Improvements relating to airflow direction indicators

1,069,086. Stall warning indicators. FERRANTI Ltd. May 6, 1965 [May 13, 1964], No. 19873/64. Heading B7W. [Also in Divisions F2 and G1] Apparatus for measuring the direction of airflow past an aircraft to give an indication of an impending stall, comprises a hollow probe rod 11 (Fig. 1) protruding through a flexible diaphragm 12 let into the fuselage of the aircraft, the inner end of the rod being attached to the slider of a potentiometer 19 extending perpendicular to a flexible ligament 16 attaching the rod 11 to an annulus 18. When the external end of the rod is deflected by the air flow it pivots about the diaphragm 12 and the inner end is displaced perpendicular to the ligament, producing an output signal from the slider of potentiometer 19. This signal is fed to a motor 20 which rotates the annulus-ligament-potentiometer assembly until the ligament is in line with the air flow, when the slider of the potentiometer is again central. A dashpot type damping device (Fig. 2) is mounted on the rod 11 between the diaphragm 12 and the annulus 18, preferably with the vanes 21, 22 coplanar when the angle of attack is close to the stalling value.