Patent GB-408936-A (GB)
Title: A combined magnetic compass and inclinometer
IPC: G01C17/00
Filed: 1932-10-14
Abstract: 408,936. Magnetic compasses; inclinometers. COOKE, M. A., Elysium, Shillong, Assam, India. Oct. 14, 1932, No. 28703. [Class 97 (ii).] A combined magnetic compass and inclinometer comprises a uni versally rotatable indicating mem ber, having a magnetic axis and a gravity axis, tending to align respectively with the earth's magnetic fielc and the gravity field, the gravity bias being re ducible to avoid inertia effects due to turning of the supporting air craft &c. In the form shown, the indicating element comprises a hollow sphere 2, having one hemispherical part fixed to a ring 11 and the other hemispherical part adapted to be screwed thereto. Two groups of magnets 1 are mounted by brackets 7 on an externally threaded tubular rod 8, which is diametrically supported by bearings 10 in the ring 11. Screws 32 enable the magnets 1 to be fixed so that they make an angle with the axis of the ring 11 corresponding to the angle of dip. A ring 12 fixed to the ring 11 at right angles thereto, carries a rod 26 terminating in a sleeve 27, which loosely surrounds the rod 8 and is held in position by a threaded rod 28, fixed in the ring 12 at right angles to the rod 8. A bracket 14, carrying adjustable weights 15 for applying gravity bias, is arranged to slide on the rod 26 and is attached to the bottom of the ring 12 by a series of spring walled capsules 16 which communicate with each other and with an aperture in the sphere 2 by a pipe 20. Increase of pressure in the capsules 16 causes them to spring into the distended position and lift the bracket 14, thus rendering the bias weights inoperative. Adjustable balance weights 29 are provided on the rods 8 and 28 and balancing screws 31, arranged at right angles are threaded through the rod 8. The sphere 2 is suspended in a liquid, e.g. alcohol, of the same density and contained in an outer sphere 3 with a window 5. The sphere 2 is centralised in the sphere 3 by jets from four nozzles 4 arranged at the four corners of a tetrahedron. Each nozzle, Fig. 2, has a central bore 4<b>, to which alcohol under pressure is supplied from pump 6 by pipes 48, and a concave spherical surface 4<a>, between which and the sphere 2 the alcohol passes to an annular passage 4c and from thence through pipes 49 back to the pump. Before accelerating or turning of the supporting craft, the pressure in the sphere 3 is increased either by the manually operated pump 21, 22 or automatically in response to movement of the controls of the craft, so that the capsules 16 are distended and the gravity bias eliminated. In a modified form the clamping screws 32 are dispensed with and the rod 8 provided with two friction discs. The latter are normally engaged by brake pads on the ends of two spring-urged levers, the free ends of which are arranged adjacent a flexible part in the wall of the sphere 2. When it is desired to reset the magnets 1, a plunger 41, Fig. 1, is pressed against the flexible part and causes the levers to rock and withdraw the brake pads. The magnets 1 then settle in accordance with the angle of dip and may be clamped again by withdrawing the plunger 41. The sphere 2 may be marked with lines of latitude and longitude and the window 5 with cross wires. According to the Provisional Specification a fixed bias weight may be mounted at the bottom of the sphere 2 and its effect counteracted when desired by forcing the alcohol up a normally vertical passage to a chamber above the centre of the sphere 2. Specification 408,973 is referred to.