GB998766A - Improvements in flight control of aircraft - Google Patents

Abstract

998,766. Controlling jet-propelled aircraft. BRISTOL AIRCRAFT Ltd. March 11, 1963 [March 16, 1962], No. 10282/62. Heading B7G. An aircraft having a jet-propulsion engine with a rotatable nozzle, includes means receiving vertical and horizontal acceleration demands and applying each of these partly to the engine throttle control and partly to the nozzle angle control, in proportions determined by the instantaneous nozzle angle, so that during hovering with jet lift, horizontal acceleration is produced predominantly by altering the nozzle angle, and vertical acceleration by throttle adjustment, and during cruise, the opposite obtains. The Figures show the control system of a pilotless aircraft, which receives information from a terrain following radar system 50, a programming and inertial guidance system 54 receiving commands by an aerial 56, an inertial guidance table having gyroscopes and accelerometers, and from a radio altimeter 58. Signal gain and limiting devices are indicated by G and LIM. An altitude demand signal from programmer 54 is compared with the measured altitude from altimeter 58 in summing amplifier 60, which also adds a stabilizing signal equivalent to rate of climb. The result is taken as a vertical acceleration demand signal, and provides one input to an " or " gate 62. The other input is a vertical acceleration demand signal from the terain following radar 50. The gate 62 selects the input which demands the greater upward acceleration, and this signal is fed over line 64 to a summing amplifier 66, which compares the demand with the signal from a vertical accelerometer 69, and deducts a constant " one g " signal. The resulting vertical acceleration error signal is fed to proportioning devices 70, 72, which multiply their inputs by factors U<2>/Uc<2> and 1-U<2>/Uc<2> respectively, where U is the airspeed measured by a pitot-static head 74, and Uc is the cruise speed. At cruise speed therefore, the output of device 72 is low, and vertical acceleration is controlled by device 70, which energizes equally the port and starboard elevon servos 132, 134, a pitch rate stabilizing signal from gyro 126 being added by summing amplifier 130. At low speeds, the output of device 70 is low and the vertical acceleration error signal is passed on line 96 to a resolver 80 driven by the nozzle angle servo 82 (gamma being the nozzle angle measured from the position of vertical discharge). The error signal is multiplied by cos gamma and passed to the throttle servo 92, and is multiplied by sin gamma and passed to the nozzle servo 82, so that vertical acceleration is adjusted by the throttle when the nozzle is discharging downwardly, and by the nozzle angle setting when the nozzle discharges rearwarely. A pitch demand signal from programmer 54 is fed on line 128 to summing amplifier 122 which deducts the pitch angle measured by gyro 124, and adds a pitch rate stabilizing signal from gyro 126. The resultant controls pitch altitude controlling jets 120 to provide pitch control at low speeds when the elevons are ineffective. An airspeed demand signal on line 84 from programmer 54 is compared with the measured airspeed in summing amplifier 86, the error signal being taken as the horizontal acceleration demand signal. This is compared with the horizontal acceleration measured by accelerometer 90 in amplifier 88, and the error signal is fed to resolver 80, so that it is multiplied by sin gamma and passed to the throttle servo, and by cos y and passed to the nozzle angle servo, whereby horizontal acceleration is controlled by the throttle when the nozzle is discharging horizontally, and by the nozzle angle when the nozzle is discharging vertically. To give vertical acceleration demands precedence over horizontal acceleration demands when the combined demands require a thrust that the engine cannot supply, the throttle servo total input is fed through limiter 98 and multiplied by sin gamma in resolver 80, to provide a suitable negative feedback signal to amplifier 88 when the total demand is excessive. A yaw demand signal from programmer 54 is fed over line 106 and is compared with the yaw measured by gyro 110 in amplifier 104, which also adds a stabilizing yaw rate signal from gyro 112. The resultant yaw error signal operates yaw control jets 100, which are effective only at low speeds. At high speeds, the rudder is effective, and is used solely to reduce sideslip as measured by a lateral accelerometer 114, to the output of which a yaw rate signal is added in amplifier 116, the resultant controlling the rudder servo 102. A roll demand signal from programmer 54 on line 136 is compared with the roll measured by gyro 140 in amplifier 138, and a stabilizing roll rate signal from gyro 144 is added to the roll error signal by amplifier 142. The resultant signal operates roll jet controlling vanes 146 and also operates the elevon servos 132, 134, differentially.