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Aviation History
1976
1976 - 0048.PDF
60 FLIGHT International, w/e 10 January 1976 1111111 DEFENCE The YUH-6IA can be transported in the C-130, C-I4I and C-5A without any major components having to be removed. Preparation of the aircraft, loading and securing in a C-130 can be achieved in 70min by four ground crew and, at its destination, the aircraft can be unloaded and returned to flying status in under two hours by the same number of men. Re-rigging of the controls and blade repack ing are not necessary military flying prototypes (there is also a prototype civil derivative flying) an November 19 last year was un doubtedly a blow to the programme and the US Army Preliminary Evalua tion (APE) will probably not now begin until March, but the crash at least proved to a certain extent the integrity of the design. The pilots were conducting power-recovery tests in autorotation when the tail rotor shaft broke as a result of some main tenance steps, left inside the fuselage, rubbing against it. In the ensuing one direction will always be limited by the eventual net drag effect of the tail rotor). The lift capacity of the rotor system has been tested up to 21,9001b, rather more than the maxi mum gross weight of the Uttas, and the main rotor has been started in winds of up to 50kt. Substantial inroads have been made into testing the more operational aspects of the Uttas, with landings made on 14° slopes and the carrying of sling loads qualified. Manoeuvr ability and special techniques for Qualification testing of the Boeing Uttas dynamic system in the ground test vehicle has been completed. The same components were used throughout the programme which consisted of a 50hr pre-flight release test, 200hr pre-production qualification and 300hr endurance and reliability trials. Complete disassembly and inspection of the components after each test revealed "no significant problems" small amounts of negative g have con firmed that control is not degraded as with other systems. The glass-fibre composite blades (see photograph) have proved to be trouble- free and no removals have been neces sary as a result of failure or deteriora tion, nor because of any indications of inherent unreliability. Boeing's ex perience with the blades has con firmed their tolerance of minor manu facturing defects arising from the load-sharing characteristics of the multi-fibre construction and, com pared with their metal-spar pre decessors, they are expected to pro vide a major improvement in reliability. The YUH-61A transmission intro duced the use of Vasco X-2 (modified) high-hot-hardness steel in the gears and this and other innovations have resulted, says Boeing, in the "excep tional" reliability already demon strated. The ground test vehicle has completed the 200hr dynamic-system pre-production qualification run and the 300hr endurance test—the latter some 11 months ahead of the dead line laid down in the contract. The Mean Time Between Removals (MTBR) for the transmission averages more than l,800hr compared with a US Army requirement of l,500hr in the production aircraft. Boeing is con fident that it will achieve its objec tive of components subject to on-con- dition maintenance eventually having a 2,500hr MTBR. The accident to the first of the three crash all four main blades broke off and the fuselage snapped at the tail intersection, but the main cabin sec tion remained virtually intact and the crew escaped without any injury. Boeing reckons that extensive re dundancy of critical systems, fail-safe construction and thorough testing of its Uttas will increase overall safety threefold compared with its pre decessors. Meanwhile, preparation of the aircraft for APE continues and the company reports that performance in many respects has already exceeded requirements. A maximum speed of 199kt TAS has been achieved and a density altitude of 22,200ft reached. The aircraft has been flown backwards at 55kt, side ways to the right at 55kt and sideways to the left at 45kt (speed sideways in operating in confined areas have been investigated and tail-skid landings performed (the Boeing helicopter, un like its Sikorsky competitor, has a nosewheel). Flying with partial sys tems failures (including the stability and control augmentation system) has been extensively tested and full power-off autorotational landings made. Engine air-starts have been done at altitudes up to 12,000ft. During the course of flight testing Boeing has notched up some notable achievements: for example, 760hr of running was completed on one set of dynamic components, one flight lasted 3-2hr and one aircraft flew six times on a single day, while another made 47 test flights in one month. In fact the Uttas fleet has averaged four flights every working and flyable day. The main structural member of the Boeing Uttas rotor blades is a D-shaped spar formed by laying up glass fibres in a continuous loop from the tip of the blade, into and around the root end and then back out to the tip again. To the rear of the spar is a non-corroding honeycomb core with the spar and the core covered by cross-plies of glass-fibre. The complete blade is cured in a closed die to control dimensions and aerodynamic contours accurately. The blades are claimed to be in vulnerable to armour-piercing rounds up to 23mm "fllHim, • '*rf<J|
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