Patent GB-734437-A (GB)
Title: Improvements in or relating to aircraft
IPC: B64C1/00
Filed: 1953-02-02
Abstract: 734,437. Fluid-actuated valves. HOBSON, Ltd., H. M., GREENLAND, L. S., WESTBURY, R., and SMITH, C. P. Feb. 2, 1954 [Feb. 2, 1953], No. 2894/53. Class 185. [Also in Group, XXXIII] A feel simulator of the type in which movement of a pilot's control member linked to a piston in a housing displaces liquid from the housing against hydraulic resistance, the linkage being such that the hydraulic resistance increases with displacement of the control member, the simulator also comprising a control valve to vary the hydraulic pressure with airspeed, is characterized in that the control valve is subjected to the hydraulic pressure in the housing and to an opposed force applied by an airspeed responsive device, the valve normally closing the outlet for liquid from the housing, and being movable from its normal position to increase or decrease the pressure in the housing, or to permit liquid flow in response to the movements of the control member. In the embodiment of Fig. 3, a port 32 in the simulator device 29 is connected to a high pressure supply line, and leads past a valve member 50 adapted to drop the supply pressure by an amount corresponding to the force of spring 53 to a space 39 surrounding one head of a valve member 41. A space 40 surrounding the other head communicates with a port 33 leading to a fluid reservoir. A central space communication with a port 28 leading to the housing containing the piston for exerting a force on the pilot's control member. This central space leads by a bore 43 to a space 44, beneath the valve member. A plunger 49 operates between the head of valve member 41 and one end of a lever 47 pivoted at 56 and controlled by a spring 58 and the movement of a bellows 46 connected internally by port 87 to pitot pressure. The spring 58 may have any characteristic to provide a given relation between hydraulic feel resistance and airspeed. An increase in airspeed will expand the bellows to depress plunger 49 and valve member 41, placing port 28 in communication with the high pressure space 39, the pressure building up until the pressure in space 44 is sufficient to return valve member 41 against spring 58 and the bellows force. A decrease in airspeed similarly allows the pressure in space 44 to raise the valve member, fluid exhausting then to space 40 until equilibrium is restored. Movement of the control member from neutral position increases the pressure in the housing and therefore that in space 44 to raise the valve member and'allow fluid to exhaust, and return to neutral position lowers the pressure, allowing fluid to flow in. Should the valve jam, an increase in the pressure in the housing forces fluid through passage 59 past a relief valve 57 to exhaust, and a decrease draws fluid past the lands of the pressure dropping valve 51. If passage 59 and valve 57 are omitted, spring 58 may also be omitted, and the valve member 41 be spring-biased against its housing, as in Fig. 2 (not shown). As an alternative way of producing given characteristics a conical compression spring, Fig. 4 (not shown) may be inserted between lever 47 and the housing 63, the plunger 49 then abutting a member slidable in a bore in lever 47 against a spring adapted to bias the member on to the plunger. Alternatively, a plurality of compression springs may be provided of different lengths as in Fig. 4A (not shown) so that each starts to be compressed only when the longer ones are partly compressed. A leaf-spring may be interposed between lever 47 and housing 63, or the lever may have a rounded surface 69 contacting housing 63 as a pivot to give a variable mechanical advantage, Fig. 6, the pin 48 sliding in a slot 68 in the lever. In the embodiment of Fig. 8, the bellows are replaced by a diaphragm 74 subjected to pitot presure on its upper surface and prevented by a spring 75 from acting on push-rod 49 until a predetermined airspeed is reached. Otherwise the embodiment is the same as that of Fig. 3, like parts being numbered similarly. Compression springs may be used to provide given characteristics as when a bellows is used. An abutment may be provided to limit movement of the diaphragm to provide a maximum feel resistance. As shown in Fig. 12, two diaphragms 81, 74 may be used, diaphragm 81 operating the valve member by lever 82 against spring 84, until the end 85 of lever 82 abuts diaphragm 74 which then acts on the lever in opposition to diaphragm 81, and may be made of larger area, to give decrease in feel resistance with increase of airspeed after a predetermined point. As an alternative, the bellows 46 of Fig. 3 may be fed from the pitot head through a constricted passage, and be provided with a bleed comprising a conical member fitting into a hole communicating with the bellows feed, movable axially of itself by a second airspeed controlled bellows to vary the bleed orifice and thus the pressure drop across the constriction. The conical member may be profiled to give any desired hydraulic feel to airspeed characteristics.