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Aviation History
1955
1955 - 0966.PDF
MINIATURESTICK POWER CONTROL UNIT GYRO DATA UNIT (AUTO-PI LOT) HEAT EXCHANGER! ARTIFICIAL FEEL UNIT SIGNAL^* AMPLIFIER COMMAND UNITS BOMBING SYSTEM SHORT RANGENAVIGATION <-BLIND APPROACI ELEVATOR Fig. 3.—Possible future control system, shown for pitch control only. THE ANGLO-AMERICAN CONFERENCE . the autopilot, and (e) bombing control system or (f) automatic flight stability systems. Fig. 3 showed a rationalized system in which all the initiation signals were fed into a centralized signal amplifier, which mixed as necessary the different inputs, and then provided a single out- put signal to the powered control unit. Air conditioning and pressurization, continued Air. Joy, were further requirements for the high-flying jet aircraft. But, despite the vital need of providing against failure, the actual weight penalty of a pressure cabin was small in a circular-section fuselage, unless sealing compounds were used over-generously. The main prob- lem lay in detail design at doors, windows, windscreens and other discontinuities, which affected not only strength and weight but fatigue life. Supply of the cabin air presented less of a problem, apart from the difficulty of stowing such things as cold-air units, heat- exchangers, humidifiers, valves and ducting, because jet aircraft could draw off from their powerplants all the heated high-pressure air they needed. The real problem for future supersonic aircraft would be to cool, not heat, their cabins; but Fig. 4 showed how this could be turned to advantage by integrating the cooling and auxiliary power generating systems. At supersonic speeds, ram air would be used initially to drive a turbine which, in turn, would drive a generator supplying all the aircraft's power requirements. The air would then bifurcate, one supply going through a compressor/ turbine unit to the cabin; the other, after passing through two heat-exchangers, would be used to cool various items of equipment. Dealing next with fuel systems, Mr. Joy explained that the first problem was to keep e.g. travel within reasonable limits now that a combination of large fuel capacity and swept wings often resulted in fuel being located at considerable distances fore and aft of the aircraft's normal e.g. He described the two basic methods of proportioning the fuel as (a) to determine the con- tents of each tank at intervals and adjust the booster pump speeds to compensate for uneven emptying, either manually or by com- plicated computing equipment; and (b) by the use of a series of "hydraulic motors," each having a fixed displacement proportional to the tank it served. Each motor was driven by fuel, pressurized by the corresponding tank booster pump; and, since the motors were on a common shaft and rotated at the same speed, all tanks emptied in the same time. Such a system was extremely reliable and ensured that some fuel was taken from a tank in which the booster pump had failed. The basic design problem was maintenance of satisfactory internal clearances to avoid clogging while keeping efficiency. For pressurizing wing integral or bag tanks, without a formid- able weight penalty, the lecturer suggested a special wing structure PRESSURE BULKHEAD iSTABILIZINGDEVICES TOP SURFACEOF, WING PRESSURIZEDCABIN FLOOR PARACHUTE 4 BREAK PINS LOWER SURFACEOF WING LONGERON ENGINE COMPRESSOR1 COMPRESSOR RAM INTERLINKED CONTROL VALVES Fig. 4.—Layout of cabin- and equipment- EXHAUST coo//ng system for supersonic aircraft. AT HIGH SPEEDS with multi-spar webs and a distributed sandwich type flange with omni-directional bending strength and stiffness. With such an arrangement, the bending stresses due to tank pressures were at right angles to the stresses due to normal wing bending, so that tank pressurization could be provided for a negligible increase in structure weight. Although, like engines, facilities for crew escape in flight do not come under the general classification of equipment, Mr. Joy showed that they affect the positioning of equipment and play an important part in deciding the general design. Even the loca- tion of hatches for normal ejector-seat escape, he said, could play havoc with the local structure of a pressure-cabin and determine the whole crew layout. An attractive solution for very-high-speed aircraft was a jettison- able cabin of the type shown in Fig. 5, although it involved the difficult problems of ensuring a clean "break" and stability afterwards. To ensure minimum loss of structural efficiency, the break should be at a point where discontinuity was inevitable for other reasons, such as where the wing structure broke the continuity of the fuselage structure. An added advantage would be that a four-point cabin attachment could be directly to the main spar. It was equally important to locate as much equipment as possible aft of the break, to reduce the weight of the cabin and, hence, the weight and size of parachutes needed during its descent. After discussing briefly the comparative merits of hydraulic, electrical and pneumatic systems, during which he again empha- sized the possibilities of system integration, Mr. Joy completed his equipment survey with some notes on "black boxes"— the innumerable components containing electrical or electronic "magic" for which the unfortunate designer had to find room in his airframe. These, in particular, needed to be considered from the very start of the design, because some items weighed up to 100 lb or more and required careful positioning to minimize the need for complicated, heavy support structure. Access panels had to be provided, and the need to cool or pressurize some items of equip- ment also complicated matters. Finally, it must be remembered 55OO 5OOO 4OOO 3 3OOO O |2OOO 1OOO RUISING SPEED APPROX M-2RANGE APPROX 4,000 NAUTICAL MILES \A SAVING IN EQUIPMENT WEIGHT. m 5OO / I /- REDUCTION IN FUSELAGE DIAMETER SAVING IN EQUIPMENT WEIGHT (Ib) 1OOO 15OO 2OOO 25OO 3OOO i i i i 6 9 12, .15 REDUCTION OF FUSELAGE DIAMETER (in) 18 Fig. 5 (left).-Jettisonable cabin "break" structure. Fig. 6 (right).—Effect of reducing fuselage diameter, and of saving equipment weight, on the all-up weight of supersonic aircraft.
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