Patent GB-778475-A (GB)
Title: Improvements in and relating to aircraft flight simulation apparatus
IPC: G09B9/18
Filed: 1955-06-10
Abstract: 778,475. Flight training apparatus. CURTISS-WRIGHT CORPORATION. June 10, 1955 [June 14, 1954], No. 16758/55. Class 4. A thrust computing system in flight training apparatus comprises an electrical compuring system for representing net thrust of an engine-propeller combination, a second electrical system for computing airspeed and having means for deriving control quantities as functions of airspeed, and a third electrical system for computing brake horsepower and having means capable of deriving control quantities as functions of brake horsepower said thrust computing system being responsive to said combined control quantities. For the purposes of the invention the equation for computing propeller thrust is expressed as T=([T/BHPo-K 1 ]¸f(h)¸K 1  BHP + [T/ BHP Àf (BHP@BHP) Àf(Sfw) Àf(lg) where (T/ BHPo-K 1 ) =fVt ; f(h)-f( Vt) ; t/BHP=f (Vt) ; T/BHPo represents the thrust to brake horsepower for the basic condition of the computation ; K 1  is a constant ; h represents altitude ; S(fw) represents wing flaps deflection; P is air density and f(lg) represents a function of landing gear position. The servo system 1 for computing true air speed (Vt) comprises a summing amplifier 2 fed with a plurality of a.c. singals from the main flight computing system, the output from the amplifier energizing the control coil 3 of a two-phase A.C. motor M, the other coil 4 of which is energized by a reference alternating voltage e 1 . The motor drives a two-phase feedback generator G having one coil 5 energized by a reference voltage e2 and a generating coil 6 connected to supply a feedback voltage to the amplifier. The motor M positions the slider contacts 9, 10 of the airspeed servo function potentiometers 11 and 12 for deriving voltages representing functions of airspeed. Card 11 is earthed at its mid portion and energized at one terminal by a voltage +E and at its other terminal by a function voltage from the altitude (h) servo card 14 through a lead 16 connected to the slider arm 15 which is adjusted by the altitude servo system 13. The voltage derived at slider 9, which represents the part (T/BHPo-K 1 ) Àf(h) of the equation is fed by lead 17 to amplifier 19 of the T/BHP system 18, the ouptut of which energizes the primary winding 20 of a transformer 21. An input voltage -E to amplifier 19 represents constant K 1  so that the voltage at terminal 22 of the secondary winding represents T /BHP corrected for altitude but not propeller shaft horsepower. Card 12, energized at one end by a voltage -E is designed for derivation of a function voltage at slider 10 representing T/BHP in the equation and this voltage is fed by conductor 23 to an amplifier 24 which energizes the primary winding 25 of a transformer 26 which produces at a secondary terminal 27 a function voltage corresponding to factor T /BHP. The system 30 for computing net thrust (T) comprises a summing amplifier 31 having an output connected to the primary winding 32 of a transformer 33, the secondary terminals 34, 35 of which produce voltages-T and + T for use as hereinafter described. The inputs to the amplifier are as follows. Terminal a is fed from terminal 27 of transformer 26 through lead 36 and a card 37 of the BHP servo system 38 ; terminal b is fed from terminal 22 of transformer 21 through lead 48 and card 49 of servo 38 ; terminal c is fed from card 51 which is adjusted by a simulated wing flap control member ; terminal d is either grounded or energized by a signal derived from a switch 55 representing an undercarriage control. Reverting to servo 38, a card 46 provices an answer voltage and the remaining inputs are a feedback voltage at b and a signal on lead 44 which is derived from a simulated engine " on-off " switch 39 through a card 40, the slider of which is adjusted by a simulated throttle and a card 42 controlled by a simulated speed or governor control. One method of using the signal from transformer 33 representing net thrust is shown in connection with the computation of airspeed. Since the effect of thrust on airspeed depends on the mass of the aeroplane, the signal from terminal 34 is first modified by a reciprocal function card 57 of a servo system 60 representing gross weight or mass of the simulated aircraft, the card being grounded at its other end through a resistance so that the derived voltage at slider 58 represents -T /M. This is fed by lead 59 to the input network of airspeed amplifier 2. The motor of servo 60 operates also an answer card 62 and the other input to the amplifier is derived from a card 63, the slider 64 of which is adjustable by the instruct- or's gross weight dial 65.