GB451520A - Improvements in or relating to variable pitch airscrews for aircraft - Google Patents

Abstract

451,520. Screw propellers. BRISTOL AEROPLANE CO., Ltd., FEDDEN, A. H. R., and OWNER, F. M., Filton House, Bristol. March 9, 1935, No. 7438. [Class 114] [See also Group XXXV] In a variable-pitch air screw the control mechanism is actuated automatically in accordance with the engine speed, the controlling means being either an electrical or a centrifugal mechanism which functions also as an engine-speed indicator. The speed-indicator has an armature 10 connected to a generator 13 driven by the aircraft engine and has a resistance 14 included in the circuit so that the deflection of the armature corresponds to the engine speed. There is fitted on the armature spindle 15 a disc 16 carrying two conducting strips 17, 18 cooperating with the brushes 19, 20, in a circuit which is part of the blade actuating mechanism. The disc 16 also carries a pointer 21 movable over a scale 22 indicating engine revolutions per minute and there is a further pointer 24 carried by a sleeve 23. The outer end of the spindle 15 is surrounded by the sleeve 23 which has a knob 25 whereby it may be adjusted so that the tail of the pointer 24 which carries a third brush 26 may also co-operate with the contacts 17, 18, The brushes 19, 20 and 26 are connected to a relay 29 which is on the input side of the battery 30. This relay may operate the piston of a hydraulic control mechanism or where the pitch changing mechanism is electrical will operate a relay. In a modification, a centrifugal governor 31 is driven by the engine and its spindle carries the disc 33 of insulating material, but with a conducting rim 34. The brush 35 is connected by a lead 36 to a source of electric current and mounted adjacent to the governor are a pair of arms 37, 38 carrying conductors 44, 45 in the relay circuit 46. The arms are held under spring restraint 42, 43 upon a rod having a rack-and-pinion gearing with a pointer 51. The pointer is further connected by gearing with a screw and nut mechanism 47, 48 upon the governor spindle. Changes in speed are followed by contact of the rim 34 with the brushes 44, 45 and a subsequent adjustment of the pitch of the blades. Specifications 151,917, and 250,292, [both in Class 114], and 411,601 are referred to.