Piasecki compound X-49 makes first flight

 - July 25, 2007, 6:47 AM
Retrofit technology that could turn the Pentagon’s fleet of Black Hawks and other helicopters into 200-knot, high-altitude speedsters, and later be applied to the civil market, is one step closer to reality.

Piasecki Aircraft’s vectored-thrust ducted propeller (VTDP) compound helicopter made its first flight June 29 at Boeing’s New Castle County, Del. flight-test facility. During the 15-minute flight, test pilots conducted various maneuvers, including takeoff to hover, left and right pedal turns, left and sideways flight, low-speed forward flight, additional hovers and hover to landing. Another flight was scheduled for the middle of last month.

The X-49A mates a Sikorsky SH-60F to Piasecki’s second-generation “ring-tail” ducted fan, which replaces the tail rotor on a conventional helicopter. The VTDP provides forward thrust in addition to anti-torque, vectored thrust and yaw control. The system also mates a lifting wing with flaperons to the fuselage–in this case from an Aerostar FJ-100 VLJ.

The thrust augmentation from the VTDP, combined with the lifting wing, has the effect of unloading the main rotor, transferring more lift to the fixed wing, allowing it to fly faster and avoiding retreating blade stall.

It also provides an increase in gross weight, payload, range, service ceiling and forward speed (from 150 to 200 knots). The increased payload will be necessary to allow for additional fuel because the goal is to increase the Black Hawk’s range from 108 nm to 540 nm to meet the Pentagon’s force-projection goals.

The conversion also adds 1,600 pounds to the aircraft’s basic empty weight. To compensate for the additional weight in hover, Piasecki proposes replacing the APU with a supplemental power unit, which will be installed during Phase 2 of flight testing next year and is likely to be the Rolls-Royce 250, according to the company.
The SPU would provide supplemental power to the helicopter’s two main General Electric T700-701C turboshaft engines in hover and be brought back to idle in cruise. Maximum available shaft horsepower on the compound ship would be 2,700. The modification also includes adding a hardened driveshaft to replace the existing tail-rotor shaft.

The $16 million Phase 1 of the program is a U.S. Army advanced technology demonstration initiative being managed by the Aviation Applied Technology Directorate of Fort Eustis, Va. The technology is under consideration to upgrade the capabilities of the AH-64 and Marine Corps H-1 helicopters, as well as future potential platforms, such as the Joint Multi-Role rotorcraft. To date, Phase 2 of the program, which covers the SPU upgrade, further drag reduction features and flight verification of the performance enhancements, is not funded.

Piasecki has extensive experience in ring-tail design. Its first-generation system flew on the 16H-1 Pathfinder in 1962, and it was later involved with the development of Lockheed’s fast attack helicopter, the AH-56 Cheyenne.
John Piasecki, vice president for contracts, said combat applications in Iraq and Afghanistan and operations in Pakistan revealed the limitations of current-construction helicopters, reviving the Pentagon’s interest in ring-tail designs. “These environments limit the capabilities of existing platforms. Retreating-blade stall limits often restrict forward speed to 90 knots and shorten range in the Black Hawk. The Army’s current workaround is to use the CH-47 Chinook to conduct air assaults, a mission for which that helicopter was not designed.”

He commented that the advantages of the VTDP conversion include costs that are about half those of developing a new platform, a much shorter development time and more efficient use of existing military assets.

“It is obvious that a replacement platform won’t be available for a long time,” he said. “But the H-60 platform will be around for another 30 years, and this program allows spiral insertion of new technology to existing aircraft and builds a technology base for future platforms.

“The most important point that needs to be made is recognizing that our conventional helicopters are fundamentally limited. To be able to do what [military] services want to be able to do with power projection and war-fighting capability, we need to change the physics, and this [VTDP] has a lot of promise as a practical means to do this.”

Other OEMs are taking a hard look at ring-tail technologies. Sikorsky is proposing it for its X-2 coaxial helicopter. Piasecki said the company has received inquiries from OEMs for civil applications but that helicopter technologies are traditionally proven in military applications before filtering down to the private sector.