快猫短视频

Robot helicopters and aeroplanes capable of perching on steep surfaces are being developed by two separate US researchers. They say such drone aircraft could land on moving vehicles, unsteady ships or even hide inside caves.

鈥淏irds and bats can alight in all sorts of positions very well, but [normal] aircraft are limited to level surfaces,鈥� says , an aerospace engineer at the Georgia Institute of Technology, Atlanta, US, who is developing perching helicopters.

Feron鈥檚 small autonomous helicopters can land on surfaces inclined at up to 60掳. In 2002, he developed an autonomous helicopter capable of performing other aerobatic moves, including the first 360掳 roll performed autonomously.

Free-fall manoeuvre

Some military helicopters can land on slopes of 20掳, by touching one end of their landing gear down and then lowering the rest to meet the surface. Feron鈥檚 aircraft lands on steeper slopes by flipping in the air to plant all of its landing skids at once.

Feron and colleague Selcuk Bayraktar worked out a way for their computer-controlled helicopters to perform the trick, using external cameras to track the aircraft from several different angles.

The helicopter accelerates towards a Velcro-covered landing pad and, when near, tilts its rotor as far backwards as possible. That rolls it backwards in free fall, bringing its Velcro-covered skids, or feet, parallel to the landing pad to grip on. If the helicopter misses the landing, it performs a recovery manoeuvre to prepare for another attempt. (see video, upper right)

Feron plans to do away with the Velcro by having the helicopter reverse its rotors. 鈥淭hat would suck them down onto the pad,鈥� he says. Grabbing onto surfaces using claw-like attachments is another possibility.

Sitting ducks

Jonathan How, at MIT in Boston, US, is also developing small autonomous aircraft capable of unique landing manoeuvres. He suggests Feron鈥檚 trick could be useful for landing helicopters on ships. 鈥淚t could also help land UAV helicopters on moving platforms like jeeps, instead of becoming sitting ducks when they land on a stationary vehicle,鈥� he says.

How and colleagues have found a way for small autonomous aeroplanes to land and take off vertically from a perch fixed to a wall (see video, lower right). It does this by hovering vertically in a manoeuvre known as a 鈥減rop hang鈥�.

How was inspired after seeing a video of a skilled radio-controlled plane 鈥減ilot鈥� making his aircraft hover while standing on its tail. He asked a student to perform the same stunt to investigate how a computer-controlled craft might do the same.

鈥淲e saw it is pretty hard, but at least we knew it could be done,鈥� he told 快猫短视频.

The 鈥減rop hang鈥� is particularly challenging because all of the plane鈥檚 controls come into play and shifting one requires changing the others to compensate. The propeller provides lift, while the flaps on the wings prevent the body from spinning, and the tail controls the aeroplane鈥檚 horizontal position. 鈥淚t鈥檚 like a dolphin standing on its tail,鈥� says How.

Next he hopes to develop control software that can learn how to perform such manoeuvres with any aircraft.

Broken wings

Switching from hovering back to horizontal flight entails entering freefall momentarily and applying maximum power to move back to normal flight.

鈥淲e had several instances where it didn鈥檛 quite work,鈥� says How. These caused a few broken wings, although the polystyrene planes are fairly robust. Feron suffered a similar incident, when his helicopter missed the landing pad and ploughed straight into a wall.

How believes such accidents highlight the value of testing indoors with off-board control systems and sensors. 鈥淭he bit in the air is the cheapest part of these experiments,鈥� he says.

Feron鈥檚 work is available online at

How鈥檚 work was presented at the , held in August 2007.

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