Patent GB-814308-A (GB)
Title: Improvements relating to aircraft controls
Inventor: FOWLER JOHN LAWRENCE
IPC: B64C13/24
Filed: 1956-01-25
Abstract: 814,308. Controlling aircraft. FAIREY AVIATION CO. Ltd. April 25, 1957 [Jan. 25, 1956], No. 2536/56. Class 4. [Also in Group XXIX] An aircraft includes a power operated main control surface moved by a power actuator; an auxiliary control surface mounted on the main surface and capable of manual deflection relatively to the main surface in flight, and mechanism arranged to lock the main control surface when moved to its neutral position, the mechanism being normally inoperative, but operating automatically on failure of the main power supply for the power actuator. Fig. 1 shows an all moving tailplane 10 pivoted to the aircraft at 11 and supporting on a torque tube 27 an elevator 12 rotatable on axis 13. A rod 25 linked to the pilot's control member is pivoted to a crank arm 26 on tube 27, a second such arm 29 being pivoted to a rod 28 pivoted at 30 to a floating lever 31. A second pivot 32 is connected to the valve rod 24 of a valve controlling a hydraulic jack of which the casing 16 is pivoted to the aircraft at 17, and the piston rod 19 is pivoted to the tailplane at 20. The third pivot 33 of lever 31 is connected to a rod 34 pivoted to the tailplane at 35 and containing a telescopic spring portion 60. Movement of rod 25 controls the elevator 12, and also displaces the servo valve through rod 28 and lever 31. The tailplane is thus deflected in the same sense as the elevator until rod 34 has moved lever 31 to restore the valve rod 24 to its neutral position. The load in the elevator 11 provides " feel " in the pilot's control. In Fig. 3, the piston rod 19 of the jack has two notches 40, 41 engageable by pawls 42, 43 when the rod is central, i.e. when the tailplane is undeflected. These pawls are normally held disengaged by pistons 52, 53, acting on the tails 47, 48 of the pawls and kept apart by the hydraulic pressure in duct 55 derived from the supply line 22. If the supply fails, the pistons are urged together by springs 49, 50, and the pawls engage rod 19 and lock it as soon as it reaches its central position. Pressure fluid from line 22 passes through a non- return valve 72, and bores 70, 71 to the valve 23 for distribution to the jack. A piston 68 separating a fluid reservoir 65 from an air chamber 66 charged with air under pressure through an inlet valve 67, is normally maintained in the position shown by the pressure fluid acting through valve 69. If the pressure fails, the fluid in reservoir 65 is kept under pressure by the pressure in chamber 66. A piston 74 is normally held in contact with an abutment 78, the pressure on its two faces being equal, but the upper face (as shown) having less area because of a piston rod 75 normally holding open a micro switch 76. If the pressure fluid supply fails, the pressure in its lower face drops, and the piston moves downwardly. The micro switch closes, actuating a warning light, and a bore 79 is exposed, connecting the reservoir 65 with valve 23, to provide sufficient energy for the pilot to centre the tailplane through the servo. Movement of piston 52 or 53 also operates a micro switch (e.g. switch 57 through rod 58) to actuate a warning horn. Specification 606,620 [Group XXIX] is referred to.