Airborne Drones, Mimicking Gulls, Alter Wing Shape For Agility

At least, that’s what University of Florida engineers are working toward.

Fundedby the U.S. Air Force and NASA, UF aerospace engineers have builtprototypes of 6-inch- to 2-foot- drones capable of squeezing in and outof tight spots in cities — like tiny urban stunt planes. Their secret:seagull-inspired wings that “morph,” or change shape, dramaticallyduring flight, transforming the planes’ stability and agility at thetouch of a button on the operator’s remote control.

“If you flyin the urban canyon, through alleys, around parking garages and betweenbuildings, you need to do sharp turns, spins and dives,” said RickLind, a UF assistant professor of mechanical and aerospace engineeringwho heads the project. “That means you need to change the shape of theaircraft during flight.”

The Air Force’s Predator Unmanned AerialVehicle and other military drones have been key to military operationsin Iraq and Afghanistan. But the drones, which shoot surveillanceimages and sometimes also fire missiles, are designed to soar highabove the landscape. That limits their ability to snoop up close in thewindows, alleys, corners and other urban crevices of the tightneighborhoods that define many cities, Lind said.

The UF planesare intended to correct this deficiency and add new capabilities, suchas landing in tight spots during a mission. That could be useful, forexample, if the planes, equipped with sensors for biological orchemical weapons, were investigating single buildings where the weaponswere suspected of being made, Lind said.

Lind came to UF in 2001from NASA, where one of his last projects involved modifying the wingsof an F-18 fighter to change shape during flight. He drew on thisresearch for the drones, but he also had another source of inspiration:the Wright brothers’ first plane.

As Lind noted, unlike laterplanes, the wings of that biplane had no flaps, or ailerons. Instead,the brothers controlled the plane’s roll by using cables to twist theshape of the wings up and down during flight. Birds also change wingshape.

“Birds morph all the time, and they’re very agile,” Lindsaid. “There’s no reason we can’t achieve the same control that birdsachieve.”

The first prototype in the 3-year-old UF effort copiedthe Wright Brothers’ approach by using tiny motors to twist threads andmove flexible wings. A traditional rudder and elevators on the tail,meanwhile, control up-and-down and side-to-side motions.

Thedownfall of the thread approach was that the wings could only be pulleddown, not pushed up, which limited their capabilities. The next versionreplaced the threads with metal rods, allowing both up and down motionand improving performance.

The latest version, built bymechanical and aerospace engineering doctoral student MujahidAbdulrahim, goes a step further. Impressed by seagulls’ ability tohover, dive and climb rapidly, Abdulrahim photographed the gullsclose-up during flight. The images showed the gulls’ wings flexing atboth their shoulder and elbow joints as they altered flight patterns.

Abdulrahimadded this ability in the new prototype, with promising results. Withthe wings mimicking the gulls’ elbow in the down position, the planeloses stability but becomes highly maneuverable. With the wings in theelbow straight position, it glides well. And with the wings in theelbow up position, it’s highly controllable and easy to land.

Motorscan transform the wings from the down to the up position in flight in12 seconds, “fast enough to use in a city landscape,” Abdelrahim said.

Thebird-like prototypes are strikingly maneuverable, capable, for example,of completing three, 360-degree rolls in one second. (An F-16 fighterjet can manage at least one roll per second, but three rolls wouldproduce excessive gravity force, killing the pilot). Flying invideotaped demonstrations, they are so agile they appear out of controlat times, and indeed the planes require considerable talent by theremote control pilot.

The Air Force and NASA have so far providedabout $3 million for the UF research, a substantial portion of which isaimed at addressing that issue by making the planes easier to fly. Theengineers’ goal is to make the planes autonomous, or flyable withouthuman pilots. That won’t be easy, but it would give the planesremarkable utility. ”If the vehicle can search an area by itself, youhave almost instantaneous response to what’s being threatened,” Lindsaid.

Lind, Abdulrahim and other researchers involved in theeffort have authored nine academic papers on the research, includingtwo on the gull-wing aircraft.