Patent GB-839053-A (GB)
Title: Improvements in feel simulators for aircraft
Inventor: GREENLAND LEONARD SIDNEY
IPC: B64C13/46
Filed: 1957-10-28
Abstract: 839,053. Fluid-pressure servomotor control systems. HOBSON Ltd., H. M. Oct. 7, 1958 [Oct. 28, 1957], No. 33556/57. Class 135. [Also in Group XXXIII] An aircraft feel simulator of the type including a pilot's control member actuating a control surface and linked to an hydraulic jack, the housing of which communicates with one end of a valve chamber containing a control valve movable in opposite directions from a neutral position to connect the jack housing to pressure and exhaust, the valve moving in response to movements of the control member to permit liquid to flow to and from the jack housing, and also moving in response to a force on the valve opposing the hydraulic pressure in the valve chamber and exerted by an airspeed responsive device, to vary the pressure in the jack housing with varying airspeed, also comprises two restricted orifices respectively permitting liquid flow from the housing into the valve chamber, and liquid flow out of the chamber, the control valve when in its neutral position permitting liquid under pressure to flow into the housing to replace that flowing out through the orifices, and comprises normally ineffective means controlled by a Mach number responsive device for controlling a valve regulating the effective area of one of the orifices to change its area when a given Mach number is attained, thereby modifying the relationship between the pressure in the jack housing and airspeed as the Mach number increases. In the Figure, which shows a modification of the apparatus described in Specification 734,437, a diaphragm 16 is subjected on its two sides to total pressure Pt and static pressure Ps, and is connected by linkage 17a, 17b to act on the control valve 10 through a push-rod 18. The valve co-operates with ports connected to a pressure fluid supply line 12 and return line 13. The valve can connect either port to a conduit 11 leading to the jack housing (not shown). The chamber 14 is connected to conduit 11 through a restricted orifice 15, and to exhaust through a restricted orifice 20. In this arrangement, the valve is in its neutral position when the force exerted on it by diaphragm 16 balances that exerted by a spring 21 and the pressure P in chamber 14, which is a proportion of the pressure Pc applied to the jack housing, the proportion depending on the relative areas of orifices 15, 20. In this neutral position, fluid leaks into conduit 11 from conduit 12 at the same rate as it leaks out through orifices 15, 20. Any change in airspeed unbalances valve 10, opening the appropriate port until the pressure P rebalances the valve, the pressure Pc being correspondingly altered. The Mach number sensitive device comprises a piston 22 in a cylinder 23, the piston-rod bearing an arm 25 having a pin 38 serving as fulcrum for a slotted lever 36. Forces are exerted on lever 36 by an evacuated capsule 39 subjected externally to total pressure, and by a diaphragm 32 subjected on its two sides to total pressure and static pressure. Movements of lever 36 are transmitted by linkage 33a, 33b to a shuttle valve 35 controlling the connection of cylinder 23 to pressure and return hydraulic lines. By this arrangement, the piston 22 is driven towards a position such that pin 38 is located at that fulcrum point of lever 36 where the moments exerted on the lever by the capsule 39 and diaphragm 32 balance. The piston-rod 24 is provided with a stop limiting its movement to the left, as shown, so that on exceeding a predetermined Mach number, the piston commences to move to the right from the position shown, its position thereafter depending on the Mach number. A cam face 26 on the pistonrod rocks a lever 28 pivoted at 29 and operating a needle valve 31 regulating the effective size of orifice 20, and thus the relationship between pressures P and Pc. Since pressure P is a function of airspeed, the relation between Pc and airspeed is thus modified in accordance with Mach number, above a predetermined Mach number.