Oh, for the wings of an insect

A Cranfield University team is developing flapping wings powered by piezoelectric motors for future military surveillance micro-planes.

Piezoelectric-controlled wings could better mimic an insect’s complex wing motion – the holy grail of flapping-wing flight researchers. Piezoelectric crystals change shape by a small amount when a voltage is applied.

The team claimed that the military is likely to be interested in the results of the project because highly manoeuvrable micro-air vehicles (MAVs) could one day be used for surveillance using flapping-wing propulsion. The US has invested heavily in flapping-wing technology in the past decade, and MoD interest prompted the Cranfield research. Flapping-wing systems are much better at slow speeds and can make very fast manoeuvres, something that is impossible on a normal aircraft.

Dr. Nicholas Lawson, project leader at Cranfield’s school of engineering, said an MAV powered by electrical inputs and piezoelectrics would be simpler, lighter and easier to control. ‘The few groups that have attempted to develop the technology so far have relied on mechanical designs with linkages and cogs. There are many inefficiencies with that and you end up with a heavier system that needs more power,’ he said. Other researchers have struggled to match the exact movements of an insect wing and have needed stabilisation from a tailplane for example, he added.

‘The wing beats of an insect system are very complex. The wing doesn’t just move back and forth – it pitches, flexes and sweeps. There is a reasonable amount of data on flapping wing systems, but nobody has got a device to fly for an extended period of time.’

The team will place up to four different piezoelectric materials at the root of the wing, each with a different mechanical response to voltage. The wing will be made of three fanned carbon fibre spars joined by lightweight and flexible plastic material, with a span up to 200mm. The piezoelectrics will be linked to a control chip with a power source such as a fuel cell to give sufficient power to fly.

The main challenges in the three-year project, which will begin in January, are to optimise the piezoelectric arrangement and to get the wings to respond efficiently, said Lawson.