Phoenix Demonstrator Aircraft First to Use Variable Buoyancy Propulsion

Researchers led by Andrew Rae of the University of the Highlands and Islands Perth College in Scotland have developed and flown the first aircraft powered by variable-buoyancy propulsion. The ‘Phoenix’ demonstrator aircraft uses a technology similar to the swim bladder in a fish, generating thrust for propulsion by repeatedly transitioning from being lighter than air to being heavier than air. Resembling a blimp with wings, the ultra-long endurance, autonomous craft is 15 m (50 ft) long and has a wingspan of 10.5 m (34 ft).

“The Phoenix spends half its time as a heavier-than-air airplane, the other as a lighter-than-air balloon,” says Rae. “The repeated transition between these states provides the sole source of propulsion. 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.”

According to the researchers, the Phoenix could also operate on the edge of space, where it could act as a launch platform for micro-satellites. The current goal is to get the Phoenix to operate at an altitude of 20,000 m (66,000 ft), where it will be powered by its wing-mounted solar panels to allow it to stay aloft for several days.

“Vehicles based on this technology could be used as pseudo satellites and would provide a much cheaper option for telecommunication activities. Current equivalent airplanes are very complex and very expensive. By contrast, Phoenix is almost expendable and so provides a user with previously unavailable options,” added Rae.”

The three-year project was funded in part by by the British government’s Innovate UK agency through the Aerospace Technology Institute. The team is currently looking for major manufacturers to help with the next phase of development.