Patent GB-553730-A (GB)
Title: A continuously-functioning combination blind-flying instrument
IPC: G01C23/00
Filed: 1939-11-25
Abstract: 553,730. Fluid-pressure servomotor-control systems. BRAMBLE, A. E. C. Y. Nov. 25, 1939, No. 30778. [Class 135] [Also in Group XX] In a gyroscopically controlled device for aircraft, for indicating altitude and motion, or for automatic control or for stabilizing bomb sights or cameras, comprising a gimbal mounted gyroscopic element for providing continuously (without interruption or failure during evolutions of the craft) a datum in the form of a plane fixed relatively to the horizon, the gimbal-carrying chassis is arranged so that normally it is fixed on pivotal supports but is allowed to pivot freely if the gimbal rings become coplanar or approach such condition, whereby the degrees of freedom of the gyroscopic element may be maintained substantially continuously and the fixed datum continuously maintained in each and every attitude of the device. As applied to an attitude and motion indicator, the instrument embodies three gyroscopes viz. an horizon gyroscope 8, an azimuth gyroscope 27 and a rate-of-turn gyroscope 36. The outer gimbal 2 of the gyroscope 8 is pivoted on horizontal fore-and-aft trunnions 10, 10<SP>1</SP> and its 'lateral level is maintained by the gyroscope. The end face 5 of the gimbal carries lines 20, 20A, Fig. 2, which indicate the true horizon, or departure therefrom, against graduations 4R on the chassis 3. The outer ring 28 of the azimuth gyro 27 is pivoted in a carrier ring 25, journalled in the gimbal 2. The horizon gyro 8, operating through a gear connection 26 maintains the outer ring 28 in a vertical plane. The gimbal 2, gyro 8 and ring 25 are shown in Fig. 1 displaced through 90 degrees from their normal operating positions. If the aircraft makes a partial loop thereby bringing the inner and outer gimbals 2, 21 into a co-planar position and then makes a turn, the application of a disturbing torque to the gyroscopes 8, 27 is prevented by unlocking the instrument case 3 so as to permit it to pivot about trunnions 23, 24. As the gimbals approach coincidence compressed air passing through the pivots 23, 24 and channels 80 is admitted to a cylinder 77 by a release valve 81 operated by a servomotor 33 (described below) thereby withdrawing a piston rod 71 from locking engagement with a recess 72 in an inclined circular track 76. The case 1 thus becomes free to rotate about the pivots 23, 24 and the imposition of a disturbing torque on the gyroscope is avoided. On separation of the gimbal rings, the release valve returns to normal position, the piston rod 71 descends on to the inclined track 76 under the pressure of a spring 74 and the pressure on the track causes the case 1 to rotate back to normal position. The heading in azimuth during either normal or inverted flight is indicated in one or other of two sector windows 12 or 12A, Fig. 2, the irrelevant window being masked by a shutter 13. On change of heading of the aircraft relative displacement occurs between the outer gimbal ring 28 of the azimuth gyroscope and its carrier ring 25 thereby causing rotation (as described below) of a servomotor pinion 29, contrary motion of the differential rings 30, 30A, similar rotation of the differential discs 42, translation of pinions 32 and rotation of an azimuth disc 14 to display an indication of change of heading at the window 12, Change of fore-andaft level of the aircraft causes relative displacement between the carrier ring 25 and the chassis 3 but owing to the intervention of the differential gear effects no displacement of the graduated azimuth disc 14. In a modification the azimuth gyro 27 is replaced by a magnetic element 55, Fig. 11, carried in a frame 54 pivotally mounted on a vertical pivot 53 within the carrier ring 25. The frame 54 also carries a graduated azimuth scale 56 the readings of which are observed at the sector windows by reflection at mirrors 52. The rate of turn is indicated at a window 18, Fig. 2, on a graduated sector actuated by the rate-of-turn gyro 36. A pointer 17 for indicating the lateral trim of aircraft is pendulously balanced by a counterweight or by the shutter 13 upon a bush 7 in the glass cover 4 and co-operates with a pip 11 or 11A (or normal and inverted flight respectively) fixed in the normal axis of the aircraft. The degree of bank is indicated by the position of horizontal marks 20, 20A relative to graduations 4R. A further indication of lateral attitude is provided by the relative movements between a miniature aircraft 6<SP>1</SP> on a disc 6, and the dial 5, the movements of the miniature as seen by the pilot simulating the movements of the aircraft as seen from behind. If the aircraft inverts by pitching, the tail unit of the miniature appears to change place with its undercarriage. To effect this change the shapes of the tail unit and landing wheels of the miniature are cut out of the disc 6 bearing the miniature representation and are repeated above and below the wing shape. These apertures are backed by a shutter or slide which moves up and down under the influence of gravity to display luminous areas giving an impression to the pilot of an apparent inversion of the miniature. " Sky indicators" 19 in the form of drums, discs or endless bands are provided and are marked with symbols denoting "horizon erect," " zenith," horizon inverted," "Nadir," "45 degrees inclinations erect," and " 45 degrees inclinations inverted." During pitching of the aircraft displacement occurs between the inner gimbal 21 of the gyro 8 and the outer gimbal 2. This displacement is followed up by the servomotor 33 (described below) to drive the sky indicators through gearing 26 and present to the pilot an indication in the appropriate sense of the apparent movement of the sky area past the sky Slots S, Fig. 2. The servomotor devices 33, 34, 35 for transmitting movements without imposing reactive torques, for example for transmitting the movements of the gyro 27 to the indicator without imposing a torque on the gyro, are shown in Fig. 4 wherein the air supplied to the jet 58 to drive the rotor 27 is by-passed through the stub axle 60 of the gimbal ring 57 and is directed radially towards the rotatable jet boss 62 carrying a toothed indicator-driving wheel 63 and two vane wheels 64. If relative movement from the normal position of rest occurs between the gimbal ring 57 and the jet boss 62, a jet seal 67, Fig. 5, admits the air to one or other of two channels 69 and thence to jets 68 playing upon the vane wheels 64. The vane wheels, acting through pinions 65, and a gear-wheel 66, Fig. 4, impart rotary movement to the driven disc 63 of the indicator mechanism to follow up the gimbal ring 57 until the normal relationship shown in Fig. 5 is restored. The gyroscope 8 is self-erected by means of pendulous shutters co-operating with vent ports. Acceleration disturbances of the shutters are minimized by providing the shutters with spring-pressed extensible pins which are pressed by centrifugal force into engagement with roughened arcs on the rotor case in order to brake the movements of the shutters.