Using Flow Separation to Fly

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Fixed-wing flight typically favors the efficiency of long skinny wings, which is why so many aircraft have them. But for smaller flyers, like micro air vehicles (MAVs), short and stubby wings are necessary to stand up the disruption of sudden wind gusts. But a new MAV design eschews that conventional wisdom in favor of a biological tactic: intentionally disrupting the flow.

Usually designers aim to have a smooth, rounded leading edge to wings in order to guide air around the airfoil. But here researchers instead chose a sharp, thick leading edge that immediately disrupts the flow, causing a turbulent separation region over the front section of the wing. A rounded flap added over the trailing edge of the wing guides flow back into contact, giving the wing its lift generation.

Odd as that design choice seems at first blush, it actually makes the aircraft extremely resilient, especially to the turbulence that so often thwarts small flyers. When your flow is already disrupted, a little extra turbulence doesn’t make a difference.

The thicker wing also allows them to use a longer wingspan — thereby gaining that skinny wing efficiency — and move most of the components that would normally be in a fuselage into the wings themselves. By essentially turning most of the MAV into a wing, the designers avoid the loss of lift associated with the fuselage section of the wings.

Diagram of new micro air vehicle wing design, showing the full device as well as a cross-section with flow separation and reattachment.

(Image, video, and research credit: M. Di Luca et al.; via IEEE Spectrum; submitted by Kam-Yung Soh)

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