London, Feb 24 : Several international research groups are working on developing a small robotic aircraft powered by rotating "paddle-wheel" wings, which would be inspired by a bizarre aircraft design dating from the late 19th century.
According to a report in New Scientist, this antique design, known as "cyclogyros", was first proposed a hundred years back.
A "cyclogyro" flies using "cycloidal propellers" - several wings positioned around the edge of a rotating cylindrical framework, a bit like a paddle-wheel. As each wing rotates, its blades move through the air generating lift and thrust.
And, since each wing rotates through a full circle, altering the angle of the individual blades can pull the aircraft forwards, backwards and down as well up. The manoeuvrability that cycloidal propellers could offer provides benefits over more established flying methods.
Although no cyclogyro has yet flown without being tethered, its proponents say the design could prove more efficient and manoeuvrable than helicopters at small scales.
Now, a team of Singapore researchers is leading the race to construct a working cyclogyro with a prototype that hovers on the end of a line.
In fact, Lim Kah Bin and Hu Yu at the National University of Singapore have already built a small cyclogyro that hovers and turns on the end of a tether, which delivers power to its electric motors.
The researchers heard about the cyclogyro's design while working on a miniature aircraft with flapping wings. They performed simulations confirming that cycloidal propellers can be more efficient than those used on aeroplanes and helicopters.
"They will also be potentially much quieter than screw rotors," they added.
After studying the performance of different cycloidal designs, the pair modified a toy helicopter, giving it two cycloidal propellers with three blades each, and a small tail rotor for stability.
"On the tether, the aircraft can spin, move directly up and down or fly forward and backward," said Hu.
According to Hu, "This is perhaps the first recorded flight for a cyclogyro."
"Cyclogyros are more relevant now because people want to build small, agile UAVs (uncrewed aerial vehicles)," said Daniel Weihs, an aerospace engineer interested in cyclogyros at the Technion Israel Institute of Technology (TIIT), Haifa.
"At such sizes they have greater advantages over helicopters," he said.
According to Weihs, "Cyclogyros can also be more manoeuvrable."
Helicopters must tilt to travel laterally. But cycloidal propellers can generate thrust in any direction so the craft can remain level, or adopt any other position and still fly in any direction.