Patent GB-981591-A (GB)
Title: Aircraft and method of operating same
IPC: B64C29/00
Filed: 1961-02-16
Abstract: 981,591. VTOL aircraft; variable pitch propellers. CURTISS-WRIGHT CORPORATION. Feb. 16, 1961 [Feb. 23, 1960], No. 5823/61. Headings B7G, B7V and B7W. An aircraft capable of horizontal and vertical flight has a pair of laterally spaced fixed cyclic pitch propellers, the blades of each propeller together having an activity factor of at least 480, the propeller axes being tiltable between substantially vertical and nearly horizontal attitudes, and wings which during horizontal flight provide substantially less than the total lift required, the remainder being provided by the vertical component of radial forces developed by the propellers. Fig. 7 shows the aircraft in outline. One or more gas turbines 36 drive propellers 162 through clutch 132, bevel gears 130, 131, shaft 38, and bevel gears 158, 157. Alternatively, an engine may be located in each nacelle. Each nacelle is tiltably mounted on a hollow boom 41 within a small wing 32, which may also tilt. The tilting is controlled by jacks 136 operable by a switch 146 on the control column 68. The up-sweeping blade of each propeller passes in front of its wing. The engines exhaust through a nozzle assembly 53 to provide some thrust and pitching and yawing couples as described later. In Fig. 4, rudder pedals 56 operate the rudder 58 conjointly with a yaw couple control on the nozzle 53, through cables 61, 64, and fore-and-aft movement of the control column conjointly operates an elevator 51 and a pitching couple control on nozzle 53, through cables 71, 76. Lateral movement of the control column 68 rotates a torque tube 70 connected by arms 88 to cables 86 operating the ailerons 84. A collar 94 on tube 70 may be moved by control lever 104 to engage a fixed collar 98, or a collar 96 secured on the torque tube. Collar 92 operates cables 94, which are thus locked, or moved in response to roll demand, at the will of the pilot. A housing 90 contains two sets of differential gears, Fig. 5 (not shown). Each has one input from a servomotor controlled by a governor 107, and another input from a respective one of cables 92. Each differential drives a shaft 119, external pinion 122, ring gear 123, internal pinion 124, shaft 121, and gears 212, 208 controlling the (collective) pitch of propellers 162. The arrangement is such that the governor 107 varies the pitch of the two propellers in the same sense, to maintain constant engine speed, and cables 92 vary the pitches of the propellers in opposite senses, to provide roll control when the propellers provide lift and the ailerons may be ineffective due to low forward speed. Fig. 24 shows the nozzle assembly 53 and the pitch control valves 80, 82, the roll control valves being similar but smaller, and mounted on the sides of the assembly (as at 60). A rectangular exhaust duct 266 discharges normally through apertures 278, 282. Two pairs of vanes 274, 277 are mounted on end plates (not shown) so as to be pivotable about axes 273 by cables 76, as shown in broken lines, so that the vane 274 of one pair diverts part of the gas to flow as shown by the broken arrows, and the vanes of the other pair restrict flow through the opposite aperture 278 or 282, to give a pitching couple. Fig. 13 shows a propeller blade, which decreases in chord and increases in pitch towards its tip. Figs. 9 and 10 show the rear part of a nacelle, and the forward part and propeller hub, respectively. Each blade root 161, Fig. 10, is mounted in a pitch change bearing 163 in a hub 152, and is in compression between a retaining nut 166 and a central member 173 common to all blades. A pitch changing lever 168 on each blade is connected by link 169 to a piston 171 sliding within the hub 152 and steadied by an extension 180 sliding in a part 180<SP>1</SP> of the hub. The hub is supported in the nacelle by a bearing 151, and is splined at 178 to a hollow drive-shaft 156 supported in the nacelle by bearings 147 and connected to bevel gear 157 shown in Fig. 7. A member 176 is locked to the hub, and a sleeve 183 is locked to member 176, by abutting shoulders, splines, and a split-ring in each case. The forward end of sleeve 183 is closed by a disc 191, so that a fluid chamber 174 is formed between member 176 and disc 191, and piston 171. The chamber can be supplied with pressure fluid to increase the blade pitch, or to reservoir pressure whereupon the centrifugal forces on the blades decrease their pitch. A sleeve 181 on piston 171 slides between member 176 and sleeve 183 to steady the piston further. A hollow tube 189 is locked to piston 171 by a splined member 192 and nut 193, and is supported within sleeve 183 by a splined flange 188 engaging internal splines on the sleeve. Tube 189 contains a fluid conduit 194 communicating with chamber 174 through ports 190, and having at its rearward end, Fig, 9, a port 197 normally centred within a landed valve sleeve 203 having a pressure fluid supply port 202 and a reservoir port 201. The reservoir is the interior of the nacelle, and pressure fluid is supplied to port 202 through an annular space between tubes 204, 234, on which the valve sleeve 203 is secured, through port 218, gallery 216, and channel 222, from a pump 217 driven from shaft 156. Tubes 204, 234, and thus sleeve 203, are movable relatively to port 197 by worm gearing 206, 207, 208, and gear 212 (shown also in Fig. 7) in response to blade pitch change demand. Such movement connects port 197 to pressure port 202 or reservoir 201, for pitch increase or decrease, respectively, to produce a corresponding pressure change in chamber 174 and movement of piston 171 and conduit 194, until port 197 is recentred within sleeve 203. Means are provided to lock the piston 171 should the fluid pressure supply fail. A spring- biased valve, Fig. 11 (not shown), is arranged to supply pressure fluid to a conduit 231 only while the supply pressure is adequate. Conduit 231 communicates through chamber 232, port 233, and tube 234, with an annular space 235 between conduit 194 and a tube 236, which is connected with an annular chamber 238 through ports 240, 237. Chamber 238 is formed between a member 241 splined to tube 189 and urged to the right by a spring 248, and a member 239 which supports a sleeve 243 by bearing 242. Members 241 and 239 have clutch teeth 251, 244 normally separated by the pressure in chamber 238. A helically grooved shaft 246 is locked to member 243 by splines 245 and split-ring 250, and engages a nut 186 within sleeve 183 through balls 247 which can be recirculated in known manner, so that axial movement of the shaft relatively to the nut produced by movement of piston 171, is accompanied by rotation of shaft 246 relatively to the hub. When the fluid pressure fails, spring 248 engages teeth 244 and 251, so that shaft 246 cannot rotate relatively to the hub, and therefore cannot move axially within the nut, and piston 171 is locked.