GB921267A - Improvements in dirigible craft - Google Patents

Abstract

921,267. Vehicles supported by gaseous cushions. SPERRY GYROSCOPE CO. Ltd. Jan. 12, 1962 [Nov. 4, 1960], No. 37953/60. Class 4. A vehicle supported over land or water by a gaseous cushion, and propelled and manoeuvred by at least two devices each exerting a reversible horizontal thrust at a height above the cushion, the lines of action of the devices being rotatable in azimuth, is provided with means which, when the thrust reversing mechanism of a device is operated in a sense to brake the vehicle, rotates the line of action of that device so as to eliminate any athwartships component of force in a sense opposite to that of any athwartships component of force exerted immediately prior to the reversal of the thrust. Fig. 1 shows such a vehicle propelled and steered by two airscrews 2, 3, rotatable about vertical axes 7, 8. The vehicle is executing a right hand turn along a path 16, the thrust vectors of the airscrews being represented at 9 and 10 and giving rise to an appropriate nett lateral (centripetal) force and yawing torque. If now the thrusts of the airscrews are reversed by blade pitch reversal, the resultant lateral force and yawing torque will cause the vehicle to execute a left hand turn while decelerating, which is in general undesirable, especially if braking is desired in an emergency. To obviate this, blade pitch reversal of the airscrews is accompanied by rotation about axes 6 and 7, at least until the lines of action are parallel to the fore-and-aft centre line of the vehicle. Rotation of the lines of action may continue until they make the same angles with the centre line as before, or until they make lesser but proportional angles with the centre line. Fig. 3 shows apparatus for effecting this rotation for one airscrew, the apparatus for the other being similar. The line of action of the airscrew is rotatable by a motor 25 controlled by amplifier 26, which has two inputs, one from a potentiometer 21 driven by a manual steering control 24, and the other from a potentiometer 27 driven by motor 25, so that the motor shaft position is driven into correspondence with the setting of control 24. In one mode of operation, movement of the airscrew pitch control 34 to a reverse pitch setting operates switch 33 to ground one input of amplifier 26 so that motor 25 is driven to its neutral position, thus eliminating any lateral force on the vehicle. The pilot may disengage switch 33 from the pitch control 34 to resume steering control. In another mode of operation, switch 33 is omitted, and movement of control 34 to a reverse pitch setting moves switches 35 and 36 to make their upper contacts. This reverses the polarity of the voltage across potentiometer 27, so that the airscrew axis will be rotated from its instant position until it is parallel to the vehicle centre line, and then on again through the same angle. In a third mode of operation, switches 35 and 36 make their lower contacts which reverses the polarity of the voltage across potentiometer 27 and increases this voltage by cutting out series resistors 39, 40. The airscrew axis will therefore be rotated from its instant position until parallel to the centre line and then on again through a smaller angle. The airscrew engines are those driving the fans which generate the air cushion. According to the Provisional Specification, an airscrew and its engine may be in a rotatable unit.