Bat wing membranes inspire development of micro air vehicles

Bat wing-like membranes that change their shape in response to the prevailing wind conditions have been tested in-flight, taking them a step closer to use in Micro Air Vehicles (MAVs).

The membranes have no mechanical parts, and alter their shape in response to the forces acting upon them, making them more efficient and easier to maintain than traditional rigid wings.

The membrane wings are being developed in a combination of experimental research at Southampton University and computational modelling at Imperial College, with funding from EPSRC, and the United States Air Force European Office of Aerospace Research and Development.

The team have used the findings from the computer models to build a 0.5m-wide test vehicle, according to Prof Bharath Ganapathisubramani of Southampton University’s Aerodynamics and Flight Mechanics Group, who led the overall project.

“Since the wing is a flexible, thin rubber membrane, it can change shape depending upon what the wind hitting it comprises of,” said Ganapathisubramani. “So if it is in a gusty environment then it would continuously change shape, but if it was in a steady wind it would form a single shape and then maintain it.”

The researchers are also working on a future version of the bat wing, which will incorporate electro-active polymers that allow the membrane to stiffen and relax in response to an applied voltage.

Bats use muscles to stiffen and relax their wings as needed, he said. “We can essentially sag the membrane a little bit, or stiffen it up a little bit, depending on the voltage we apply, which mimics the bat’s behaviour,” he said.

In this way the shape of the wing can be changed irrespective of the wind conditions, said Ganapathisubramani. “You can also use it as a sensor to sense the oncoming wind conditions, because when you apply a voltage and the membrane changes shape, it will also change the voltage that you have applied,” he said.

The researchers have developed a prototype version of the electro-active wing, which they have tested in the laboratory, but they have yet to attach it to a vehicle.

Powering the artificial muscle-inspired wing will require a high voltage and low current, so the team is working towards miniaturising the equipment needed to supply this.

They hope to be able to fit the electro-active wings to an MAV within the next five years.