GB670552A - Improvements relating to governor means for prime movers and the like - Google Patents

Abstract

670,552. Gas turbines. POWER JETS (RESEARCH & DEVELOPMENT), Ltd. March 28, 1946. [March 28, 1945; May 2, 1945]. Nos.7831/45 and 11188/45. Class 110(iii). [Also in Groups XXVII, XXIX, XXXIII, XXXV and XXXVIII] In an aircraft speed control system the difference between a value dependent on engine speed and an adjustable reference value controls one adjustable element of an engine fuel valve to maintain engine speed at a desired value and a second adjustable element of the engine fuel valve is provided to adjust the datum of fuel flow. In a system for controlling aircraft engine speed, airspeed and propeller pitch, Fig. 1, the opening of a throttle 1 (see Group XXIX) controlling the fuel supply to the engine, which may be a gas turbine, is dependent firstly on the setting of a spindle 13 coupled through a linkage 25 to a hand lever 21 and secondly on the setting of a spindle 16 coupled through reduction gearing 17 to an electric motor having a stator winding 20 and rotor winding 18. Stator 20 is supplied from a three-phase alternator driven by the engine, and rotor 18 is supplied from a master oscillator-amplifier 19 so that the motor rotates at a speed proportional to the difference in frequency of the stator and rotor supplies until the engine speed is such that the two frequencies are equal. Engine speed is normally held automatically at a value determined by the position of lever 21 which adjusts the master oscillator frequency through linkage 24, but below a predetermined low speed contacts 28 are opened by stop 27a to disconnect the motor and direct manual operation of the throttle only is available through linkage 25. Such direct manual operation is available in the event of electrical failure. Excessively rapid changes of speed setting are prevented by a spring 22 and dashpot 23 associated with lever 21. An airspeed pressure-responsive capsule 29 adjusting the master oscillator frequency by movement of linkage 24 without affecting the position of lever 21 automatically corrects variation of airspeed, e.g. due to altitude change, from a value corresponding to the setting of lever 21. To maintain automatically the most efficient angle of attack of the airscrew 31 in a manner which is the subject of Specification 670,553, a reversible. servomotor 32 adjusting pitch is selectively controlled by a switch having a contact 40 positioned relative to opposed contacts 36 by coils 41 and 42, energized from a tachometer generator 56 driven by the engine, interacting with a permanent magnet 43. A true airspeed responsive capsule 48 adjusts a rheostat in series with coil 41 so that the position of contact 40 is dependent both on airspeed and engine speed and motor 32 adjusts pitch until a mechanical follow back through linkage 37 moves contacts 36 to a neutral position. Adjustment of pitch with movement of linkage 24 results from movement of contacts 36 relative to linkage 37 by nuts 39 on a screw 38 having oppositely threaded ends operated through gearing 53 and linkage 54, a lost motion coupling 55 eliminating pitch changes in this manner due to small movements of linkage 24. Over-riding manual control of pitch is available by lever 49 operating contact 40 through linkage 50 and lost motion coupling 51, coils 41-42 being then de-energized by the opening of contact 52. There are references to electric or hydraulic servo mechanism between capsule 29 and linkage 24 and substitution of a yawmeter responsive to differential pressure between the two sides of the propeller for capsule 48.