Innovation in aviation to green the industry

Materials World magazine
,
29 May 2019

Aerospace pioneers are using buoyancy control and electric propulsion to advance the use of green technologies. Idha Valeur reports.

The aviation industry is working to address its poor environmental credentials and several projects are ongoing to partially or fully use energy-saving approaches. Carbon emission reduction is coming from several areas, include increasing the efficiency of existing engines and using biofuels as opposed to fossil fuels, but there is also promising research in the field of all-electric aircrafts.

One such project is a collaboration to achieve zero-carbon aviation by Hybrid Air Vehicles (HAV), Collins Aerospace and the University of Nottingham, UK. Following a grant of around £1mln for a three-year programme from UK Aerospace Research and Technology Programme, the group is building electric propulsors for the world’s largest aircraft, the blimp-aeroplane concept, Airlander 10.

Airlander 10 is being designed as a luxury commercial craft. But it is also suitable for the defence and cargo markets as it doesn’t require much fixed infrastructure and can operate without a runway.

Electric flight

The project, called E-HAV1, will create and deliver a full-size prototype of a 500kW electric propulsor for ground testing, with fully developed technologies ready for future production. It is hoped the design can reach the stage where the conventional engines can be replaced with electric-powered ones while retaining the same capabilities.

‘An aircraft like Airlander, with its large available payload and piston engines, is suited to adopting electric engine technology. We can potentially adopt battery technology earlier than other aircraft types which are more weight-sensitive,’ Hybrid Air Vehicles Media and Communications Manager, Rebecca Zeitlin, told Materials World.

‘In addition, we will be able to include technologies like photovoltaic cells as they become available to eventually achieve zero-carbon flight.’

Each project partner is working on a different aspect. Collins Aerospace will develop the electric motor, the University of Nottingham will supply the power electronics and motor drive, and HAV will perform the integration. The company previously defined the specification of the engine and provided the initial commercial application of the technology.

Airlander 10 is claimed to be more energy-efficient than other fuel-burning aircrafts. By combining buoyant lift from helium, aerodynamic lift and vectored thrust, the aircraft is able to run with less fuel than an equivalent conventional model.

‘We use this quality to offset most of the weight of the aircraft. As a result, less engine thrust is required to move the aircraft forward to generate aerodynamic lift to keep the aircraft airborne. [This] makes it especially suited to adopting electric engines,’ Zeitlin said.

HAV emphasised that engines currently in development are 100% electric-powered. When finished, the team will use them to replace two of four existing fuel-burning engines, making the aircraft hybrid-electric. Then they will replace the remaining two engines, resulting in an all-electric aircraft.

Like a fish

Another UK-based team experimenting with buoyancy is a team of universities and private companies, led by Andrew Rae from the University of Highlands and Islands Perth College, Scotland, UK.

The prototype, Phoenix, completed its first indoor flight of 120m in March 2019. The aircraft measures 15m-long with a 10.5m-wide wingspan and has solar panels mounted on the exterior.

Similar to how a fish swim bladder enables it to generate thrust by switching between being lighter and heavier than water, the Phoenix uses comparable technologies to stay afloat in the air.

‘The Phoenix spends half its time as a heavier-than-air aeroplane, the other as a lighter-than-air balloon. The repeated transition between these states provides the sole source of propulsion,’ said Rae.  ‘The vehicle’s fuselage contains helium to allow it to ascend and also contains an airbag which inhales and compresses air to enable the craft to descend. This motion propels the aeroplane forwards and is assisted by the release of the compressed air through a rear vent.’

This system effectively makes the Phoenix energy self-sufficient as the battery is charged by the solar cells on the wings to power the aircraft’s pumps and valves.

Moving forward, the goal is for the Phoenix to fly at 20,000m in altitude and stay afloat for several days, using only power generated by the solar panels.