Patent GB-1461069-A (GB)
Title: Aircraft with variable diameter rotors
IPC: B64C27/46
Filed: 1969-09-09
Abstract: 1461069 Convertible aircraft; aircraft propellers UNITED AIRCRAFT CORP 9 Sept 1969 [12 Sept 1968] 44581/69 Headings B7W and B7V An aircraft, e.g. a convertiplane, has at least two variable diameter rotors, varying means to vary the diameter of each rotor, and synchronizing means to synchronize the operation of the varying means so that the diameters of the rotors are substantially the same at all times. In one such aircraft having two rotors, pods 26 are positioned at the outer end of each wing and serve to support variable diameter rotors 30 for rotation about axes 34. The after ends of the pods 26 are fixed to the wings while the forward ends 26b are pivotable between a vertical position (for a helicopter mode of operation) and a horizontal position (for a propeller mode of operation). Each rotor 30 consists of a central hub 41 supported from a rotor drive shaft 43 and having blades 44 connected to it through appropriate stack bearings (not shown) for rotation when varying pitch. An engine 38 drives a transmission input shaft 72 via a power chain 42, including reduction gear 70, and shaft 72 is connected to a bevel gear 74 coacting with bevelled gear 78 to drive the rotor drive shaft 43. The diameter of rotor 30 can be changed by means of a mechanism comprising two coaxial shafts 80, 82 carrying at one end bevel gears 84, 86 respectively, of a differential 88 which also includes pinion or planetary gears 90, 92 (and others, not shown) each connected to a jack screw 95 in each blade 44. Shafts 80, 82 rotate with rotor 30 and each has a pilot-operated brake 100, 102 connected to it. When brake 100 is applied, shaft 80 and bevel gear 84 are stopped and, as shaft 43 and hub 41 continue to rotate, the pinions 90, 92 are caused to rotate and thereby rotate jack screws 95. This results in translation of a nut 110 connected to outer blade portion 44b relative to fixed blade portion 44a, thereby varying the diameter of the rotor 30. Application of brake 102 causes the rotor to vary diameter in the opposite direction. An identical rotor transmission is provided for each of the rotors 30 and to ensure that their diameters vary synchronously, a shaft 116 coaxial with pod tilt axis 118 connects gears 91 of each rotor 30 through bevelled gears 120 located at opposite ends of the shaft 116. Pod end 26b is caused to pivot about axis 118 by means of an arcuate gear 130 coacting with a gear 132 driven by a pilot-operated motor 136. Whenever relative rotation occurs between shafts 80, 82, a stop nut 94 threaded on the end of shaft 80 and engaging shaft 82 via splines 93, 96 is caused to translate along axis 34. This nut 94 serves to limit the degree of extension or retraction of the blades 44 so that they do not interfere with one another or with the fuselage by abutting stop members 142, 144 at either end of its travel. Mechanisms are described whereby the position of stop member 142 (the extension stop) is varied in response to pod tilting, being at a maximum during the helicopter mode of operation and at a minimum during the propeller mode of operation, whereby the rotor diameter is caused to vary in response to the degree of pod tilting, and whereby the rotor extension and retraction brakes 100, 102 are released when stop nut 94 reaches the appropriate end position.