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from Av-week:

YC-15 To Fly Again
Boeing is rebuilding a 27-year-old STOL aircraft as a next-generation transport to carry advanced weaponry

DAVID A. FULGHUM/ORLANDO, FLA.

Boeing plans to have a demonstrator aircraft flying in two years that eventually may evolve into a tailless, short takeoff and landing assault transport.

Moreover, the company is eying manned and unmanned derivatives of the design that could serve as future-generation gunships carrying miniaturized directed-energy weapons--lasers and high-power microwave devices--instead of cannon.

Boeing's venerable YC-15 will re-emerge in the test world with tilt wings carrying turboprop engines and, after some experimentation, will shed its tail.
The demonstration of an advanced transport concept is part of a full-court press by the company to capture more military business. Other new products are to include a stealthy, long-endurance, unmanned combat aircraft with high-aspect ratio wings to increase operational altitude and payload-carrying capability.

To speed along development of its Advanced Tactical Transport (ATT), the company is taking out of flyable storage a 1976-vintage YC-15, a prototype McDonnell Douglas STOL (short takeoff and landing) transport. The goal is to convert the outsized transport for even shorter field operations. As a special operations airlift demonstrator, the reduced-radar-signature aircraft is expected to carry 80 tons of payload and take off or land on a 750-ft. runway. The 1976 requirement was 2,000 ft.

"If we stay on track, we're probably two years away," said George Muellner, Boeing's senior vice president for Air Force systems. "The market we're going after is the C-130 and [larger]." Boeing is looking in particular at the Army's future combat system and focusing on the fact that a C-130 can carry only one of the new armored fighting vehicles. "We're concentrating on getting more firepower around the battlefield quicker," he said. "The other thing is that the C-130 requires, in the best case, 2,500 ft." to take off and land.

The YC-15's fixed wings and four jets will be replaced with four turboprops and a wing that rotates 20 deg. from horizontal for additional lift. Once helicopter-like cyclical engine controls are proven, the aircraft's tail will be removed to reduce weight and radar reflectivity. Pacing of the project will depend on the technical maturity of two items--the engines and propellers that permit cyclical control.

"They both exist, but they don't exist in the size you need for that size vehicle," Muellner said. "Interestingly, the size engine we need is exactly the same size as the [EADS-designed] A400 [transport] needed--a turboprop up in the 12,000-13,000 shp. range. We've done [cyclical control] for years in helicopters. We've just never used it as a control mechanism on fixed-wing airplanes.

"We want to [put the engines] on a tilt wing to validate the STOL and the low-speed performance," he said.

While removing the tail would reduce the transport's radar reflectivity, creating a full-up stealth design would be too expensive. Boeing also looked at a two-engine concept, but researchers concluded that the cross shafting needed to ensure safety of flight if one engine failed was too complicated, heavy and costly.

The ATT design also has been considered for a new gunship design possibly with new weapons such as the advanced tactical laser and other directed energy devices or even small diameter bombs. "Does a gunship really need guns?" Muellner asked.

"We looked at both the C-17 and ATT for the gunship role," he said. "The ATT could do it, but you probably want something with more endurance and range. The Air Force has asked us to look at an unmanned gunship, a UCAV-like vehicle that could persist in an area and be more survivable."

This "persistent kill mechanism" over the battlefield could be an offshoot of the X-45 unmannned combat air vehicle (UCAV) program, Muellner said. "Does that mean it has to look like a gunship? I'll say no. In the future, I think you're likely to see an unmanned platform. Then you call for the effect you need. I don't think it has to be with a 20 mm. or a 40 mm. round."

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