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Aviation History
1996
1996 - 0599.PDF
J~U009>TE* TECHNOLOGY FOUR DECADES OF DEVELOPMENT THE TILT-ROTOR is a remarkable air craft. With the "proprotor" nacelles ver tical, it can hover, fly sideways and backwards and turn on the spot — just like a tandem-rotor helicopter. With the nacelles horizontal, it has the speed, range and cruising altitude of a conventional twin turboprop. The Bell Boeing V-22 Osprey is the result of more than 40 years of tilt-rotor development, beginning with the experi mental Bell XV-3, flown in 1955. The highly successful Bell XV-15 technology demonstrator was first flown in 1979 and is still being flown today. First flown in 1989, the V-22 is the first tilt-rotor destined for production. It incor porates several new technologies, com pared with the XV-15, including an all-composite airframe and fly-by-wire flight controls. The aircraft is being devel oped as a tactical transport for the US Marine Corps and a special-operations and combat-rescue aircraft for the US Air Force and Navy. The tilt-rotor is an entirely new class of aircraft, introducing the capability to take off vertically, fly at 250kt (460km/h) at tur boprop altitudes for more than 1,800km (970nm), then land vertically. Bell Boeing says that the V-22 is quieter than a heli copter — or a turboprop — because of a lower proprotor RPM and the lack of a noisy tail rotor. In forward flight, with the nacelles hori zontal, conventional fixed-wing controls (flaperons, elevators and rudders) are used. During conversion to vertical flight, con trol is transferred automatically to the proprotor swash plates which, just like in a helicopter, are used to control blade pitch in the hover. You can hear this happen. The converse occurs during transition to for ward flight. The two 12m-diameter proprotors each have three composite blades. For below- deck stowage, the blades fold parallel to the wing leading-edge and the wing slews to he along the top of the fuselage. This reduces width by over 25m, to 5.6m, but increases length by nearly 2m, to 19m. Allison's T406 was developed specifically for the V-22. Flat-rated at 4,580kW rolling, pitching or yawing. When I remarked on this to Tatro, however, he mentioned that we had actually landed about a minute earlier and were taxiing along the road. For the running take-off, power was applied and the nacelles brought down from the verti cal to 65'° of tilt. We broke ground quickly, I applied a lot of power, full horizontal nacelles and, this time, caught the nose-down pitch. We accelerated idly to 2 50kt. FLIGHT © Reed Business Publishing Bell Boeing V-22 Osprey is a multi-mission tilt-rotor (6,150shp), it has a lOmin emergency- power rating of 5,090kW. A connecting shaft allows either engine to drive both pro protors, to enable flight on one engine in helicopter, conversion and fixed-wing modes. Fuel is stored in the wing and landing- gear sponsons, in crash-resistant self-seal ing cells. Normal capacity is 7,6001itres, but up to four auxiliary tanks can be installed in the cabin, holding an additional 9,2001itres. Air-to-air refuelling is also available. The V-22 is designed to cruise at 275kt, with a 340kt dash speed. Vertical rate of climb is l,090ft/min (5.45m/s) in heli copter mode and 2,300ft/min in fixed-wing mode. Cruise ceiling is 26,000ft with both engines, and 11,300ft on one engine. Hover ceiling with both engines, out of ground effect, is 14,200ft. Empty weight is about 15,000kg. Nor mal vertical take-off weight is 21,500kg, increasing to 25,000kg with a short take off run. Maximum weight with auxiliary fuel and a short running take-off is 27,500kg. The cabin will accommodate 24 Tatro ran through an engine fire drill. The warning systems gave lucid notice of the prob lem, but no information on emergency operat ing procedures — these have to be done from memory and the checklist. BENIGN HANDLING After only 50min in the simulator I felt that, although the Osprey is a complicated and sophisticated aircraft, the ease of management combat-equipped troops and two gunners, 30 passengers, or 9,000kg of cargo. A full-width rear loading-ramp is hydraulically operated. There is provision for a 900kg-capacity cargo-handling winch and roller rails. A single belly cargo-hook rated at 4,500kg, or two hooks with a com bined limit of 6,800kg, can be fitted. Maximum forward speed with an under- slung load is 130kt, although the V-22 has carried an 1,800kg load at 175kt. Range after a vertical take-off with 5,400kg payload is 2,200km, increasing to 3,300km with a short running take-off and 9,000kg payload, and to 3,900km with full auxiliary fuel and no payload. Self-deploy ment range with air-to-air refuelling is more than 4,600km. Anti-icing of the proprotor blades and spinners, engine air-intakes and cockpit windscreens allows operation in moderate icing. The landing gear will absorb heavy landings up to 3.6m/s vertical speed, and crashworthy crew seats and crash-attenu ating troop seats are installed. • of the systems, the information available at the appropriate times on the MFDs and the benign handling qualities (apart from the nose-down pitch), I would be capable of taking the actual aircraft safely through the same rou tine. Bell tells me that helicopter pilots have no problems with the fixed-wing mode and that fixed-wing pilots with no helicopter experi ence have few problems once they accustom themselves to hovering manoeuvres. • FLIGHT INTERNATIONAL 13 - 19 March 1996 31
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