All-electric, hybrid aircraft engine research taking off.

• Author: Magnuson, Stew

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.

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