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Aviation History
1998
1998 - 0032.PDF
FLIGHT tmsr Is this the future of city-centre-to-city-centre transport? Quick-change artist The Bell XV-15 proved the tilt-rotor concept: now it is a lead-in to the civil Bell Boeing 609 PETER GRAY/ARLINGTON THE TILT-ROTOR concept has been around for many years, but only recently has the first military application (the Bell-Boeing V-2 2 Osprey) received production approval from the US Department of Defense. Even more recently, Bell and Boeing have launched the Model 609 civil tilt-rotor which is scheduled to fly in mid-1999, with deliveries starting in 2001. Although it is an earlier-generation machine (the first of two demonstrators was flown in 1977), the Bell XV-15 is proving to be a useful research and development tool for the 609 project and, indeed, the sole flyingXV-15 has been re-liveried to represent that aircraft. It is because the tilt-rotor looks like becoming a commercial, as well as a military, success that Flight International arranged with Bell to test this XV-15 and to try to gauge just what sort of transition a fixed-wing or helicopter pilot will have to make when flying this new breed of aircraft. The outstanding impressions, as John Ball, Bell's senior experimental test pilot, and I approached the XV-15 are of die two large, ver tical, engine nacelles housing four of the five transmissions on the ends of the wing, the large 7.6m (25ft) prop-rotors on top, and the6.5° for ward sweep of the wing. The sweep is to give the rotors plenty of clearance when they flap back when in the fixed-wing, horizontal-flight, mode. The rest of the aircraft looks much like any other nine-seat turboprop. As Ball took me round the outside, I noted the large area - 2.9m: (31ft-')- of flaps and flaperons. This is to help offset the effects of the downwash in the wing from the rotors while in the hover. This peculiarity of tilt-rotors can destroy 8% of the lift. The flaps also help provide a more effi cient wing at low speeds. As we stepped inside among the banks of test equipment, I saw the complicated mixing unit in the roof between the two wings. This is entire ly mechanical, a wonder for its age (it was designed over 20 years ago), and does every thing necessary to convert the controls and con trol movements from helicopter to fixed-wing mode. This includes changing the rotors from the cyclic-pitch mode of vertical lift to the con stant-pitch mode of fixed-wing flight. Although most of the systems and even the materials in the 609 will be different from those of the XV-15, the handling, I am told, will be much the same. It will be about the same size. So, although I read the flight manual before my flight, received a comprehensive briefing, had a question-and-answer session and understood most of the systems (including the ejection seat) I concentrated on the handling and how the average pure- helicopter pilot and pure-fixed- wing pilot would manage the tilt-rotor. (I have the advantage of being dual-experienced.) Although the XV-1 5 is old, Bell has updated it over the years to continue the research, espe cially in support of the development of the larg er V-22 for the US Marines, Air Force and Navy. Flight International has flown the V-22 simulator (13 -19 March, 1996), but this was to be my first flight in the real thing. We had two Lycoming LTClK-4Ks (T53 turboshafts modified to run vertically) capable ofproducingl,155kW(l,550shp)eachfortwo- engined take-offs and l,340kW for single- engine contingency. The five gearboxes are not designed for this amount of single-engined 30 FLIGHT INTERNATIONAL 7 - 13 January 1998
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