Patent GB-878355-A (GB)
Title: Improvements in lift computing systems for aircraft ground training apparatus
IPC: G09B9/20
Filed: 1959-01-01
Abstract: 878,355. Grounded aircraft trainers. CURTISS-WRIGHT CORPORATION. Jan. 1, 1959 [Jan. 13, 1958], No. 111/59. Class 4. Grounded aircraft training apparatus comprises means computing the simulated lift coefficient from simulated angle of attack and from a lift coefficient decrement simulating loss of lift due to stalling air flow, the decrement being computed as a function of simulated lift coefficient. The position of the elevators and wing flaps, the flight Mach number M, and an instructor's wing ice control setting are also used in the computation described. A trainee's elevator control 34 drives the wiper 36 of a poten tiometer 38 energised at its ends by oppositely phased A.C. reference Voltages ŒE and grounded at a centre tap. The signal ŒCL (#e) is fed over a summing resistor to the lift coefficient (CL) summing amplifier 20. A further input -CL (α, #fw) representing the effect on CL of angle of attack α and wing flaps position f#w, is derived in known manner, e.g. as in Specification 792,676, and forms a second input to amplifier 20. A term + # CL representing the lift loss due to stalling is derived as explained below, and fed to amplifier 20. The amplifier energizes the primary of a transformer 24, the secondary of which is grounded at a centre tap 28 and provides signals ŒCL, one of which provides a feed back signal for amplifier 20, and the other of which provides input on one line 60 to a summing amplifier of a conventional electro-mechanical motor-generator servo 44 driving ganged wipers 46, 48, 50 of potentiometers 52, 54 56. The servo 44 computes CL/ CL MAX  i.e. the ratio between the actual simulated CL and the maximum CL attainable under the same conditions of flight by varying the angle of attack. A further input to servo 44 is a signal Œ # CL (# e) fed over line 62 from wiper 36. The servo has the usual velocity feedback signal FDBK, and two further inputs + # 1CL (M, # fw) and + # 2CL (M, # fw) in the nature of answer signals, being derived from potentiometers 52 and 54, and modified by the operation of an M2 servo 80 and the trainee's wing flaps position control 82. Two modified answer signals are used in order to generate the relationship between CL MAX  (M<SP>2</SP>) and CL MAX  (0) by linear potentiometers. Potentiometer 52 has a voltage +E applied at a tap 67 corresponding to CL/CL MAX  = 0À85, the value at which buffeting due to imminent stall occurs. It is grounded at a tap 70 corresponding to CL = CL MAX , and at its upper end, to which the wiper 46 may be driven in certain circumstances discussed below, and corresponding to full stall when CL may be temporarily greater than CL MAX . The signal on wiper 46 energizes a potentiometer 64 driven by an M2 servo 80 energized by a conventional M servo 78 in conventional manner. The signal on wiper 94 is connected across resistor 114 and potentiometer 104, the wiper of the latter being driven by the trainee's wing flap control 82, and deriving a signal fed over line 118 to servo 44 as # 2CL. (M, # fw). Potentiometer 54 driven by servo 44 is grounded at its lower end and at a tap 63 corresponding to tap 67 on potentiometer 52, has a voltage +E applied at a tap 72 corresponding to tap 70 in pocentiometer 52, and is grounded through resistor 74 at its upper end. The signal on wiper 48 is applied to potentiometer 66 in series with resistor 100. Wiper 96 driven by the M2 servo 80 derives a signal applied to potentiometer 106 in series with resistor 116. Wiper 110 driven by the wing flap control 82 derives a signal fed over line 120 to servo 44 as # 1C2 (M, # fw). By this arrangement, the inputs to servo 44 sum to zero when its shaft position represents CL/CL MAX . The decrement in the lift coefficient + # CL is obtained from the wiper 50 of potentiometer 56 driven by the servo 44. The potentiometer is energized by a voltage +E, and has taps 122, 124 bridged by resistor 126, tap 122 representing CL/CL MAX  = 0À5, the value at which the rate of increase of CL with α begins to fall away and tap 124 representing CL = CL MAX . Tap 122 is connected to the wiper 128 of a potentiometer 130 energized by voltage +E and driven by the instructors wing ice dial 132. If there is no ice, tap 122 is at ground potential, and for CL/CL MAX  less than 0À5, + # CL is zero. When CL/CL MAX  increases above 0À5, wiper 50 derives a non-zero + # CL, which decreases the value of CL summed in amplifier 20. The response of the servo system 44 is such that when CL is increased due to alteration of α, #fw or #e, the output of transformer 20 rises correspondingly, and there is a time delay before the value of # CL is correspondingly altered by the response of the servo to the -CL input to servo 44 on line 60. CL thus attains a temporarily high value, perhaps greater than CL MAX , but is reduced when the servo re-balances. This is stated to simulate the time delay which occurs before stalled air flow sets in when stalling conditions are attained. Resistor 126 permits a linear contour to be used for potentiometer 56. If the instructor rotates dial 132 to simulate a certain extent of icing, wiper 128 desires a corresponding signal from potentiometer 130, and thus raises the + # CL potential on wiper 50, resulting in a smaller computed CL to simulate loss of lift due to icing. Servo 44 may operate cams, such as cam 134 which, when CL/CL MAX  equals 0À85 closes a contact and energizes a relay to complete circuits (not described) simulating buffeting effects. Other cams may operate relays to simulate stall warning or crash landing. Specification 748,557 also is referred to.