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Published: Sunday, 1/5/2003

Clip the Osprey's wings

The Marine Corps must decide soon whether to fish or cut bait on the V-22 Osprey. For the sake of our Marines, our national defense, and our longsuffering taxpayers, I hope they cut bait.

The tilt-rotor Osprey can take off and land like a helicopter but fly like an airplane, because the rotors at the end of each wing tilt forward to act as propellers.

The Osprey promised to go farther and faster than any helicopter in military history. The Marine Corps should be commended for its boldness in taking risks on the new technology.

But technology does not always keep its promises. And boldness, which is good, can ossify into stubbornness, which is not. Real-world experience indicates the tilt-rotor is a technology whose time has not yet come. Thanks to the “vortex ring state,” it may never come.

The vortex ring state was the culprit in a crash in Arizona in April, 2000, that killed 19 Marines. An Osprey was at an altitude of about 300 feet when it suddenly flipped over and plunged into the ground. When another Osprey crashed in December, flight testing was suspended until May, 2002.

The vortex ring state is a wing-induced rotor stall unique to tilt-rotors. Carlton Meyer, a former Marine who edits the Web site G2Mil.com, explains: “As a tilt-rotor descends vertically, each wing pushes the airflow away from half its rotor. The faster it descends, the greater the vacuum the wings create, resulting in less lift. As the pilots maneuver a V-22, they may shift the airflow causing one rotor to lose so much lift that it literally falls and flips the aircraft over.”

A skilled pilot can avoid the vortex ring state by descending slowly; by not going straight down, and by not making sudden maneuvers during descent. This would be fine if the Osprey were to be used for commuter flights. But for a Marine assault force approaching a landing zone which has turned “hot,” coming in slow and straight can be hazardous to health.

The vortex ring state can be avoided if the Osprey descends no faster than 800 feet per minute. But most military helicopters can descend safely at 2,000 feet per minute. And because they don't have to worry about flipping over if they juke and weave, conventional helicopters can take evasive action to avoid enemy fire.

The Osprey has two other problems. There are no door gunners, because the tilt rotors on the end of the wings would block much of a gunner's view and his field of fire. And the V-22's small rotors kick up substantial “downwash,” kicking up clouds of dust thick enough to impair a pilot's vision, and forcing dismounting Marines to lie flat on the deck until the Osprey has departed.

The Osprey costs a great deal more than other helicopters that perform the same missions, so even if the safety problems are solved, the Osprey's performance must be a great deal better to justify buying it. It isn't.

The Osprey can cruise at 240 knots, about 40 percent faster than the helicopters it is supposed to replace, the CH-46 Sea Knight and the CH-53E Super Stallion. Its range (515 nautical miles) is considerably greater than that of the Sea Knight (132 nautical miles), but less than that of Super Stallion (540 nautical miles), or the Navy's new MH-60S “Nighthawk” helicopter when it is equipped with external fuel tanks. Boeing claims the Osprey can lift 15,000 pounds externally, but it has yet to lift more than 11,000 pounds in tests. The CH-46 could lift 10,000 pounds when it was new. The CH-53 can lift 28,000 pounds vertically.

The Osprey weighs as much as a Super Stallion, and is much more likely to tip over in a choppy sea. The Osprey burns fuel at twice the rate of the Sea Knight, and breaks down more often than does that 35-year-old-helicopter.

The defense budget for this fiscal year calls for purchase of 11 Ospreys at $120 million each. This compares with a cost of $25 million each for the Nighthawk, and an estimated cost of $21 million each to extend the life of the Super Stallion. You don't need to be an engineer or a tactician to realize the Marines would be better off with a mixture of MH-60s and CH-53s than the Osprey. You only need to do the arithmetic.



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