Patent GB-941112-A (GB)
Title: Improvements in flight simulators
IPC: G09B9/20
Filed: 1959-11-12
Abstract: 941,112. Grounded aircraft trainers. GENERAL PRECISION Inc. Nov. 12, 1959 [Nov. 12, 1958], No. 38482/59. Heading B7W. A flight parameter analogue computer in a flight simulator comprises means for deriving selected aerodynamic analogue quantities referred to the X-axis of the aircraft stability axis system as opposed to the X-axes of the body and wind axis systems. Computation is effected with reference to three sets of orthogonal axes having their origin at the centre of gravity of the simulated aircraft. The body axes, indicated by suffix a, have as X-axis the fore-and-aft axis of the aircraft, as Y axis the line normal to the plane of symmetry, and an axis, perpendicular to the X and Y axes, as Z axis. The stability axes, suffix s have the Y axis in common with the body axes, and are obtained by rotating the body axes about the common Y axis through the angle of attack α until the Z axis is perpendicular to the instantaneous flight path. The wind axes, suffix w, have the Z axis in common with the stability axes, and are obtained by rotating the stabiltiy axes about the common Z axis through the angle of side slip #, until the X axis is aligned with the instantaneous flight path. Thus p a  refers to the rate of roll measured in the body axis system, r 8  to the rate of yaw measured in the stability axis system, and Ay w  is the acceleration along the Y axis of the wind axis system. Computation is by A.C. voltages throughout, amplifiers being used for phase inversion where necessary. Fig. 2 shows apparatus for computing Ax w , the X wind axis acceleration, and Vp, the true air speed. The equation used is where T N /m is the power plant thrust to aircraft weight ratio, qSCD 8 /m is the drag in the absence of side slip, qSCy 8 /m is the coefficient of drag due to side slip, g is the acceleration due to gravity, and γ is the flight path elevation angle. A voltage -T N /m is applied to a tapping 220 on potentiometer R-222 which has a cosine function and is driven by shaft S-222 in accordance with α, to derive - T N  cos α/m fed over summing resistor R-224 to amplifier A-228. The quantity SCD 8 /m is computed from a " clean " drag component energizing potentiometer R-120, and a component due to operation of landing gear, flaps, and the like, energizing potentiometer R-212. The potentiometer wipers are driven by a shaft in accordance with q, the dynamic pressure, and the resultant signals summed in amplifier A-242 to produce an to lift. This is available at terminal 402 and fed output qSCD s /m fed over resistor R-244 to amplifier A-228. Oppositely phased signals representing lateral forces in the stability axis the wiper of which is driven by a shaft in accordance with # to derive qSCy s #/m fed over resistor R-254 to amplifier A-228. The output of amplifier A-228 is thus Ax w , and this is fed over the upper contact of switch 262 (closed during airborne conditions) to amplifier A-262 which has a feedback capacitor C-262 and thus integrates Ax w  to obtain -Vp, which energizes a Vp servo 268 and indicator 269. When ground travel is simulated (altitude = 0), the lower contacts of switches 262 and 264 are closed, and amplifier A-262 is energized from terminal 266 by signals appropriate to ground travel (not described) and acts as a conventional summing amplifier. The lower contact of switch 236 is also closed during simulated ground travel, and adds forces on the undercarriage signals over resistor R-234 to amplifier A-228, so that the simulated transition between ground travel and flight takes place smoothly on changeover of the switches. Fig. 3 (not shown) shows apparatus for computing Ay w , the lateral wind axis acceleration, from the equation where # is the angle of pitch and # the angle of roll. The rate of yaw in the wind axis system r w  is then computed as Ay w /V p  by conventional division using a Vp servo driven potentiometer in the feedback circuit of a summing amplifier. In Fig. 4, the vertical accelertion Az w  is computed from where qSC L /m represents the acceleration due system are applied across potentiometer R-252, over resistor R-402 to amplifier A-420. Oppositely phased signals representing T N /m are applied across potentiometer R-409 driven by the α servo to obtain T N α/m fed over resistor R-410 to amplifier A-420. A signal - g cos # is applied to amplifier A-404, the feedback circuit of which includes a secant function potentiometer R-405 driven by a shaft in accordance with #, so that a signal g cos # cos # energizes potentiometer R-404 which has a cosine function and is driven by the α servo to derive g cos # cos # cos α fed over resistor R-406 to amplifier A-420. Oppositely phased signals representing α energize potentiometer R-407 having a sine function and driven by the 0 servo to derive a signal scaled by summing resistor R-408 to represent g α sin # fed to amplifier A-420, which thus has an output Az w . The same inputs are applied to summing amplifier A-414, which has a potentiometer R 415 driven by the Vp servo in its feedback circuit, and thus has an output Az w /Vp or q 1w , the rate of pitch in the wind axis system. In Fig. 5, the body axis rates of roll and yaw, p a  and r a , are converted to stability axis rates of roll and yaw, p s  and r s , by the equations and α is determined from where q 1a  is the rate of pitch in the body axis system. Oppositely phased signals representing p a  are applied at terminals 502, 504, across potentiometer R-501 driven by the α servo to derive P a α fed to amplifier A-502. Oppositely phased signals representing r a  are applied at terminals 506, 508 across potentiometer R-505 driven by the α servo to derive r a α fed to amplifier A-506. A signal - r a  from terminal 508 is fed to amplifier A-502, which thus has an output r s , and a signal p a  from terminal 502 is fed to amplifier A-506, which thus has an output - p s . This signal and an equal but oppositely phased signal energize potentiometer R-513 driven by the # servo to derive p s # fed over switch 508 and resistor R-515 to amplifier A-520. Signals -q 1a  and + q 1w  are fed over switches S-150 and S-512, and resistors R-150 and R-512, respectively, to amplifier A-520, which has a feedback capacitor C-520, and thus integrates its inputs to derive α. During simulated ground travel, resistors R-515, R-510, and R-512 are earthed by switches S-508, S-510, and S-512, and the only input to amplifier A-520 is a - # signal fed over switch S-514 and resistor R-514. Switch S-520, during ground travel converts amplifier A-520 to a non-integrating summing amplifier, and α is thus taken as equal to #. In Fig. 6, sin γ and cos γ are computed from the equations- A resolver R-616 is energized at one input by a - α signal over terminal 608 and at the other input by a constant voltage. The shaft is driven by the # servo, and one wiper derives a signal - cos # used elsewhere in the computer, and the other wiper derives - α cos # fed over resistor R-618 to amplifier A-620. Oppositely phased sin # signals energize a potentiometer R-630 driven by the # servo to derive - # sin # fed over resistor R-620 to amplifier A-620. The amplifier output energizes a cosine function potentiometer R-624 driven by the 0 servo to derive cos # (# sin # + α cos #) fed over resistor R-626 to amplifier A-612. Amplifier A-620 also energizes potentiometer R-636 which has a sine function and is driven by the # servo to derive - sin # (# cos #) + α sin #) fed over resistor R-638 to amplifier A-638. Potentiometer R-604 is energized by constant voltages and contoured so that its wiper driven by the # servo derives a signal - # + sin 0. This signal together with a + 0 signal on terminal 602 is summed in amplifier A-602 which thus has a - sin 0 output. This energizes a potentiometer R-610 having a cosine function and driven by the α servo to derive - sin # cos α which forms the second input of amplifier A-612 which has an output sin γ. A cosine function potentiometer R-644 is energized by a constant voltage and driven by the α servo to derive a signal cos α which is reversed in phase and energizes a cosine function potentiometer R-650 driven by the # servo to derive - cos α cos # fed as the second input to amplifier A-638, which thus has an output cos γ. Figs. 7, 8 and 9 (not shown) compute the body axis pitch, roll, and yaw rates p a , q 1a , and r a , and the corresponding accelerations, from the equations where Mx 8 , My 8 , Mz 8  are aerodynamic moments in the stability axis system, Mx a T N , My a T N  Mz a T N  are moments due to the power plant thrust, and the I's and Jxz are the moments and a product of inertia of the aircraft. In Fig. 10 (not shown), Mx 8 /Ixx is computed from signals assumed to be available in the computer, and taking into account side slip, coefficient of lift, induced drag, rate of yaw (as r s  C L /V p ), rate of roll (as p s  q/V p ), the deflection of each aileron, and lift on the vertical tail surfaces. In Fig. 12, #, # and the heading # and their time derivatives are computed from the equations A resolver R-1202 is energized by oppositely phased q 1a  signals and is driven by the # servo, to derive signals q 1a  sin # and q 1a  cos #, fed over resistors R-1204, R-1206 to amplifiers A-1204, and A1206 and A-1207 respectively. Resolver R-1210 is energized by oppositely phased r a  signals and is driven by the # servo, to derive signals r a  cos # and r a  sin # fed over resistors R-1212 and R-1208 to amplifiers A- 1204, and A-1206 and A-1207, respectively. Amplifier A-1207 sums its inputs to produce an output d#/dt, and amplifier A-1206 integrates its inputs, having a feedback capacitor C-1206, to provide an output #. The feedback circuit of amplifier 1204 has a cosine contoured potentiometer R-121