GB522436A - Improvements in or relating to magnetic compasses - Google Patents

Abstract

522,436. Magnetic compasses. SPERRY PRODUCTS, Inc. Dec. 8, 1938. No. 35826. Convention date, Jan. 21. [Class 97 (ii)] In order substantially to eliminate errors due to the effect of the vertical component of the Earth's magnetic field during the initial stages of a turning movement of the supporting aircraft, the movable system of a magnetic compass has a long undamped period of oscillation. The compass card may carry an annular metal ring to increase its movement of inertia or the magnets may be of low strength. The Figure shows the compass errors which occur whilst an aircraft is making a turn through 360 degrees at a banking angle greater than the complement of the angle of dip. Curves 51, 52, for cards having undamped periods of 6 and 12 seconds respectively, show that the cards turn in the direction in which the aircraft turns from the beginning of the turn. Curves 53, 54, 55, for cards according to the invention having undamped periods of 60, 120, 180 seconds respectively, show that the card does not turn with the aircraft during the initial period 32 of the turn. Further increases of the undamped period to 360 and 600 seconds (curves 56 and 57 respectively) provide cards which give a substantially correct reading throughout the turn.