PAUL LEWIS / USS IWO JIMA
Osprey faces deck-handling tests onboard assault ship before crucial decision in May
The Bell Boeing V-22 Osprey has returned to sea after an absence of almost three years for renewed ship compatibility trials, another crucial milestone for the US Marine Corps/US Air Force programme before the Office of the Secretary of Defence decides in May on the future of the tiltrotor.
Test aircraft No 10 landed aboard the amphibious assault carrier USS Iwo Jima (LHD 7) on 14 January at the start of five days of trials off the US East Coast.
The V-22's deck-handling was one of several areas investigated in a series of independent reviews during the tiltrotor's nearly 18-month-long grounding after its last fatal crash in December 2000.
As well as requalifying V-22 test pilots for shipboard operations, the new trials will focus on developing flight-control damping to counter uncontrolled roll on deck.
On deck, the V-22, with its tandem proprotors turning, is susceptible to roll from wake vortex generated by rotorcraft landing directly ahead of it. Lateral movement greater than 14° could damage the Osprey and as a result there is a space of two deck spots between the V-22 and other rotorcraft, limiting shipboard operations.
"We believe we'll be able to minimise that roll on deck with some lateral flight-control laws that we're evaluating," says Lt Col Kevin Gross, V-22 government chief test pilot. "Our final check will be in Phase 4. Now we're in Phase 3, where we're evaluating and collecting data and taking a look to see if our lateral control laws are reacting the way we want them to react."
The programme is also considering modifications to bolster the longitudinal authority of the V-22's cyclic control to counter pitch-up and side-slip movements. This occurs when the V-22 lands on deck into a 45° crosswind of at least 20kt (40km/h), which can cause proprotor wake on one side to impinge on the horizontal stabiliser.
Defence undersecretary Pete Aldridge wants answers to concerns about the V-22's handing qualities, including shipboard compatibility, by May.
Also critical is the need to test the tiltrotor's vertical rate-of-descent envelope available before the aircraft enters the dangerous vortex ring state. A three-phase effort is being pursued, initially to validate the 800ft/min (4m/s) descent rate at 40kt in two axes by May and then expand the envelope.
Source: Flight International
