Patent GB-838211-A (GB)
Title: Improvements in or relating to aircraft attitude indicator apparatus
Inventor: BARNETT DOUGLAS
IPC: B64D45/00
Filed: 1955-05-07
Abstract: 838,211. Aircraft attitude indicators. KELVIN & HUGHES Ltd. Aug. 7, 1956 [May 7, 1955], No. 13278/55. Class 4. An aircraft attitude indicator comprises an index representing the zenith or nadir carried on a member movable relative to a frame in a first direction in response to changes in the inclination of the aircraft's OY axis to the horizontal, and in a second direction at right angles to the first in response to changes in the inclination of the aircraft's OZ axis to the horizontal. Fig. 1 shows one form combined with a conventional artificial horizon display. In normal flight, an artificial horizon bar marked on a roller blind 21 is adjusted relatively to an aperture 23 in the instrument face. The blind is fastened to rollers 19, 20 carried on a frame 14, and the rollers are rotated in accordance with an aircraft pitch signal which may be derived from a gyro-stabilized platform. The frame 14 is rotated on bearings 13 by a motor 15 in accordance with an angle of roll signal. In steep (climbing or diving) flight, at more than say, 75 degrees to the horizontal the angle of roll may change rapidly by up to 180 degrees when the aircraft pitches or yaws slightly near the zenith or nadir. Accordingly, the horizon bar is arranged to disappear from the aperture 23, and an aperture in the blind exposes an index carrying member 22 which is mounted on a twin D'Arsonval movement to swing about two axes at right angles, so that as seen by the pilot, the index moves in two directions at right angles across the instrument face. The two movements are energized from signals derived by a resolver from conventional pitch, roll, and yaw signals, and the roller blind actuator and motor 15 are de-energized. The position of the index thus shows the extent and sense of the deviation of the aircrafts fore-and-aft axis from the vertical, Fig. 11b for example, shows the display when the aircraft OZ axis is horizontal, and the right wing points outwardly twelve degrees below the horizontal. On reverting to normal flight, the horizon bar reappears, and should do so from the correct part of the instrument face in accordance with the aircraft roll at that instant. To this end, the roller blind actuator and motor 15 are not suddenly energized when the angle of pitch drops below say 75 degrees, but are gradually re-energized as the pitch drops from say 80 to 75 degrees. In the embodiment of Fig. 3, a motor 38 drives a yoke 35 about the aircraft fore-and-aft axis, and a motor 37 on the yoke rotates a frame 36 mounted on the yoke. The frame supports the rollers 32, 33 of a blind 31. In normal flight, a horizon bar marked on the blind is actuated by unwinding the blind in response to changes of pitch, and actuating motor 38 in accordance with roll. When the angle of pitch exceeds 75 degrees, the horizon bar disappears from the face of the instrument, and a spot on the blind representing the zenith or nadir moves towards the centre of the instrument face. This spot is then moved in one direction by actuating the blind rollers, and in a second direction at right angles to the first by motor 37, motor 38 being de-energized. Actuating signals are derived as for Fig. 1. In a development, motor 37 is omitted and frame 36 is rigid with yoke 35. Movement of the zenith or nadir indicator in the two directions at right angles is then obtained by actuating the roller blind and motor 38 to position the spot in accordance with the polar co-ordinates of its correct position. As the pitch changes from 75 to 80 degrees, the energizing signals are gradually changed from those appropriate for positioning the horizon bar to those for positioning the zenith or nadir indicator, and vice versa.