Tiltrotor claims tested as Osprey deploys to Iraq

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US Marine Corps confident of enhanced survivability compared with helicopter

The greater survivability claimed for a tiltrotor versus a helicopter will be put to the test when the US Marine Corps' Bell Boeing V-22 Osprey begins its first combat deployment on September, to al Asad in Iraq.

Combat operations overseas will also put stress on the new aircraft's reliability and maintainability. Upgrades planned before deployment include changes to the engine air particle separators to prevent hydraulic leaks and nacelle fires. Manufacturer's support personnel and an augmented spares "superpack" will be deployed with the tiltrotor.

The deployment of 10 MV-22B Block B assault transports by VMM-263, the first operational Osprey squadron, will come 24 years after the tiltrotor was selected to replace the USMC's Boeing CH-46 helicopters, now almost 40 years old.

The Marines have lost seven CH-46s in Iraq, and believe the V-22 will be more survivable because it can fly faster and higher than the helicopter. The Osprey "goes twice as fast, three times as far, and is six or seven times more survivable than the aircraft it replaces", says USMC aviation commandant Lt Gen John Castellaw.

The MV-22's infrared and acoustic signatures are lower that the CH-46's, Castellaw says, and the aircraft is equipped with missile warning system, laser and radar warning receivers, chaff dispenser and ramp-mounted gun, but the Marines will rely heavily on its ability to get in and out of hot zones quickly.

Using the tiltrotor's ability to transition rapidly between helicopter and aeroplane modes, the USMC has developed operating techniques that include flying in at 240kt (450km/h) and descending at up to 6,000ft/min (30m/s) to a 200ft altitude on approach to the landing zone, then transitioning to helicopter mode for a vertical landing.

While making the aircraft harder to hit, the high-speed fixed-wing approach also avoids the possibility of encountering vortex ring state - a form of rotor stall responsible for an MV-22 crash in 2000 that killed 19 people - during a high descent-rate approach in helicopter mode. "We do not intend tocome out of a high altitude in helicopter mode," says Castellaw.

Departing the combat zone, the Osprey will convert to aeroplane mode to accelerate and climb as quickly as possible out of range of small-arms fire, rocket-propelled grenades and surface-to-air missiles. "It can be at 200kt-plus and climbing to altitude in 15s," says Castellaw.