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Aviation History
1962
1962 - 0704.PDF
The British Messier (Dowty-Rotol Group) main-undercarriage units are equipped with temperature-resistant tyres by Goodyear. The complete gear had fully retracted three seconds after the photograph at the foot of the opposite page was taken BRISTOL 188... the fuselage. From the point of view of the sealant maker, the fuel cell is best made of simple, stiff, lowly-stressed members which do not get hot and with good surface roughness for adhesion. The Type 188 tanks are far from this, and the techniques had to be adapted to the circum stances. The sealing materials are usually rather poor conductors of heat, and tend to suffer from conducted heat from the skin even when the inner surface is under fuel. The sealant which is exposed by the fuel has a correspondingly worse time. In addition to extensive joint tests under load, representative tanks were "flown" through flight cycles of heat and cold and pressure and fuel drainage. This seemed particularly necessary as simple evaluations at peak temperatures alone were dis couraging and difficult to relate to a working life. The aircraft design was well advanced before a fillet sealing treatment involving successive coats of different sealants was shown to have reasonable promise." System capacity may not be divulged, but it is clear that there are three fuselage tanks ahead of the wheel bay and two aft. Each tank is sealed in the manner described above, and the bulkheads are of light alloy so that the different coefficients of expansion of the tank materials shall minimize the stress due to this factor. Each bulkhead is provided with a manhole through which access may be gained to the next cell, and each tank has its own series of dipsticks, float valves and booster pumps. The system is filled through a pressure coupling in the aft fuselage. The engines are supplied with up to 15,000 gal/hr from the Dowty proportioner driven by two hydraulic motors. Hydraulics As in the case of the fuel system, the hydraulic system was developed with the aid of a comprehensive ground rig, including the landing gear and doors, flaps, airbrakes and flying controls. The bulk temperature of the fluid is minimized by reject ing as much heat as possible to the fuel, but it proved impossible to cool the most exposed portions of the system where the fluid may be at rest or moving very slowly. It was therefore essential to find a fluid with acceptable high-temperature properties, and eventually the choice fell upon the RD.6195 disilicate ester-base fluid. Although fully satisfactory at 188 temperature, this fluid is inflammable and must be kept scrupulously clean and dry. This entirely new fluid aggravated the already severe plumbing problems, and all portions of the system are of suitable grades of steel incorporating new types of static and moving seals. Each engine drives two Super Vardel pumps at up to 10,000 r.p.m. to produce a nominal 4,0001b/sq in, and the combination of high pressure and large fluid flow has necessitated the development of a new range of swivel pipe-joints and flexible hoses. There is an emergency electrically driven pump but no ram-air turbine. 702 FLIGHT International, 3 May 1962 Electrics It was explained at the beginning of the "Com ponents and Systems" section that the philosophy followed in the aircraft was to adhere to orthodox practice wherever possible, and protect conventional components against the full effects of severe ambient conditions. But this is not always possible, and in any case one of the reasons underlying the construction of the aircraft was that such problems might be faced and overcome. The temperature experienced by most of the electrical system exceeds that met in other British aircraft by a margin wide enough to demand a completely new range of cables, connectors and plugs; and for extreme-temperature applications a further range of mineral- insulated cables was eventually found inescapable, together with a further range of connectors. On the other hand the main generation equipment is force-cooled, and presented no temperature problem. Engine bleed-air is used to drive at 20,000 r.p.m. a Dowty-Rotol turbine power-pack in the forward fuselage, on which is mounted a combined 10kVA alternator and 4.5kW generator giving a constant-frequency supply at 28.5V. Emergency power is supplied by Ag-Zn batteries. Air-conditioning Again a background can be provided bv Mr D. I. Vickery:— "Taking into consideration the speed, altitude and duration of flight for this aircraft, an air-cycle system of the regenerative type, using engine-tapped air as the source of supply, was considered to be the most suitable to meet all conditions. This type of system uses the cabin discharge air as the cooling medium for the primary cooler, the tapped air passing through this cooler before going through a water boiler and the turbine of the cold-air unit and into the cabin. The water boiler is essential at high altitude when the air mass flow through the system is down to a minimum, water being an excellent refrigerant under these conditions. The boiler vents to atmosphere and this vent had to be carefully designed to prevent water discharging with the steam when violent boiling occurs at altitude. With a regeneration system, the air passing through the fan or compressor of the CAU can be at temperatures around 400°C, and ... a small amount of turbine-cooled air is bled through the CAU shaft into the bearing housing to maintain the oil and bearing at an acceptable temperature. "Under all normal flying conditions, the air for the pilot's ventilated suit is supplied direct from the cabin incoming air supply, this being at a pressure and temperature suitable for this purpose; but in case of system failure, a cold-air supply from a compressed-air bottle is auto matically switched on to protect him. The pilot can also switch this cold-air supply system on if the air-conditioning system is running too hot, but he must use his discretion over this as the air supply is limited. The auxiliary equipment, telemetry, etc, is cooled by closed-circuit air cooling using fuel as the heat sink. To prevent a large air mass flow variation, the system is pressurized to the same pressure as the cabin. A similar system looks after alternator cooling. It will be realized from the foregoing that the main problem in air-conditioning has been simply to extend fairly normal practice to meet the flight conditions. Determina tion of the heat inputs in these conditions has been a matter for con siderable calculation and practical experiment." Instrumentation In a research aeroplane, this is primarily the recording and telemetry equipment which forms the payload; but before turning to this it is appropriate to add a word about the aircraft's own equipment. Security forbids publication of a cockpit picture, but the main panel is naturally related to the Service OR.946 scheme, with horizontal tape ASI/machmeter and roller-blind hori zon. All air-data is obtained from a centralized system, and, since the steel structure makes a magnetic compass impracticable, the only heading reference is a master reference gyro. The best way of outlining how flight data is recorded on board and simultaneously telemetered to a ground readout is to describe what happens when ever the 188 is in the air. This has been done by Dr W. J. Strang, and it is evident from his narrative that old-fashioned methods are unacceptably slow and expensive:— "Throughout its flight development programme the 188 will be under continuous VHF control from the ground. The aircraft has no naviga tional aid, and is tracked and positioned by a radar station. The ground control room maintains continuous contact with this station, and the aircraft position is logged on a map transparency beside the control console. "The aircraft is fitted with several hundred transducers of various types for the measurement of pressures, temperatures, altitude, accelera tion and other quantities. All this measuring equipment has had to be protected against the effects of kinetic heating. "Two independent telemetry systems of RAE design are provided in the aircraft. One is the permanent air-to-ground data link, and the second is used during flight flutter investigations. The signals from both telemetry receiving sets and all VHF radio conversation will be recorded on magnetic tape in the control room. Selected data on systems func tioning and other engineering quantites will be telemetered to the control
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