Experts in Scotland have created a new type of aircraft that can continue flying indefinitely.

The Phoenix is the first-ever large-scale aircraft powered by ‘variable-buoyancy propulsion.’

The craft stays in the air and propels itself by changing its buoyancy - repeatedly transitioning from being lighter than air to heavier than air.

Andrew Rae, Professor of Engineering at the University of the Highlands and Islands led the team designing the new ultra-long endurance autonomous aircraft.

"Completely self-sufficient"

“The vehicle’s fuselage contains helium to allow it to ascend and also contains an air bag which inhales and compresses air to enable the craft to descend,” he said.

“This motion propels the aeroplane forwards and is assisted by the release of the compressed air through a rear vent.

“This system allows the Phoenix to be completely self-sufficient.”

He said the energy needed to power the aircraft’s pumps and valves is generated through lightweight flexible solar cells on its wings and tail.

Test flight

The aircraft is 50ft feet long with a wingspan of 35ft.

It was flown successfully and repeatedly over a distance of 120 metres during indoor trials at the Drystack facility in Portsmouth in March.

The team has worked for three years attempting to prove the viability of aircraft powered by variable-buoyancy.

“Vehicles based on this technology could be used as pseudo satellites and would provide a much cheaper option for telecommunication activities,” said Professor Rae.

“Current equivalent aeroplanes are very complex and very expensive.

“By contrast, Phoenix is almost expendable and so provides a user with previously unavailable options.”

Pseudo-satellites are high-altitude aircraft that operate in the stratosphere and can be used for purposes including communications, monitoring, surveillance, and environmental observation.

The team is now exploring ways to collaborate with major manufacturers to take the technology to the next phase of development.