Aircraft Employs Variable-Buoyancy Propulsion

A group of U.K. experts has successfully flown the first ever large-scale aircraft powered by variable-buoyancy propulsion. The Phoenix is designed to repeatedly transition from being lighter than air to being heavier than air so thrust is generated to propel the craft forward.

Variable-buoyancy propulsion is used in underwater remotely operated vehicles, but has never before been harnessed for large aircraft. The system means the uninhabited vehicle is self-sufficient in energy so could, in theory, be operational for an unlimited period of time, an innovation which could revolutionize the telecommunications industry.

The team behind the ultra-long endurance autonomous aircraft includes representatives from academia and industry. Andrew Rae, Professor of Engineering at the University of the Highlands and Islands Perth College UHI Campus, led the design of the airplane. "The Phoenix spends half its time as a heavier-than-air airplane, the other as a lighter-than-air balloon. The repeated transition between these states provides the sole source of propulsion," Rae said.

“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. This motion propels the airplane 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. 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.

“Vehicles based on this technology could be used as pseudo satellites and would provide a much cheaper option 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 options.”

The prototype airplane, which is 49-feet long and has a wingspan of 35.5 feet, was flown successfully and repeatedly over a distance of about 400 feet 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 are 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.

(Images from Highlands and Islands Perth College video)

FMI: www.perth.uhi.ac.uk