of their bombers, he said, but they will carry a load higher with a bigger measure of safety and a higher degree of efficiency.
Later Boeings, the B-17Fs and others to be produced under the 500-per-month program, will have more defensive armament, greater bomb capacity, more armor for the crews, and radio locators for enemy aircraft, which should increase their effectiveness considerably.
But the steadiness at extreme altitudes beyond effective reach of AA fire and interceptor planes, which makes for accurate bombing, would appear to be a performance characteristic required in long-range, heavy bombers if they are to carry out their missions efficiently. This characteristic the Boeing Flying Fortresses have, and possessed long before Britain became aware of its tactical value.
This article was originally published as a "Foreign Flying Equipment" feature in the December, 1941, issue of Aviation magazine, vol 40, no 12, pp 104-105, 218.
The original article includes 5 photos and a three-view line drawing.
Photos credited to Press Association, British Combine.