1,074,356. Measuring rate of turn electrically; gyroscopic apparatus. PNEUMODYNAMICS CORPORATION. April 6, 1966 [May 3, 1965], No.15273/66. Headings G1C and G1N. A fluid-rotor rate gyro 51 (Fig. 1) has Piezocrystals 115 mounted in the rotor chamber 71 which sense relative displacement between the fluid 91 and container 71, whereby the crystals produce output signals which are indicative of the magnitude of the rate of turn of the assembly 51 about an axis perpendicular to the nominal rotor spin axis, causing the relative displacement between fluid and container. The signals are fed to a synchronous resolver 35 to determine the polar position of the turn axis. A spherical rotor fluid chamber 71 is formed in a cylindrical body 72 supported by resilient end plates 61, 62, and filled with mercury to which thallium has been added. Mounted centrally by struts 111 in the chamber 71 is a spherical or, as shown, cylindrical support 101, carrying two crystal bars 115, or a single bender bi-morph crystal bar, with a paddle 121 attached to each outer end. When the assembly is rotated about an axis perpendicular to the nominal rotor spin axis, the fluid 91 is displaced relative to the chamber 71, the rotating paddles 121 sense a sinusoidally varying pressure which is conveyed to the crystals 115, giving an A.C. output, fed via slip rings 42 to the stator windings of synchronous resolver 35 to establish the magnitude and phase of the A.C., which is indicative of the magnitude and polar position of the rate of turn of the assembly.