Patent GB-444485-A (GB)
Title: Improvements in aircraft sustaining rotors
IPC: B64C27/00
Filed: 1934-09-17
Abstract: 444,485. Aircraft sustaining rotors. CIERVA AUTOGIRO CO., Ltd., Bush House, Aldwych, London, and BENNETT, J. A. J., Genista, Newton Mearns, Renfrewshire. Sept. 17,1934, No. 26708. [Class 4] In an aircraft sustaining rotor of the type in which the blades are each articulated to the hub member by joint means having at least two independent axes permitting each blade not only to " flap " but also to oscillate in a plane perpendicular to the rotational axis (drag oscillation), the articular pivot means of the rotor blade mounting is so arranged that a drag oscillation has necessarily associated therewith an oscillatory movement in the flapping plane also whose amplitude is of the same order of magnitude as that of the drag oscillation, the objects being to make the natural frequency of the drag oscillations differ sufficiently from the rotational speed to avoid resonance effects and to provide an appreciable degree of aerodynamic damping. Fig. 1 shows a two-bladed rotor hub of the type described in Specification 444,395 in which the flapping or " delta " pivot is common to the two blades, the drag links 13, 14 being yoke-shaped and journalled on trunnion axles 12 mounted on the sides of the hub. To the outer ends of drag links 13, 14 are bolted forked members 15, 16 carrying pins 17, 18 constituting the axes of the drag or " alpha " pivots on which are articulated blade root members 19, 20. The pivot axes are arranged as shown in Fig. 4, the plane of which is perpendicular to the longitudinal axis of the blade. The projections of the rotational axis, the delta axis, and the alpha axis are shown at 0-0, 1-1 and 2-2 respectively, the outline of the rotor blade is shown at b and the chord is substantially parallel to the delta axis 1-1 which is perpendicular to the rotational axis 0-0. The alpha axis is inclined at an angle of about 45‹ to the line 0-0, displacement of the blade about the alpha axis being, therefore, resolvable into a drag displacement in the direction 1-1 and a flapping displacement in the direction 0-0, the forward inclination of the alpha axis causing the blade to rise as it moves back and vice versa. The movement of the blade about the alpha pivot is limited by means of a pin 23, Fig. 3, secured between the jaws of fork 15 parallel to pivot 17 and engaging in a slotted hole 24 formed in blade root member 19. In a modification, Fig. 5, in addition to the alpha and delta pivots a third pivot is provided of which the axis lies in a plane containing the longitudinal blade axis and the alpha axis, but is inclined at an acute angle to the blade axis so that blade displacements about this third axis give rise to changes in the pitch angle of the blade. The alpha axis 5-5, Fig. 6, is in this case inclined backwardly and upwardly with respect to axis 0-0 at an angle of about 45‹, i.e. in opposite direction to the arrangement of Fig. 4. It is stated that with the above arrangements if a disturbance setting up a drag oscillation acts solely in the drag plane, the flapping oscillation of the blade will take place substantially about the centre of inertia of the blade. In a further modification, Figs. 9 to 11, the alpha pivot axis is inclined to the longitudinal blade axis so that movements about the alpha pivot give rise to changes in the pitch angle of the blade. The rotor hub 31, Fig. 9, incorporates a flat pivot lug 32 lying in the flapping plane and carrying a pin 33 forming the axle of the delta pivot. Drag link 34 terminates inwardly in a forked end embracing lug 32, flapping movement being limited by a stop pin 37 carried by lug 32 and projecting into arcuate slots 38 formed in jaws 35 of link 34. Link 34 terminates outwardly in a stub axle 39 on which is rotatably mounted a housing 41 integral with blade root socket 42, this assembly constituting the alpha pivot. The projection of the alpha axis 10-10 and delta axis d-d on a plane containing the rotational axis 0-0 is shown in Fig. 11. Specification 420,322 also is referred to.