GB539128A - Improvements relating to retractable undercarriages of aircraft - Google Patents

Abstract

539,128. Retractable aircraft undercarriages. HAERLE, H. R. May 10, 1940, No. 8435. [Class 4] [Also in Group XXIX] The retraction mechanism of an aircraft undercarriage is controlled, so that retraction can only be effected after the aircraft has reached a predetermined air speed, by means of a fluid operated device coupled to the operating mechanism by valve or relay means. The control may be applied to the hydraulically or electrically operated systems of the retraction mechanism, the circuits in either case being interrupted until the above condition is fulfilled, or it may be applied to the control members of either of these systems whereby such members are kept in a locked position until the predetermined air speed is reached. In an embodiment of the former application, a fluid supply line of a hydraulically operated system is provided with a valve 5 arranged between inlet and outlet passages 2a, 8 respectively, the valve being housed in a lower enlargement of a housing 1 which latter also accommodates a piston 13 in an enlargement 3. Both the valve and piston are spring urged in the same direction and their stems contact so as to move together. The parts 2a and 3 communicate through passages 21, 22 via a relay valve comprising a ball 19 spring urged on to its seating at the base of a cylindrical bore 17, the ball contacting with a rod 20 accommodated in the latter. Supported on the housing 1 is a cover 23 housing a bellows 24 normally expanded by a spring 28 and an adjustable screw 26, the bellows being connected by a pipe line 27 to a source of negative pressure on the aircraft. The latter may be obtained from a venturi or the pressure difference between the upper and lower surfaces of the wing aerofoil by accommodating the casing of the bellows or diaphragm within the wing and when this reaches a sufficient value according to the speed of the craft, the bellows collapses and through linkage 30 and rod 20 forces the relay valve 19 off its seat thereby connecting the inlet 2a to the cylinder 3. The valve 5 is thereupon lifted off its seating and the fluid line of the retracting system restored to continuity. In a form of the invention applied to the control member of an electrically operated system, the fluid responsive device comprises a two-part casing 31, Fig. 2, with a diaphragm 32 held there-between, the upper part being connected by a pipe line 34 to a venturi 35 mounted for example on the undercarriage 36. A spring 38 and adjusting screw 37 are provided. The lower part of the casing houses a fixed contact 39 and a pivoted contact 40 movable by a rod 41 so that flexure of the diaphragm upwardly causes the contacts to be closed. The latter are in circuit with a solenoid 42 which is adjacent to the control member 43. When the contacts are open the catch 44 locks the control member in the " down " position as shown, the catch unlocking when the contacts are closed. Specification 538,700 is referred to.