GB1228468A - - Google Patents

Abstract

1,228,468. Compasses. PATRICK HARRISON & CO. Ltd. July 11, 1968, No.33222/68. Heading G1F. A magnetic compass for aircraft comprises a housing 30 containing a magnet 28, the housing being mounted on bearings 50 in a ring 48 to allow the magnet pivoted movement in dip, the ring 48 being in turn mounted on bearings 54 in a ring 52 for movement in azimuth, and carrying a compass card 56, a ring 60 with bearings 62 for mounting the ring 52, and bearings 64 by means of which it is mounted in a ring 20 carried by a casing 10 for the compass, small weights 58, 59 attached to the rings 48, 52 sewing to maintain the azimuth axis of the ring 48 vertical, and a dip weight 44 on the housing 30 provided to reduce the dip angle of the magnet 28 from its true value so as to preclude the possibility of the magnet 28 turning over about its dip axis during tight turns of the aircraft thus causing a 180 degree error in the reading of the compass the casing 10 being filled with a damping fluid for the compass. The housing 30 comprises two generally hemispherical end members sandwiching a control disc-like member having above parallel to its plane into which the magnet 28 is fitted. The dip weight 44 is also carried in a base in the disc member. A balancing ring is provided around the housing 30 and adjustable along the direction of the dip axis to allow the housing to be balanced about its rotational axis. The housing 30 and the rings supporting it are preferably of plastics material and have a specific gravity which is equal to that of the damping liquid in the casing 10. This casing has a transparent cover 12 which clamps the ring 20 in place and a bellows 22 allows for thermal expansion of the damping liquid. The weights 58, 59 are also adjustable to allow the rings 48, 52, to be balanced, and these weights are as small as is compatible with providing the necessary force to keep the azimuth axis of the ring 48 vertical, whilst being affected as little as possible by aircraft turns. The dip weight 44 reduces the named dip cycle of the magnet 28 so that during turns the condition in which the magnetic axis is vertical will not be reached thus preventing the compass from possibly giving false readings after such manoeuvers,