GB807423A - Improvements relating to helicopters - Google Patents

Abstract

807,423. Helicopters. FAIREY AVIATION CO. Ltd. Feb. 7, 1957 [Feb. 8, 1956], No. 3972/56. Class 4. [Also in Group XXXII] A helicopter rotor head comprises a tiltable hub 11 on which the inner ends of the blades 10 are mounted, an upwardly extending tiltable control shaft 21, connections between the control shaft and the blades for varying the blade pitch in accordance with movement of the control shaft, and a bridle coupling 23 between the control shaft and the hub, which coupling is resilient, whereby the transmission of vibrations between the hub and the control shaft is reduced. In Fig. 1, the hub 11 is universally mounted through a gimbal ring 12 to a ring 13 rotatably mounted on a pylon 14 fixed to the helicopter fuselage. The control shaft 21 is universely mounted at the centre of tilting 22 of the hub 11. A member 25 is fixed to the shaft, and each of two links the length of which are adjustable by turnbuckles (not shown) is universally mounted at its two ends to the member 25 and to a blade pitch change horn 17 respectively, so that tilting of the control shaft controls the blade pitch cyclically, and vertical movement of the shaft effects collective pitch control. An inverted U-shaped member 23 is slidably and non-rotatably mounted on shaft 21 e.g. by splines, and the arms 29 of the U are connected to pivots 30 on the hub, so that the hub is tilted as cyclic pitch is applied. Transmission of vibration from the hub to the shaft is reduced by making arms 29 leaf springs, which may be laminated, or by including a piston and cylinder type shock absorbing unit in each arm, relative movement of the piston and cylinder being restrained by springs or rubber blocks (see Group XXXII). In the embodiment of Figs. 2 and 3 (not shown), flyweights are mounted on the ends of arms extending radially from the hub in a vertical plane at right angles to that containing the blades. The vertical shaft 21 is hollow, and contains a hollow tube rotating with the blades and supplied with fuel through a rotary pipe joint which fuel is supplied to blade tip jet engines through a distributer at the top of the tube. The tube also carries electrical cables connected to slip rings at the bottom of the tube for the engines ignition supply. The interior of the hollow hub is sealed from the atmosphere and acts as a distributer for compressed air fed to the engines through the hollow blades. The hollow tube also drives a revolution counter and rotational speed indicator, and a rotor brake is provided for stopping the rotor when power is cut off.