All-Electric, Hybrid Aircraft Engine Research Taking Off

By Magnuson, Stew | National Defense, November 2016 | Go to article overview

All-Electric, Hybrid Aircraft Engine Research Taking Off


Magnuson, Stew, National Defense


While hybrid and electric engines are becoming commonplace for cars and trucks, that is not the case for aircraft.

However, basic and applied research on all-electric, turbo-electric and hybrid power sources for aircraft is ongoing in civilian agencies such as NASA, the private sector and at least in one Defense Department program.

"It is very similar to what is playing out in the automotive industry to some degree," said Richard "Pat" Anderson, professor of aerospace engineering and director of the Eagle Flight Research Center at Embry-Riddle Aeronautical University's Daytona Beach, Florida, campus.

"There is a desire to move toward lower direct operating costs... less dependence on fossil fuels and lower noise," he said in an interview.

The military may at some point benefit from some of these new ideas to power aircraft, experts said. The Defense Advanced Research Projects Agency has one program looking into the technology.

Brian German, associate professor at the Daniel Guggenheim School of Aero-space Engineering at Georgia Tech, said there are no distinct lines in the sand yet for aircraft categories, but generally researchers are looking at all-electric, or battery only, systems for smaller aircraft and various hybrid or turbo-electric systems to power the larger ones.

"You've got to be a little bit of a futurist and be in it for the long haul and say, 'I think 15 to 20 years from now, we might be able to do that,'" he said.

One of the ways the technology can be applied for larger aircraft is distributed power systems, German said. For example, the larger a gas-turbine engine is the more efficiency can be squeezed out of it. That's why there tends to be only a few massive engines hanging off aircraft such as the C-17. Researchers have known for many years that putting many smaller propellers or engine fans, distributed at key areas would be even more efficient.

Every aircraft has a boundary layer, an area of dead air above the wing that builds up and creates drag as the plane flies. By placing several smaller fans along the aircraft, the boundary layer is "ingested" and almost disappears, making the aircraft faster or more energy efficient, German explained.

Engineers look at this one of two ways. It's either making the engine fans more efficient, or creating less drag on the wing. Both effects are at play, German said.

This is the principle behind DARPA's LightningStrike vertical takeoff and landing X-plane that it is developing with Aurora Flight Sciences. An artist's rendering of the plane shows 26 hybrid-electric propulsion fans distributed on the aircraft. The program has flown a 325-pound scale model and expects to build a full-scale version within the next two years, the company said in a statement. Operating from austere landing zones is the requirement the program is seeking to fill, it said.

There are few efficiency penalties for doing this with electric motors, German said. "If you tried to do that around the plane with gas motors it would be terrible," he added.

Another possibility for larger aircraft is simply a charged battery that gives the aircraft additional power when it takes off and lifts. This would allow the gas-turbine engine to be smaller, German said. Traditional engines are most efficient when traveling at one consistent speed, and a battery could provide auxiliary power as it increases thrust.

Anderson said another flight profile might be an unmanned aerial surveillance aircraft that uses the gas engine for the flight to a targeted area, then switches over to the much quieter battery in order to be more stealthy, or extend its range.

The issue now is weight, Anderson added. The automotive industry--as it moves toward a world with all-electric cars--is supremely concerned about the batteries' price point. In the aviation world, it's all about making the batteries lighter. …

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