Patent GB-927904-A (GB)
Title: Aircraft flight control system
IPC: G05D1/08
Filed: 1959-07-20
Abstract: 927,904. Automatic control of aircraft. UNITED AIRCRAFT CORPORATION. July 20, 1959 [Oct. 3, 1958], No. 24777/59. Class 38 (4). [Also in Group XXXIII] An aircraft flight control system includes means responsive to a first signal representing craft motion and to a second signal representing movement of a craft control member to provide a difference signal which is continuously integrated, and means, responsive to the movement of the control member and to the movement of a member controlled by the integrated difference signal, to control motion of the aircraft. The Figure shows fore-and-aft cyclic pitch, and collective pitch, control systems for use in a helicopter, similar systems being used for the roll and yaw channels, Fig. 2 (not shown). Cyclic pitch control (fore-and-aft).-The pilot's cyclic pitch control member 2 is journalled at an intermediate point to a link 3 which is journalled to a link 6 of which one end is journalled to the input shaft 7 of an hydraulic servomotor 9, the output shaft 10 of which adjusts the cyclic pitch control mechanism 11. The other end of link 6 is connected to the output shaft 8 of an electrical positioning servomotor 28. Link 3 is connected by means of a transducer 32 and a centering spring 4 to the output shaft 5 of an integrating or velocity servomotor 31. The case of a transducer 30 is attached to the air-frame and the input shaft is connected to link 3 so that the transducer 30 provides an electric signal representing the absolute position of control member 2 and the transducer 32 provides a signal representing the stress in spring 4. A vertical gyro is provided with a pitch pick-off 18 and an accelerometer 20 is mounted on the fuselage to provide an output which is combined in a network 21 with the output from gyro 18 so that the output from 21 is proportional only to craft fore-and-aft acceleration 25 and independent of fuselage tilt relative to the horizon. Doppler equipment 45 responsive to craft velocity 24 energizes a fore-and-aft velocity meter 47. The output from 21 is combined at 44 with the velocity signal from 47 and this in turn is combined at 36 with the signal from transducer 32 and a velocity adjustment potentiometer 33. The signal from gyro 18 is combined at 37 with a signal from transducer 30 and a signal from a centre of gravity trim adjustment potentiometer 34. A pair of switches 41, 42 are controlled through a relay 40 on the stick 2, and depending on the selected position of switch 42 the output from either network 36 or 37 (through a differentiating network 38 and directly, for the latter) is fed to an integrating circuit 26, the output of which is taken through a network 27 to the position together with an unintegrated signal servo 28 so that with relay 40 de-energized the cyclic pitch control mechanism 11 is responsive both to the movement of stick 2 and to movement of the servo 28 which is controlled by an integrated difference signal derived at 37. Switch 35 can be operated to train the feel by energization of servo 31 over switch 41. When relay 40 is energized, motor 28 is positioned by the integrated signal from circuit 44 and velocity trim potentiometer 33, fed over switch 42. Limit switches 29 operated by the shaft 8 of motor 28 prevent saturation of integrator 26. Collective pitch control.-A collective pitch lever 52 is journalled to a link 53, one end of which is attached to a feel spring 54 and the case of a transducer 90 and the other end is attached to the input shaft 57 of an hydraulic servo 59 which controls rotor blade collective pitch and thereby craft vertical velocity 62 and altitude 64. The feel spring 54 and transducer 90 are also attached to the output shaft of velocity servo 89 so that transducer 90 provides a signal representing the position of lever 52 to the position of shaft 55. A Doppler section 103 energizes a vertical velocity meter 92 and a radio altimeter 93 is connected to a differentiating circuit 93 and its output is also combined at 95 with a signal from an altitude adjustment potentiometer 94 the sum being limited at 96 and fed to one contact of a switch 81. A signal from a barometric altimeter 67 is limited at 68 and fed to the other contact of switch 81. The output from a barometric rate of climb meter 65 is fed to one terminal of each of a pair of timer switches 100 and 101, which, together with a further switch 99, are controlled by a timing circuit 98. The armature of switch 99 is connected through terminal 111 to switch 43 controlling the relay 40 of the pitch circuit and also to one contact of a switch 88 controlling a relay 80. The armatures of switches 100 and 101 and the output from rate of climb meter 65 are connected to the three terminals of a switch 102, the armature of which is connected to a network 75, which has other inputs from transducer 90 and a rate of climb adjustment potentiometer 74. The output from network 75 is fed to one contact of a switch 84, controlled by relay 83, the other contact being energized from a network 85 provided with inputs from a switch 81 controlled by relay 80 and from rate of climb meter 65. The signal from the armature of switch 84 and from a hysteresis circuit 77 responsive to rotor speed are combined in a network 82 the output from which is integrated at 69, the outputs from network 82 and network 69 being combined at 70 and fed to position servo 71. Thus the collective pitch mechanism 61 is responsive to the movement of lever 52 and to the movement of servo 28 which is controlled by the integral of a signal which is the difference between the position of the lever 52 as derived by transducer 90, and the rate of climb is measured by meter 65.