Successful First Flight

One of our board trustees – Andrew Rae, Professor of Engineering at the University of the Highlands and Islands Perth College UHI – has led the design, and successful first flight, of the first ever large-scale aircraft powered by variable-buoyancy propulsion.

The ingenious new aircraft called Phoenix moves through the air like a porpoise through water. “She looks a bit like an airship, except airships don’t have wings. It’s a proper aeroplane,” says Andrew. “It flies under its own propulsion although it has no engines”.

“The central fuselage is filled with helium, which makes it buoyant so it can ascend like a balloon. And inside that there’s another bag with compressors on it that inhales air from outside, compresses the air, which makes the aeroplane heavier and then it descends like a glider.”

This ability to “breathe” – to switch quickly between being heavier or lighter than air – doesn’t just make the plane go up and down. It is the key to driving it forward.

It is designed to repeatedly transition from being lighter than air to being heavier than air so thrust is generated to propel the craft forward.

“This system allows the Phoenix to be completely self-sufficient. The energy needed to power its pumps and valves is provided by a battery which is charged by lightweight flexible solar cells on its wings and tail. It can travel long distances and stay aloft for long periods.

“Vehicles based on this technology could be a much cheaper option than launching satellites for telecommunication activities. Current equivalent aeroplanes are very complex and very expensive. By contrast, Phoenix is almost expendable and so provides a user with previously unavailable lower cost options.”

The prototype aeroplane, which is 15 metres long and has a wingspan of 10.5 metres, was flown successfully and repeatedly over a distance of 120 metres during indoor trials at the Drystack facility in Portsmouth in March. The test flight was the culmination of a three-year project to prove the viability of a variable-buoyancy powered aircraft.

The Phoenix team is now exploring collaborations with major manufacturers to take the technology to the next phase of development. The project has been part-funded by Innovate UK, the UK’s Innovation Agency, through the Aerospace Technology Institute.