FlightGlobal.com
Home
Premium
Archive
Video
Images
Forum
Atlas
Blogs
Jobs
Shop
RSS
Email Newsletters
You are in:
Home
Aviation History
1988
1988 - 1289.PDF
Those who have followed the story of the V-22 Osprey have become used to the facts surrounding tilt-rotors. Yet, when it appears in public for the first time this month, it will still seem incredible to many that such an innovative flying machine has been specified in such enormous quantities by three of the four US Services. That the Osprey exists at all is a tribute to the farsightedness and imagination of a few committed souls. Many such aviation novelties die while still in the fledgling stage, either because of insurmountable technical difficulties or because develop ment costs get out of hand. The Osprey has survived, and to find out why it is necessary to look briefly at the history of tilt-rotor aircraft. Rotating a pair of wingtip-mounted engines through 90° to achieve both verti cal and high-speed horizontal flight is only one of many ideas that have been tried over the years. Some have succeeded—the Harrier, with its vectored-thrust nozzles, being the most notable to date, The majority, by far, have failed. Very often the problem arose because the designs did not provide a wide enough "conversion corridor", meaning that the aircraft was difficult, or impossible, to control during transition from one mode to another. Serious ground-effect problems were Above The first V-22 takes shape at Bell's Fort Worth plant. Left A complex folding arrange ment allows Osprey to fit inside US Navy aircraft carriers another often-encountered difficulty. A wide conversion corridor is an inherent feature of tilt-rotors, however, and one mid-1950s design, the Bell XV-3, proved successful. Achieving its first full conversion in late 1958, the XV-3 was the world's first tilt-rotor aircraft, and although it suffered from aeroelasticity problems (resulting from harmonic coupling of the large wingtip mass with the rotor downwash), a further 110 conversions and a total of 250 flights were made over the next seven years. Cutting short a decade-long story in which the fundamentals of tilt-rotor design were readdressed, the XV-3 project spawned a US Government initiative to develop an all-new tilt-rotor research aircraft. A competition between Bell and Boeing Vertol (now Boeing Helicopters) led in 1972 to a $40 million contract for Bell to construct two prototype XV-15 tilt-rotor aircraft. The first XV-15 flew in April 1977, the second achieved conversion two years later, and the 300kt design speed was reached a year after that. The two XV-15s (one operated by Nasa Ames Research Centre, the other by Bell) have now amassed more than 650 hours of flight time between them. The Nasa aircraft is still flying, and has recently been fitted with advanced-technology composite rotor blades for better hot-and-high performance. Only 100 hours of XV-15 flight testing were originally planned, but as the hours built up it became clear that the aircraft were every bit as capable as had been hoped, and indeed had potential far beyond that level. Highly successful flight demonstrations at the 1981 Paris Air Show lent publicity to the programme and, the same year, the Department of Defence initiated the Joint Services Vertical Lift (JVX) programme. In 1982 the tilt-rotor concept was selected from a number of candidates for further development, Bell and Boeing (which had carried out considerable tilt- rotor research of its own, primarily using models) teaming for the $200 million preliminary design phase. This led in 1985 to the awarding of a $1-81 billion fixed- price V-22 full-scale-development contract to the Bell/Boeing team. In the meantime, the XV-15 carried out an extensive series of military proving trials, including operations from aircraft carriers and nap-of-the-earth missions. The first flight of the Osprey, originally set for June, has been put back to September, "which isn't bad when you consider the schedule was set in 1982," says Chuck Ellis, deputy director of the Bell/Boeing joint programme office. Delivery of the first of 682 production aircraft (552 for the Marines, 80 for the US Air Force, and 50 for the Navy) is currently set for December 1991. Responsibility for construction of the nine development V-22s is split about evenly between Bell and Boeing, with Bell in charge of the wing, nacelles, and asso ciated systems, and Boeing producing the fuselage and its systems. Six aircraft will be used for flight testing, aircraft numbers one, three, and six going to Bell, and the other three to Boeing. Approximately 4,000 flight-test hours are planned, about 70 per cent of which will be flown by Marine, Air Force, and Navy pilots. By far the largest V-22 operator will be the US Marine Corps, which plans to buy 552 aircraft for combat assault, assault support, logistics resupply, and medical evacuation. Management of the Osprey programme is carried out by the US Navy, which is the procurement agency for the Marines. The Osprey programme manager is Marine Col Harry Blot. Largely responsible for intro ducing the Harrier to the Marine Corps, Blot was hand-picked for the Osprey job by then Navy Secretary John Lehman. A committed V-22 enthusiast, he has relentlessly pursued the programme goals. Col Blot does not see the Osprey as a high-risk endeavour. "Right from the beginning, we said it would be a low-to- medium-risk programme. The tilt-rotor idea may be new, but the technologies for implementing the ideas are not that new." Col Blot nevertheless thinks it is "amazing" that a programme as large as the Osprey has come together with as few technical problems as there have been. The Marines receive Ospreys first, and delivery of the first MV-22A is currently set for between December 1991 and April 1992. Marine aircraft will come in the most basic configuration, meeting the principal requirement of being able to deploy 24 troops out to a 200 n.m. radius of action, and to carry 8,3001b externally for 200 n.m., hovering at mission midpoint at 3,000ft/91-5°F. The US Air Force has a requirement for 80 aircraft for Special Operations Forces (SOF) missions. For this, the CV-22A Osprey will have slightly more sophis ticated avionics to enable low-level terrain following, and extra fuel capacity. The main USAF requirements are to carry 12 troops over a 520 n.m. mission radius, and to hover out of ground effect at mission midpoint, at 4,000ft/95°F. The Navy plans to buy 50 HV-22A Ospreys, to be used for combat search and rescue, special warfare, and logistics FLIGHT INTERNATIONAL, 14 May 1988 23
Sign up to
Flight Digital Magazine
Flight Print Magazine
Airline Business Magazine
E-newsletters
RSS
Events
