The U.S. Marine Corps' sword gets a brand-new edge.
- By George C. Larson
- Air & Space magazine, November 1998
(Page 3 of 5)
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.
A ramp folds down at the rear to accommodate two utility vehicles, and the craft has two belly hooks so that it can carry cargo on a sling beneath it. Once aboard a carrier, the Osprey takes only 90 seconds to fold into a package slightly longer than its 57-foot, four-inch fuselage. Although the equipment for the stowing cycle exacts a penalty in weight and cost, self-stowage means that more aircraft can be carried, and all can be launched and recovered within minutes. The Osprey can be refueled in flight through a probe, and it carries a rescue hoist plus a "fast rope"the line commandos slide down when they arrive in their special way. With inflight refueling, the V-22's ultimate range depends only on having enough tankers and on how long the crew can stay awake. Fuel tanks are located in the sponsons and the wings (plus three that can be installed in the cabin for transoceanic trips). Should gearbox lubricant be lost, the craft can fly another 30 minutes.
The Osprey has three independent flight control systems, any one of which can fly the aircraft. All three use fly-by-wire technology that employs electronic signals rather than cables and pulleys to operate the controls. There are two mission computers and three inertial navigation systems to help you figure out where you are, and the displays in the glass cockpit can be routed to any of the video tubes in the event one of them fails. All information for a mission can be loaded in seconds from a cartridge that plugs into a computer system. In addition to the various alerts and warning lights, an audio annunciator tells you what kind of trouble you're in. (The disarmingly dulcet voice belongs to Barbara Smith, deputy to Colonel Nolan Schmidt, the Marines' program director for the V-22.)
There are four electrical generators, two located with the engines and two more in the upper fuselage, and a battery good for 20 minutes of flying if all else fails. An onboard generator extracts nitrogen gas out of the air and floods the fuel tanks, displacing oxygen and reducing the risk of fire. The outer skin has a fine copper mesh embedded in it to form a conductive path in the event of a lightning strike. The aircraft has three completely independent hydraulic systems, which operate at 5,000 pounds per square inch; out in the fleet, only the F/A-18 has such high hydraulic pressures. But the V-22's hydraulic lines are made of titanium, which is thinner and lighter and thus saves weight. "We had to invent the connectors for that system," Buyers says. The engineers also had to rewrite all the criteria for replacing a line that has been scratched or nicked.
A little less than half the airplane is manufactured of composite materials, which, while incredibly light, are also corrosion-resistant and strong. Should a bullet penetrate it, the composite fibers ensure that the hole won't expand or start to crack. Systems and controls are distributed and separated throughout the aircraft so that one bullet can't take out all of anything. When things fail, they fail "softly"only half a control surface at a time, for example.