GB649671A - Improvements in engine controls for aircraft - Google Patents

Abstract

649,671. Engine controls for aircraft; variable-pitch propellers. HOBSON, Ltd., H. M., and SWAAB, C. H. Aug. 30, 1948, Nos. 22804 and 24571. [Classes 4 and 114] [Also in Group XXIX] An aircraft fitted with a variable-pitch propeller has combined therewith a throttle lever movable beyond the slow running position into a braking range and arranged, when so moved, to effect progressive opening of the throttle, a pitch reversing mechanism, means coacting with the throttle lever and operable thereby, when the throttle lever is moved to a position in the braking range corresponding to a throttle opening sufficient to prevent engine stall, to render the pitch reversing mechanism effective to reverse the pitch of the propeller blades, in the case of movement of the lever to said position in the braking direction (i.e. from the slowrunning position) and to return the blade pitch to normal in the case of movement of the lever to said position in the opposite or unbraking direction, and a stop mechanism, controlled by the pitch-reversing mechanism, for preventing substantial continued movement of the throttle lever beyond said position in the braking direction until after the blades have been moved into reverse pitch, and in unbraking direction until after the pitch-reversing mechanism has commenced to return the blade pitch to normal. The lever 10 which controls the throttle opening and in the arrangement shown is coupled to a second pilot's control lever 20, is formed integrally with a cam 13 engaging a roller 15 mounted on a lever 16 connected by a rod 18, bell-crank 19 and rod 40 to the throttle control. The normal throttle lever range is defined by the positions C-D and at position D a pin 31 on lever 10 engages the nose of a stop 12 to prevent the throttle lever from moving into the braking range. To enable the throttle lever 10 to enter this range the upper part of the lever is raised to enable the pin 13 to clear the stop 12 and ride on the top face thereof, When the lever 20 is being controlled by a second pilot, movement of the interconnected levers 10 and 20 past the position D is effected by raising the lever 20 to move a trigger 37 which closes a micro-switch 39 to energise a solenoid 42. This solenoid moves axially a rod 43 on which a stop 47 becomes disengaged from the tail of the lever 12 to permit it to pivot under the action of a spring 49 to free the pin 31. The levers 10 and 20 can then be moved to the position E, shown on lever 10 only, when a cam 17 attached to the lever 10 operates a micro-switch 32 to start the pitch-reversing mechanism. Movement of the levers 10 and 20 to position F before the blade pitch is fully reversed is arrested by a stop mechanism comprising a lever 50 pivoted at 51 and provided with a pin 52 engaged by a tail 62 of the cam 17. The lower end of the lever 50 is engaged by a pivoted bell-crank 54 hooked at 63, 75 and pivotally connected at 57 to a solenoid 59. When the blades are fully reversed in pitch they move, by means of rods 69, a plate 68 which closes contacts 70, 72 to energize the solenoid 59 to release the tail of the lever 50 and so enable the throttle levers to be moved to the fully open position G with the propeller blades in reverse pitch. The propellers are of the constant speed type and normal adjustments of blade pitch are obtained by a valve 77, Fig. 2, controlled by a governor 78 which may be adjusted by a manual control 84. An engine-driven pump 79 which is provided with a relief valve 184 supplies hydraulic fluid through a non-return valve 80 to a chamber 81 of the valve 77, axial displacement of which will transfer hydraulic fluid through pipes 109, 108 or 104, 105 to act on the piston 64 of a constant speed unit 76 to increase or decrease the blade pitch through a link 65 and arm 66. When it is desired to vary the pitch either before or after a braking operation, hydraulic fluid from a pipe 119 is admitted either above or below the piston 103 of an over-ride valve 93, movement of which in either direction will cut off the connection between valve 77 and the constant speed unit 76 and connect either the pipe 105 or the pipe 108 with an electricallydriven pump 120'to vary the blade pitch. The connection between the pipe 119 and the valve 93 is effected by a pair of valves 113, 114 actuated by solenoids 118, 129 respectively which are energized by the micro-switch 32 through the medium of a further switch 126 which can close only when the aircraft is supported by the undercarriage. On a multiengined aircraft the throttle levers of the corresponding engines on each side of the aircraft are ganged to ensure that variable movement does not produce swinging of the aircraft during landing or take-off and in practice the connection between the levers 10 and 20 is made by a chain circuit in preference to the duplicated cam arrangement shown in Fig. 1. In a further arrangement (Fig. 8, not shown), the lever 16 may operate a micro-switch to energize an oil pressure warning mechanism when the throttle is open.