893,114. Grounded aircraft trainers. CURTISS-WRIGHT CORPORATION. Dec. 2, 1958 [Dec. 3, 1957] No. 38898/58. Class 4. Apparatus for simulating the operation of the turbine of a turbo-prop driven aircraft, comprises means for simulating turbine speed, means for computing simulated fuel flow controlled according to the position of a simulated power lever, means controlled by the fuel flow computing means for computing simulated turbine inlet temperature, and means controlled by the temperature computing means for computing simulated turbine shaft horsepower. The apparatus shown simulates a four engine plant. Each actual engine simulated has a power lever movable over a "beta" range extending over full reverse, ground idle, and taxi positions; and a " flight " range extending between flight idle and full power take-off positions. In each engine, the fuel flow is governed by a coarse flow valve and a fine flow valve. Within the flight range of the power lever is a position referred to as the temperature cross over position. For power settings below this position, the turbine inlet temperature is controlled solely by the coarse fuel flow valve, but mechanism which can be manually disabled is provided to limit this temperature to a predetermined maximum. For power settings above this point, the turbine inlet temperature is controlled to a scheduled value corresponding to the power set, by mechanism acting on fuel the fine flow valve. To achieve this, the power lever controls the coarse valve to permit more than the scheduled fuel flow for the power demanded, this flow being corrected retroactively, by the fine valve to maintain the scheduled turbine inlet temperature. The fine valve can be locked manually. Each engine has a starter control and a " condition " lever with positions " air start", " normal " ground stop ", and "feather". On starting, there is an enriched fuel flow below 9000 R.P.M. Which can be manually reduced to normal, the fuel cocks being opened at 2200 R.P.M. Ignition is cut off above 9000 R.P.M. In the feather and ground stop positions, fuel is cut. Air may be bled from the engine compressor for various purposes. A " panic " handle is provided for cutting..the engine in emergency. All these effects are simulated, as are various failures. The simulated turbine inlet temperature, torque, and fuel flow of each engine is indicated, as is the total fuel flow. The parts of the simulator used to simulate one engine, or common to all the engines, are described below. . Computation of simulated fuel flow. (W#), (Figs. 7, 8, 9 and 10). The. simulated fuel flow is first computed as #Wf = W f /#2 ##2, where #2 = P2/P0 and #2 = T2/T0, P 2 and T 2 being the compresser inlet pressure and temperature respectively, and P0 and T 0 the sea level datum pressure and temperature respectively. The inputs to the Wf summation amplifier 222 depend on the condition of the engine. On starting, with the power lever in the idling position (within the beta range) Wf is computed as a single component #Wf(T2)a representing fuel flow while the turbine is accelerating. In Fig. 9, a potentiometer 248 is energized by a signal -1/##2 and is operated by the T 2 servo 178. The wiper signal, together with a -1/##2 signal, is fed to summing amplifier 244 which energizes a transformer 242. The output energizes a potentiometer 236 driven by the turbine r.p.m. (N) servo 42, and the signal on wiper 234 is available at the NC contact 1 of a relay 64. While the power lever is in the starting range relay 64 is de-energized, Fig. 1, so the signal is fed to line 232, see now Fig. 10, through phase inversion amplifier 226, line 228, and the NC contact 1 of a relay 230, to the #Wf summing amplifier 222. Also, at 2200 r.p.m., a fuel enrichment valve relay 122 is energized, Fig. 2, to add a fuel surge signal-1/##2 over its NO contact 2. The fuel flow during the steady state of the engine while the power lever is in the beta range is computed from three components, -#Wf(LEV, N) s , #Wf(1/##2)s, and -#Wf(LEV, T2) s . A potentiometer 276, Fig. 9, has a wiper 274 driven by the power lever 22 and comprises a short circuited portion 278 grounded through resistor 281 and corresponding to the ground idle to flight idle range of the power lever. Its ends are connected directly, and through resistor 282 respectively, to a -1/##2 signal. The signal on wiper 274 is fed over line 272 to a tap 270 on a potentiometer 264 driven by the N servo 42 and grounded through resistor 268 at a tap 266. By this means the signal on wiper 262 remains that on wiper 274 until 12,500 r.p.m. is exceeded. The resultant signal 0-#Wf(LEV, N)s is fed over an NC contact 2 of relay 64, while the power lever remains in the beta range, to line 250. A +1/##2 signal is fed over NC contact 3 of relay 64 to line 252 to represent #Wf(1/##2)s. A potentiometer 292 driven by the T 2 servo 178 is connected in series with resistor 300 across signals Œ1/##2, and is earthed at its centre tap. The derived signal energizes both ends of a potentiometer 286 driven by the power lever and grounded through resistor 298 at two taps 294, 296 representing the ground and flight idling positions. The signal on wiper 284 representing -W f LEV, T2)s is fed over the NC contact 4 of relay 64, while the power lever is in the beta range, to line 254. The sum of the signals on lines 250, 252, and 254, Fig. 10, is compared with the signal on line 232 by a summing amplifier 256 energizing a phase sensitive relay 258, whereby when the signal #W f (T 2 ) a representing fuel flow during turbine acceleration reaches the steady state fuel flow computed as #W f (LEV, N)s-#W f (1/## 2 )s + #W f (LEV, T 2 )s, a thyratron 260 is triggered and energizes relay 230. Contact 1 of this relay removes the signal -#W f (T 2 ) a from amplifier 222, and contacts 2-4 apply the signals on lines 250, 252 and 254. The #W f output of amplifier 222 thus reflects that the turbine has reached a steady state. When the power lever is moved into the flight range, relay 64, Fig. 9, is energized, Fig. 1, and contacts 1-4 ground lines 232, 250, 252, 254. The inputs to the #W f amplifier 222 are now provided by lines 302, 304, 306 over the NO contacts 5, 6 and 7 of relay 64. #W f is now computed as #W f (LEV) s + #W f (1/# 2 )s + #W f (N/## 2 )s. A potentiometer 328 driven by the " equivalent "r.p.m. (N/## 2 ) servo 308 is constantly energized at one end and grounded through resistor 332 at a tap 330. The wiper 326 bears the signal -#W f (N/## 2 )s, fed over line 324 to the NO contact 7 of relay 64. A potentiometer 320 driven by the N/## 2 servo is energized by a signal -1/# 2 at one end and grounded at a tap similar to tap 330. The signal -#W f (1/# 2 ) is fed over line 322 to NO contact 6 of relay 64, and also energizes a potentiometer 314 driven by the power lever, at a tap 316. This potentiometer is also grounded at a tap corresponding to tap 330. The signal -#Wf(LEV)s on wiper 312 is fed over line 310 to NO contact 5 of relay 64. Thus #W f is computed as #W f (T 2 )a on starting, as #W f (LEV, N) s -#Wf(1/##2)s +#W f (LEV, T 2 ) s as soon as this exceeds #Wf(T 2 )a, and as #W f (LEV)s+ #W f (1/#)2)s #Wf(N/## 2 ), when the power lever is moved into the flight range. The effects simulated above are those affecting the coarse fuel flow valve. The effect of the fine fuel flow valve, or temperature datum valve, are simulated in Fig. 7. When the power lever is in its beta range and the flight range relay 64 is thus de-energized the turbine inlet temperature Ts is automatically limited, but not otherwise controlled. To simulate this, NC contact 8 of relay 64 applies the signal on line 360 to a summing amplifier 394 of the temperature datum valve servo 358. The other input is derived from contact 2 of an over temperature relay 83, being zero if the relay is de-energized, and a constant value if the relay is energized. Amplifier 394 energizes a motor driving potentiometer 364, which is connected in series with resistor 366 across equal and opposite constant signals ŒE, and grounded at a tap as shown. Its wiper 362 is connected to line 360. A Ts servo 368 (energized as in Fig. 6, drives a constantly energized potentiometer 380 to derive a -T5 signal fed over line 384 and the NO contact 1 of a limit selector relay 80 to a summing amplifier 386. Relay 80 is energized when the engine conditions are such that the Ts limiting mechanism in the real engine would be operative, Fig. 1. A further constant input to amplifier 386 represents 2150‹K, and a further signal representing 350‹K is added if a 13000 r.p.m. relay 34 is de-energized, Fig. 1, i.e. if N> 13,000 r.p.m. The output of amplifier 386 is fed to a phase sensitive relay 388, thyratron 390, and relay 83. Thus the relay is energized if Ts> 2150‹K(N< < 13,000 r.p.m.) or T5> 2500‹K(N> 13,000 r.p.m.). While T5 is not excessive, the only input to amplifier 394 is the answer signal from wiper 362, which is thus driven to the grounded tap on potentiometer 364, representing a datum position for the fine fuel flow valve. When Ts becomes excessive relay 83 is energized and a signal + O.T is applied to amplifier 394. Wiper 362 is thus driven towards the negative end of potentiometer 364, simulating closing of the fine fuel flow valve. This results in a drop in the computed W f as explained below, Fig. 8, and thus a drop in the computed T 5 , Fig. 6, until relay 83 releases, whereupon wiper 362 returns to its datum tap. When the power lever is in the flight range, and relay 64 is thus energized, T 5 is to be automatically controlled in dependence on the power lever setting. To simulate this, the -T 5 signal from wiper 378 is fed to amplifier 370 as is a + T 5 REQUIRED signal derived by a wiper 372 driven, by the power lever 22 over a potentiometer 374 energized and grounded as shown. The output of amplifier 370 is thus the error between the computed and required T