Patent GB-673534-A (GB)
Title: Improvements in or relating to automatic control apparatus for aircraft
IPC: G05D1/00
Filed: 1948-08-06
Abstract: 673,534. Controlling aircraft. SPERRY CORPORATION. Aug. 6, 1948 [Aug. 7, 1947]. No. 20808/48. Class 4. [Also in Group XXXV] In apparatus for atomatically maintaining an aircraft in a predetermined path in a vertical plane, lift-varying surfaces movable with respect to the wings are controlled in response to signals preduced by vertical deviation of the aircraft from the predetermined path, and the elevator is controlled both by these signals and by signals produced by pitching cf the craft, the vertical deviation signals being applied for the two purposes in such proportions that the aircraft is moved without pitching into the predetermined path. In Fig. 1 the output of an E- type pick-off 34 of an accelerometer-gyro combination 29, 31 of the type described in Specification 642,911, [Group XXXV], is dependent on vertical acceleration of an aircraft and is applied in the same sense, through an integrating network 37, 38, an isolating valve 39, and lines 41. 42. to two servo amplifiers 25, 26 which introduce derivative components. The outputs of amplifiers 25, 26 control the excitation of Ward-Leonard generators 23, 24 supplying servomotors 13, 14 operating control surfaces 11, 12 e.g. ailerons or flaps, in the same sense to maintain, automatically, the craft at a constant altitude or inclination. Control surfaces 11, 12 are located to be effective at the aerodynamic centre of lift of the craft to effect lift without appreciable change of attitude. The servo systems operating control surfaces 11, 12 may be provided with electrical or mechanical followup (not shown). The accelerometer-gyro combination 29, 31 produces zero output when vertical acceleration is zero in straight line flight or a function of the secant of the angle of bank during banked turns. By manual operation of a switch 44 the control may be supplemented by signals from an altimeter 43 or a radio glidepath receiver 48. Accelerometer control may be rendered ineffective by opening switch 40. Strain gauges placed in the wing section and responsive to lift may replace the aceelerometer. The output of a selsyn pick-off 83 of gyro vertical 31 is dependent on pitch of the craft and is applied through a selsyn 82 to a servo system 47 controlling the elevator so that the pitch of the craft is automatically maintained in correspondonce with the position of the rotor of selsyn 82 which is set by movement of a handle 67 about an axis 81. To compensate for weathervane action, i.e. pitching due to air acting on the stabilizer when the aircraft moves vertically, a component of control is introduced in the appropriate sense through lines 45, 46 to elevator servo system 47. The output of a selsyn pick-off 70 of gyro vertical 31 is dependent on bank of the craft and is applied in opposite senses to amplifiers 25, 26 through a selsyn 72 and lines 73, 74 so that control surfaces 11, 12 also function as ailerons normally maintaining the craft level. The output of a selsyn pick-off 62 of a directional gyro 61 is dependent on the heading of the craft and is applied through a selsyn 65 and lines 63, 64 to a servo system 66 controlling the rudder so that flight is normally in a straight line. Turns are effected by operation of handle 67 about an axis 68 whereupon contacts 69, 71 close and the rotor of selsyn 72 is moved to develop a signal. The closing of contacts 71 energises a relay 75 to render directional gyro 61 ineffective to control the rudder, while the closing of contacts 69 applies the signal from selsyn 72 to the rudder servo system 66 to cause turn. The signal from selsyn 72 remains applied to amplifiers 25, 26 so that a banked turn is executed. Energisation of relay 75 applies the output of selsyn 65 to an amplifier 78 controlling a servomotor 79 which adjusts the rotor of selsyn 65 so that when straight flight is resumed the new heading will be maintained. In Fig. 2 control surfaces 11, 12 are operated, through rigging 94, in opposite senses by a pulley 96 driven by a servomotor 101 responsive to an aileron signal and in the same sense by a plate 98 rotated by a servomotor 103 responsive to a lift signal. As an alternative to or in addition to operation of the ailerons in the same sense, lift may be produced by operation of a spoiler, a Handley-Page slot, a combination of spoiler and slot, or a flap, on the wing.