Patent GB-841517-A (GB)
Title: Improvements in or relating to flight training apparatus
Inventor: MURRAY THOMAS BRIAN
IPC: G09B9/20
Filed: 1955-05-20
Abstract: 841,517. Flight training apparatus. COMMUNICATIONS PATENTS Ltd. July 4, 1956 [May 20, 1955], No. 14620/55. Class 4. Flight training apparatus includes dummy flight controls, computing means controlled by the flight controls and adapted to compute the assumed airspeed of an aircraft, and means controlled by the computing means for giving an audible indication when the assumed airspeed rises above or falls below a safe band of airspeed. A flight control unit 1 applies electric signals to a computer 2 which includes a servomotor for adjustment of the wiper of a potentiometer 3 in accordance with the computed speed of the aircraft, the voltage from the wiper being an alternating potential the amplitude of which represents the aircraft airspeed. This voltage is applied to an input circuit of a summing amplifier 4, to further input circuits of which there are also applied inphase voltages derived from the wipers of potentiometers 5 and 6 which are adjusted to provide signals representing the normal safe approach speed and the overload safe approach speed respectively, the potentiometer to be used being selected by a switch 7 operated by a student pilot. Amplifier 4 forms part of an airspeed error servo which includes a two-phase motor 8 driving through gearbox 11 the wiper of an answer potentiometer 12 which is centre tapped and supplied at its ends with alternating potentials of equal amplitude and opposite phase whereby the wiper is positioned in accordance with the airspeed error. A further potentiometer 13 driven by motor 8 consists of an earthed contact section 14 which connects two resistive sections 15 and 16 connected to alternating potentials of the same amplitude and phase. The wiper of this potentiometer is connected to an amplifier 17 of an interrupter servo unit which includes a two-phase motor 18, generator 19, gearbox 20 and an interrupter cam 21. Winding 23 of generator 19 is connected to the input circuit of amplifier 17 to provide a rate feed-back signal which is in phase opposition from the signal from potentiometer 13 whereby the speed of motor 18 is proportional to the assumed error in the speed of the aircraft. A switching device consisting of three insulated contact sections 25, 26, 27 and a wiper connected to a source of D.C. voltage and driven by motor 8 is connected through the windings of relays RLA/1, RLB/2 and RLC /1. When the wiper is in contact with section 26, which represents the safe airspeed band, contacts RLB-1 and RLB-2 are closed thereby connecting a high-frequency oscillator 28 through capacitor 29 to the grid of a triode 30 which applies a continuous signal of high audio frequency through a capacitor 32 to the pilot's telephones 33. If the computed airspeed is higher than the safe band of airspeed the wiper of potentiometer 13 is moved on to contact section 15, the switching device rests on contact 25, relay RLA/1 is energised and oscillator 28 is connected to the grid of triode 30. The alternating voltage from section 15 of potentiometer 13, which is proportional in amplitude to the airspeed error, is applied to amplifier 17 and the interrupter servo rotates cam 21 and periodically closes contacts 24 which are in parallel with relay contacts RLB-2. This relieves the bias on triode 30 and the pilot therefore hears a highfrequency audio note interrupted at a frequency which increases with increase of the assumed airspeed error. If the computed airspeed is lower than the safe band the contact of potentiometer 13 is placed on section 16, the switching device rests on contact 27 and relay RLC/1 is energised to close contacts RLC-1 and connect a lowerfrequency audio oscillator 34 to the grid of triode 30. The cam 21 therefore rotates and the bias on triode 30 is periodically relieved so that the pilot hears a low-frequency audio note interrupted at a frequency which increases with increase of the assumed airspeed error. A switch 35 is provided to enable the pilot to remove the voltage from the anode of the triode 30 and short-circuit the output of amplifier 17 when the audible indication of airspeed is not required.