Calling a halt to stalling

Engineers at North Carolina State University have found a way to reduce stalling in aircraft using small jets of air.

Dubbed In-Flight Active Flow Control, the North Carolina State Engineers’ method employs the additional airflow from small holes near the rear of a wing to avoid staling and help steer the plane.

In a recent test flight, engineers at NC State successfully initiated a roll manoeuvre on a remotely piloted aircraft by using In-Flight Active Flow Control.

‘This technology has been demonstrated in a lab before, it has been demonstrated in a wind tunnel, but until now it’s never been demonstrated on a flying aircraft,’ said Dr Ndaona Chokani, professor of aerospace engineering.

For the experiment, the NC State team designed and built a remotely piloted plane — called the ‘Mantra’ — with a nine-foot wingspan.

Weighing in at approximately 60 pounds, the Mantra can fly at a speed of 80 miles per hour and is powered by a two-stroke gasoline engine.

The Manta’s air streams are generated by a small onboard tank of air pressurised to 2,500 psi.

Bespoke regulators control the volume and speed of the pulses of air that flow through the holes and exit as jets at a speed slightly faster than an adult could blow air through a drinking straw.

The air jets are activated only when needed, preserving pressure in the air tank.

In an October 5, 2000 test flight at the Johnston County Airport, the Manta was flown above the runway with its wing flaps in the down position.

The air jets on one wing were activated, increasing lift on that wing and causing the plane to ‘roll’ on its horizontal axis. A second flight gave the same results.

Chokani explained that being able to quantify the results is an important part of being able to improve the technology.

The Manta has a relatively large payload area that carries sophisticated instruments to measure air pressure at the wings, air speed of the aircraft, speed of the roll, and the amount and speed of air coming through the small holes in the wings. After a test flight, data is downloaded to a laptop computer.

‘The first place you may see this technology is on unmanned military aircraft,’ Chokani said, adding that the technology could also be used on jet fighters. A very small amount of the air sucked into the jet engine could be diverted to the small holes to make the aircraft more manoeuvrable, he said.

‘This technology reduces drag, which means greater fuel efficiency for aircraft, and that could mean lower ticket prices for passengers,’ said Chokani, commenting on the commercial implications of the development.