GB966226A - Improvements in aircraft-lifting and -sustaining rotors - Google Patents

Abstract

966,226. Helicopters. J. G. WEIR. Feb. 23, 1962 [Nov. 28, 1960; Dec. 30, 1960], Nos. 40791/60 and 44793/60. Heading B7W. A helicopter rotor has a pair of contrarotating rotors in which the rotor shafts 12, 14 are driven through gearing 20 from a power unit 22. Referring to the upper rotor only, blades 32, 34 are mounted on pivots 28, 30 offset a distance d from the spanwise axes S of the blades and carried by arms 24, 26 normal to the axis of shaft 12, though in the case of a single two-bladed rotor it may be arranged to teeter. As shown in Fig. 3, when axis S and the coincident axes of shafts 24, 26 lie on a common plane AB normal to the axis of shaft 12 the blades are set at a positive angle of incidence α between 6 and 18 degrees. In second the Provisional Specification the range is given as 18 to 22.5 degrees. In the position of zero pitch of the blades shown the leading edge of a blade should preferably lie in a plane containing the hub axis and the axis of pivots 26, 28. This geometry is stated to ensure that in all conditions of flight the blades will automatically assume a position of angular displacement about the pivot axis such that the angle of attack with respect to the local relative wind, averaged along the span, is substantially constant and below the mean stalling angle of the blade aerofoil sections. A further embodiment is described in which the hub is mounted on a drive-shaft by a constantvelocity universal joint, whereby it may be tilted for pitch and roll control.