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Extreme Machine

The U.S. Marine Corps' sword gets a brand-new edge.

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(Continued from page 1)

The tiltrotor effectively trumps this effect by turning the rotor into a propeller. No more advancing blade, no more retreating blade, just simple thrust, and all of it moving the airplane forward, supported on its wings. As Bill Leonard, Bell Boeing senior test pilot for the integrated test team from all three services that will operate the Osprey, puts it: "Don't think of this thing as a helicopter. Think of it as an airplane that hovers."

It is also important to think of it as an invention and to recognize the V-22 as the first wholly new aircraft configuration in the sky since the Harrierthe British jet that can take off and land verticallywhich entered service in 1970. (Accordingly, last August, the Federal Aviation Administration issued its first powered-lift ratingsspecifically for tiltrotor aircraftto eight V-22 test pilots.) While much of the inventing was accomplished by research aircraft, most significantly Bell's XV-15 for NASA and the Army, the final design of the V-22 has benefited enormously from the march of technological development in the broader fields of materials, electronics, and computer software. In fact, the aircraft that will be fielded first to the Marines as the MV-22 (the Air Force version is the CV-22; the Navy's, the HV-22) represents a wiser design that has benefited from some of the delays that have affected the program. The first prototypes were all-composite, but the decision to mate advanced composite materials with more traditional aluminum in the production aircraft, to cite just one example, appears smart: The most recent engineering and manufacturing development (EMD) aircraft are lighter and cheaper to build than earlier prototypes.

After the XV-15 showed that a tilt rotor aircraft could evolve into something more than a research platform, the next step was to build and fly six full-scale development (FSD) prototypes of the V-22. Although the program began as the JVX in 1981 under management of the Army, the Navy and Marines took over early in the game, with the Air Force as an interested partner looking at a smaller number of a special long-range V-22 version for the U.S. Special Operations Command, a combined force that would be called upon if something like the Tehran situation arose today.

Bell and Boeing formed a joint venture to build the craft in 1982, and a year later received a contract. Peering into the future, the Marines were especially anxious to replace their medium-lift Boeing Vertol CH-46 Sea Knights, a large, tandem-rotor helicopter designed and built in the 1960s, battle-tested in Vietnam, and refurbished, renovated, and rebuilt more often than George Washington's hatchet. The average Sea Knight is about 30 years old.

Crashes claimed two of the FSD prototypes. Following uneventful first flights in 1989, initially as a helicopter and later as a fixed wing, the first loss occurred on June 11, 1991, when one aircraft crashed due to incorrect wiring in the flight control system. The loss of a second aircraft and its crew on July 20, 1992, dealt the project a severe setback. While on approach to Quantico, Virginia, a series of component failures in one engine nacelle ignited a fire. Testing was halted pending an investigation and a redesign of the failed parts.

The V-22 program hit another rough patch in 1989, when Secretary of Defense Richard Cheney canceled it during the budget balancing battles of the early Bush administration. While the Reagan administration had allocated almost $1.5 billion for research and production, Pentagon analyst David Chu convinced Cheney that the V-22 was unaffordable. Chu and Cheney wanted more helicopters instead.

In his first appearance before Congress as the civilian head of defense, Cheney was mindful of enormous changes in global politics. A new Soviet leader named Mikhail Gorbachev was charming Americans, who were beginning to see their former adversary in a new light, and a budget balancing law called Gramm-Rudman-Hollings was pressing Cheney to make cuts in defense. At a hearing before the House of Representatives' National Security Committee on April 25, 1989, he testified in part: "we opted to stay with established weapons programs where production lines are operating efficiently rather than pursue the development of unproven technology."

But Congress wouldn't allow the V-22 to die, perhaps because some members had not forgotten Tehran. Also, there were election districts and states that had a lot to lose if the project were terminated, and Congress ordered Cheney to restore funding. A timely independent study stated that the tiltrotor concept was the best solution for the future Marine mission. The V-22 was alive, but those charged with its care and nurturing would proceed with a degree of caution that prevails even today as aircraft numbers 7 through 10 undergo testing at Patuxent River Naval Air Station in Maryland. Though the budget now looks bulletproof and the first parts for production aircraft are coming off the line, there seems to be a common understanding among the test team on one point: no mistakes. "Just one drop of rain and they don't fly," say people in the test crew, and that's only partially an exaggeration: The instruments on the test aircraft can be ruined if they get wet.

Not that Ospreys are prone to crash; they're even difficult to shoot down, mainly because of inherent damage tolerance built into the aircraft and two or more of everything that you absolutely need to stay in the air, beginning with the engines. A pair of Rolls-RoyceAllison T406-AD-400 turboshaft engines rated at 6,150 (and capable of nearly 7,000) shaft horsepower powers the craft through a system of shafts and gearboxes that can provide power to both rotors if one engine is lost. The engines are offspring of the proven T-58 turboprop, and its cousins are flying in the C-130 Hercules. The Osprey cannot land as an airplane because its 38-foot-diameter rotor blades would strike the ground, but the designers have already thought about the unthinkable: If, for some reason, the rotors won't transition into helicopter mode for landing, the graphite-and-fiberglass rotor blades will not fragment on impact but instead will "broomstraw"reduce themselves to a bundle of fibers like a straw broom flailing harmlessly at the asphalt. In a crash, the wings are designed to fail and separate from the fuselage, and the nose has a tilted bulkhead that works like the upturned tip of a ski to keep the airplane from flipping over if the nose tries to dig in. The structure is designed to tolerate battle damage and keep flying, and critical parts as well as both pilot seats are armored.

The MV-22 is designed to hold 24 fully armed Marines (and there's a seat for the crew chief), equivalent to a reinforced rifle squad, but the airplane's size has been defined by the vessels from which it will operate: amphibious assault ships, which resemble traditional straight-deck aircraft carriers but with shorter stern portions that are high and square. John Buyers, an easygoing Texan who serves as V-22 program manager for Bell Boeing, says the 38-foot diameter of the rotor blades is mandatory, defined by a required blade tip clearance of 12 feet, eight inches in the vicinity of these ships' islands and five feet from the wheels to the edge of the deck. "If we could have, we'd have made the rotors bigger," he says. "Optimum would have been about 43 feet," adds Boeing senior manager Gregory McAdams. So where did they get 12 feet, eight inches? "That was the CH-53's actual blade tip clearance, and the Navy just didn't want to give up any more than that," says McAdams. While the rotors defined the overall size and weight of the Osprey, its cabin interior dimensions are almost the same as those of the CH-46, which it will completely replace by about 2010.

About George C. Larson

George C. Larson served as editor of Air & Space from 1985 to 2005. He is currently an inactive pilot, but holds a commercial pilot's license, with instrument and multi-engine ratings. He is between airplanes at this time, but has owned or operated a Grumman American AA-5B Tiger and a Mooney 201. He has been writing about aviation since 1972, when he joined the staff of Flying Magazine.

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