Patent GB-685895-A (GB)
Title: Improvements in or relating to grounded aviation trainers
IPC: G09B9/28
Filed: 1951-03-12
Abstract: 685,895. Electric analogue calculating systems. LINK AVIATION, Inc. March 12, 1951 [March 11, 1950], No. 5962/51. Class 37. [Also in Group XXXIII] Apparatus for applying variable loading forces to the primary flight controls of a ground aviation trainer similar to those resisting the movements of corresponding controls of an aircraft in flight, comprises a computer responsive to adjustments simulating air density p and true airspeed Vp, whose output actuates a servomotor positioning a mechanical output member, according to the dynamic pressure q=¢pVp<SP>2</SP> to actuate a regulating valve which controls the pressure in a pneumatic system applied to an air piston and cylinder, operatively connected through a double pivotal linkage to the appropriate flight control member, the linkage being dimensioned so that the pressure within the cylinder applies to the control a resisting force proportional to the value of q and to the deflection of the control from the zero position. Fig. 2 shows the dynamic pressure computer 44 wherein a transformer T1 energizes a potentiometer R1 in series with a variable resistance R2 and the slider of R1 supplies a variable resistance R3 in series with a variable resistance R4. The sliders of R1 and R3 are linearly adjustable proportionately to air density p by a simulated altitude unit 46 and the slider of R3 energizes a potentiometer R5 whose slider supplies a potentiometer R6, the two sliders being linearly adjustable proportionately to Vp by a simulated true airspeed unit 48. The sliders of potentiometers R2 and R4 are adjustable for calibration, and the voltage on the slider of R6 is proportional to q=¢pVp<SP>2</SP> and energizes position servo amplifier 50 controlling the direction and magnitude of rotation of a conventional servo motor generator system MG, which adjusts the arm of a follow-up potentiometer R7 energized by transformer T1 to apply a rebalancing voltage to the amplifier input. The displacement of the servomotor output shaft 42 is proportional to q and rotates a pinion 40 to traverse a rack connected to the inner piston 36 of a servo regulating valve 26 (Fig. 3) whose outer cylindrical body 52 has a longitudinal bore 54 connected through exhaust port 58 to atmosphere, through port 56 to a constant pressure air supply tank 14 supplied by a motor-driven compressor 12 (Fig. 1) and through port 60 to a buffer tank 98. An intermediate tubular piston 64 having lands 66, 68, 70, 72 separated by circumferential ports 74, 76, 78 and vented to the atmosphere at 116 is reciprocable within the bore 54 by a spring-loaded collapsible -expansible pneumatic bellows 92 connected to the buffer tank, and the inner piston 36 (having lands 104, 106, 108 separated by circumferential ports 110, 112) is positioned within the piston 64 by the servomotor traversed rack in accordance with the instantaneously computed value of q. On an increase or decrease of q, the inner piston is deflected to connect the buffer tank to the compressed air supply or to the atmosphere to raise or lower the air pressure therein until the bellows 92 expands or collapses to deflect the intermediate piston 64 in a direction appropriate to cut off the compressed air or atmospheric vents from the buffer tank, and thus stabilize pressure therein at a value proportional to the instantaneous computed value of q. The buffer tank is connected by a line 120 to a cylinder 122 containing a piston 178, which members are respectively connected through linkages 158, 154 and 172, 168 to a rocker member 144 having arms 146, 148 fixed to the control shaft 128 and linked to the simulated flight control member 188. Extensions of links 158, 172 are pivoted to the right and left ends of a trim frame 130, which is pivotable about shaft 128 by a geared screw-and-nut device driven by a reversible trim motor 136 controlled by two-way switch 140 operated by the pupil. Control shaft 128 is Selsyn coupled to a known flight computer 198. Displacement of control member 188 away from or towards its neutral trimmed position in either direction compresses or de-compresses the air in cylinder 122, and bellows 92 expands or contracts to reciprocate the intermediate piston 64, thus venting the buffer tank to atmosphere through port 58 or connecting it to the air line through port 56, so that the buffer tank and cylinder pressure is maintained proportional to the instantaneous computed value of q regardless of the control member position. The mechanical linkage system connecting the piston and cylinder with the operating shaft 128 and the control member 188 is designed so that its mechanical advantage decreases linearly with the displacement of the control member from its neutral trimmed position, so that the resistance to the movement thereof is made to increase linearly with the displacement, and with the computed dynamic pressure loading q, as in flight of an actual aircraft. The member 188 may control the simulated elevator, rudder, or ailerons of the trainer, and similar loading units 204, 208, associated with the remaining controls are connected to the buffer tank through lines 202, 206. A procedure for adjusting the neutral trim of the simulated aircraft controls is described. The control member load is variable in accordance with the control surface area by adjusting the mechanical advantage of the linkage between the control member and the control shaft.