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Aviation History
1989
1989 - 0023.PDF
USA senses small-helicopter resurgence Most US manufacturers of small helicop ters seem to sense a resurgence in demand for their products. McDonnell Douglas believes the signs are sufficiently encour aging to launch development of an all-new helicopter, the MDX. Others are more cautious, preferring to improve on existing designs. To offset the dip in commercial helicop ter sales in recent years, manufacturers have concentrated their resources on devel oping military versions of established designs. The market for multirole military helicopters has become increasingly competitive as a result. Sensing a revival of the civil market, companies are now shifting resources back to commercial helicopter development. This is most apparent at the volume end of the market—small helicopters. Since acquiring Hughes Helicopters, McDonnell Douglas has seen the four- place single-turbine MD500 series continuing to sell steadily, if not strongly, particularly to police forces. Encouraged, McDonnell Douglas Helicopters has continued to, improve the product. To the current production MD500E and "hot-and-high" MD530F, introduced by Hughes in 1982, MDH has added the higher-performance 520L and 530K. Both of these variants feature increased-diameter main and tail rotors which increase lifting capability and operating altitude, and decrease noise. Based on the 500E, the 520L is powered by the new 450 s.h.p. Allison 250-C20R turboshaft. MDH has also launched a new variant, the 520N, which is based on the 520L and which will be the first commer cial application for the company's unique Notar (no tail rotor) anti-torque system. The Notar tailboom is, in effect, a circular-section circulation-control aero foil. Main-rotor downwash mixing with higher-velocity air ejected from slots running the length of the boom generates a sideforce which opposes main-rotor torque. A rotating nozzle at the tip of the boom is used for directional control. MDH plans to build two 520N proto types, which will be used to certificate Notar in mid-1990, ready for its use on the all-new MDX helicopter. Launched last month, MDX is an eight- seat twin-turbine helicopter and MDH's first totally new programme since the US Army's AH-64 Apache was launched in the mid-1970s. In addition to Notar, MDX will feature an all-composite bearingless main rotor, grease-lubricated transmission which will eliminate oil pumps and coolers, and an electronic cockpit possibly combining all instruments on a single screen. ? Under its helicopter advanced rotor programme (Harp), MDH has flown a five- blade composite flexbeam main rotor experimentally on the MD500. Although there are no plans to fit the Harp hub to the MD500 line, it will feature on the MDX. MDH plans to begin delivering the MDX in the mid-1990s and sees potential sales of 800 machines over the next ten years. Bell Helicopter, among others, will be watching the MDX programme with interest. Bell launched a new seven-seat twin-turbine helicopter, the Model 400 TwinRanger, in 1983, only to see the expected market upsurge fail to appear. The TwinRanger programme was trans ferred to Bell Helicopter Canada, but remains essentially dormant, awaiting a market upswing. Derived from the seven-seat, single- turbine Model 206L LongRanger, the TwinRanger features a four-blade "soft-in-plane" main rotor with composite hub and blades and a new transmission with "run dry" capability. The main rotor was originally developed for Bell's military Model 406, an improved version of the OH-5 8 scout helicopter. The original Model 400 flew in June 1984, but has been superseded by the initial-production Model 400A, powered by the 940 s.h.p. Pratt & Whitney Canada PW209T twin-turbine engine, which is to be followed by the composite-fuselage Model 440. Improvements just announced for the five-seat JetRanger III and seven-seat LongRanger III—now produced in Canada—are aimed at keeping the types competitive until the market warrants production of the new TwinRanger. In a joint venture between Bell, Soloy Conversions, and Allison, the JetRanger III will be fitted with an uprated Allison 250-C20R turboshaft.and an improved tail- rotor drive system. The conversion, to be certificated early this year, will increase hover ceiling at maximum gross weight to around 2,000ft. In a second move, Bell is to improve the reliability and maintainability of the Long Ranger III transmission. Improvements will be incorporated in new production aircraft from May onwards. Bell is currently studying potential improvements to its Model 222 eight-seat twin-turbine helicopter. Potential features of the Model 222X include composite structures, improved transmissions, elec tronic cockpit, and possibly a four-blade bearingless main rotor. use of new materials not only reduces weight, but also reduces the number of components vulnerable to corrosion. MBB admits that, at this early stage in the development of composite primary struc tures for helicopters, it- is cost, rather than technical constraints, which limits wider use. It is worth remembering, however, that composite rotor blades have been flying for nearly 20 years. Economic advantages are a further bonus offered by composites. Assembly time can be reduced significantly by their use. Further developments in construction techniques and simpler designs using composites will, according to MBB, produce cost savings as well as weight savings. What is needed, says MBB, is a "substantial change in design philosophy to get the full benefits from the use of composites". At MBB's Ottobrun factory an all- composite BK.117 is being prepared for flight test, while a second all- FLIGHTINTERNATIONAL, 7 January 1989 Hingeless, bearingless rotors reduce drag and weight and improve maintainability
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