Patent GB-875703-A (GB)
Title: Aircraft stabilizer trim force simulation
IPC: G09B9/28
Filed: 1959-04-10
Abstract: 875,703. Grounded aircraft trainers. ACF INDUSTRIES Inc. April 10, 1959, No. 12155/59. Class 4. A grounded aircraft trainer simulating the forces on a stabilizer trim wheel due to aerodynamic loading on the stabilizer and control cable stretching, comprises a differential having input members connected to receive respectively the control moment applied by the trainee, and moments applied by a braking means and a driving means, and having an output member biased to a neutral position and connected to means deriving a first voltage proportional to the displacement of the output member from its neutral position, a fixed voltage source connected to the driving means only when it is greater than the first voltage, and means to connect a voltage from a flight parameter computer to the brake means only when it is greater than the first voltage. In the Figure, a dummy stabilizer trim wheel 50 is connected to one input shaft 52 of a mechanical differential 54. The other input shaft 56 is connected to an electrically actuated brake 60, and an electrically actuated motor 58. The output shaft 66 is urged to a datum position by spring means 62, 64 which also contain rotational limit stops, and drives the wiper 68 of a potentiometer 70 grounded at its mid point and connected at its two ends to oppositely phased equal A.C. voltages. A comparator 78 has one input voltage from wiper 68 over lines 74, 76, and another input voltage over line 81 from a trainee's simulated power trim switch 84 which has three positions, up, down, and off, in which line 81 is at a positive reference phase potential, a negative reference phase potential, and ground potential respectively. Comparator 78 has an output on line 114 which is the difference between the signal on line 81 and that on line 76 if the former is greater, and is otherwise zero. A suitable construction of comparator is described. The signal on line 114 is fed to a demodulator 88 energizing motor 58. Similarly, a comparator 80 receives one input signal on line 76, and another, representing stabilizer aerodynamic loading, on line 24 from a conventional flight computer, and demodulator 82 energizing brake 60 has an input signal representing the difference between the loading signal on line 24 and that on line 76, if the former is the greater and otherwise a zero input. Brake 60 is also constantly energized from a D.C. source over resistor 94, to simulate frictional forces. Shaft 56 drives the wiper 100 of a constantly energized potentiometer 96, to derive a signal representing stabilizer trim displacement, fed to the flight parameter computer. If, initially, the computed aerodynamic load on the stabilizer is zero, and the trainee puts the power trim switch 84 in the off position, the signals on lines 24 and 81 are zero. When the trainee turns trim wheel 50, brake 60 prevents rotation of shaft 56, so shaft 66 turns, stressing the spring means 62, 64, until they offer such resistance that further force exerted by the trainee overcomes the friction of brake 60, and shaft 56 rotates. This simulates stretching of the control cable runs, and ultimate trimming of the stabilizer when frictional forces are overcome. The potentiometer wiper 100 then derives a signal for use in the flight computer. Any aerodynamic stabilizer loading signal computed is fed to comparator 80, and if the signal is greater than that representing the force applied by the trainee, derived by wiper 68, the comparator output increases the energization of brake 60, simulating the fact that the trainee must exert a greater force to move the stabilizer. If the trainee selects power trim by switch 84, an energizing voltage is fed to motor 58 to rotate shaft 56, simulating power trimming, unless the input on line 76 to comparator 78 exceeds that on line 81, simulating that by exerting sufficient force on wheel 50, the trainee can manually over-ride the power trim forces. Specification 869,265 is referred to.