Aviation firm aims to stir interest in compound helos.

• Author: Erwin, Sandra I.
• Position: Brief Article

Proponents of compound helicopters are hopeful that the Defense Department will consider including these aircraft in the mix of rotary-wing military platforms. Compound helicopters have been around for at least 35 years, but have not caught on for various reasons. Advocates now believe that the time is right to reintroduce this technology, as a low-cost alternative to buying new helicopters and as a way to improve the speed and range of current helicopters.

A compound is a modified conventional helicopter that has an auxiliary propulsion system to provide additional thrust--beyond the thrust already produced by the rotors. The extra thrust helps unload the rotor in forward flight and increase forward speeds.

The only compound helicopter concept currently funded by the Defense Department is called the Vectored Thrust Ducted Propeller (VTDP). This compound helicopter is a modified Sikorsky H-60 airframe. A technology demonstration for the VTDP is under way at the Naval Air Systems Command, with funding from the Office of Naval Research.

The VTDP has fixed wings and a rail-mounted ducted propeller. It was designed by Piasecki Aircraft, in Essington, Penn.

The company's director of business development, John Piasecki, describes the VTDP as "an evolutionary step for the helicopter."

The tail-mounted ducted propeller, called the ring-rail, provides auxiliary thrust and control in forward flight, Piasecki explained. While a conventional helicopter gets all its lift and propulsion out of the main rotor, he said, "this tail helps to unload the main rotor from its propulsion responsibilities, because it can provide forward thrust, whereas the conventional rail rotor cant.

The VTDP also has fixed wings that work in concert with the rail to unload the rotor during lift. "By unloading the rotor from its lift and propulsion responsibilities, you can delay the onset of retreating blade stall, which limits the speed of helicopters," said Piasecki. The wings can fold and can be removed for stowage.

According to a Navair spokesperson, "the Navy is evaluating the VTDP/compound concept as a technology demonstration." Piasecki Aircraft received a $26.1 million contract in October 2000 to design, modify and test the VTDP technology on a YSH-60F aircraft.

Program officials involved in the demonstration declined to be interviewed. Through the Navair spokesperson, a program official said, "Results on the potential for the technology will be forthcoming after we...