Patent GB-850042-A (GB)
Title: Apparatus for loading a simulated aircraft rudder pedal control in ground flight training apparatus
IPC: G09B9/28
Filed: 1958-07-04
Abstract: 850,042. Grounded aircraft trainers. CURTISS-WRIGHT CORPORATION. July 4, 1958 [July 17, 1957], No. 21548/58. Class 4. Apparatus for loading a control of a ground flight trainer comprises means for producing a signal representing the aerodynamic loading force on the control, means for producing a signal representing the effect of a preloaded spring on the control, and means for producing a force on the control in accordance with a combination of the two signals. In the apparatus described, the effect of aerodynamic and centering spring forces on the rudder and rudder trim are simulated on the trainer rudder pedals, together with the effect of a simulated preloaded spring providing a threshold force on the pedals, which force must be overcome before the pedals can be deflected more than a very small amount. In the Figure, aerodynamic rudder spring force and trim signals are summed in an amplifier 3 to provide an output F<SP>1</SP>p. The rudder pedals 1 (one shown) are connected to the wipers 23, 25 of linear potentiometers 19, 21. The former is energized by Œ Vi<SP>2</SP> (i.a.s. squared) signals of opposite phase derived from an a.c. operated flight computer so that its slider derives a potential representing the aerodynamic centering force due to rudder deflection, the signal being fed over line 67 to amplifier 3. Potentiometer 21 is energized by constant signals Œ V, and its slider is connected to a grounded resistor 70 and over line 69 to amplifier 3. This signal simulates the effect of a rudder centering spring, resistor 70 being included to simulate that the relationship between rudder deflection and rudder pedal deflection is not linear. The trainee can position a rudder trim dial 64 connected to the wiper of a constantly energized potentiometer 63, feeding a pedal force trim signal over line 59 to amplifier 3. To simulate the effect of side slip, a potentiometer 47 in series with resistors .49, 51, is energized by Œ Vi<SP>2</SP> potentials, and its slider is driven by a side slip angle servo 55, the resulting signal being fed to amplifier 3 over line 44. The output of amplifier 3 provides a feed back signal on line 43, and is fed over lines 39 and 41 to summing amplifier 5. To simulate the effect of the preloaded spring on the rudder pedals, the output -F<SP>1</SP>p of amplifier 3 is fed over lines 39 and 71 to energize potentiometer 73, the slider of which is driven by a Vi<SP>2</SP> servo 77. The resulting signal is fed through amplifier 79 to a limiter 7 comprising opposed diodes 85, 87 in parallel with a phase correcting capacitor 95. The limited signal is fed through a low pass filter 9 with matching input and output resistors 89 and 93, to restore the sine wave form of the limited signal, which is then fed over line 91 to amplifier 3. The two inputs on lines 41 and 91 give a graph of rudder pedal force against pedal deflection from the trimmed position, comprising a very steep initial portion, simulating the very small deflection obtained until the threshold force of the preloaded spring is overcome. For higher pedal deflections, the limiter 7 comes into operation, and the signal on line 91 is constant, so that the slope of the graph decreases to a value representing normal increase in pedal force with pedal deflection. Amplifier 5 energizes a split phase motor generator system 13, 17, provided a damping velocity feed back signal from generator winding 37. The motor 13 acts as a torque motor, being connected to the rudder pedals 1 and providing the centering force required. To simulate the shaking effect occurring if a maximum rudder deflection e.g. 15 degrees, is exceeded in flight, an altitude servo 97 operates a cam 101 to close a switch contact 107 when the simulated aircraft is off the ground. A D.C. operated relay 109 is thus energized to close contact 113 connected to d.c. voltage source. Deflection of the rudder pedals by 17À9 degrees either way, corresponding to a rudder deflection of 15 degrees either way, is arranged to close one or other of contacts 123, 125, to energize a relay 133 through contact 113. The resulting closure of relay contact 139<SP>1</SP> feeds a 59 c.p.s. input signal from an oscillator 141 to amplifier 5. Since the line frequency of the amplifier is 60 c.p.s., this shakes the rudder pedals at a beat frequency of one c.p.s. Relay contact 137<SP>1</SP> is also closed, to provide a 55 c.p.s. input signal from oscillator 143 to amplifier 3, and this modulates the one c.p.s. shake with a five c.p.s. beat frequency, which is stated to produce a realistic simulation of the pedal shake which actually occurs. Reference has been directed by the Comptroller to Specifications 754,354 and 755,700.