Patent GB-773105-A (GB)
Title: Improvements in and relating to apparatus for simulating engine operation in an aircraft trainer
IPC: G09B9/18
Filed: 1955-06-09
Abstract: 773,105. Aircrew training apparatus. CURTISS-WRIGHT CORPORATION. June 9, 1955 [June 14, 1954], No. 16637/55. Class 4. Apparatus for simulating engine operation in an aircraft trainer according to simulated flight and engine controls, comprises means representing a mixture control for deriving a control quantity, means representing mass airflow for deriving another control quantity, and a fuel-air ratio computing system responsive to said control quantities for deriving control quantities representing functions of fuel-air ratio. Indicated horsepower. Fig. 1 shows computing circuitry for determining indicated horsepower (I.H.P.) in terms of functions of altitude (h) engine R.P.M. (represented as the engine governor setting), manifold air pressure (M.A.P.), fuel-air ratio (F/A), and carburetter air temperature (C.A.T.). Tne form of the equation for I.H.P. is: I.H.P. =K.f(h).f (R.P.M.).#(M.A.P.)+I.H.P..#(C.A.T.)-I.H.P..# (F/A) where K and f respectively represent a constant and a function. In Fig. 1, the servo systems for h, F/A and M.A.P. are conventional. Summing amplifier 5 is energized by input voltages representing components of vertical air speed and it controls motor M so as to represent integrated vertical air speed i.e. altitude. Motor M positions contact 9 of potentiometer 10 to derive a voltage representative of altitude, the potentiometer being energized at its mid-portion by voltage -E and the motor may control a relay 11 which is energized only when the altitude is zero. The voltage at 9 is fed to potentiometer 15, the slider 16 being adjusted according to the setting of a R.P.M. control 17. The derived voltage at 16 representing functions of h and R.P.M. is fed to the potentiometer 18 of the M.A.P. servo system 3 and the derived voltage at 19 representing a combined factor (h, R.P.M. and M.A.P.) in the equation is fed to terminal d of I.H.P. summing amplifier 4. The factor in the equation which is a combined function of I.H.P. and F/A is produced by combining the output of amplifier 4 and function potentiometers 20 or 21 of the F/A servo 22. The output from 4 energizes primary winding 23 of transformer 24, the secondary producing at terminals 25 and 26 voltages of opposite instantaneous polarity representing I.H.P. The voltage at 25 is fed to the slider contacts 29 and 30 of potentiometers 21 and 20 so that the derived voltages on 31 and 32 vary on accordance with the positioning of the F/A servo and the characteristics of cards 21 and 20. These voltages are fed to terminal a on amplifier 4 through a relay operated switch 37 which is set to simulate a spark advance of either 30 degrees of 20 degrees. A further relay operated switch 36, when in the 20 degrees spark advance position, connects terminal 25 to a simulated ignition check system operated by an instructor, wherein with arm 49 on contact 50 no signal is transmitted but with the arm on either of contacts 51 or 52 a signal is transmitted to terminal b of amplifier 4 representing loss of power when either of two magnetos is being checked. A signal voltage representing loss of power due to "back-fire" may be fed to terminal c of amplifier 4 when a switch 46 is closed by an instructor. This operates a relay controlled switch 46‹ which closes on terminal a and connects lead 47 to lead 48 and terminal 25. A voltage representing a function of C.A.T. is fed to terminal e of amplifier 4 and it is derived from a potentiometer 40 energized from terminals 25 and 26 of transformer 24 the slider 42 being positioned by a C.A.T. control element 43. Brake horse-power. The resulting I.H.P. output voltage at terminal 25 is fed to terminal d of a B.H.P. servo amplifier 55, Fig. 2, as a positive voltage, the remaining input, which are negative, being a feed back voltage E f b at terminal a, derived from amplifier 55 ; a B.H.P. signal at terminal b from terminal 79 of B.H.P. transformer 78 ; a C.H.T. signal at terminal c from servo 73 representing cylinder head temperature ; a signal at terminal e from potentiometer 61 representing power loss due to an engine cooling fan and a signal at terminal f from potentiometer 58 representing power loss due to friction and blower. The sliders 57 and 60 of potentiometers 58 and 61 are adjusted by R.P.M. control 17 and potentiometer 58 is energized by a reference voltage -E. The cooling fan signal at terminal e is a function of R.P.M. and outside air temperature O.A.P. and card 61 is energized from O.A.P. transformer 63 through either a voltage divider 68 or altitude relay switch 70, Fig. 1 also, depending on the position of an engineer's " fan " switch 64 which sets high or low speed fan speeds and an instructor controlled " fanfail " switch which when set on contact a de-energizes card 61. The C.H.T. card 74 has an earthed centre tap to simulate high and low cylinder head temperatures. The output at terminal 79 of B.H.P. transformer 78 is fed to input terminal d of the amplifier of torque servo system 90, Fig. 3, which provides a visual indication of engine torque on indicator 90a. Torque indicating system. The equation solved by servo 90 to determine torque is R.P.M. Q=K. B.H.P. where Q is torque and K. B.H.P. is the signal fed to d from the B.H.P. system. A signal representing the other side of the equation is fed to terminal e and it is derived from an R.P.M. potentiometer 92, adjusted by R.P.M. control 17, the slider 93 of which supplies a voltage through lead 94 and a " windmilling " relay 96 to energize a torque servo potentiometer 97. The resulting voltage picked off at 98 is fed to terminal e of servo 90. When the engine speed is less than idling speed, relay 96 is energized and card 97 is supplied with a contant voltage E derived from terminal a of relay 96 whereby the voltage signal at terminal e of servo 90 is representative of torque only. An R.P.M. signal is fed from slider 92 of R.P.M. potentiometer 93 to terminal b of servo 90 to ensure that the lower position of the torque servo corresponds to a positive value of Q by shifting upwardly the zero position of answer card 97. A feedback voltage is fed to terminal a of servo 90 and a " backfire " voltage to terminal c. This is under the control of the instructor who can close a switch to energize relay 45 to move switch 99 from earthed terminal b to terminal a which supplies a+E signal voltage to servo 90 tending to run the motor toward zero. Means are provided to simulate detonation, which results in a critical rise in cylinder head temperature, as the result of high power operation with incorrect fuel-air mixtures. A thyratron 100 is adapted to " fire " under predetermined conditions representing detonation to energize a relay 101 which controls input signals for a C.H.T. servo system to be described. An anti-detonation injection (A.D.I.) switch 102, when on earthed terminal a simulates a water injection position with no detonation ; cousequently thyratron 100 cannot fire. When switch 102 is on terminal b a positive voltage E is fed to card 103 of the torque servo system and the voltage derived at 104 is led to terminal a of the thyratron to represent actual torque. A positive voltage representing detonation torque is obtained from the fuel-air servo 22 and supplied to terminal b of the thyratron from either of two cards 106, 107, controlled by the fuel-air servo 22, and representing 30‹ and 20‹ spark advance respectively, which may be selected by switches controlled by spark advance relay 35. Fuel-air system. The fuel-air computing system is shown in greater detail in Fig. 4, in association with a fuel-flow computing and indicating system. The input voltages to F/A amplifier 115 are : (a) a feed-back voltage from the amplifier ; (b) a fuel-air signal representing fuel-priming for engine starting wherein a signal is transmitted from an engineer's prime switch 130 through a cam operated switch 132 operated by a fuel pressure control 134, lead 135 and weight of engine air potentiometer 136 ; (c) a signal to represent carburetter metering which originates at the card 126, adjusted by mixture control 118, and is fed through card 128 adjusted by weight of engine air servo system 121 ; (d) a signal from the anti-detonation injection switch 102, which when on contact a simulates water injection ; (e) a basic fuel/air signal voltage derived from card 119, adjusted by mixture control 118, and fed through card 122 of weight of engine airflow servo 121, and through switch 124 of windmilling relay 96 ; (f) a signal'representing a decrease in fuel/air ratio for a decrease in normal fuel pressure derived from a reciprocal function card 140 adjusted by fuel pressure control 134, and fuel/ air servo card 116. Fuel flow system. The fuel flow system is shown also in Fig. 4. A main signal is derived at terminal 26 of I.H.P. amplifier 4, Fig. 1, and fed to a card 149 controlled by M.A.P. amplifier 3, Fig. 1. The derived voltage at slider 150 is fed to F/A card 117 from which a derived voltage is fed to terminal b of fuel-flow amplifier 146. A feed-back signal is supplied to terminal a and an answer voltage is derived from card 147 positioned by servo 146, which controls also a fuel flow indicator 148. Cylinder head temperature system. The system for calculating and indicating cylinder head temperature (C.H.T.) is shown in Fig. 6, wherein input voltages a-h are fed to the amplifier 195 of servo system 73 which computes the temperature shown on indicator 193. The equation to be solved is C.H.T.+y. CHT.=y .tg+O.A.T. where C.H.T. is cylinderhead temperature ; tg is the combustion gas temperature ; O.A.T. is outside air temperature and y is a factor which is determined as a function of air density, true air speed, cowl flap position and weight of engine airflow by a computing system in Fig. 5 (not shown). The input voltages to amplifier 195 are as follows : (a) a feed-back signal from the amplifier ; (b) a signal representing term y. C.H.T. of the equat