Patent GB-815003-A (GB)
Title: Thrust control for aircraft
IPC: G05D1/06
Filed: 1956-09-17
Abstract: 815,003. Automatic airspeed control systems. BENDIX AVIATION CORPORATION. Sept. 17, 1956 [Sept. 22, 1955], No. 28391/56. Class 38 (4). In a system in which the throttle of a supercharged piston engine in an aircraft is automatically controlled to maintain the airspeed at a preset value, a decaying signal proportional to engine intake manifold pressure is added as a follow-up signal, the throttle setting is also modified according to the altitude, rate of climb and Mach number, and a limiter takes over if a preset Mach number is exceeded. The rotor of a selsyn transmitter 10 is positioned in accordance with airspeed by a servomotor 28 which also rebalances the inductive pick-off of the airspeed measuring bellows 20. A rate component is added by a tachometer generator 31. The rotor of the selsyn receiver 17 is positioned by an airspeed selector lever 19, and any resultant error signal in the rotor is normally connected via a switch 55 to an amplifier 56 and phase-sensitive amplifier 57 which controls a motor 58 to adjust the throttle lever 59. A rate component is added by a tachometer generator 58A. A signal proportional to engine intake pressure is obtained from a bellows 61 which controls a selsyn link 64, 65 to add the manifold pressure signal over line 69 to the speed error signal in the output transformer of the amplifier 56. A phasesensitive amplifier 70 controls a motor 68 to rebalance the selsyn receiver 65 so that the manifold pressure signal decays with a time constant determined by the amplifier 70 and motor 68. A rate component is added by a tachometer generator 74. A signal proportional to altitude is obtained from an aneroid 151 which has an inductive pick-off and selfbalancing servo system, the motor 155 of which also adjusts the slider of a potentiometer 162 from which a D.C. signal proportional to the altitude is obtained. A rate component is added by a tachometer generator 156 and this rate of change of altitude signal is also applied to an inductive device 173 where it is compared with a manually selected rate set in on the rotor. Any error signal is amplified at 183 and added to the speed error signal in transformer 184. The rate of change of altitude error signal also controls the motor 178 which actuates the elevator 180. A signal proportional to Mach number is obtained from bellows 82, 83 which control an inductive pick-off and self-balancing servo-system, the motor 94 of which also controls the sliders of potentiometers 130, 101. The potentiometer 130 provides a D.C. signal proportional to Mach number, and this signal is added to the altitude signal to vary the bias on the control grid of the pentode 120 in the amplifier 56 so as to compensate for the reduced air resistance at increased altitudes. Should the Mach number exceed a set value, the motor 94 closes contacts 105 and relay 109 is energized from an external source over contact 108. Relay 109 closes self-holding contacts 110 and changes over contact 55 so that the main input to the amplifier 56 is now a signal from potentiometer 101 proportional to Mach number error and the throttle lever 59 is controlled to maintain the set value until such time as an airspeed below this value is set in by the airspeed selector lever 19, then relay 167 is energized by valve 165 due to the reduced airspeed error signal applied to valve 164 to open contact 108 and return the control system to normal. When the automatic speed control system is not in use, contact 40 is closed so that the airspeed selector lever 19 is controlled by a motor 38 to follow changes in measured airspeed and thus there is no airspeed error signal present in the system to cause false operation when changing over from manual to automatic control.