EXPERIMENT WITH GIANTS ,..
By JOHN WILLIAMS
THE Bristol Brabazon, in its present form, is a research pro- ject intended primarily to explore the problems of the practicability of the roo-ton aircraft. The lessons which it is hpped to learn ,during the trials will be used in the design of later aircraft. The £6,000,000 scheme for developing the Brabazon (with another £6,00op0o for the Assembly Hall where the machine is serviced, and the runway from which it operates) is like the Cheops Pyramid—the symbol of a monumental accumulation of knowledge. This information will provide guidance in the evolu- tion of very large aircraft or, as they are more fashionably described, global super-bombers and super-transports. The Brabazon seems very large indeed because it skips a stage in evolution. For some reason which has not, so far, been satisfactorily explained, the Government's supply department has failed to sponsor at the right time the development of 15o,000 lb. transport aircraft. This class should, logically, bridge the gap between existing transports like the 80,000 lb. civil Avro Tudor, and the Brabazon, which has a design gross weight of 285,000 lb. Thus, in Britain, we have no counterpart to the U.S. Navy's 150,000 lb. transport, the Lockheed Constitution. B.O.A.C. have consequently been obliged to buy Boeing Stratocruisers from America—a purchase of such doubtful wisdom that it is rightly being challenged on technical grounds in Parliament. The prototype Brabazon has been constructed with nothing to help us but the successful completion of. two 130,00o lb. Short Shetland flying-boats and the zoo,000 lb. Avro Shackleton long- range military reconnaissance aircraft—the first of which has recently flown.
Many people outside and inside the aircraft industry shake their heads at the Brabazon. Even Lord Brabazon himself, at one time, seemed doubtful about the merits of the major project evolved from the recommendations of his committee. Nevertheless, techno- logically, the Bristol 167 design is up to date by the most recent standards, although the operators have not, as yet, been publicly persuaded of its practicability. A test of the success of the Brabazon is to set it beside the American counterpart, the Convair XC-99 (a somewhat larger civil version of the B-36 bomber in U.S.A.A.F. squadrons), one of which has been flying for nearly a year. The Convair and the Brabazon are the two largest landplanes in the world. The Convair with zo,000 h.p., or even with the theoretical 21,000 h.p., is relatively underpowered and its fuselage too large for it to be able to take passengers over a very long range. Although the Brabazon and the Convair were built on opposite sides of the Atlantic, with no interchange of information, the dimensions, weights and general configuration of the two aircraft are practically identical.
We can be proud of the Brabazon as an engineering achievement. It is a daring attempt on the part of the chief •designer—Mi. A. E. Russell—to introduce many innovations. These include, first, the principle of using four pairs of buried engines, which are coupled and drive the four contra-rotating propellers through a system of gears and shafts. - The history of the Brabazon's power-plants goes back to the period at the end of the war, when in Britain we decided that the industry had not the man-power'M continue large-scale development and research on both piston engines and gas turbines. The ruling to deverop turbines exclusively haesince been the subject of some controversy, which is interesting in itself. But it only affects the Brabazon because it was necessary to undertake the design of a suitable turbine for this particular airframe. Aircraft gas turbines, despite earlier optimism, do, in fact, require many years of development, and the Bristol Proteus of 3,20o h.p.—eight of which were designed for the production Brabazon—could not be developed in time for the first prototype. The company's chief test pilot—Mr. A. J. Pegg—will therefore fly' it initially with eight Centaurus piston engines. Unfortunately, also, the wing structure has had to be arranged deep enough to bury entitely the large bulky piston engines. Designed from the start for the slimmer turbines, the wing could have been made &hinner. However, the cruising speed of the production version, proposed for the North Atlantic route, will be about 35o m.p.h. (which is only z5 m.p.h. less than the maximum speed of Spitfires used in the first half of the war).
A significant technical point about the Convair and the Proteus. Brabazon is that the faster the Convair goes the greater is the specific fuel consumption, with corresponding reduction in range. The gas turbines of the Brabazon reach maximum efficiency only at full throttle, so the nearer the Brabazon can creep to 400 m.p.h. cruising speed the better is its specific fuel consumption, and the greater is the range. The principle of using buried engines appeals to any designer, since with the engines stowed out of sight there is far less wing drag, which allows a greater cruising speed. An additional advantage is the accessibility of the engines during flight. Another new device fitted to the aircraft is the gust alleviator. - During flight at altitude or in certain kinds of cloud the air pockets —or bumps or gusts, as they are called in aviation circles—impose a sudden load on the structure, especially at high speeds, besides throwing the passengers about. By the use of a gust detector in the extreme nose, the unpleasant affects of the gust can be anticipated and then, by allowing some parts of the structure to operate more flexibly, the effects of the gust can be alleviated. A third important innovation is the use of very large power-operated flying controls, necessary because the pilot can only exert about zoo lb. with his hands and 200 lb. with hist feet. The pilot controls a series of valves which pass hydraulic power to the control surfaces, but an elaborate system of duplication is necessary' to make any system of this kind acceptable.
The main problem in the Brabazon has been the necessity success- fully to " scale up " various components. Often scaling up in size introduces inordinately difficult problems. The undercarriage has proved to be a vast and remarkable piece of engineering. Varioui wheel layouts were considered, and a conventional system of dupli- cated main-wheels under each wing and a pair of steerable nose- wheels in front was chosen. The object is to produce wheels and tyres which distribute the load as much as possible. The Brabazon must have big " footprints " ; otherwise its great weight will tip the corners of the concrete blocks which form the runway. Pioneer work was carried out in developing the pressure equipment neces- sary to maintain comfortable conditions in the huge cabin when the aircraft is flying at cruising altitude. Every door, window and crevice must be hermetically sealed to prevent the air, which is pumped under pressure into the cabin, from leaking away, except through the proper discharge valve. It was found, for instance, that air can even get between the strands of electric wire passing through pressure bulkheads. Every one of the hundreds of controls, pipes and cablei entering the pressure region from outside needs special treatment to prevent pressure losses. If the pressure equip- ment fails, the Proteus-Brabazon will be able to descend at once to about zo,000 feet without discomfort to the passengers, and at this low altitude (unfavourable for all gas turbines) the fuel consumption will not rise so far as to prevent the aircraft from reaching land with reasonable safety margins on the Atlantic service. In other words, life in the Brabazon does not depend upon the propel functioning of the pressure system.
It is worth-while remembering that both the Brabazon and the Convair are dwarfed by the Hughes Hercules flying boat which, designed for a gross weight of 400,000 lb., has flown in America. If you are looking for the perfect " white elephant," then you have it in the Hercules, a wooden flying boat of old-fashioned layout, doubtful durability and with inadequate power. The Brabazon could be fairly described as the forerunner of a practical, very long- range transport, which holds promise of doing a good job for B.O.A.C. and offering new standards of comfort and speed. The second Brabazon powered by Proteus turbines will probably fly some time in 1951. This will be a momentous period in British aviation, for the first 300,000 lb. Saunders-Roe Princess flying-boat is expected also to fly about the same time. These two projects, if successful, are likely to set the pace in transcontinental air travel ; offering speed and reliability with a quiet, effortless, vibrationless motion. And, most important, the turbines burn paraffin—a safe fuel of low volatility. The present weight limit of 300,000 lb. is an arbitrary figure, and, aerodynamically, there is no apparent reason why a z,000;000 lb. (450-ton) aircraft should not be constructed, if such a Behemoth could be put to some useful purpose.
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