GB492911A - Improvements in and relating to sustaining rotors for aircraft - Google Patents

Abstract

492,911. Aircraft with rotary wing systems. CIERVA AUTOGIRO CO., Ltd., and BENNETT, J. A. J. April 6, 1937, No. 9801. [Class 4] A lifting or sustaining rotor for a helicopter or a gyroplane includes a compound flapping pivot mechanism having two independent pivot axes or groups of axes #, #b, together with physical constraints interconnecting the articular mechanisms of the several blades in such a way as to prevent the fundamental component at least of the " non-differential flapping " from producing motion about the #b axis or axes or to prevent the coning and " differential flapping " from taking place about the # axis or axes, the # and #b axes, when projected on a plane perpendicular to the hub axis, being inclined at different angles to the radial blade-axes, so that a given angular flapping displacement is accompanied by a different change of blade pitch according as it takes place about a # or #b axis. According to the Specification, if the flapping motion of the rotor blocks is analysed into a Fourier series of harmonic terms, of which the fundamental expresses a periodicity of once per revolution, the expressions will differ in phase by an amount equal to the angular setting of the blades in the rotor disc and if the expressions are added together, those terms, the ratio of whose frequency to the fundamental frequency is an integral multiple of the number of blades, are additive and represent the components of " differential flapping." On summing the expressions representing the total flapping of the several blades, all the other terms, representing the components of " non-differential flapping," disappear. In one form, the rotor blades 14 are pivoted about the axes #b to a member 12 pivoted to the hub 10 about an axis #. In a modification, the #b axes are coincident, the pivots being formed by a cranked member. In another form, the member 12 is formed of two links hinged about coincident # axes and the links are connected to a slider movable axially on an extension of the rotor hub. In the case of a three-bladed rotor, the links, one for each blade, are pivoted in lugs on the rotor hub, and in a modification the links are connected by ball-ended links to a centrally disposed link connected by a ball-joint to the hub.