Patent GB-740466-A (GB)
Title: Improvements in or relating to speed control systems for propulsion units having reversible pitch propellers
Inventor: MORGAN WILLIAM GEORGE
IPC: B64C11/30
Filed: 1953-01-14
Abstract: 740,466. Variable pitch propellers; controlling aircraft. BRISTOL AEROPLANE CO., Ltd. Jan. 6, 1954 [Jan. 14, 1953], No. 1149/53. Classes 4 and 114. Relates to a speed control system for a propulsion unit having a reversible pitch propeller of the kind in which movement of a manual speed-control lever 70, such as a throttle lever, in one direction from a reverse initiating. setting, speeds up the unit in ahead pitch for forward propulsion and movement in the other direction speeds up the unit in reverse pitch for braking. According to the invention the reverse initiating-setting of the speed control lever 70 corresponds to an intermediate speed of the unit in ahead pitch and the lever is movable from that setting in one direction into a higher speed range in ahead pitch and in the other direction into a lower speed range in ahead pitch; two propeller pitch reversal initiating means (electric switches 110, 112) act in combination to bring about the pitch reversal of the propeller, one reversal means 112 becoming operative when the lever 70 is in its reverse initiating setting, and the other, 110, becoming operative when a separate manual control 106 is moved to a reverse selecting position; return means ensure return to ahead pitch when the lever 70 is moved back through its reverse initiating-setting from a setting in said lower speed range, a further means maintains reverse pitch, once obtained, while the lever 70 is in its lower speed range, and speed control reversing means, rendered effective by the manual control 106 on movement to its reverse selecting position, to reverse the action of the lever 70 on the unit when the lever is moved from its reverse initiating setting to a position in its lower speed range so that the speed of the unit is increased instead of being reduced. The lever 70 rotates on a primary shaft 71 between two inner plates 73 and two outer plates 74 also rotatable on said shaft. The inner plates 73 and the outer plates 74 are connected by links 95 and 96 respectively to the arm 94 of bell-crank levers 91 mounted on a secondary shaft 90, the arms 92 of the levers being linked to Selsyn transmitter units 93 electrically connected to corresponding receiver units associated with the engines for speed control of the latter. The inner and outer plates 73, 74 are arranged to be alternatively coupled to the lever 70 by a roller 81 carried by a swinging link 82 pivoted to the lever 70 and moving from a driving slot 83 in the plates 73 to a driving slot 84 in the plates 74, said slots projecting respectively inwardly and outwardly from equal radius arcuate edges 85 on the plates 73, 74, the arrangement of the links 95, 96 being such that the slots 83, 84 come into alignment as soon as the control lever 70 moves through its reverse initiating setting into the lower speed range. The ends of the roller 81 project into arcuate slots 100 in plates 101 journalled on a tertiary shaft 102 and constituting a reversing lever connected by a torsionspring 103 to the shaft 102 which has a lever arm 104 connected by a link 105 to the manual control reverse selection lever 106. When the latter is in its normal ahead propulsion position the springs 103 urge plates 101 towards shaft 71 to maintain rollers 81 in the slots 83 of the inner plates and the lever 70 operates transmitter units 93 in the normal manner, i.e. forward movement of the lever gives increased speed in ahead pitch and rearward movement gives decreased speed in ahead pitch. As noted above, when lever 70 is moved to the flight idling setting, the slots 83, 84 are brought into alignment, so that if the lever 106 is then moved to its reverse selecting position the switches 110 and 112 are both actuated to close the circuit to reverse the pitch of the propeller and the springs 103 urge the roller 81 outwards into the slot 84 so that the transmitters are driven by the outer instead of the inner plates, the direction of movement being reversed, the units speeding up instead of slowing down. Reverse pitch is held by a holding circuit until lever 70 is returned to its flight idling position, where, if the lever 106 is in its " off " or normal ahead position, a roller 109 on the lever 70 engages the cam surface 108 on the reversing lever 101 to move the latter to push roller 81 into the slot 83 in the inner plates. The flight idling setting of the lever 70 is apparent to the pilot since at that setting a fixed spring-pressed detent 97 enters a recess in a quadrant 98 on the levers 91 and a greater effort is required to move the lever. To obtain time for pitch reversal to take place and to prevent inadvertent movement of lever 70 when reverse pitch has been selected, movement of the control 106 to its reverse selecting position moves ramps 115 into the path of resilient detents 116 on the outer plates 74 so that movement of the lever 70 requires additional effort. A manual locking control lever 117 mounted on a pivot 120 is connected by a link 122 to one arm 123 of a two-armed lever fixed to the secondary shaft 90, the other arm being connected by a link 125 to the system which centralizes and locks the aerodynamic control surfaces. Bellcrank levers 128 journalled on the shaft 90 carry an abutment 132 which, when said shaft is turned by moving lever 117 into the controlslocked position, engages an abutment 133 on the shaft, thereby turning the levers 128 into a position in which their arms 134 lie in the paths of the faces 135 of the levers 91. The arms 134 carry spring-loaded pins 140 of such a length that two levers 91 of a pair cannot be moved simultaneously past a pin. The interlock device is arranged to become effective at the flight idling setting of the levers 91, the device being such that any one engine, or any two on opposite sides of the aircraft, may be run up to maximum speed for ground-testing purposes while the flying controls are locked but the attainment of maximum speed of a sufficient number of engines to permit the aircraft taking off is prevented. The levers 128 are maintained in their locked position by an electromagnetically retractable detent 144 which engages under an abutment 145 on crank-pin 129 until the flying controls are unlocked. When detent 144 is retracted, levers 128 are held in their inoperative position by a spring 150.