Patent GB-889025-A (GB)
Title: Improvements in and relating to ground aircraft trainers
IPC: G09B9/24
Filed: 1958-01-08
Abstract: 889,025. Grounded aircraft trainers. GENERAL PRECISION Inc. Jan. 8, 1958 [Jan. 8, 1957], No. 827/58. Class 4. A grounded aircraft trainer comprises a computer controlling a visual indicator simulating an attitude gyro, the computer comprising means for modifying simulated roll and pitch angle quantities in accordance with simulated accelerations of the aircraft, to produce quantities for application to the indicator to represent the functioning of an attitude gyro including processional errors. The apparatus described simulates the erroneous indications of a gyro vertical that may occur during linear accelerations and turns of an aircraft, due to departure of the apparant vertical standard in the aircraft, to which the gyro vertical is slaved by an erecting apparatus, from the true vertical and due to lack of static balance in the gyro, giving rise to inertial forces during accelerations, both these effects causing precession of the gyro. The particular gyro simulated is slaved to the standard so as to be pitched forward 2 degrees with respect thereto, this causing the gyro precession errors to be zero at a standard rate of turn, as explained in the specification with reference to Figs. 3A and 3B (not shown). The roll error # Ï and pitch error # #, are given by # Ï = Ïi - Ï, (1) where Ïi is the indicated roll angle and Ï is the true roll angle, and # # = #i  - # + 2‹, (2) where #i is the indicated pitch angle and # the true pitch angle, the latter being taken from the gyro pitched forward by 2‹ as noted above. # Ï and Ï # are computed from # # = # E sin # + # N cos # (3)   # Ï = # N sin # -# E cos # (4) where is the aircraft heading, # N is the angular displacement of the gyro spin axis from the vertical, measured about an East-West horizontal line, and # E is the angular displacement of the gyro spin axis from the vertical, measured about a North-South horizontal line. The last two quantities are computed from ## N = PÏ sin # + P# cos # (5) ## E=P# sin # -PÏ cos # (6)   where PÏ is the precession rate about the gyro roll axis and P# is the precession rate about the gyro pitch axis. These two quantities are computed from where # is the ball bank angle, axa is the OX axis acceleration, and f 1  is the characteristic function of the erecting mechanism, which in the example chosen produces a precession rate of 3/10 degrees per minute per degree of error between the gyro vertical and the apparent vertical standard, subject to a maximum of 3 degrees per minute, this relationship constituting f 1 . The apparent vertical standard is a mercury switch system. Provision is also made for simulating caging of the gyro, i.e. locking it in a datum position during violent manoeuvres, and instrument failure may be simulated. In Fig. 11A, constant positive and negative vol-. tages are applied to energize potentiometer R 1101  the slider of which is driven by the ball bank angle servo of a conventional flight computer, deriving a signal fed over contact a of relay K 1101  and summing resistor R 1102  to summing amplifier U 1101 Potentiometer R 1115  is energized by constant positive and negative voltages and earthed as shown, its slider being driven by a conventional Ï servo to derive a signal,- Ï fed to amplifier U 1101  over resistor R 1103 . Signals # N sin # and -# E COS # derived as explained below are applied to terminals 1105 and 1106, and fed over resistors R 1104  and R 1105  to amplifier U 1101 , the output of which, from equations (4) and (7) above, is thus PÏ. This signal is applied through contact b of relay K 1103  to one end of each of potentiometers R 1109 , R 1110 . The other end of each potentiometer is energized by a-PÏ signal obtained from a polarity reversal amplifier U 1102 . The sliders are driven by shafts whose angular positions represent sin # and cos #, e.g. obtained by non-linear gearing driven by a shaft whose angular position represents #. Alternatively, potentiometers R 1109  and R 1110  may have non-linear characteristics. The sliders derive signals PÏ sin # and - PÏ cos # at terminals 1112, 1113. Fig. 11B a signal axa from the flight computer is fed over normally closed contact c of relay K 1102  and summing resistor R1113 to summing amplifier U 1103 . A flight computer signal # is also available at normally open contact b of relay K 1102  when the relay is energized, for simulating caging as explained below. Signals # E sin # and # N cos # derived as explained below are applied over resistors R 1114  and R 1118  to amplifier U 1103.  A constant signal from potential divider R 1120 , R 1121  is applied over resistor R 1119  to amplifier U 1103 , and is scaled to represent a signal of magnitude 2 degrees. The output of amplifier U 1103  thus represents P#, by equations (3) and (8) above, and is applied over contact b of relay K 1104  to one end of each of potentiometers R 1125 , R 1126 . The other end of each potentiometer is energized by a -P# signal obtained from polarity reversal amplifier U 1104  The sliders are driven by sin # and cos # shafts, deriving signals P# sin # and P# cos # at terminals 1114, 1115. In Fig. 10A, signals P# sin # and P# cos # obtained in Figs. 11A and 11B are summed in resistor network B 102 , R 103 , R 104 , R 105  and fed to an electronic integrator I 101 , normally having a feedback through capacitor C 101  and contact a of relay K 101 . The integrator output is thus -#N, by equation (5) above, and energizes one end of each of potentiometers R 120 , R 121.  The other end of each potentiometer is energized by a + # N signal obtained from polarity reversal amplifier U 101.  The potentiometer sliders are driven by sin # and cos # shafts, deriving signals # N sin # and # N cos # at terminals 108, 109, these signals being used in Figs. 11A and 11B. In Fig. 10B, signals P# sin # and- P# cos # obtained in Figs. 11A and 11B are summed in resistor network R 110 , R 111 , R 112 , R 114  and fed to an electronic integrator I 102  normally having a feedback through capacitor C 102  and contact c of relay K 101 . The integrator output is thus - # E, by equation (6) above, and energizes one end of each of potentiometers R 122 , R 123 . The other end of each potentiometer is energized by a + # E signal obtained from polarity reversal amplifier U 102 . The sliders are driven by sin # and cos # shafts, deriving signals # E sin # and - # E cos  # at terminals 110, 111, these signals being used in Figs. 11A and 11B. Fig. 9 shows one way of solving equations (1) and (4), or (2) and (3), applied to the pitch system, involving equations (2) and (3). A signal representing # from the flight computer is applied over terminal 901, contact a of relay K 902,  and summing resistor R 901,  to summing amplifier U 901 . Signals # E sin # and # N cos # derived in Figs. 10A and 10B are fed respectively over contacts a and c of relay K 901,  contacts c and e of relay K 902,  and resistors R 902,  R 903,  to amplifier U 901.  A constant potential at terminal 904 energizes a potential divider R 908,  R 904,  deriving a signal scaled to represent 2 degrees and applied over contact e of relay K 901,  contact g of relay K 902,  and resistor R 905  to amplifier U 901.  The amplifier output is fed to a unit within line A, comprising a magnetic amplifier energizing a conventional biphase rotor generator servo with rate damping feed back, the shaft of which positions the slider of a constantly energized position feed back potentiometer R 906,  the signal from which is fed to amplifier U 901.  The system thus continuously solves #i =# -2‹ + # E sin # + # N cos # from equations (2) and (3) and the servo shaft position represents #i. This shaft drives two synchro transmitters S 901a  and S 902a,  and the trainee's indicator (e.g. a horizon bar) and the instructor's indicator are driven by synchro repeaters S 901b  and S 902 b to indicate #i. Figs. 8 and 7 show another way of solving equations (1) and (4) or (2) and (3), applied to the roll system, involving equations (1) and (4). In Fig. 8, signals # N sin # and - # E cos # are fed over resistors R 801 , R 802  and summed in amplifier U 801,  the output of which is fed to magnetic amplifier M-801 energizing a bi-phase motor SM-801. The shaft of this drives the slider of a constantly energized feed back potentiometer R 807 , the signal from which is fed over resistor R 803  to amplifier U 801.  The combination C 801,  R 804  introduces a damping rate feed back. The position of the shaft of motor SM- 801  thus represents # Ï, by equation (4). In Fig. 7, the constantly energized rotor of a synchro transmitter S 701  is positioned by the shaft of the flight computer Ï servo. The stator energizes the rotor coils of a synchro differential S 702,  the rotor being angularly positioned by the # Ï shaft of motor SM -801,  Fig. 8. The stator coils energize the stator of a synchro S 703  through contacts a and c of relay K 701 . The resultant signal in the rotor of synchro S 703  energizes an amplifier-motor-generator servo combination within line A, which positions the horizon bar of the trainee's indicator, and drives the rotor of synchro S 703.  This rotor is thereby driven until the signal developed in it is null, when the shaft position of the motor represents Ïi, by equation (1). Similarly, a synchro S 704  and an amplifiermotor-generator system within line B is energized by the stator of synchro S 702,  and operates the instructor's indicator to indicate #i. To simulate caging of the gyro, the trainee operates a knob on his instrument, which energizes relays K 701,  Fig. 7, K 902,  Fig. 9, K 101,  Figs. 10A and 10B, K 1101,  Fig. 11A, and K 1102,  Fig. 11B. Contacts a and c of relay K 701  are opened, and contacts b and d made. The stators of synchros S 703  and S 704  are thus energized by a constant signal from terminal 701 and potential dividers R 702,  R 703  and the trainee's and instructor's indicators are driven to indicate zero