Funding concerns could see Pentagon recreate the multinational industrial co-operation plan used for the F-35
The US Department of Defense is on track to formalise a requirement for a C-130-sized vertical lift aircraft with a range of up to 925km (500nm) able to carry a payload of around 21,800kg (48,000lb). If produced, this vertical take-off and landing (VTOL) aircraft would carry twice the maximum payload of Sikorsky's CH-53E heavylift helicopter.
An initial capabilities document is being prepared for approval in December, but supporters are struggling to secure a funding stream for development. Resource concerns are fuelling interest in a multi-service programme, and may drive the Pentagon to recreate the Lockheed Martin F-35 Joint Strike Fighter's multinational industrial co-operation plan to support the development of a heavylift vertical aircraft.
The project has evolved out of a study of military rotorcraft needs by the Joint Vertical Airlift Task Force (JVATF), a year-old planning group reporting to Pentagon acquisition chief Michael Wynne, says JVATF chairman Michael Walsh.
The aircraft would be designed to transport the US Army's 20t-plus Stryker or Future Combat System vehicles, as well as supporting resupply needs for the US Navy's Sea Base strategy, which calls for pre-positioning several massive floating staging areas around the globe.
In calling for a VTOL capability, the JVATF has attracted a diverse mix of ideas from four major US players. Bell has offered its quad-tiltrotor (QTR) design to meet the requirement.
A scale model will enter aeroelastic tests later this year, and an early fluid-dynamics downwash study has encouraged Bell's engineering team, says Mark Gibson, the company's director of advanced concepts development.
On take-off and landing, the four proprotors produce a huge downwash that has an unusual effect: rather than scattering outwards after striking the ground, the flow of air turns inwards and rises, generating several thousand pounds of extra lift, says Gibson.
Boeing could team on Bell's QTR design, but is preparing a range of other options, says Waldo Carmona, Boeing director of advanced rotorcraft systems.
Lockheed Martin favours a fan-and-wing concept that borrows from the lift fan developed for the F-35Bshort take-off and vertical-landing variant of the JSF, say industry sources. This would involve embedding a lift fan in each wing. The F-35B's lift fan is expected to provide 18,000kg of vertical thrust.
Finally, Sikorsky is proposing a co-axial counter-rotating rotor system that builds on the company's experience with the H-53 heavylift family, says Sikorsky president Steve Finger. Using counter-rotating rotors removes the need for an anti-torque tail rotor, improving overall propulsion efficiency.
The development schedule for the heavylift vertical aircraft is still under debate. Carmona favours a proposal to launch full-scale development in 2006, with initial operational capability in 2012. However, Walsh advocates a more patient, 15-year development programme for the capability, which may require multiple technological breakthroughs. "Let's make sure we spend some time to get it right," he says.
STEPHEN TRIMBLE / BALTIMORE
Source: Flight International
