GB586191A - Improvements relating to magnetic compasses - Google Patents

Abstract

586,191. Magnetic compasses. SPERRY GYROSCOPE CO., Inc. Feb. 10, 1944, No. 2491. Convention date, Feb. 28, 1942. [Class 97 (ii)] An apparatus for reducing the northerly turning error in a magnetic compass carried on a craft, comprises a magnetic-field compensating device and a shielding means for the device which are relatively moved by a turn indicator to apply to the magnetic needle the requisite correction. Fig. 1 shows the instrument panel 21 of an aircraft on which is mounted the. casing 20 of a magnetic compass with a pendulous compass card 22 supported on a jewel post 23 and bracket 24 and maintained in azimuth by magnets 25. The lower casing 31 encloses a bank indicator comprising a ball and fluid in the curved tube 30, the gyroscopic rate of turn indicator comprising a pneumatically driven rotor 35, the supporting frame 34 and disc 37 processing about an axis defined by the trunnions 32, 33 and the compensating device consisting of magnets 50, 51 fixed in an arcuate sleeve 52 and mounted by the arm 53 on the disc 37. Precession of the disc 37 against the action of the centralising spring 36 is proportional to the rate of turn, being measured by the movement of the pointer 41, the pin 42 engaging a slotted member 43 which controls the nuts 44 and causes the magnets 50, 51 arranged linearly so that the south poles are at the extremities to emerge from their shielding sleeve to exert their compensatory effect on the magnetic needle of the compass. By adjustment of the strength of magnets 50, 51 and their distance from the magnets 25, the compensating torque can be made proportional to the northerly turning error in any properly banked turn. If the craft crosses the magnetic equator, the polarities of the magnets 50, 51 must be reversed and the shielding plates 80, 81 are adjustable by the screw 82 and knobs 83 for change of latitude. In a modification the shield 54 is moved by precession of the disc 37 to uncover the magnets 50, 51 which are then arranged so that the north poles are at the extremities. In a further modification, the compensating magnets are mounted in a piston reciprocating in a cylinder to damp the oscillations of the gyroscope. Specification 103,530, [Class 97 (ii)], is referred to.