GB474178A - Improvements in or relating to speed indicators for aircraft or other moving bodies - Google Patents

Abstract

474,178. Indicating speed of aircraft. BRONZAVIA SOC. ANON. Sept. 28, 1936, Nos. 26320 and 26321. Convention dates, Sept. 26, 1935 and Sept. 22, 1936. [Class 106 (iii)] Apparatus for determining the ground speed of aircraft comprises an optical sighting system 1... 5, 7 having a pivoted mirror or prism 6 which is moved by a hand or motor actuated device so that the image of an observed point on the ground remains stationary on the cross-wires of lens 2. The prism 6 is moved by a pinion 10 and rack 9 which the operator actuates by turning a knob 8, which also drives through gearing and a fly-wheel a speedometer 11 giving the required speed at a given altitude. A plurality of scales may be provided to correspond to various altitudes, or changespeed gear may be used for different ranges of altitude. To compensate for deviations of the line of vision from the vertical, the uniform movement of the knob 8 and speedometer may be converted into a variable movement of the mirror by the use in the transmission to the rack 9 of a cam or other device such as a pin 13 carried by the toothed wheel 17 and adapted to engage a slot 15 of a toothed wheel 16 engaging the rack. In a modification, Fig. 5, wherein the prism is actuated through change-speed gear 27 by a motor 20 controlled by a rheostat 31, the prism is actuated by a cable 33, which is wound round a shaft 0 by the movement of a rod 21 having one end slidable in a member 24 positioned by the movement of a screw 23 driven by the motor, the height h being adjusted for different altitudes by turning a knob 30 to lift a nut 28 supporting the screw 23. The speed ratios of the change-speed gear correspond to different ranges of altitude. Provision is made for disengaging the part 24 from the screw 23 so that the rod 21 may be set at any desired initial position. In another modification, the speedometer 11 is arranged in the upper part of a casing alongside the altitude adjustment button, which operates also an altitude indicator having three scales for three ranges of altitude, and press-buttons for operating a change-speed gear of the brakedrum and planetary type.