GB564221A - Improvements in or relating to variable pitch propellers, especially for aircraft - Google Patents

Abstract

564,221. Electric control systems. FORSYTH, A. G. April 5, 1943, No. 5415. Convention date, June 30, 1942. [Class 38 (iv)] [Also in Groups XXXIII and XXXVII] A control arrangement for a propeller pitch-changing mechanism comprises a pair of switches 35, 35<SP>1</SP>, Fig. 2, operated by a governor 36 driven by the propeller engine, closure of one or other of these switches completing a circuit to drive a reversible electric motor 10 in one direction or the other to actuate the pitch - changing mechanism towards fine or coarse pitch respectively, the electric motor also driving separate means 48 for actuating fine and coarse pitch limit switches 38, 39 after predetermined operation of the pitchchanging mechanism. There is also provided a manually operable feathering switch 34, a feathering limit switch 40, and a manually operable switch' 37 for overriding the governor 36. In a modification, there is, in addition, a braking switch similar to the switch 34, and a braking limit switch similar to the switch 38. Fig. 1 shows two propellers 2, 3 mounted on coaxial hollow shafts 4, 5 and driven in opposite directions by two independent engines, their pitch - control gearing being operated by two reversible electric motors 10, 21, and the pitch-limit switches being disposed in housings 90, 90<SP>1</SP>. In a modification, there may be a single engine and a 'single electric motor. The switch 34 comprises a hand knob 44, Fig. 7, or a spring- urged rod 43 carrying branched members 45 to engage selectively with pairs of diagonally opposite contact studs 42. The shaft 48 carries a slidable switch block 50, Fig. 4, within a hollow support 47. The block 50 has two end projections 50<SP>1</SP>, 50<SP>11</SP> on its opposite sides to engage spring-urged contact arms 52, 521, 54<SP>1</SP> of the limit switches 38, 39, 40. The contact arm 54<SP>1</SP> is pivoted on a member 55 pivoted at 56 under the control of a spring 57 and provided with a stop 58. The Specification as open to inspection under Sect. 91 states also that the electric motors may be replaced by hydraulic motors. This subject-matter does not appear in the Specification as accepted.