Patent GB-689839-A (GB)
Title: Improvements in or relating to plants for supplying air to an aircraft cabin
Inventor: MASSEY BERNARD SIDNEY
IPC: B64D13/08
Filed: 1949-12-23
Abstract: 689,839. Ventilating aircraft cabins. BRISTOL AEROPLANE CO., Ltd. Dec. 15, 1950 [Dec. 23, 1949; Dec. 4, 1950], Nos. 32984/49 and 29671/50. Class 137 [Also in Group XXIX]. In an aircraft-cabin air-supply plant having a heat-exchange heater between the air intake and the compressor, or first compressor, for supplying air to the cabin, the heating medium for the heat-exchanger is heated otheriwse than by energy derived from the air stream to the cabin, and means are provided to control the input of heat to the air stream from the heatexchanger. As shown, the apparatus is housed in a wing, air being supplied from a ram inlet 14 through a heat-exchanger heater 16 to a compressor 6 driven from a main power unit 7 through a variable speed gear box 8. Control of the air flow and the gear box is effected as described in Specification 686,547. The air is delivered to the cabin space 1 through a heat-exchange cooler 23 using rammed air admitted at 14<SP>1</SP> as the refrigerant, and through a silencer 27. Heating is effected by air from a cooling-jacket of the power unit 7, the supply duct 17 being controlled by a valve 21. The cooler is controlled by valves 24, and both valves 21, 24 are operated by servomotors 34, 39 responsive to movements of a cam shaft 30 which is itself responsive to a thermostat 28 in the cabin space. The thermostat 28 controls the rotation of a reversible motor 29 which drives the cam shaft 30 through reduction gearing 31. If the thermostat signals for a reduction in temperature, the shaft 30 is rotated in one direction, the cam 32 thereby swinging a lever 37 having a rack and pinion connection with the control valve 35 of the servomotor 34, the' power output arm 65 of which is connected to the valves 24. Another servomotor 39 is made operative by the opposite rotation of the shaft 30, the cam 33 swinging a lever 42 having a rack and pinion connection with the valve 40 of the servomotor, the power output arm 82 being connected to the valve 21. A pump 45 feeds the servomotors each of which comprises diametrically disposed vanes on the power output shaft, the pressure fluid being admitted to one or the sired rotation in the desired direction. Pressure fluid is supplied to an annular space 56 of the servomotor 34 by branches 46, 55. The valve 35 is rotatable in the shaft 63 which carries the vanes 61, and when the servomotor is at rest, the lands on the valve 35 close the ports 73 in the shaft. When the valve 35 is turned by the cam 32, the ports 73 are uncovered so that one pair of vane chambers are connected to pressure by the grooves 68 whilst the other pair of chambers are exhausted through passages 70 leading to a central discharge 71 in the shaft. The vane shaft 63 turns until the lands of the displaced valve 35 again close the parts. The liquid is discharged into the bottom of a casing enclosing the servomotors and serving as a pump suction sump. The servomotor 39 has a similar arrangement of vane shaft following-up a control valve, but differs from the servomotor 34 by the provision of a shuttlevalve 83 which enables anti-icing i.e. the avoidance of ice formation on the matrix of the heater 16, to be rapidly effected. The shuttle valve 83 is prevented from turning in the valve 40 by a pin and slot 85 and is moved to the left by pressure fluid supplied from the pipe 53, when anti-icing is not required, and to the right by a spring 84 when it is required. The pipe 53 is connected either to a pressure supply 48 or to an exhaust pipe 54, according to the position of a solenoid-actuated valve 52. When the switch 51 is opened, the pipe 53 is connected to exhaust. When, as shown in Fig. 2, anti-icing is not in use, the pressure fluid is supplied by a pipe 58 to the centre of the valve 83 and from thence through ports 93, 97, 99 in the shuttle 83, valve 40 and vane shaft 80 respectively to two diametrically opposite vane chambers, the other two chambers being exhausted through passages 95, 96. When the valve 83 is moved to the right, the ports 93 communicate with ports in the valve 40 which are displaced relatively to the ports 97 by an angle equal to the full angle of movement of the vanes 78. If, therefore, the switch 51 is opened when the cam shaft 30 is in the neutral position with the valves 21, 24 closed, the vanes 78 swing though their full travel to give maximum heating conditions. The effect of the opening of the switch 51 is thus to obtain immediately maximum heat, followed as the thermostat signals for a reduction in temperature by an overlapping action of heating and cooling means, the servomotors operating under thermostat control until a new state of balance is established. The heater control is responsive, during anti-icing operation, to smaller movements of the cam shaft than is the case during normal operation. It is uneconomical to overheat air to be compressed subsequently, so that the anti-icing provision is used only when ice formation on the matrix of the heater 16 is to be prevented. To this end, the valve 51 could be operated automatically by a barometric capsule, or where the variable gear 8 is controlled by an altitude responsive device, the valve 51 could be linked to the gear changing mechanism. It is possible to obtain the desired overlap by operating on the cooler control valve, or both servomotors may be provided with shuttle valves.