-T / T / +T | Comment(s)

Monday, November 1, 2004

Editor's Notebook

James T. McKenna

V-22 Questions

Recently, Managing Editor Douglas W. Nelms and I had the opportunity to fly V-22 simulators. Doug and I flew the engineering simulator at NAS Patuxent River with the V-22 integrated product team's chief test pilot, Tom Macdonald. I later had the chance to fly a line simulator at MCAS New River, home of the VMX-22 squadron, which will conduct another, critical operational evaluation of the V-22 early next year, and VMMT-204, the V-22 training squadron.

At Pax River, Macdonald took us through some of the emergency procedures V-22 pilots will be trained to use, then allowed us to "fly" the procedures. Of particular interest were those for avoiding vortex ring state and for recovering from entry into it.

Vortex ring state, you will recall from Doug's reporting in last month's issue, has been determined as a key cause of the April 2000 Osprey crash in Marana, Ariz. that killed 19 Marines. That crash was one of two that led to the 17-month grounding of the V-22, major changes to its design and the pending OpEval that could determine the fate of this aircraft program.

A retired Navy CH-53 pilot, Macdonald could now be considered the world's foremost expert on vortex ring state. As part of the effort to define the problem of vortex ring state, he flew the V-22 close to its limits again and again. In the process, he discovered that there were few warning signs of the phenomenon's onset. But he helped defined the boundaries of the conditions that create it, giving engineers the data they needed to refine the V-22's safe operating envelope and work with pilots to craft procedures to recover from vortex ring state.

Macdonald also flew into departures from controlled flight caused by vortex ring state to verify the recovery procedures. In the process, he became "the first test pilot in history to fully define a high-rate-of-descent/low-airspeed envelope," according to The Society of Experimental Test Pilots, which last year honored Macdonald with the Iven C. Kincheloe Award. It recognizes outstanding professional accomplishment in flight test, and its receipt puts Macdonald in prestigious company. Past winners include Scott Crossfield, Neil Armstrong, John Glenn, and Dick Rutan. We are long overdue in congratulating Macdonald on that award.

Experts agree that any rotorcraft is vulnerable to vortex ring state. (Macdonald's flight test work, therefore, may help advance the safety of all helicopters eventually.) Relative to the phenomenon, though, the V-22's side-by-side rotor design poses a unique problem. The likelihood is that one rotor will enter vortex ring state before the other, resulting in the kind of severe roll-over seen in the Marana crash sequence. The recovery procedure that Macdonald developed and demonstrated is impressive. By rotating the nacelles and rotors forward for just 2 sec., enough forward thrust is generated to dissipate the vortex ring state and allow the aircraft to fly away safely.

Macdonald stresses that the emphasis must be on avoiding vortex ring state, not recovering from it. Even with the effective procedures, a V-22 will lose 300 ft. or so in altitude before recovery is achieved. Since vortex ring state most likely will be encountered near the ground, at the end of an aggressive descent, Macdonald notes, "it just not a place you want to be."

The vortex ring state work should be the benchmark for the V-22 program. Still, our visits to Pax River and New River revealed some curious matters.

Despite all that has been learned about vortex ring state, the full-motion simulators being used to train V-22 pilots are not programmed to emulate the phenomenon in flight. None of the VMX-22 pilots who will conduct the next OpEval have experienced vortex ring state in a V-22 in flight, according to squadron officials, nor can they in the simulators.

There may be sound reasons for this. If, as Macdonald's flight tests revealed, there are few warning signs of vortex ring state, the phenomenon's emulation in a simulator may be of little training value. Macdonald says pilots are better avoiding vortex ring state, and the V-22 now incorporates a sink-rate warning to help them do that. Still, the aircraft is intended for combat, where aggressive maneuvers and harsh conditions are to be expected. Would V-22 pilots not be better suited for such operations if they had at least experienced a fully developed vortex ring state in a simulator?

Another related curiosity concerns the V-22's defensive maneuvering capabilities. Critics of the aircraft argue it can't safely do the hard flying needed to enter and exit combat landing zones. Advocates say the greater maneuverability of the tilt-rotor over helicopters allows escape maneuvers well within the V-22's design limits. But The Ft. Worth Star-Telegram newspaper reported in late September that the "most severe maneuvers" have been excluded from flight testing, in part because of concerns over their effects on the aircraft.

VMX-22 is developing the tactics, techniques and procedures for V-22 pilots in combat. The unit's OpEval should provide a good assessment of whether the Osprey is a combat-ready platform. But squadron officials said their development work and the OpEval will be based entirely on the flight envelope defined by the test program. The envelope will not be expanded in OpEval.

I've never flown in combat. But I think it's safe to say that an aircraft in combat will be flown in ways that the rule-writers don't cover fully. If that's the case, isn't that the way it should be tested beforehand?

Live chat by BoldChat