Patent GB-707446-A (GB)
Title: Improvements in or relating to gyro compasses
IPC: G01C19/36
Filed: 1950-05-26
Abstract: 707,446. Gyroscopic apparatus. SPERRY CORPORATION. May 26, 1950 [May 28, 1949], No. 13299/50. Class 97(3) In a dual period gyrocompass for ships having gravity-responsive control means for rendering it North-seeking by the application of torques about a horizontal axis, the gravity-responsive control means comprises two torque-applying means which are together operative during normal operation, to give the compass a short period, e.g. one half or less of the standard 85 minute period for setting the gyro in the meridian when initially displaced by 30 degrees or more, and one of the torque-applying, means is rendered ineffective during accelerations of the ship of the order of those occurring during turns or changes of speed to give the compass the long, e.g. 85 minute period during such turns and changes of speed. The gravity-responsive control means may comprise a solid mass mounted on the directional element so that on tilt of the latter the mass is displaced parallel to the North-South axis of the element and towards its lower portion to exert a torque about the horizontal axis and additional torque-applying means, e.g. an air jet is brought into action by movement of the mass to exert the additional torque on the element about the horizontal axis in the same sense as the torque exerted by the mass, the additional torque being rendered ineffective on displacement of the mass beyond a predetermined range. As shown a mass 13 supported in antipendulous fashion by leaf springs 14, 15 on an extension 25 of the gyro casing 6 applies a meridian seeking torque about the E-W horizontal axis 7 of the compass and is movable along the direction of the gyro axis 8 under the influence of gravitational and other accelerations. On shifting, baffle plates 21, 22 attached to the mass 13 vary the normally balanced upward and downward jets produced by e.g. rotation of the rotor wheel or by impeller 25<SP>1</SP> and issuing from slots 24, 24<SP>1</SP> to produce an unbalanced force or torque which is added to that of the mass 13, thus giving the compass a short period but upon further shift of the mass 13, e.g. due to turns or change of speed of the ship, the slots 24, 24<SP>1</SP> are wholly covered by the baffle plates and rendered ineffective and the compass has the long period during such turns or changes of speed. The jets from slots 24, 24<SP>1</SP> are also used in accordance with the invention claimed in Specification 707,518 to damp the compass about the meridian by inclining the direction of the jets to the vertical so as to produce a torque about that axis to reduce the tilt. Damping means such as a paddle in a viscous liquid, e.g. silicone fluid, retards the shift of the mass 13 so that it is not responsive to accelerations due to pitch or roll. In an alternative construction masses such as 13 are similarly mounted on each side of the rotor, the damping means of one of the masses, e.g. the South mass being so stiff that it is relatively unresponsive to short period oscillations such as are due to turns or change of speed but is responsive only to the slow earth induced tilt of the gyro. The air jets are associated with this South mass and disposed in an East-West direction so that the compass damper formed thereby remains unchanged during turns or changes of speed of the craft. The North mass is damped so as not to respond to roll or pitch accelerations but to respond to changes in speed and course as well as earth induced tilts. In a modification of this construction the dampers associated with the masses may be interchanged so that the North mass is non- responsive to turns of the ship and the air-jetdamping means is retained on the South mass but is charged in construction so as to become ineffective when the South mass moves an increased amount to close both jet ports. Specification 612,723 also is referred to.