Patent GB-676804-A (GB)
Title: Improvements in engine controls for aircraft
IPC: F02D29/00
Filed: 1949-12-13
Abstract: 676,804. Controlling aircraft; variable-pitch propellers. HOBSON, Ltd., H. M., and SWAAB, C. H. Nov. 22, 1950 [Dec. 13, 1949], No. 31975/49. Classes 4 and 114. A throttle control installation for an aircraft engine fitted with a reversible pitch propeller of the type in which the throttle lever is movable beyond the slow running position into a braking range and is arranged, when so moved, to effect progressive opening of the throttle and also to render a pitch reversing mechanism effective to reverse the pitch of the propeller blades is so arranged that the pitch reversing mechanism coacts with the throttle lever so as to be actuated thereby to reverse the blade pitch when the lever has been moved into a position in the braking range corresponding to a throttle opening sufficient to prevent engine stall, and to be actuated thereby to return the blade pitch to normal only after the throttle lever has been moved out of the braking range and to a position sufficiently beyond the slow running position to prevent engine stall, and comprises a stop mechanism, controlled by the pitch-reversing mechanism, for preventing substantial movement of the lever into the braking range beyond said first mentioned position until after the blades have been moved from normal into reverse pitch, said stop mechanism being ineffective at any time to prevent movement of the lever out of the braking range. The throttle box arrangement is of the type described in Specification 649,671 and includes a throttle lever 10 formed with a slot 14 to actuate a throttle control rod 18, a cam 13 to actuate switches of the type known under the Registered Trade Mark "Micro-switch," and a stop arm 40. The lever 10, which normally moves between the positions SR and FT, and may be moved rearwardly in two movements to the position FB for braking purposes during the landing run and forwardly from the braking position in one movement during an emergency take-off, is provided with a pin 22 which normally engages a stop 19 pivoted at 27 and formed with a tail which rests on a projection 29 of a slidable bar 28 urged upwardly by a spring 30. When a switch 20 on the lever is closed a circuit is completed through a further switch 24 actuated by the lowered undercarriage to energise a solenoid 25 to draw the bar 28 downwardly. This movement frees the stop 19 which is urged anticlockwise by a spring 26 to enable the lever 10 to be moved to the position shown by full lines and a cam 34 formed on the bar 28 closes a switch 35 to complete a circuit through a further switch 36, closed by the cam 13, to complete a holding circuit for the solenoid 25. Before the lever 10 reaches the slow-running position SR the cam 13 closes contacts 38a and opens contacts 38b of an unbrake selecting switch 38 and after the lever has passed position SR the cam 13 closes contacts 37a and opens contacts 37b of a brake selecting switch 37. The lever 10 is arrested in the position shown by full lines by a pivoted stop 39 which engages with the arm 40. Closing of the contacts 37a completes a circuit through a coil 52 and contacts 53a of a relay 53, the coil 52 moving a valve (not shown) into a position in which liquid is supplied to actuate the pitch changing piston 54 and the contacts 53a complete a holding circuit for the coil 52. As the blades 55 move into reverse pitch a ring 56 bridges a pair of contacts 57 to prepare a circuit for an unbraking coil 58. When the blades are fully reversed in pitch the ring 56 engages a contact 59 to energise a solenoid 49 which disables the stop 39 and permits the lever 10 to be moved to the braking position FB. During unbraking, forward movement of the lever 10 breaks the holding circuit passing through contacts 37a and coil 52 and contacts 53a to the coil 52 and completes a circuit through contacts 57 and the now closed contacts 53b to energise the unbraking coil 58 to cause the blade pitch to return to normal. Separation of the ring 56 and the contact 59 breaks the circuit to the coil 49 thus allowing the stop 39 to return to its intercepting position and then separation of the ring 56 and the contacts 57 breaks the circuit to the unbraking coil 58 and the governor resumes control of the blade pitch and further forward movement of the lever 10 opens contacts 36a and restores the stop 19 to its operative position.