Patent GB-902202-A (GB)
Title: Improved aircraft training apparatus for simulating the propeller system of turbo-propeller aircraft
IPC: G09B9/18
Filed: 1958-12-04
Abstract: 902,202. Grounded aircraft trainers. CURTISS-WRIGHT CORPORATION. Dec. 4, 1958 [Dec. 5, 1957], No. 39194/58. Class 4. Grounded flight training apparatus simulating a turbo prop aircraft, comprises a power lever movable over " ground " (or " beta ") and " flight " ranges, a system computing turbine speed and producing an automatic governing signal, and a propeller blade pitch angle system responsive to said signal when the power lever is in its " flight " range, and responsive to movements of the power lever when in its " beta " range, the turbine speed system being responsive to the blade pitch angle system and to a torque computing system. The simulated controls available to the trainee are a condition lever 1, Fig. 1, having air start, normal, ground stop, and feather positions, a master engine selector switch 4, an emergency or panic handle 3, a throttle or power lever 2, the beta range of which is used for ground operations, including producing reverse thrust for braking by reversible pitch propellers, and the flight range of which extends from flight idle to full power (takeoff) positions, and an electronic propeller governor switch 5 having an off position, in which mechanical governing is simulated, and an on and a synchronize position, in which electronic governing is simulated with and without synchronization to the selected master engine, respectively. In the apparatus to be described, some parts are repeated for each of four engines and some are common to all four, as appropriate. Ground starting operation. For this, the condition lever 1 is at normal, the panic handle 3 is at normal, the power lever is at ground idle setting in the beta range, the governor switch 5 is at sync, and switch 4 selects say, No. 1 engine as the master. Initially, turbine r.p.m. (N) is zero, and a 7,000 r.p.m. relay 56 and a 13,000 r.p.m. relay 60, Fig. 1A, are energized from a supply line 7 through switches operated by cams 57, 63 driven by the N servo 17. On pressing the starter button, 14, a start valve relay 15 is energized from line 7 over contacts 50, 51, contact 53a of relay 60, and contact 59a of relay 56. A relay 54 is energized over contacts 50, 52, and contact 55a of relay 56, and serves to hold the starter button depressed. Energization of relay 15, Fig. 5, closes its contact 26b to energize a thermal time delay relay 30, which closes its contact 31a feeding a fixed signal over contact 25b of relay 15 to one input terminal 28 of the N servo 17. N accordingly starts to rise. At this time, N is less than 9,000 r.p.m., so that a 9,000 r.p.m. relay 35 is energized by a cam switch 23a driven by the N servo. Also, no flame in the engine is simulated, and a flame relay 16 is de-energized. The velocity feedback damping signal from the generator 20 of servo 17 is thus fed to the amplifier 18 at terminal 33, over contact 36a at terminal 34, and over contacts 36a and 38a at terminal 37, to simulate sluggish acceleration of the turbine. When the flame relay is energised to simulate flame in the engine at about 2,000 r.p.m. e.g. as in Specification 893,114, an additional fixed input is fed to terminal 40 of servo 17 over contact 39b, and part of the damping of the servo is removed by grounding of contact 38b. Increased acceleration of the turbine is thus simulated, until N reaches 7,000 r.p.m. At this point, relay 56, Fig. 1A, is de-energized by cam switch 58. The holding relay 54 is de-energized by breaking contact 55a and the starter button 14 is released. The start valve relay 15 is de-energized by contact 59a, and the starting signals at terminals 28 and 40, Fig. 5, are removed by contacts 25 and 26. The principal input to the N servo is now N(PL, Q) representing the effect of propeller load PL and torque Q, fed over contact 27a to terminal 41. This signal is proportional to #Q (Q positive) and to #-Q (Q negative), and is derived by energizing a potentiometer (or pot) 42 in series with a fixed resistor, with ŒPL signals derived as described later. The wiper 42<SP>1</SP> is driven by the Q servo 43, and is connected by resistor 42a to a +PL or a -P L  signal according as Q is positive or negative, by a relay 43a energized by a cam switch 43c driven by the Q servo, when Q is negative. A further input # N(N,VT) at terminal 43, representing the effect of airspeed VT on N, is derived by energizing a pot 44 with an RPMVT signal (derived as explained later) at terminal 44a and a -VT signal at terminal 44b. The wiper 44<SP>1</SP> is driven by the blade pitch angle Bp servo 45 to derive A N(N, VT). At 9,000 r.p.m., relay 35 becomes de-energized, further decreasing the damping of servo 17. An instructor's trouble control 48 drives a pot 47 to introduce a high or low r.p.m. disturbance signal at terminal 46. The start valve relay 15 may be prematurely de-energized at below 7,000 r.p.m. by throwing the panic handle 3, Fig. 1A to de-energize the 13,000 r.p.m. relay 60 and open contact 53a. The same may be done by the trainee operating the emergency shut-off valve circuit breaker 64. The propeller load PL is computed as a function of V T , B p , and air density p, see Fig. 4. The VT servo 125 drives a pot 126 to derive a signal -VT, used in Fig. 5, and fed to amplifier 127 which has an output RPMVT representing the effect of airspeed on N. A transformer 128 produces outputs +RPMVT, used in Fig. 5, and -RPMVT, which energizes a potentiometer 131 and forms one input to an amplifier 132. The wiper of pot 131 is driven by a # servo 130 and provides the second input to amplifier 132. The pot is contoured so that the amplifier output is RPMVT v #, fed to transformer 134. This energizes a pot 142 driven by the B P  servo 45 to derive PL (RPMVT, B p ) fed as one input to amplifier 141. The # servo 130 also drives a pot 136 to derive a signal which, when added to a constant signal by amplifier 137, produces an output 1/#p fed over transformer 139 to energize pot 140 driven by the BP servo 45 to derive PL(#, B P ) forming the other input to amplifier 141, which has an output P L . Transformer 144 produces ŒPL signals used in Fig. 5. The turbine is now running at ground idle r.p.m., with zero propeller blade pitch. Take-off and normal flight. For this, the power lever is advanced to full power. During the initial movement of the lever, up to the end of the beta range, B P  is controlled directly by the power lever to increase to about 9 degrees. The beta range relay 6, Fig. 1, is energized by a cam switch 12 driven by the power lever, as long as the power lever is in the beta range. The principal input to the B P  servo amplifier 75, Fig. 3, is a signal derived by a pot 65 driven by the power lever 2, and fed over contact 66b of relay 6 to terminal 68. An answer signal from a pot 70 driven by the B P  servo 45, is fed to amplifier 75 over contact 69b of relay 6, so that the servo acts as a position servo, the shaft of which is driven to an angular position in accordance with the signal from the power lever pot 65. When the power lever is advanced into the flight range, the beta range relay 6 is de-energized, Fig. 1, and contacts 66 and 69, Fig. 3, remove the power lever and answer signals from amplifier 75. Contact 67a adds a fixed flight idle stop signal at terminal 73, from contact 71b of an automatic governing control (auto) relay 71 when de-energized. Contact 89 of this relay, when de-energized, feeds an answer signal to amplifier 75 over contact 69a of relay 6. The servo 45 is thus held at a flight idle position corresponding to the constant signal at terminal 73, while relay 72 is not energized. When relay 72 is energized, the flight idle position and answer signals are removed from amplifier 75 by contacts 71 and 89, and a propeller underspeed (or overspeed) signal substituted by contact 88 at terminal 87. There being no answer signal, the Bp servo acts as an integrating servo, and an underspeed signal on terminal 87 results in an alteration in B P  until the effect of B P  on N removes the underspeed signal as described later. Relay 72 is energized while B P  is greater than the flight idle angle of 9 degrees by a cam switch 186, Fig. 1, driven by the B P  servo, which energizes relay 184 for B P  greater than 9 degrees, and closes contact 187a to energize relay 72. Relay 72 is also energized by contact 194a of the propeller underspeed relay 92, when propeller overspeed occurs, irrespective of the value of Bp. Advance of the power lever to the flight range also operates a cam switch 112 to energize a relay 105 (shown twice in Fig. 1) provided that the trainee's switch 5 selects electronic governing, with or without synchronization. Contact 114a of relay 105 then energizes an acceleration responsive governing relay 96, contact 97a of which, Fig. 3, adds further damping to servo 45. The propeller speed error and synchronization system is shown in Fig. 2. In the normal condition, a cam switch 155a is closed by the N servo 17, a relay 99 is deenergized, relay 96 is energized (power lever in the flight range, electronic governing selected), and relay 6 is de-energized (power lever in the flight range). A constant signal, representing the governed speed, is thus fed to amplifier 150 at terminal 156. The signals at terminals 164, 168 and 170, are grounded. The other input, at terminal 152, represents N and is derived from pot 153 driven by the N servo. This servo is now presumed to simulate No. 1 (master) engine, and the output of amplifier 150 represent PU 1 , the No. 1 engine under or overspeed. This signal is fed to terminal 161, Fig. 3, to correct B p  when appropriate. The signal is also fed to a phase sensitive rectifier 162 and thyratron 163, so that relay 92 is energized when PU 1  is zero or positive. The PU signal is fed to the B P  servo, Fig. 3, while relay 72 is energized, i.e. during underspeed or while B P  is greater than 9 degrees. If overspeed occurs with B P  less than the flight idle angle