Patent GB-654041-A (GB)
Title: Improvements in or relating to flight control systems for aircraft
IPC: G05D1/04
Filed: 1943-07-08
Abstract: 654,041. Automatic aircraft control systems. HONEYWELL-BROWN, Ltd. July 8, 1943, No. 11122. Convention date, June 22, 1942. [Class 38 (iv)] [Also in Groups XX and XL (c)] In an automatic flight-control system for aircraft the rudder-controlling means and aileron-controlling means are both operated automatically in accordance with the tilt of the aircraft about its longitudinal axis and its deviation from a predetermined course, the basic control being exercised by vertical and directional gyroscopes. The vertical gyro also controls the elevators to move always in the same direction irrespective of the direction of tilt about the longitudinal axis of the craft. The gyroscopes operate " control devices " comprising potentiometer arms in balanceable electrical bridge circuits, the circuits associated with rudder and ailerons being interconnected so that when either of those control surfaces responds to a primary control signal received from its control device an additional control signal is received from a control device associated with the other, when the latter operates beyond a predetermined range. Fig. 12 shows an automatic pilot having a directional gyroscope 10 adapted to control a rudder cable 81R, and a gyro vertical 91 adapted to control aileron and elevator cables 81A, 81E, respectively, the system being also provided with a pilot's control knob 585, whereby the rudder and ailerons may be jointly controlled by a manually-produced signal actuating the rudder control, the directional gyroscope control being locked simultaneously. Each control surface, i.e. rudder, ailerons and elevator, is operated through a reversible power-transmission gearing 50 from its own constantly-running electric motor 60. Each gearing comprises a pair of electromagnetically actuated clutches operated selectively against constantly-energized windings holding the movable clutch members against friction brakes. The clutch actuating-windings are respectively energized by relays in the output circuits of an amplifier 500 in accordance with the phase of an input signal received from a resistance network fed with A.C. The amplifiers are constructed to provide intermittent energization of the relays when the input signal exceeds a minimum value but does not exceed a higher value, and to give a continuous energization when this higher value is exceeded. Each resistance network comprises a Wheatstone bridge 15 constituted by potentiometers 14, 24 connected in parallel across an A.C. supply, the former having a slider 12 operated from the associated gyroscope and the lattera slider 22 moved in accordance with displace ment of the control surface and constituting a follow-up device. The amplifier input is taken from these sliders in series with the output of other control potentiometers. The rudder control 15R includes also: (1) an automatic rudder compensating potentiometer 97R with slider 96R operated from the gyro vertical 91 and having a proportioning adjustment 106R; and (2) pilot's control 504R. The aileron control 15A includes also : (1) automatic aileron compensating potentiometer 97A with slider 96A operated from the directional gyroscope 10; and (2) pilot's control 504A. The elevator control 15E includes an elevator compensating potentiometer 514 with slider 512 dependent on tilting about a longitudinal axis, and operated from the gyro-vertical 91. Each network also includes resistances which may be adjusted manually to balance the control surface. As shown, these comprise coupled resistances 27, 30 for use at will, and trimmers 20. To start the system, power is supplied from a battery 64 through switch 544 to the motors 60 of the power transmission units, and also to the gyroscopes and a rotary converter 542. The rotary converter feeds full-wave rectifiers 553, 570 connected across a transformer 551. Anode voltage for the first two stages of the amplifiers 500R, 500A, 500E is furnished over wire 536, and grid-bias for the output stage of the amplifiers over wire 537. The A.C. terminals of the rotary converter supply transformers furnishing the anode voltage for the output valves of the amplifiers 500R, 500A and 500E, and A.C. voltage for the control networks and potentiometers, so that after each control surface has been correctly balanced by the manual controls 20, 27, 30 (evidenced by neither of the signal lamps 205, 207 lighting), the braking coils of each of the power transmission units are energized from the battery 64 through the closure of individual switches 580; these switches may be opened simultaneously by the depression of a bar 581. The compensating potentiometers 97 and 514 have adjustable dead spots which render them ineffective for a predetermined minimum deflection of the controlling gyroscope. The pilot-operated potentiometers 504 have similar dead spots permitting an ineffective range of operation of the control 505 whenever a cam 588 operates switches disabling the erecting means of the gyro-vertical 91 and operating clamping means for the directional gyroscope 10. A cam 115 operated by the directional gyroscope also disables the erecting means aforesaid when a turn is called for. A system, Fig. 1 (not shown), is also described having no pilot control potentiometer 504 and without the corrections applied by potentiometers 97R and 514. Directional gyroscope.-A ring 212, Fig. 3, is clamped to the casing 211 of the gyro 10 by a spring 220 when a toggle 221 is operated by turning a knurled head on an eccentric 224. The ring carries an arm 225 operating, between limits set by stops 232, 233, a slide 230 carrying a cam 115, slider 12R of the rudder control potentiometer 14R, and slider 96 of the aileron compensator 97A. The slider 12R is pivoted at 235 and restrained by a dashpot 240 and centralizing springs 236 so that its movement is in part proportional to the rate of change of the deflection. The arm 225 may be clamped substantially in its mean position by a lever 606, Fig. 13, operated through a linkage 602- 606 from a solenoid 597 when the pilot-operated switch 591, Fig. 12, is closed by cam 588. Gyro-vertical.-The gimbal ring 252, Figs. 4 and 6, of the gyroscope 91 turns a shaft 90 (shown also in Fig. 12), carrying an insulating block 268 supporting potentiometer arms 12A, 96R and 512, and the gyro casing 250 pivoted on an axis in the ring at right-angles to the shaft 90 carries a roller 265 which may travel in a semi-circular channel 262 carried by shafts 260, 261. The shaft 260 actuates the slider 12E of the elevator control. Erecting means is provided to correct gyro-wander, and comprises magnets 256, 266 on shafts.253, 260 and stationary coils 273, 274 and 282, 283, the energization of which is controlled by gravity responsive bails 286, 287 suspended on pivots from the gyro-casing and adapted to complete circuits for the appropriate coils by contacting with a member 276 fixed to the base of the casing 250. Wires 291, 297 supplying the erecting currents include the contacts of relays controlled by the cam 115 and also by the pilot's switch 585. Amplifiers.-The output from each control network is an A.C. signal of reversible phase and variable amplitude, and this is applied to the grid of a triode 330, Fig. 11. A gain control potentiometer 325 may be employed. The output of the triode is applied through a second amplifier 360 to a double tetrode output valve 380 which, in the form shown, has its anodes energized in opposite phase from a transformer 310 supplied from the battery 64, Fig. 12 (by way of terminals 70, 71), through a vibratory switch 302. The anode circuits comprise relays 186, 187 which energize selectively the clutch coils of the power transmission mechanism and produce the required movement of the control surface (rudder, ailerons, or elevator). Auxiliary windings 317, 318 furnish A.C. for the control network and compensating potentiometers. Auxiliary rectifiers 323, 324 are provided, which furnish respectively : (1) at 344, anode potential for amplifier valves 330, 360, and at 373 an adjustable bias potential, and (2) at 406 another adjustable bias potential. The arrangement is adapted to give an intermittent operation of relay 186 or 187 with increase in the period of its closure in proportion to the amplitude of the input signal up to continuous closure. This is achieved by bias voltage developed across resistances 370 and 350 as explained in detail in the Specification. The signal amplitude at which intermittency ceases is determined by adjustment of resistance 370, and the sensitivity of the control by adjustment of contact 373. Power transmission mechanism.-This is shown in Fig. 2, and includes sleeves 131, 151 adapted to be driven in opposite directions by the motor 60 when clutches 132, 152 are selectively operated by electromagnets 144, 164 against the action of electromagnets 145, 165 tending to hold collars 140, 160 on the sleeves against braking surfaces 141, 161 respectively. The sleeves 131, 151 are geared through a differential to a pulley 80 engaging the cable 81 operating the associated control surface, viz. rudder, ailerons, or elevator, and operating the balancing potentiometer arm 22 of the control network. Limit switches 199, 203 are in series with the exciting circuits of the electromagnets 144, 164, the energization of which is controlled by the relays 186, 187 in the amplifier circuit, Fig. 11.