Patent GB-740510-A (GB)
Title: Improvements in or relating to aircraft
IPC: B64C13/46
Filed: 1953-09-29
Abstract: 740,510. Aircraft feel simulators. HOBSON, Ltd., H. M., GREENLAND, L. S., WESTBURY, R., and SMITH, C. P. Sept. 2, 1954 [Sept. 29. 1953], No. 26760/53. Class 4. An aircraft feel simulator comprises a piston 23 in a housing 24, Fig. 4, the hydraulic pressure in which is determined by a pressure reducing valve 36, and further comprises a linkage actuable by a pilot's control member to effect relative movement of the piston and housing, thereby conveying liquid to or from the housing through said valve, the linkage being such that the hydraulic resistance which opposes movement of the control member increases with displacement of the control member in either direction from a neutral position, air speed responsive means 40 applying to the valve 36, below a selected Mach member, a force varying with airspeed to establish higher or lower hydraulic pressure in the housing corresponding to increased or decreased airspeed, and a normally ineffective device response to Mach number arranged, when the selected Mach number is exceeded, to apply to the valve a force opposing that applied by the airspeed responsive device. In Fig. 4, a unit 29 has a hydraulic pressure inlet 32, an outlet 33, and a port 28 connected by a conduit 27 with the right-hand side of piston 23, the left-hand side being connected to a reservoir. The valve 36 comprises two lands 37, 38 and a waisted portion 41, the space 42 round which communicates with the space 44 below the valve through a passage 43, and with the port 28 and a passage leading to one side of a pressure differential valve 51, the latter being subject also to a spring force 53 on the same side and to the hydraulic pressure prevailing at a port 39 on its other side. An extension of valve 51 abuts a spring-biased inlet valve 50. The valve 36 is subjected to a spring 45 and to the force of a diaphragm 40 subjected to total pressure above and static pressure below. An increase in airspeed forces the diaphragm and valve 36 downwards, allowing fluid to flow in from port 39 to space 42 and therefore the housing 22, until the pressure therein rises sufficiently to push the valve 36 back to its neutral position. Similarly a reduction in airspeed results in lower pressure in the housing 22. Movement of the control column from the neutral position moves piston 23 to the right, increasing the pressure in space 42 and raising the valve to allow fluid to flow through the outlet 33. Similarly return of the control column towards the neutral position lowers valve 36 allowing fluid to flow into unit 29. The pressure differential valve 51 may be omitted if a supply of fluid at a suitable pressure is available at inlet 32. The device responsive to Mach number comprises an evacuated bellows 54 acting between the housing of unit 29 and part of the surface of a diaphragm 55, the rest of the surface being subject to total pressure and the opposite side to static pressure. At the selected Mach number, the diaphragm 55 expands to contact a lever 56 pivoted at 57 to exert a force on the valve 36 opposing that exerted by diaphragm 40, so that at, say, Mach 0.95, the full force generated remains constant or decreases with airspeed, depending on the relative areas of the two diaphragms. In Fig. 5 (not shown) a further bellows and diaphragm, similar to those numbered 54 and 55, comes into operation at a further selected Mach number, say 1.05, to assist the diaphragm 40, so that after this Mach number is reached, feel force again increases with airspeed. In the modification of Fig. 6, the diaphragm 40 acts on valve 36 through a plunger 49, and the diaphragm 55 is replaced by a bellows 155. The lever 57 is pivoted to the housing at 63, at 69 to a member 70 supporting a spring 60 adapted to abut diaphragm 40, and at 57 to a member supporting a spring 61 adapted to abut the housing. Below a selected Mach number, the diaphragm 40 acts alone on valve 36. At, say, Mach 0.95, the bellows 155 expands and brings spring 60 to abut diaphragm 40 and oppose the force exerted thereby. At a higher Mach number spring 61 abuts the housing and opposes bellows 155, so that feel forces again increase with airspeed. To prevent variation with altitude in the difference between the upper and lower Mach numbers, an evacuated bellows 62 is pivoted to the housing and to one end of lever 57, to " stiffen " the linkages at low altitudes. The bellows 12 may be given a pre-loading so that it exerts a compression force on lever 57 which is progressively reduced as altitude is reduced. Specification 734,437 is referred to.