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Aviation History
1964
1964 - 2167.PDF
184 FUGHT International. X July 1964 SCOUT AND WASP ing gear with four castoring wheels, plus naval equipment. The first Wasp flew on October 28, 1962, with production deliveries starting during the latter part of last year. During trials on HMS Nubian in February 1963, over 200 day and night landings were made in all weather. A number of this version has been delivered to South Africa for operation from frigates, and three have been bought by Brazil. Design and Construction The basis of the P.531 is a light-alloy box-girder chassis, with two longitudinal underfloor webs, continued upward at the rear to the engine "deck" level. Underfloor bulkheads extend the full width of the fuselage, as do the cabin rear bulkhead and another which carries the rear undercarriage attachments. These two structures extend up to the engine deck and, with the longitudinal webs, form fuel-tank bays which lie about the e.g. under the rotor. Round this area the skin is of stainless steel. The steel engine deck has a central trough from which any oil is fed to a drain tank, since it is essential in the case of the Wasp that no oil should reach the ship's deck. The sides of the engine deck are reinforced to act as servicing platforms. By positioning the load-carrying structure well inboard, there is no restriction on the number of access panels and doors. In the bottom skin are three stressed hatch openings to the flying controls, fuel pumps and other equipment. The relatively light cabin structure and four large doors are of standard light-alloy sections and sheet. The box girder keel carries all the concentrated loads from the other components. In addition to taking the four undercarriage units, it has a bolted transport joint for the tail boom as well as fittings for the engine mountings and triangulated welded steel-tube rotor pylon. The tail boom is a light-alloy semi-monocoque; it has channel-section frames, and skin panels reinforced by external longitudinal riveted channels. Built-up inverted-T members carry the pulleys for the tail rotor controls within the boom. The drive shaft for the tail rotor is mounted on top, inside detachable fairings. The four bolts at the transport joint secure long finger plates to diffuse the stresses into the boom. In the Wasp the joint at the crank of the boom is hinged, with a quick-release locking bolt to port. Aft of the crank the boom (fin) consists of a flanged-sheet spar with "trailing-edge" ribs, and detachable leading skin. Because of its folding and lengthened boom the Wasp has a single fixed tailplane opposite the tail rotor> instead of the symmet- rical tailplane with end-plates fitted to the Scout under the crank. The Wasp plane has a tubular spar, nose and tail riblets and a wrapped skin. That on the Scout has two sheet spars, ribs and a wrapped skin with central spanwise stiffeners. Undercarriage design on a helicopter is always a problem because of the need to avoid ground-resonance zones, and the P.531 also had to meet two entirely different alighting conditions. In his paper to The Royal Aeronautical Society last November, The Development of the P.531, Dipl Ing Ciastula explained why the Wasp and Scout have such different undercarriages neither of which resembles the perfectly satisfactory one on the prototype. The basic reason is that the three aircraft are not the same in shape, mass distribution, stiffness or structural frequencies. For each a ground resonance programme was needed in which the theoretical blade data were matched with empirical undercarriage characteristics following impedance tests in a shaking rig. P.531 results were analysed on Southampton University's Pegasus computer, and those for the Wasp on Westland's Elliott 803 computer at Hayes. In order to obtain the desired tolerance of some 10° blade swing at the take-off rotor speed of 410 r.p.m., and 5° under overspeed conditions, the solution for the Scout is as follows. The rigid skid, which is better suited to rough-field conditions than wheels, gets the energy absorption necessary mainly from its steel-tube cross- members, but also from the four legs and the skids themselves. The oleos connecting the rear cross-tube to the top of the rear tank bulkhead act only in tension, thereby damping the reflexing. The
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