GB1190361A - Gas Turbine Engines - Google Patents

Abstract

1,190,361. Gas turbine ducted gas engines; axial flow fans. DOWTY ROTOL Ltd. April 11, 1967 [April 12, 1966; May 25, 1966], Nos.16008/66 and 23428/66. Headings F1C and F1J. A gas turbine ducted fan by-pass engine comprises a single-stage fan having flow-varying blading, the blading being adjustable under the control of a servo mechanism. The engine shown comprises a ducted fan assembly 1, the fan being mounted at the forward end of the gas turbine engine, the forward part of the compressor of which is shown in broken lines at the right of Fig. 1. The fan is driven from the engine through reduction gearing indicated at 7 and having an output shaft 18. The shaft 18 is connected at its forward end 17 to a rear casing portion 16 of the fan rotor, the rotor comprising also a forward casing portion 13 and a disc assembly 4 at the periphery of which the fan blades 2 are mounted. The fan blades comprise root portions 9 which are mounted in needle bearings 10 for angular adjustment, a bevel gear pinion 30 being mounted on each blade root, the plurality of pinions being engaged by a gear wheel 20 the hub portion 27 of which is mounted for angular movement in bearings 28 within the disc assembly 4, so that as the gear wheel 20 is moved angularly the fan blades are rotated about their axes so as to vary the pitch thereof. The casing portion 13 constitutes a cylinder within which is disposed a piston 14, the piston being secured to a cylindrical piston rod 22 which is axially slidable on a cylindrical spigot portion 15 of the rear casing portion 16 there being interengaging axial splines 23 so as to ensure that the piston moves axially with respect to the spigot. The piston rod 22 is provided on its outer surface with helical splines 25 which engage corresponding splines 26 formed internally of the hub portion 27 of the gear wheel 20, so that as the piston 14 moves axially so the gear wheel is moved rotationally. Hydraulic fluid is supplied through the line 36 and is passed to one side or the other of the piston 14 under control of valve 32 which is mounted within the part 33 of the piston assembly, the valve 32 being controlled manually by the tube 35. The ducted fan assembly in Fig.2 again comprises fan blades 2 mounted by their root portions 9 at the periphery of the rotor disc assembly 4, but in this embodiment a crank arm 43 having a crank pin 44 is secured to each blade root, the crank pins of all the blades engaging in a groove at the periphery of a unison ring 40, a bearing 42 being disposed between each crank pin and the peripheral groove. Thus as the unison ring is moved axially so the fan blades are rotated about their axes so adjusting the pitch thereof. A hydraulic servomotor 12 is again provided, the servomotor comprising a piston 14 disposed in cylinder 13, the piston being connected to the unison ring 40 by means of a number of rods 41, the rods sliding in bearings 46 located in the radial wall of the casing 13 and in the rearward wall of the rotor disc 4. The assembly comprises a fixed cylindrical spigot 47 on which the rear casing part 53 of the rotor assembly is rotatably mounted in bearings 48, the casing part 53 extending forwardly as a spigot portion 52 on which the piston 14 is slidably mounted. The rotor assembly is driven by shaft 49 which is drivingly connected to the spigot portion 52 of the casing portion 53 by means of a spline connection 50. Hydraulic fluid is supplied through line 54 and passed to one side or other of the piston 14 under the control of valve 32. A relief valve 55 is provided at the forward end of the line 54. A valve device 57 is provided to prevent fluid escaping from the cylinder 13 in the event of leakage occurring in the supply line. The rotor assembly comprises a fairing cone or spinner 56 which is of double-wall construction so as to permit flow of hydraulic fluid for antiicing purposes. The fan blades rotate within an annular duct formed by an outer annular wall 3 and inner casing structure. In Fig.4 not shown the engine is of the three-shaft type comprising LP and HP rotor assemblies and the ducted fan assembly 1 is driven by a separate turbine downstream of the HP and LP turbines. The fan blades may be disposed in positive pitch disposition to give forward thrust, negative pitch disposition to give aerodynamic braking to an aircraft in which the engine is mounted, zero pitch which is selected at starting and feathered pitch which is selected in the event of engine failure so as to prevent windmilling.