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Aviation History
1987
1987 - 0850.PDF
distributing lift loads to several fuselage frames. Systems also have multiple redundancy. There are three hydraulic systems with duplex main and tail rotor jacks, two elec trical generators plus standby generator, dual fuel pumps in each tank plus pumps on each engine, and a dual/duplex auto matic flight control system. An important safety "multiplier" is health and usage monitoring of trans missions, engines, and rotor hub. The system developed for the Westland 30-300 has been refined for the EH.101. Health and usage monitoring is a function of the aircraft management computers and, for the transmission, includes quantitive wear debris monitoring, a form of enhanced chip detection, and real-time vibration analysis. The latter will provide early warning of gearbox failure by detecting trends away from the correct vibration pattern. Safety is also greatly influenced by performance, and here the EH. 101 has an inherent advantage because it has three engines. The use of three engines may originally have been dictated by the availability of suitable powerplants, EHI admits, but subsequent events mean that three-engine safety is now fundamental to the EH.101 design. Although capable of vertical flight, most helicopters, including those with two engines, are not legally capable of zero- distance take-offs. Enough distance must be allowed for a safe landing should an engine fail before sufficient speed and height has been gained to stay airborne. The EH.101 is a true zero-distance take-off aircraft up to "quite sensible" weights, says EHI. With 30 passengers and fuel for 300 n.m. plus reserves, the EH.101 can legally take off in zero- distance. With one engine failed, the heli copter is able to hover out of ground effect at maximum weight. This ability to oper ate into confined spaces is particularly relevant to the commuter market, says EHI. The EH.101 looks thoroughly con ventional apart, perhaps, from the distinctive wide-chord tips to its stubby main rotor blades. A product of the British experimental rotor programme, the effi cacy of these blades was ably demon strated last August when they took the Westland Lynx to a new world helicopter speed record of 216kt. Although EH.lOl's never-exceed speed is more modest, at 167kt, the new blades will allow the helicopter to cruise close to its maximum speed, around 160kt, and some 20kt faster than comparable existing helicopters, says EHI. Producing 30 to 40 per cent more thrust than conventional blades, they enable the helicopter to fly faster without excessive vibration. Between 70 and 85 per cent blade span, an aft-loaded cambered aerofoil section is used to delay retreating-blade stall and increase lift. Inboard of this an aerofoil with reflex trailing-edge camber is used to counteract the nose-down pitching moment of the high-lift section. Outboard, the wide-chord tip uses a combination of sweep, thickness, area, and vortex effects to increase lift, reduce drag, and delay stall. The resulting complex shape of the blade is only made possible by the use of composites. A combination of carbonfibre and glassfibre is used to produce a stiff blade with "soft" failure characteristics and long life. The main rotor hub is fully articulated, but with low-maintenance elastomeric bearings. The hub is metal, but with redundant composite inner and outer loops to transmit blade centrifugal loads. Blade lift loads are carried by a metal arm. Should this fail, however, the inner composite loop carries the lift load. The gearbox is attached to the fuselage at four points by eight struts, two of which can fail and the helicopter remain opera tional. For the 28,6001b naval variant, with three 1,700 s.h.p. T700-401A engines, the gearbox is rated at 4,640 s.h.p. For the 31,5001b commercial helicopter, powered by three 2,000 s.h.p. CT7-6 engines, the gearbox is rated at 5,100 s.h.p. Up to 1,850 s.h.p., equivalent to the power of one engine, will go to the tail rotor. This has composite blades and a semi-rigid hub. In the event of a rotor control failure the tail rotor is biased to counteract main-rotor torque at a forward 88 FLIGHT INTERNATIONAL, 13 June 1987
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