GB818701A - Improvements in or relating to control systems for aircraft propellers - Google Patents

Abstract

818,701. Variable pitch propellers. ROTOL, Ltd. Oct. 29, 1957 [Nov. 1, 1956; Jan. 10, 1957; Feb. 20, 1957], Nos. 33448/56, 1071/57 and 5794/57. Class 114. In a multi-engined aircraft having gasturbine propeller engines, the propellers each including a constant speed unit, a control system for the propellers comprising for each propeller, a pitch stop which is operative in flight and which prevents the propeller fining off to an angle such that excessive windmilling speeds can occur in the event of failure of the constant speed unit of the propeller, sensing means for sensing when the propeller has fined off to a predetermined pitch at least approaching that set by said pitch stop, and control means for withdrawing said pitch stops, the control means is connected with the sensing means of the propellers to operate to withdraw the pitch stops of all the propellers when all the propellers have fined off to the predetermined pitch. The sensing means for each propeller comprises an electrical switch (10 in the embodiment shown) which is closed when the propeller is at and below said predetermined pitch, and the control means comprises solenoids 12, switches being connected in series with one another and the solenoids, and the solenoids being connected in parallel with one another, and energizable each to initiate the withdrawal of the pitch stop of one of the propellers e.g. by controlling a valve in a hydraulic circuit. A double pole manual switch 14 is provided to isolate the circuit from the electrical source 15 and place the withdrawal of the pitch stops entirely under the control of the pilot by closure of a double pole manual switch 13. Other embodiments include a warning light. Specification 818,611 is referred to.