GB1275265A - Ram-air turbines - Google Patents

Abstract

1275265 Fluid-pressure servomotor systems DOWTY ROTOL Ltd 5 Nov 1969 [15 Nov 1968] 54286/68 Heading G3P [Also in Division F1] A ram air turbine having rotor blades 12 the pitch of which can be varied by a hydraulic actuator 16 controlled by a rotor speed responsive governor 26 includes means for venting all the hydraulic chambers of the actuator to low-pressure below a predetermined rotor speed. Thus as the rotor slows down or stops the blades 12 can be automatically or manually moved to a coarse pitch position ready for the next restart. The governor 26 comprises flyweights 27 which control the axial position of a landed spool valve 28 loaded by a speeder spring 30. Should for example, the rotor speed rise above its set value, flyweights 27 move spool 28 to the left from its equilibrium position shown in Fig. 1 thus allowing liquid from pump 46 and pipe 51 to flow through port 36 to port 39 and thence through pipe 41 to chambers 21, 23, 25 of the vane type actuator 16. The shaft 18 and casing 19 of the actuator are thus urged to rotate in opposite directions driving bevel gears 15, 14, respectively, meshing with bevel gears 13 on the blade roots to move the blades 12 into a coarser pitch position and hence reduce the rotor speed to its set value. At the same time the remaining chambers 20, 22, 24 of actuator 16 are vented to low hydraulic pressure via pipe 42, ports 40, 37 and pipes 59, 57. Similarly with a fall-off in rotor speed below the set value the blades 12 are moved into a finer pitch position and chambers 21, 23, 25 are vented to low pressure. The rotor is mounted on an aircraft, either by means of a drop out leg or in a duct having closable entry flaps and drives an emergency hydraulic pump 44, alternator, fuel pump or pneumatic device. When it is desired to stop the rotor retraction of the leg is initiated or the entry flaps closed so that the speed falls-off. When the latter has fallen to about 800 r.p. m. flyweights 27 have moved sufficiently far inwardly to allow the spool 28 to move to the extreme rightwards position shown in Fig. 2 in which all the actuator chambers 20 to 25 are vented to low pressure via pipes 41, 42, 59. A torsion spring 17 connected between the bevel gears 14, 15 can thus move the latter so that the blades 12 are placed in a coarse pitch position ready for restarting when the turbine is next required. In a modification spring 17 is omitted and the blades 12 are moved manually into their coarse pitch position when the aircraft has landed. In a futher modification the actuator 16 is of piston and cylinder type.