NASA and the US Air Force plan to begin load tests in December on a modified Boeing F/A-18A fitted with an active aeroelastic wing (AAW) as a prelude to flight tests scheduled to begin at NASA Dryden Flight Research Center, California in mid-2001. Planners hope data from the AAW work will allow designers to use new control laws and a wider range of design configurations.

NASA believes the AAW will allow thinner and higher aspect ratio wings to provide greater speed and range, as well as new wing load management procedures. It also hopes to show superior roll control using only the wing, and higher roll response with smaller control surface deflections. Importantly for future tailless designs, it also wants the data to support low-weight wing designs.

"We want to manage the loads on the wing, instead of fighting them," says AAW chief project engineer David Voracek. To induce additional aeroelasticity in the F/A-18 wing, the upper wing panel is being subdivided to increase flexibility. This was originally strengthened to offset cracking problems on the firstF/A-18s, but is effectively being modified back to the original stiffness to suit the AAW.

The one-piece leading edge flap is also being split to allow the outboard section of the wing to be controlled by the outboard aileron and outer flap section only. The inboard leading edge and inboard main flap will all be locked for the AAW portion of the test flights. "We will also take the horizontal stabilator out of the loop," says Voracek. Loads tests will assess the modified wing to 80% of its design limit loads. The team will develop control laws for flight tests in the third quarter of next year.

The AAW F/A-18A could have a much greater full-stick-deflection roll rate with increasing speed. Predicted performance at 10,000ft (3,000m) for the AAW aircraft is around 225°/s at Mach 1 compared with under 150°/s for the current aircraft. Beyond Mach 1 the AAW aircraft roll rate is expected to more than double and could reach 450°/s at Mach 1.3 versus a little over 160°/s for the standard aircraft at the same speed.

Source: Flight International