GB558725A - Indicator for variable pitch propeller - Google Patents

Abstract

558,725. Variable-pitch propellers. ENGINEERING & RESEARCH CORPORATION. Jan. 7, 1943, No. 302. Convention date, Jan. 16, 1942. [Class 114] In a propeller in which the pitch of the blades 12 is adjusted by means responsive to differential rotation of a part 18 connected to the drive shaft 10 and a part 19 normally rotating with the shaft but capable of rotation at a different speed, the difference in frequency or other function of two electric currents, which vary in accordance with the speeds of rotation of the two parts 18, 19, is used to operate a pitch indicator 41. The parts 18, 19 are connected together by means of a spring-pressed friction clutch 23 controlled by a solenoid 25, whilst the part 19 is rotated by means of an electric rotor 21. When an electric circuit under the control of the pilot, or of an automatic governor, is energised, the clutch 23 is released and the rotor 21 is rotated at a speed greater or less than that of the shaft 10 to change the pitch of the blades 12. Secured to the part 19 and shaft 10 respectively, are two relatively rotatable rings 42, 43 of non-magnetic material containing magnetic laminations 45. These are surrounded by a fixed ring 26 of E-cross-section made up of alternate segments of magnetic and non-magnetic materials. Those carry inner windings 33 connected in series with a source 34 of direct current, and outer windings 35, 36 connected to the field and armature windings 37, 38 of a two-phase slip-ring synchronous motor the armature 39 of which is connected to the indictaor 41. Resistances R<SP>1</SP>, R<SP>2</SP> eliminate circulatory currents. In a modification, single coils in each of the grooves of the ring 26 are connected in parallel to a source of direct current and by means of transformers to the windings of the synchronous motor.