GB818611A - Improvements in or relating to hydraulic variable pitch propellers - Google Patents

Abstract

818,611. Variable pitch propellers. ROTOL Ltd. Aug. 14, 1957 [Dec. 18, 1956], No. 38606/56. Class 114. A propeller comprising, in the hub 12, a hydraulic pitch change motor 22, pitch stop means 25 operative to prevent the propeller fining off below a predetermined pitch and stop retaining means 28 displaceable between a first position (shown in Fig. 1) in which said retaining means maintains the stop 25 operative and a second position in which the stop is rendered inoperative, has a fluid pressure operated switch 51 outside the hub, conduit means 46 for communicating the switch with a source of hydraulic fluid under pressure to operate the switch, and hydraulic valve means 34 in the propeller hub, said valve means communicating said switch with a bleed 35 to relieve the pressure of fluid in said switch only when the stop retaining means 28 is in its operative position, the switch being operable only when the pressure of fluid in the switch is unrelieved through the bleed 35. A pump 17 supplies pressure fluid via a constant speed unit 14 and conduits 18, 19 to the pitch change motor 22, and also to a solenoid-operated valve 37 which is energized when it is required to render the stop 25 inoperative to permit fining off the propeller pitch, and to a control valve 39 from which a conduit 44, separate from the motor conduits 18, 19, is taken to a piston 31 for moving the stop retaining means 28 against the action of a spring 29 and to an annulus 33 communicating with said hydraulic means 34, formed by an annular recess in the stop retaining means 28 which recess is normally in communication with the bleed 35. Whenever, intentionally or unintentionally, the retaining means 28 is in the position allowing the stop 25 to be inoperative, the recess 34 is out of register with the bleed 35 so that pressure builds up on the spring- loaded piston 50 of the switch 51 to close the switch so that an indicator light (not shown) comes on. The invention is shown applied to a propeller in which the stop means has two stop positions, i.e. a first predetermined fine pitch position and then a second and finer pitch position. Specifications 742,148 and 818,612 are referred to.