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Aviation History
1949
1949 - 0674.PDF
458 FLIGHT showing the composite con- struction Fairey Gyrodyne pump is driven from the rotor shaft, fluid delivery to the rotor control jacks is ensured in the event of engine failure. For torque transmission to the rotor, the shaft used is of 3in diameter and 13 gauge wall thickness, surmounted by a further conical flexible coupling, the output member of which is splined to the bore of the reduction gear input shaft. This runs in a ball-thrust and roller-journal bear- ing assembly and is fashioned integrally with the spur sun- wheel of the first-stage epicyclic reduction gear train. It will be remembered that the engine crankshaft /rotor-shaft Detail of rotor head assembly, showing flapping and drag linkage form, swashplate-jack and azimuthal snubber-units reduction is 0.813:1 (26/32), and this is further reduced through the compound epicyclic gear in the ratio of 0.0933:1, each epicyclic stage giving a reduction of 0.3055:1. By virtue of the fact that the major order, of reduction is made immediately beneath the rotor head, the torque loading in the transmission is kept reasonably low. Each epicyclic stage consists of six planetary pinions re- acting against a common annulus, the carrier of the first- stage planets being toothed to the second-stage sun-wheel in the form of a sleeve running on a pair of ball races on the main input shaft. The carrier of the second-stage planets is the skirt of the rotor hub shaft. This runs in roller bearings top and bottom with twin ball-thrust bear- ings, the full bearing stack being carried in a steel cone member, the skirt of which is bolted to the steel-tube ring at the crown of the pylon. The epicyclic reduction gear box, a magnesium casting, is commonly bolted in conjunc- tion with the steel cone to the pylon crown ring. At the head of the hub shaft is splined a flanged sleeve to which is bolted the rotor brake drum. Although essen- tially similar to the normal twin-shoe Lockheed hydraulic expanding brake in common use on many British cars, the rotor-brake is of light alloy construction, with the rather interesting detail modification that the drum tread is of sprayed cast iron. Especially thin Ferodo shoe linings are employed and the brake anchorage plate is bolted direct to the steel cone member, whilst also serving to support the anchor stay for the swashplate. Head Articulation In order to furnish a means both of concentric location for, and torque transmission to, the rotor head assembly, the flanged sleeve carrying the brake drum is formed with a number of radially disposed taper splines, flanking the eight bolts which unite the head to the sleeve. The joint is actually made to what can perhaps best be described as the head driving centre, a fork-crowned pedestal, to which the three-armed blade-carrying spider is trunnion pivoted. Spanning the fork of the driving centre is a hollow pin" running in needle roller bearings, and through this pin, at 00 deg, is in turn carried a second (smaller-diameter) pin supporting the spider, also on needle roller bearings. Duplex ball thrust bearings are interposed between spider, pins and driving centre fork, so that the whole assembly articulates about an instantaneous centre. The spider is a D.T.D. 306 high-tensile steel forging, on the three arms of which the blade flapping hinge links are needle-roller pivoted. A ball thrust bearing on the end of each arm accommodates radial thrust loads. Flapping links are S.n steel forgings, curved in plan so that the blade axis through the drag hinge to the hub centre makes an angle of approximately 60 deg with the flapping binge axis. The root skirt of each flapping link is recessed to afford stops for coning and dropping limits of blade move- ment. A rather clever little arrangement of centrifugal bobweights is incorporated, so that, at above 85 rotor r.p.m., the weights fly out and allow the blade full flapping freedom—within the stop limits. Below 85 r.p.m., how- ever, the bobweights fall inward and stopping distance pieces are inserted so that the blade roots cannot drop below the horizontal. Blade flexure in bending is, never- theless, such as to give a tip droop of the order of 30U1. At the " free " end, each flapping link is formed as an eye to accommodate a D.T.D. 306 nitrogen-hardened hol- ' low pin. The ends of this pin are surrounded by steel- backed, lead-bronze, diamond-bored bearings, pressed into the bores of the fork-ended S.n blade carrier. A duralu- min sleeve is located inside the hollow pin and is capped top and bottom to locate the whole assembly endwise, and to afford oil-tightness. The blade carrier has a flange with clearance holes for the through-bolts from the mating flange of the blade root adaptor, so allowing 2$ deg of blade pitch adjustment. The adaptor is longitudinally split on its dia- meter and is ground-bored to mate with the ground dia- meter of the blade spar shank, these components being; pinched together by a series of tangential bolts. Blade structure is interesting in that, as previously noted,
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