University of Maryland researchers have performed flight tests to prove that a bird-like micro air vehicle (MAV) can achieve additional lift by folding its wings on the upstroke, similar to the motions of large birds in nature.

Satyandra Gupta, a professor in Maryland's department of mechanical engineering and a project lead for the flapping wing MAV programme, says a September flight test proved that the 36.9g (1.3oz) mylar-covered "big bird" could carry a heavier payload than the 10g it flew with. With its wings folded on the upstroke the MAV was still able to carry its 10g payload while flying 10% slower.

The battery-powered MAV has a 572mm (22.5in) wingspan and flaps at 4.5Hz. Unlike small birds that have identical upstrokes and down strokes, researchers have determined that large birds fold their wings on the upstroke to increase lift.

Gupta's team tested the concept by incorporating a passive joint in the MAV's wing, allowing the structure to fold on the upstroke. Future tests will include a "more aggressive" folding of the wings, says Gupta.

The work is being funded by the National Science Foundation and the US Army's multi-disciplinary university research initiative, which aims to help the Army maintain combat technology superiority.

Watch the video of the September flight test in the player below.

Source: Flight International