Patent GB-957513-A (GB)
Title: Improvements in aircraft training aids
IPC: G09B9/16
Filed: 1960-06-02
Abstract: 957,513. Grounded aircraft trainers. GENERAL PRECISION Inc. June 2, 1960 [June 2, 1959], No. 19640/60. Heading B7W. A simulated aircraft cabin pressurization system of the variable position outflow valve type comprises control means for setting in a signal representative of a selected cabin altitude (i.e. the altitude represented by the pressure within the cabin) that it is desired to maintain during a simulated flight, means for computing therefrom a variable signal representing the outflow valve position necessary to maintain that selected cabin altitude under the simulated flight conditions prevailing, means for deriving a signal representative of the actual instantaneous position of a simulated outflow valve, and servo means operable to change the actual simulated valve position to reduce the difference or error between it and the computed valve position to zero. In a system of the type being simulated, with a given quantity of air being delivered by the compressors there is only one position of an outflow valve, at some aircraft altitude h, to maintain a given pre-set cabin altitude hcs, from which valves a computed valve position signal Vc is derived. When the signal Vc is equal to a signal VA representing actual valve position, the actual cabin altitude hc is at the pre-set altitude hcs and the valve is stabilized. The Vc signal is developed by two voltage divider networks consisting of resistors 10, 11, 12, 13 and 101, 11<SP>1</SP>, 12<SP>1</SP> and 13<SP>1</SP> which connect respectively with potentiometers 15 and 15<SP>1</SP>. The resistors are bridged by switches 29, each representing when closed, normal delivery of air by an engine compressor, and the wipers 20a, 20b, of the potentiometers are operated by a servo 23 (Fig. 10) having an output representing altitude h which is selected in the simulator by an instructor-operated altimeter 25. The tappings at 20a and 20b are applied through amplifiers 33, 33<SP>1</SP> to the opposite ends of a potentiometer 37 the output from which at 39 represents the Vc signal. The arm 39 is coupled, as at X, with the arm 43 of a further potentiometer 42 representing a crew-operated cabin altitude setting control. The VA signal is developed by feeding the Vc. signal from wiper 39 (Fig. 1A) to amplifier 61 (Fig. 1B) to operate servo 63, 64, 66 which drives wiper 51 of potentiometer 52. In order to vary the position of the valve i.e. change the VA signal, at a predetermined rate a rate signal is applied to amplifier 61 in addition to the Vc and VA signals. The rate signal is derived by feeding the VA signal over line 45 to amplifier 48 (Fig. 1C) and thence to amplifier 53 and cabin altitude servo 55, 57, 59. Amplifier 53 receives also a VA signal from a potentiometer 75 (Fig. 1C) linked to servomotor 64. The opposite polarities of the Vc and VA signals determine the rate at which servomotor 57 runs, to drive a slider 82 of potentiometer 84 (Fig. 1B) which derives a signal representative of the actual cabin altitude hc. This is applied to a rate amplifier 85 together with a signal from arm 43 of potentiometer 42 and the output (limited by diodes 100 and 101) being fed through switch 109 and resistor 110 to amplifier 61. Switch 109, normally mounted on landing gear for providing pressurization on the ground, in the simulator is under the control of an instructor and/or crew member. A rate of climb indicator 112, operated by a servomotor 111 (Fig. 10) is provided. To ensure that the cabin altitude hc follows the aircraft altitude so long as the selected cabin altitude is greater than the actual aircraft altitude, a signal is supplied to rate amplifier 85 which is representative of aircraft altitude h in place of the signal representing desired cabin altitude. This is achieved by a comparison in amplifier 121 of an h signal from a potentiometer 122 (Fig. 1A), whose arm 123 is driven by h servo 23 (Fig. 1D), and a signal, from crew setting potentiometer 42 (Fig. 1A). Provision is made for simulating cabin decompression and for detecting when cabin altitude is greater than the aircraft altitude and for limiting the operation of the system so that this condition is not maintained.