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Aviation History
1964
1964 - 2170.PDF
FLIGHT International, 30 July 1964 General-arrangement drawings of the Wasp HAS. I (upper four drawings) and Scout AH. I mation (Manufacturing) Ltd of Hemel Hempstead. This device consists of a transistorized oscillator and amplifier encapsulated in Araldite, which signals an alarm on the intercom if the rotor transmission should be overloaded. The remaining engine controls are the high-pressure fuel cock and starter switch. The two-position h-p lever is spring-loaded towards the "on" position, and the run to the engine cock is by Teleflex. The automatic starting sequence is controlled by a spring- loaded start/off/cancel switch and a normal/off/test switch on the pilot's console. When the system is put "on" and released the starter-generator turns, a "starter on" lamp lights, and current is fed to the torch-igniter solenoid, the h-e unit and igniter plug. When the gas generator reaches self-sustaining r.p.m. a pressure-operated switch cuts out the starter and ignition unit. Transmission Power from the engine is split so that the main and tail rotors are each directly driven. The output pinion of the reduction gearbox engages a roller-type freewheel gear, to the spindle of which are attached the main couplings of the two rotor transmission shafts, the tail rotor shaft coupling incorporating a twin-caliper disc brake. The intermediate drive shaft between the engine and main-rotor box is a machined steel tube with a Layrub flexible coupling at each end. The main-rotor gearbox has a magnesium-alloy casing (with all joints and pockets caulked with Polycast 2 against sea-water on the Wasp), which extends upward to carry the rotor-head bearing. The box is supported by a pylon of four vees extending from the top of the casing down to the deck. Power input from the intermediate shaft passes through a spiral- bevel pinion engaging two gears which, in turn, have spiral-bevel pinions driving the rotor-shaft crownwheel. Overall reduction from the free turbine to the rotor is 71.76 : 1. The use of two pinions to drive the crownwheel makes for better loading and in the event of engine failure provides two quill drives for essential services. These quill shafts are (port) the power-control hydraulic pump and (starboard) the main-rotor gearbox top-bearing oil pump and rotor speed generator, all of which are vital in autorotation. The bevel pinions are mounted in taper-roller thrust bearings housed in the sump of the gearbox. In the port side of this sump is an oil-level window. The crownwheel, bolted to the foot of the rotor shaft, is a machined-steel forging tapered in a series of stages and lands. The upward extension, or top cover, of the annular gearbox casing carries the shaft in two taper-roller bearings. The drive is flood lubricated, apart from the upper rotor-shaft bearing which is pressure-fed. The pitch-control linkage is taken up through the gearbox and shaft and then transferred to external linkages through four slots sealed by bellows. From the rotor disc brake the tail-rotor shaft is taken along the boom in two sections, with a steady twin-bearing at the joint, to the angle gearbox and then to the right-angle rotor gearbox. The magnesium-alloy casings on the Wasp are protected like the main gearbox. The steel shaft sections have T-ends bolted at 90c to flexible stainless-steel rings. The steady bearings, which are mounted on Silentbloc fittings, support a short section of coupling shaft. On the Wasp, with its folded tail boom, the angle gearbox is the break point for folding the tail, and a serrated coupling is used. The angle gearbox itself consists of a magnesium-alloy casing, flood lubricated and with an oil-level glass, with bevel pinions mounted in taper-roller bearings. The tail folding caters for this drive coupling and the pitch control, which are automatically joined on the tappet principle when the tailcone is swung into place and the locking bolts are driven home by the actuating handle on the port side. The right-angled tail-rotor gearbox, also in a magnesium-alloy casing, has bevel gears and pairs of taper-roller bearings, and is bath-lubricated with a sight glass. The pitch-change arm is moved by a square-thread screwjack turned by an external chain and sprocket. Taper and journal bearings allow the pitch-change arm to rotate independently of the jack. Rotors The main-rotor hub is compact. The spider is a machined light- alloy forging attached to the shaft flange by 12 bolts and a locating dowel. Its four arms house twin taper-roller bearings for the large- diameter hollow flapping-hinge pins, stops limiting movement to 4|° down and 20° up. Flapping links are light-alloy forgings, with jaws fitting over the spider arm, pierced vertically for the drag-hinge taper-roller bearings and drilled for the drag-hinge dampers. The latter are pressure-cups holding a nest of Sinterlink friction discs and spacers, four alternate discs having narrower teeth for two-stage damping. The drag links are conre:ted by snubber struts—sleeved tubes with rubber compression blocks—which, while allowing limited blade move- ment, maintain blade spacing. To provide the hinge for pitch change, the root of the tabular machined light-alloy blade extension arm is plugged with an assembly which includes a ball thrust race and two roller bearings. Running inside it is a laminated-steel torsion bar pinned inboard to the drag link and outboard to the extension-arm plug. Most of the centrifugal loads are carried by the torsion bar, which also provides pitch-change damping. Beneath each flapping link is an anti-coning stop to counteract "sailing" at low rotor r.p.m. with a heaving deck and gusty wind. The stop has two swinging links bolted through light coil springs to the drag link, and a trunnion connected to the spider by a sprung plunger. At 90-100 r.p.m. centrifugal force throws the trunnion outboard, breaking the lock and freeing the flapping link within its normal limits. Strain-gauges showed high vibration in the flapping sense when flaring into the hover, which would produce severe fatigue loads on the blade extension-arm joint. This was confirmed by tests on the light-alloy parts, the results showing a large scatter. Accordingly
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