Companies defining large cargo rotorcraft under the US Army's Joint Heavy Lift (JHL) study have briefed the service on their baseline designs. Work on eight "excursion" designs, which include lighter- and heavier-payload and seabase-compatible derivatives, continues under JHL concept design and analysis (CDA) contracts scheduled to end in March next year.
Bell Boeing has used its 18-month, $3.45 million JHL CDA contract to refine the design of its Quad Tiltrotor (QTR). Recent design changes include the addition of small vertical stabilisers under the rear wing to increase directional stability.
"We have taken the baseline aircraft to a reasonable level of fidelity and provided a lot of data to the requirements community," says QTR programme manager Alan Ewing.
The baseline design is larger than a Lockheed Martin C-130 Hercules, with greater wing span and a longer, wider fuselage. Proprotor diameter is 15.2m (50ft) compared with 11.6m for the V-22 Osprey. "That's a relatively small increase over our experience base," says Ewing.
Proprotor clearance requirements result in a "cargo box" length of 19m, longer than needed for the JHL, which allows the baseline QTR to carry nine cargo pallets, 110 paratroops or 150 passengers.
"We built in the equivalent of a C-130 to C-130-30 stretch up front," says Ewing. The heavy-payload excursion design, able to carry 26t, has a 20.7m-long cargo box and a larger fuselage cross-section.
Bell Boeing is now looking at two concepts for a seabase-compatible QTR, design of which is "a bit of a problem", says Ewing, because the company wants to avoid folding the proprotors and wings as in the V-22. "We don't have folding in the baseline because it gained nothing and [its exclusion] saved weight," he says.
A JHL demonstrator could later be funded to enable a decision by 2015 on whether to develop the capability, the army says. The service is meanwhile looking at reviving its science and technology budget to accelerate work on concepts for post-2025 army aviation, which also include the Joint Multi Role vehicle - a potential replacement for Boeing's AH-64 Apache attack helicopter.