GB884552A - Improvements in or relating to propeller-driving power plant - Google Patents

Abstract

884,552. Variable pitch prollers; aircraft indicators. ROLLS-ROYCE Ltd. Aug. 6, 1958 [Aug. 13, 1957], No. 25601/57. Classes 4 and 114. [Also in Groups XIX and XXIV] In a propeller-driving power plant for aircraft in which epicylic gearing is provided between the propeller and an engine of the power plant, a torque reaction member of the epicyclic gearing is supported within fixed structure for limited movement during torque transmission and means is provided to be actuated when the movement of the torque reaction member, which occurs on transmission of negative torque, exceeds a selected value to give an indication of the extent of such negative torque conditions or to effect a desired control on the power plant. The helical epicyclic gearing comprises a sun gear 13 on the engine driven shaft 12, stepped planet gear pinions 14-15 supported by a carrier 16 secured to the propeller shaft 17, and an annulus gear 19 which forms the torque reaction member. The annulus gear 19 is supported from the fixed structure 10-11 by piston and cylinder devices, each having its axis inclined to the plane of the annulus gear at such an angle that the axial and tangential loads produced on said gear in torque transmission are supported hydraulically piston and cylinder devices 20 support the annulus gear during positive torque transmission, and piston and cylinder devices 21, 22 during negative torque transmission, the device 22 acting as a master device for controlling the hydraulic pressure written the other devices during bath positive and negative torque transmission. During positive torque transmission, the pressure of liquid in the devices 20 is controlled to oppose angular displacement of the annulus gear 19, the devices 21 being inoperative. During negative torque transmission there is a fall of pressure in the devices 20, and pressure within the devices 21, 22 opposes movement of the annulus gear in the direction of the arrow 64, Fig. 8; until said pressure increases, blows off a spring loaded valve in the device 22, resulting in sharp movement of the annulus gear in the direction of the arrow, whereupon a lug 94 on the gear 19 rocks a lever 96 connected through a linkage 97 to raise a piston valve 84. Ordinarily, with the piston valve 84 in its normal position. as shown, the pitch of the propeller blades 66 is adjusted by the hydraulic motor 67 under the control of a constant speed unit 69 having a piston valve member 73 moved by a fly-bob speed responsive device- 78 against the loading in a spring 79 which is adjustable by means of an abutment 80 to select the desired rotational speed of the propeller. When the piston valve 84 is raised by negative torque, pressure fluid is supplied to the motor 67 through pipes 91 and 76 and supply line 71 causing downward movement of the piston 68 to coarsen the pitch of the blades 66, thereby slowing down the propeller. In another embodiment the blow off valve, whereby the control action or warning is given, is arranged outside the device 22, and the load on its spring is adjusted by a cam connected to the pilot's control lever so that the selected value of negative torque is lower during take-off and climb and steady flight conditions than during descent and landing. In an embodiment enabling windmilling drag to be obtained from the propeller during landing, a lever connected to the engine throttle lever increases the load on the spring of the blow off valve as the engine is throttled down so that the hydraulic load opposing negative torque movement of the annulus gear is sufficient to prevent movement of the latter to feather the propeller. Specification 776,023 is referred to.