Patent GB-868075-A (GB)
Title: Improvements in or relating to apparatus for simulating the operation of reciprocating aircraft engines
IPC: G09B9/18
Filed: 1957-06-28
Abstract: 868,075. Grounded aircraft trainers. CURTISS-WRIGHT CORPORATION. June 28, 1957 [July 5, 1956], No. 20570/57. Class 4. Apparatus for simulating a condition of engine air flow (W e ) manifold air pressure (MAP) or engine power (BHP) of a reciprocating aircraft engine comprises means for producing an engine air density (# E ) quantity from input signals representing air temperature (CAT) and pressure (CLDP) in the simulated air intake system, and means responsive to # E  and to an engine speed (n) signal, to produce the W e , MAP, or BHP quantity. In the apparatus shown, CAT and CLDP signals represent the air temperature and pressure between the carburetter and a blower and are assumed to be available. The blower is operable in two conditions, high and low (pressure ratio). The equations used are W e  = (# E  + K 1 )K 2 f(n) + K 3 # + K 4  where # is the ambient air density, and K 1  ... K 4  are constants. Similar equations with different K 1  .. K 4  and different f(n) are used for MAP and BHP, and two sets of constants K 1  .. K 4  are available for each equation, one set being used for high blower, and the other for low blower. The CAT signal energizes an amplifier 7 and servomotor 8, which drives the wiper 91 of a potentiometer 9 grounded through resistor 10 at one end and energized at the other end by a CLDP signal from a transformer 14. The signal on wiper 9<SP>1</SP> represents # E  and is fed over summing resistor 30 to amplifier 17. A signal representing K 1  is fed to amplifier 17 over switch 26, line 27, and resistor 28, the signal being derived from a voltage source E 1  or E 2  depending on the position of switch 26, which is controlled by a relay 32 and a trainee pilot's switch 33, used to select high or low blower operation. Thus the output of amplifier 17 represents #  EK  = # E  + K 1 . To reproduce dynamic characteristics of # EK , a signal representing the rate of change of engine r.p.m., dn/dt, is fed over line 77<SP>1</SP> to amplifier 17. The # EK  signal is fed over transformer 19 and line 22 to energize six potentiometers A, B, C, A 1 , B 1 , and C 1  all driven by the n servo system 25, and some in series with fixed resistors. Potentiometers A, B, and C are selected by switch contacts 35, 36 and 37 of relay 32 during low blower operation to feed signals representing # EK  K 2 f(n) in the equations for W e , BHP, and MAP respectively, to lines 43, 48, and 53, respectively. Similarly, potentiometers A 1 , B 1 , and C 1  are selected by the relay during high blower operation. The signal, on line 43 is fed to the amplifier 45 of the W e  system 38. A further input representing K 4  is derived from switch 26 and line 84, and the remaining input representing K3 # is derived over line 56 from a potentiometer 4 driven by the servo system 1. A W e  answer signal is also supplied by potentiometer 81 driven by the W e  servomotor 80, and is available on line 87. The signal on line 48 is fed to the amplifier 50 of the BHP system 39. A further input representing K3 # is supplied from lines 56 and 58, and an input representing K 4  is applied from switch 26 and line 84. The computed value of BHP is modified in accordance with F/A, the fuel/air ratio. To this end, the output of amplifier 50 energizes a potentiometer 93 driven by the F/A servo 92, over transformer 101 switch 120 and line 103. The signal on the wiper of potentiometer 93 forms the feedback signal of amplifier 50. Switch 120 is closed by a relay 121 during simulated "engine on " conditions, by closure of switch 126 driven by the n system (n > 0), of switch 123 driven by the F/A system (F/A >0À045), and closure of the trainee's " ignition on " switch 122. The W e  signal on line 87 energizes a potentiometer 88 driven by the F/A system 90, to derive a fuel flow (FF) signal energizing a servometer 97 and indicator 99. The brake mean effective pressure is also computed as BMEP = BHP/n, the BHP signal on line 103 energizing an amplifier 107 of the BMEP servo system 108, the answer potentiometer 109 of which is energized by an n signal on line 110 from the n system 25. BMEP is shown on an indicator 112. The signal on line 53 is fed to the amplifier 55 of the MAP system 40. A further input representing K 4  is fed over switch 26, line 84 and line 113. In the case where power is recovered by turbine from the engine exhaust gases, and delivered to the crankshaft, the remaining input K 3  # requires modification. This is done by feeding the signal K 3  # from potentiometer 4, over line 60 to a potentiometer 61 driven by the simulated throttle control 62. The wiper signal on line 63 energizes a potentiometer 64 driven by the n system 25, and the signal on wiper 641 provides the remaining input to amplifier 55. MAP is shown on an indicator 117. Engine speed n is also shown on an indicator 79.