Patent GB-840991-A (GB)
Title: Improvements in or relating to flight computers
IPC: G09B9/20
Filed: 1958-04-15
Abstract: 840,991. Grounded aircraft trainers. GENERAL PRECISION SYSTEMS Ltd. [formerly AIR TRAINERS LINK Ltd.], (Link Aviation Inc.). April 15, 1958, No. 12034/58. Class 4. A grounded aircraft trainer analogue computer comprises means deriving a first quantity representing either one of simulated heading or bank angles, and deriving a second quantity representing the sum or difference of these two angles by solving equations for the sum or difference not involving expressions in pitch angle which tend to infinity as pitch angle tends to Œ 90 degrees, and means responsive to the two quantities to derive the other of the heading or bank angles. By this means, proper correlation of bank and headings angles is obtained when their rates of change are very large, as during simulation of near vertical flight. In the apparatus shown, a shaft position representing angle of pitch # is assumed to be available from a servo M-100, and signals simulating p, q and r, the angular velocities about the simulated OX, OY and OZ aircraft axes are also assumed to be available. The aircraft heading angle # is computed from #cos# = q sin ° + r cos ° ... (1) where ° is the bank angle. Resolvers R-202 and R-203 driven by the bank angle servo M-300 are energized by signals -r and -q respectively, and the resulting voltages are summed in amplifier U-109 and fed over amplifiers U-104, U-105 to the scaling input resistor R-127 of the heading servo M-200. A tachometer generator (not shown) feed back signal # energises a resolver R-201 driven by the pitch angle servo M-100, to derive signals # sin # and # cos #, the latter fed over resistor R-125 to the servo M-200, which thus solves equation (1), and has an output shaft position #. For pitch angles # such that -30 degrees < # < + 30 degrees, ° is computed from ° = p + # sin # ....... (2) A signal p from terminal 112 is fed over summing resistor R-118 to amplifier U-107. A signal # sin # from resolver R-201 is fed over summing resistor R-119 to amplifier U-107, and the output ° is fed through closed contacts d of relay K-2 and d of relay K-1, and resistor R-128 to the °-servo M-300. This has a tachometer generator velocity feed back signal ° fed through closed contact f of relay K-3, whereby the servo integrates the input, and its shaft position represents °. The #-servo M-200 drives the constantly energized rotor coil of a synchro T-1, the stator coils of which energize the stator coils of a differential synchro T-2 through the contacts of switch S-1. The rotor coils of synchro T-2 are driven by the °-servo M-300, and energize the stator coils of a synchro T-3. The rotor of this is driven by an auxiliary servo M-400, and provides a voltage available on contacts c and d of relay K-3 these contacts being closed and open respectively, the voltage at contact c being fed to servo M-400 over resistor R-133 as a position feed back signal. Switch S-1 is cam-operated by the pitch servo shaft, the result being that for # > +10 degrees, the shaft position of servo M-400 represents (# - °), and when # < -10 degrees, contacts S-1 change-over, and the shaft position represents (# + °). Preferably for -10 degrees < # < + 10 degrees switch S-1 is open, and servo M-400 is inoperative. For # > + 30 degrees, #- ° is computed from #-° =1-sin°/cos° (qsin° + rcos°)-p.. (3) and Ï is computed as # - (#- °). For # < -30 degrees, # + ° is computed from # + ° = 1 + sin #/cos # [q sin ° + r cos °] + p .... (4) and Ï is computed as (# + Ï) - #. To this end, servo M-400 becomes an integrating servo, solving equation (3) or (4), and servo M-300 becomes a summing servo. A signal representing # is derived by a potentiometer R-101 driven by the #-servo and is fed together with constant signals, to summing amplifiers U-101, U-102 which energize relays K-1, K-2, through recitfiers X-1, X-2 respectively, whereby, if # > +30 degrees, relay K-1 is operated, and if # < -30 degrees, relay K-2 is operated. Operation of either relay opens its contact d, and removes the Ï signal on resistor R-128 from servo M-300. Operation of either relay closes its contact e, and energizes relay K-3. Contact c of the latter is opened, removing the positional feed back signal on resistor R-133 of servo M-400, and contact a is closed, adding a tachometric generator velocity feed back signal to servo M-400 over resistor R-134. If relay K-1 is energized, its contacts a and b energize a potentiometer R-106 with signals Œ (q sin Ï + r cos Ï) from amplifiers U-104 and U-105. The potentiometer is driven by the # servo M-100 and is contoured to multiply by (1-sin #) /cos # (which for 30 degrees < # # 90 degrees lies between nought and one). The derived signal, one term of equation (3), is fed to amplifier U-103 over resistor R-109. The other term, -p, is derived from contact c of relay K-1 and amplifier U-106. The output, #- Ï, of amplifier U-103, is fed to integrating servo M-400. As explained above, relay K-3 is also energized, so that contact f is opened, removing the velocity feed back signal from servo M-300. Contact e is closed, adding a position feed back signal from potentiometer R-137 driven by the servo. Contact d closes, providing an input signal to servo M-300 from the rotor coil of synchro T-3. Servo M-300 is thus balanced when its shaft position represents Ï computed as # -(# - Ï). If # < -30 degrees, the computation proceeds as above, but relay K-2 is energized instead of relay K-1. Potentiometer R-106 is not energized, and potentiometer R-107 energized by Œ (q sin Ï + r cos Ï) signals over contacts a and b of relay K-2 from amplifiers U-104 and U-105, and contoured to multiply by (1 + sin #) /cos # (which for -90 degrees # # < -30 degrees lies between nought and one) derives one term of equation (4), fed with the remaining term + p from terminal 112 over contact c of relay K-2, to amplifier U-103, and servo M-400 solves equation (4). Servo M-300 then computes Ï as (# + Ï)-#. Thus while the simulated pitch angle is numerically less than 10 degrees, # and Ï are computed from equations (1) and (2), and servo M-400 is inoperative. For pitch angles numerically between 10 degrees and 30 degrees equations (1) and (2) are still solved but servo M-400 is driven to a shaft position # Œ Ï as appropriate, so that if pitch angle exceeds 30 degrees in magnitude, the servo can begin integrating #Œ Ï from a correct initial position. Alternatively, Ï can be computed directly for all pitch angles, and # found from Ï and # Œ Ï when the pitch angle is large.