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Aviation History
1964
1964 - 0448.PDF
fiiCHT International, 20 February 1964 A|R COMMERCE . Progress with the Concord ... 200°C than at 120°C although, of course, its hot strength is lower. Since the most severe stress reversals occur in rough air encountered below cruise altitude and creep is important only in supersonic flight, these conditions do not coincide but interspersion of creep and fatigue may affect fatigue life. Special attention is being devoted to the selection and development of heat-resistant trans- parencies and heat and erosion resistant fibre-glass materials for radomes. A complete airframe is to be fatigue-tested, with repre- sentative heat-soak simulation, in a new test facility at the RAE Farnborough. Fuel Management The fuel system management procedure has been designed both to assist supersonic stability and to reduce heating of bulk fuel. At Mach 2.2, it is possible both to use stan- dard aviation kerosine and to dispense with the need to insulate the fuel tanks from the skin. High altitude boiling of the fuel is prevented by pressurizing the tanks at altitudes above 44,000ft. The fuel tankage occupies most of the interior of the wing and comprises separate feed tanks for each engine and main tanks in each side of the wing, also forward and aft trimming tanks to keep control drag to a minimum in both subsonic and supersonic flight. The excess fuel tankage required is less than the cruising fuel penalty exacted if fuel trimming is not employed. During accelera- tion to supersonic speed, fuel from the forward trim tanks, where it heats up most quickly, is transferred to the main tanks and the rear trim tank where the rate of heating is much less. This transfer operation shifts the centre of gravity aft to the optimum position for supersonic cruise. Throughout cruise, fuel is drawn sequentially from the main tanks into the collector tanks, which have a substan- tial fuel mass, and, when one main tank is nearly empty, the next main tank in the sequence begins to provide part of the fuel supply. In this way the temperature of the fuel leaving the collector tanks is kept down to about 80°C. Since the maximum permissible engine fuel pump entry temperature is 150°C (with a transient rise to 165°C at the beginning of transonic deceleration) it is practicable to use fuel in the engine feed lines as a heat sink for the air condi- tioning, electrical, hydraulic and mechanical systems, which gen- erate a total of 42,000 CHU per minute in cruising flight. By in- corporating heat exchangers in the fuel feed lines about 17,500 CHU per minute can be rejected not into the bulk fuel, but direct to the engines without risk of pump cavitation or malfunctioning of engine burner nozzles. During the deceleration to subsonic speed, the fuel in the rear trim tank is all transferred into the main tanks to shift the centre of gravity forward again and provide fuel in the main tanks for the remaining subsonic phase of the flight. The fuel transfer system is designed to avoid any possibility of the aircraft remaining in an unacceptable loading condition after deceleration to subsonic speeds. It is a significant feature of the Concord's fuel system that with- out adding insulating material to the tank walls the temperatures of the fuel in the tanks and throughout the system are maintained low enough to permit the use of conventional kerosine without running into problems of thermal degradation or high tank pres- sures, nor do the structure temperatures create any risk of spon- taneous ignition. 273 IOC. 21-5 SUBSONIC 4*0 "H/ TIME M MiNUTES Fig 5 Comparative climb performance of the Concord at different speeds 1,000 2.000 3.000 4.000 5,000 6.000 SECTOR DISTANCE N.M. Fig 4 Concord payload-range diagram, showing the in fluence of different reserve fuel policies Fresh air is supplied to the cabin by tapping the engine com- pressors. To reduce demands on this source, cabin air is recircu- lated and mixed with incoming fresh air to provide ventilation flows necessary for even air and temperature distribution. The cabin is insulated from the hot skin by circulating cabin discharge air around the walls inside conduits within the trim. The tapped air at 580°C is cooled in ram air heat exchangers to below 200°C. Further refrigeration is achieved by using fuel as the heat sink in conjunction with conventional "bootstrap" open air- cycle refrigerators. Outlet temperatures below 0°C can be achieved, which when mixed with the recirculated air gives the necessary inlet temperatures of the ventilating supply. Miscellaneous cooling and ventilation of electronic and electrical equipment is provided by air from the passenger cabin on its way to discharge. Flying Controls The dual pilots' flying controls are conventional in pattern, with electrical trim for pitch and manual trim for roll' and yaw. Compared with established transport aircraft, the slender delta has a high inertia in pitch and yaw but low inertia in roll, so careful attention has been paid to pitch response and elevator- rudder co-ordination in cross-wind landings. The auto-stabilizer is designed to make efficient use of the ample control power avail- able and, with initiation of flare held to not more than 35ft a con- servative touch-down speed can be obtained; auto-stabilization also improves lateral stability in rough air. The control surfaces, comprising six elevons and a two-piece rudder, are normally actuated by hydraulic jacks controlled by a fully duplicated elec- trical signalling system, with a separate stand-by mechanical sys- tem with hydraulic servo assistance for use in the event of total electrical failure. Artificial feel is derived from the air data com- puter and restriction of combined pitch and roll demands is pro- vided mechanically. Electrical engine controls are operated by conventional throttle levers on the pilots' central console, with a duplicate set at the engineer's panel; a fixed throttle opening rate is available within limits imposed by an acceleration limiter and a jet pipe temperature limiter. With these provisions, low-speed control of the Concord presents the pilot with no new problems. More than 18 months' experience of slender delta control characteristics has already been accumu- lated on the HP. 115 low speed aircraft and by means of a flight simulator using the English Electric LACE computer system. The latter is being progressively modified and elaborated by reference to a team of BAC, Sud, RAE and ARB pilots as design proceeds and is proving itself as a means of both evaluation and training. Soon the BAC 221 will add to the actual flight knowledge. High-altitude Atmospheric Hazards Potential hazards to high altitude flight are presented by nuclear radiations arising from: cosmic rays, either galactic or solar; and radioactive debris in the atmosphere. Galactic cosmic radiation effects are negligible, but solar proton flares can give rise to much higher activity, which may have to be avoided. Fortunately, solar flares producing high levels of intensity at or below 60,000ft are quite rare—once every few years. The effects of even the highest energy solar flares can be avoided by restricting flights to below 50,000ft and/or below 50° magnetic latitude during the 24hr or so during which the solar flare effects are important. Warning of this could be given by ground monitoring stations. The period would certainly coincide with a severe radiocommunication fade-out which might restrict subsonic Continued on page 297; more Air Commerce news overleaf 200 ~J00 4uO DISTANCE-NAUTICAL MSLES
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