Tilt-rotor aircraft offer two principle advantages over conventional helicopters, speed and range. The Osprey has a maximum speed of 509 kilometers per hour versus 268 kph for the CH-46E that it replaces. Its range on an assault mission is 954 kilometers versus 244 kilometers. This capability meets the Marines' new doctrine for amphibious assault which calls for moving Marines quickly from assault ships further off shore, out of range of anti-ship missiles and mines.
These advantages are not without costs, however. The Osprey is tremendously complex. Because a single engine failure would make the aircraft impossible to land, a shaft through the wing connects the twin rotors, allowing them to share power from one engine. To fit within the limited space available on an assault carrier deck, the Osprey's three-blade rotors fold and the entire wing assembly rotates ninety-degrees to line up with the fuselage of the aircraft. This is in addition to the engine nacelles which tilt over ninety-degrees during take-off and landing. Every moving part represents a series of long and short-term maintenance issues, increasing both cost and risk.
A series of crashes has plagued the Osprey's development. Most have been due to an issue called Vortex Ring State or VRS. This occurs when one of the two rotors stalls (which seems to happen when the Osprey descends rapidly). With a sudden difference in lift between the two rotors, the Osprey rolls before the pilot has a chance to react. VRS takes place on other twin rotor aircraft, but with a traditional fore and aft rotor design, the aircraft pitches nose up or down, which is more easily corrected. Currently, the Osprey's rate of descent has been limited to prevent the most common conditions for VRS. Critics are quick to point out that rapid descent is essential for an assault landing under fire.
Another major flaw inherent in the tilt-rotor design is the high-pressure downwash from the rotors. In forward flight, the Osprey's rotors are a tremendous source of drag. To minimize this drag, the rotor disk area of a tilt-rotor design has to be made smaller than a similar size conventional helicopter, which increases the pressure of the downwash. In operation away from prepared surfaces (i.e. a ship's deck, concrete, asphalt), this means that the Osprey will land in a torrent of dirt, sand, water, snow, or debris kicked up by its own rotors, not a good experience for the Marines assaulting a hot landing zone or for the pilots landing it.
In fact, this problem is so severe that some time ago the Osprey's secondary mission of combat search and rescue was pulled. The danger presented to downed troops struggling in the downwash was simply too great. The Air Force still plans to buy about fifty Ospreys for its Special Operations mission, but its rescue squadrons are seeking their own helicopter design. The Navy, which intended to purchase a similar number of Ospreys for logistics missions and plane guards, has already begun buying the MH-60S, an upgraded version of the SH-60F.
In April 1989, the V-22 Osprey was cancelled by then Secretary of Defense Dick Cheney, to help the Department of Defense meet the smaller budgets available at the end of the Cold War. With tremendous congressional effort, the program was raised from the dead in 1993. Over ten years later the program is still plagued with difficulties and could face cancellation yet again.
Also of note, the President of the United States is shopping for a new "Marine One" and the Osprey is not in consideration. Two "off the shelf" helicopter designs are currently in the running for the White House and for the Air Force's C-SAR mission. If the Osprey is cancelled again, the winner of this competition will likely take all.
The choices are a US-built version of the European-designed EH-101 helicopter (called the US101) and the Sikorsky S-92, a significantly enlarged development of the H-60 family. Both use improved versions of the successful GE T700 engines, already proven in the Blackhawk and Apache helicopters. The EH-101 will be built by Lockheed Martin and Bell Textron (a prime contractor for the Osprey) in partnership with Europe's AgustaWestland. Ninety have been delivered worldwide to date, racking up 50,000 flight hours. Fifty more have been ordered. The S-92 has gone head to head with the EH101 in several international competitions and lost, but being an American design it might curry greater favor with Congress. By the numbers both the US101 and the S-92 are improvements over the forty-six years old
| ||Speed ||Range ||Troops ||Cargo (Ext) ||Unit Price |
|CH-46E ||268-kph ||244-km (Assault) ||14 + 5 crew ||4,000-lb ||- |
|MV-22A ||509-kph ||954-km (Assault) ||24 + 2 crew ||10,000-lb ||$80-million |
|US101 ||278-kph ||741-km (CSAR) ||24 + 2 crew ||10,000-lb ||~$60-mil (VIP)* |
|S-92 ||306-kph ||822-km (Assault) ||22 + 2 crew ||10,000-lb ||~$60-mil (VIP)* |
*This is the estimated cost based on 25 units for VIP duties in the US Capitol region.
The Osprey is a poster child for the kind of technology over-reach common in the Pentagon during the Cold War. Instead of procuring a very good system very quickly, the Pentagon accepted "only the best" and paid a great deal of cash to get it. With today's budgets these programs are dragged out over several decades. By the time they are finished, more conventional designs have nearly caught up with these technologies that started out as revolutionary. The Osprey has its advantages, but at what cost? --Andy Wagner (firstname.lastname@example.org)