Defence

Lockheed Martin’s morphing unmanned air vehicle has entered windtunnel testing under a US Defense Advanced Research Projects Agency (DARPA) programme to demonstrate long loiter time and high dash speed in one shape-changing aircraft. NextGen Aeronautics’ rival morphing UAV will meanwhile enter tests in the NASA Langley transonic dynamics windtunnel next month.

Full-scale semi-span models of the morphing wings will be tested at speeds up to Mach 0.85 and altitudes up to 50,000ft (15,200m) using a heavy gas in the tunnel, which is designed to investigate interactions between aerodynamics and structures. The tests, as well as flights of small-scale radio-controlled models, are intended to lead to selection for a flight-test phase.

The Lockheed Martin Skunk Works vehicle has a wing that folds upwards and inwards to reduce span and increase sweep for the high-speed dash. The hinges are covered by flexible silicone skins, and small flaps on the inboard leading edges close the gaps between the inward-folded wing and the fuselage. This flap is the first surface to be powered by a thermopolymer actuator, which can fit inside the wing’s thin leading edge. The model has a 2.9m semi-span when unfolded for loiter and of 1.8m when folded for high speed.

NextGen’s wing has a scissors-like articulating structure, covered with a flexible silicone skin reinforced with metal mesh. Driven by multiple actuators, the “endoskeleton” structure moves to adjust the span, area and shape, morphing from high aspect ratio and low sweep for loiter to low aspect ratio and high sweep for dash. The model has a 3m semi-span when extended, reducing to 2.2m for high speed.