Patent GB-895921-A (GB)
Title: Improvements in or relating to aircraft gas-turbine jet-propulsion engines
Inventor: DAVIES DAVID OMRI
IPC: F02K1/16
Filed: 1958-03-13
Abstract: 895,921. Gas turbine jet propulsion plant. ROLLS ROYCE Ltd. March 10, 1959 [March 13, 1958], No. 8167/58. Class 110 (3). [Also in Group XXIX] An aircraft gas turbine jet propulsion engine comprising a propelling nozzle with an adjustable member movable into a position in which the effective outlet area is reduced by fluid pressure operated means has control means controlling the supply of pressure fluid to the fluid pressure operated means comprising a differential area piston-in-cylinder arrangement having first and second positions corresponding to actuation of the fluid pressure operated means to move the adjustable member to its maximum and minimum area positions respectively and maintained in its first position by the differential action of the fluid pressure thereon. A jet pipe 11 is provided with a single area-adjusting member 12 pivoted at 13 to a convergent tubular portion 10 of the jet pipe. The member 12 is actuated by piston 16 working in a cylinder 17. The supply of pressure fluid, e.g. compressed air, from the connection 22 to the cylinder 17 is controlled by a valve mechanism 23. The valve mechanism 23 comprises a valve body 24 containing a piston valve 25 having a small diameter land 25a and a pair of axially-spaced large-diameter lands 25b, 25c. When the valve 38 is closed the pressure in the chamber 27 is equal to that in the bore 26 and the piston valve 25 is then at the right-hand end of its travel. In this position, the pressure fluid from the connection 22 is supplied to the left-hand side of the piston 16 through duct 30, space 26 and port 21. The right-hand side of the piston 16 is connected to drain through the port 20, port 34, space 28 and port 35. The piston 16 is therefore urged to the right and the area adjusting member 12 maintained in its maximum area position. When the valve 38 is opened, the chamber 27 is connected to atmosphere through the chamber 37 and port 37a. The restriction 32 then causes the pressure in the chamber 27 to drop and the valve member 25 to move to the left against the stop 29. In this position the left-hand side of the piston 16 is connected to atmosphere through the port 21 and passage 33 and the right-hand side to the connection 22 through the space 26, port 34 and port 20. The piston 16 then moves to the left and the areaadjusting member moved to the reduced area position. The valve member 38 is mounted on a pivoted lever 39 subject at one end to the loading of a spring 41 and at the other to the loading on a diaphragm 51. The diaphragm is subject through the conduits 54, 58 to the pressures from a hydro-mechanical fuel governor of the kind described in Specification 794,897. The loading of the spring 41 is determined by the position of the throttle lever 45 acting through a cam 44, bell-crank 43 and abutment 42. The arrangement is such that at settings of the lever 45 below full throttle or maximum power the loading of the spring 41 is substantially increased so that the loading of the diaphragm 51 is unable to open the valve 38. At full throttle the loading of the spring 41 is reduced and when the engine is running at full speed, the valve 38 is open to close the area reducing member 12. In a modification the spring 41 acts against a fixed abutment and a shut-off valve operated by the throttle 45 is arranged in the passage 38. In another arrangement, in which an engine having variable inlet guide vanes operated by a progressively variable ram supplied with fuel under a pressure related to engine speed, the engine rotational speed signal may be derived from the ram and fed to the lever 39. The control means may be responsive to any other variable which is representative of the power output of the engine, such as compressor delivery pressure. Specification 895,922 also is referred to.