GB467735A - Improvements in or relating to magnetic compass devices - Google Patents

Abstract

467,735. Magnetic compasses. SPERRY PRODUCTS, Inc. Nov. 22, 1935, Nos. 32430 and 32431. Convention dates, Dec. 7, 1934 and Oct. 25, 1935. [Class 97 (ii)] [Also in Group XXV] A compass for use on aircraft comprises a magnetic sensitive element supported for universal movement and a pendulous element for applying a torque to the magnetic element the pendulous element being so controlled that the law of variation of the torque is changed, when acceleration forces acting on the said element exceed a predetermined magnitude. The torque increases until the forces reach the predetermined magnitude and then remains substantially constant. In Fig. 1 the sensitive element comprises a casing 20 including two floats 12, 13 which contain the magnets 10, 101 and are mounted on a rod 11 rotatable on bearings 17, 18, complete rotation being prevented by stops 71. An inner portion 22 of the case 20 contains a bowl 60 in the shape of a surface of revolution of a circle centre 0<11> about a line 00<1>, Fig. 5, a ball B resting in the bowl comprising the pendulous element. The casing 22 also carries a pivot 58 to mount the element universally on a pivot post P inside the spherical container C which is filled with liquid and fitted with an expansion chamber 29 and a lubber line 142. The position of the pivot 58 is adjusted to be in coincidence with the centre of gravity and centre of buoyancy of the sensitive element and the ball B is so chosen that the whole element is slightly pendulous. The pivot comprises a substantially spherical end 31 to a staff 33, Fig. 4, which touches the inner surface of the spherical cup 30, carried by the post P, tangentially at the point 50. The point is prevented from moving apart by the framework 58 which is loosely mounted over the joint to permit free rotational movement, the knob 31 being held against the cup 30 by the buoyancy of the sensitive element. The floats rotate until the magnets lie at the angle of dip and the element rotates as a whole until the magnets point to the magnetic north when a bearing may be taken by the lubber line 142 on a scale on the outside of the sensitive element. For small values of the acceleration force the ball remains in the notch N, Fig. 5, and the whole swings as a pendulum, but when the force becomes greater the ball leaves the notch and runs on the smooth surface of the cup thus changing the torque on the sensitive element. In the form shown in Fig. 13 the pivot comprises a conical jewel J pressed against the pivot post P by the buoyancy of floats 120 which contain the magnets 110, 111 carried on rotatable rods 114. The jewel carries three members 131, 1311, 13111 which support the pendulous member 130 and are attached to the jewel at points such as 140, 140<1>. For small forces the pendulum swings as a whole, all three members being taut, but for larger forces one or other of the members becomes slack causing the torque about the pivot to be changed.