Long-time coming

Ron Ossi
Contributing Editor

It has a birdlike skill that lets it spring directly off the ground and straight into a 700-mile mission at 300 mph. The Bell Boeing V-22 Osprey is indeed a true hybrid of the conventional helicopter and the normal airplane. At the Farnborough International Air Show this past summer, the Osprey made its formal world debut and is now on the verge of being fully operational for the U.S. Marine Corps.

The V-22 in flight looks like an "almost normal" medium-small turboprop transport. And it sounded like an ordinary turboprop as it whizzed by crowds in level flight at Farnborough. But the Osprey seems like the caricature of a plane envisioned by a cartoonist. Its 6,150-hp engines look too big for the airframe. And they mount way-out on the wing tips and drive huge 38-ft-diameter props. These spin in opposite directions at such a leisurely pace (333 rpm) that the rotation of their three blades is discernable to the naked eye.

On the ramp, the big V-22 engines must tilt up at 45°; otherwise their huge prop-rotors will strike the ground. In its normal departure procedure, the plane executes a fuel-efficient short take-off (STO). The engines tilt up to 70° and the V-22 goes airborne after a short run of only several plane lengths. Rotors then rapidly transition to a 0° tilt to let the Osprey fly like a normal prop-driven plane.

Of course the aircraft's biggest attribute is its ability to produce direct vertical lift with its engines tilted at 90°. It can hover and move about with aplomb and precision, just like a helicopter. In this mode, it also sounds like a helicopter.

Judging by its performance at Farnborough, the V-22 is quiet. It exhibits the typical clatter of multibladed helicopters when hovering. But it is nearly silent in airplane mode except for a low-frequency rumble.

The USMC is justifiably proud of its new flying machine. Squadrons are now in advanced training, and the first units are scheduled to be in operation next year. But most of the early chatter surrounding the two V-22s at Farnborough centered on their flight to the show across the Atlantic. The Rolls-Royce engines on both planes suffered several compressor stalls during the trip. One Osprey experienced an in-flight shutdown, but immediately restarted. As a precaution, it deviated to Iceland to receive a new engine before showing up later in the week.

USMC Col. Glenn Waters, the lead pilot on the mission explained, "The aircraft flown were not the latest configuration but 'block A' models with which we have the most flying experience. Unfortunately, these block A's don't have the latest anti-icing system." USMC V-22 Program Manager Col. Bill Taylor added, "The block B's are now the standard in production. They incorporate design changes to the AIPS (airinlet particle separator) and the AE1107C engine itself. That will alleviate similar situations in the future." All block A's will eventually be rebuilt to the block B standards, which contain other improvements as well.

WHY NOW?
Gen. John Castellaw, USMC Deputy Commandant for Aviation, sums up why the Corps thinks the Osprey was worth waiting for: "Today we need 12 CH-46 helicopters and 2 hours to move 180 troopers 80 miles. Eight V-22s would let us do the same job in 17 minutes." Carrier operations will benefit as well, says Col. Glenn Waters, head of the V-22 operational test squadron. "A typical mission involving 12 helicopters would take hours to prep and assemble into a deployment formation," he explains. "The same operation with eight V-22s would take 10 minutes."

This performance results from 50 years of research and development in tilt-rotor technology. tiltrotor research started in the 1940s, but the first tilt-rotor prototype, the XV-3, did not fly until 1953. The XV-3 was derived from helicopter design conventions of the day. Its Lycoming reciprocating engine was fixed within the fuselage. Thus only its wing-tipmounted rotors tilted, giving rise to the term "tilt-rotor." Driveshafts carried power out to the rotors. A major problem with this setup was that driveshafts and gearboxes it entailed were quite heavy because they had to transfer full power and torque long distances through the wings.

But it was not until the 1970s when Bell developed the XV-15, with its 1,800-shp turboshaft engines, that tilt-rotor technology was finally recognized as truly practicable. The crux of the concept's feasibility lay in the technical success of the rotor control and aeromechanical design. But the performance advantage of the gas turbine engine to a large degree made the tilt-rotor a viable aircraft.

The XV-15 carried two engines mounted in wing-tip nacelles, each powering a rotor through a gearbox. For safety there was also a cross-driveshaft through the wings that could transfer power to the other rotor in case one engine lost power. This driveshaft assures both rotors put out equal thrust in all cases. But this shaft could be relatively light because it did not continually carry significant loads.

The Lycoming LTC1K-4K engines developed for the XV-15 introduced what are today technologies specific to tiltable engines. Principally they consist of specially designed bearing chambers and a lube oil tank, pressure, and scavenge system that works at any engine attitude. These features have become standard on several all-attitude engines.

The Allison Div. of General Motors, which is now part of Rolls-Royce North America, beat out several other suppliers to win the contract for the V-22 engine. The engine initially had the U.S. Navy nomenclature of T406-AD-400 but is now dubbed the AE1107C. It is a 6,150-shp turboshaft engine of exceptional performance. It evolved from earlier R&D work by Rolls on derivatives of production engines. The AE1107C engine "core" (the unity of the compressor, combustor, and gasifier turbine) has become the basis for two successful commercial engines, the AE2100 turboprop and the AE3007 turbofan. The V-22 engine today benefits from the success of these two civil models.

The USMC is acquiring the engine through a total service package nicknamed "power by the hour." According to Col. Bill Taylor, "This business arrangement is saving the U.S. taxpayer tons of money."

(Power-by-the-hour is a term used to denote contract deals where a customer pays a fixed price-per-hour flown. So there is a strong incentive for the engine maker to improve engine reliability because they get the same revenue-per-flight-hour regardless of how much maintenance they provide.)

The Marines have a 360-aircraft production target for the Osprey. The Air Force is now getting its own copies of the Osprey (50 expected) and the Navy will soon follow suit (48 expected). If the plane proves to be successful in its military role, talk has it that Bell Boeing could field a commercial version.

Technology drawn from the V-22 is also advancing on other fronts. A tilt-rotor plane called the Bell Eagle Eye UAV has flown for a number of years as a prototype. It has evolved into an observation platform for the U.S. Coast Guard Deepwater program. Intended for shipboard operation, it is powered by a single fuselage-mounted 600-shp turboshaft engine driving 10-ft-diameter rotors. It should be operational in 2010.

The Bell/Agusta B-A609 is a commercial craft about the size of the old XV-15 and has the same layout as both the XV-15 and the V-22. Powered by two turboshafts in the 1,800-shp class, it hits 315 mph. It is being marketed to business executives and carries up to nine passengers. It should be civil certified around 2010. One has been flying at Bell test facilities in Texas and a second should be flying at helicopter maker AgustaWestland in Italy at about the time this article publishes.

One Osprey mutation a bit down the pike is the Bell-QTR (Quad Tilt Rotor). A big unit, it features a fuselage about the size of a Lockheed-Martin C-130-30, mated to two sets of wings, engines and prop-rotors from the Osprey. The QTR has been an ongoing study effort by Bell Boeing for a 100,000-lb military combat transport. Someday it could have commercial fallout as a 90-passenger regional airliner. A great amount of design and development effort should be saved with this concept because of the technology and components it borrows from the Osprey. According to Bell Helicopter CEO Mike Redenbaugh, "A 20%-scale powered model is currently in wind-tunnel tests at Langley. The final version may need more power than the current V-22 engines have."

MAKE CONTACT
This Rolls-Royce site contains a video of V-22 flight operations and a rotational image of the AE1107c turboshaft engine: www.rollsroyce.com/defence_aerospace/products/helicopters/ae1107c/default.jspThe Wikipedia page on the Osprey contains links to several videos of it in flight, as well as one show the plane's 1991 crash: en.wikipedia.org/wiki/V22_Osprey