Conventional aircraft configurations have three power options: pneumatic, electrical, and hydraulic.

To move to a solely electric aircraft, however, requires new components, including high-speed motors, power electronics, and high-voltage cabling.

In a webinar this month titled Today’s Electric Aircraft, a reader had the following question for our speaker Pascal Thalin, Chair of SAE’s Electric Aircraft Steering Group:

Do you think that solely depending on a more efficient electrical system will be enough to develop a future of electric aircraft? Do we need a rethinking of the static design of the aircraft to optimize the design at various operating points?

Read Thalin's edited response below.

Pascal Thalin: It’s a very good question. When we’re talking about electric aircraft including propulsion: With today’s conventional aircraft shapes, like aircraft with twin engines, we have kind of reached an upper limit in terms of bypass ratios.

If you consider a turbofan engine: Basically, whenever you improve your fuel efficiency, you’re going upwards in terms of bypass ratio. If you do that, you will be dealing with larger-diameter fans. If you don’t change the aircraft design, you will end up having a very large engine that you won’t be able to install under a wing because of the ground clearance you need. That shows the limit there.

You should, overall, optimize the aerodynamics. In my presentation, we saw that when we changed the aerodynamics using, for instance, boundary layer ingestion, or changing the shape of the aircraft, we can [achieve] a bypass ratio of up to 20:1, whereas the most recent turbofan engine tops out at 12.

It’s not enough to just change components and replace given components without changing the shape and aerodynamics of the aircraft.

What do you think? Share your comments and questions below.

double bubble D8 series uses Boundary Layer Ingestion design
Engineers at NASA’s Glenn Research Center in Cleveland are testing a new kind of propulsion system that employs the design change known as Boundary Layer Ingestion. The “double bubble” D8 Series (shown) is one aircraft design concept that uses boundary layer ingestion. Analytical studies conclude that Boundary Later Ingestion has the potential to reduce the aircraft fuel burn by as much as 8.5% compared to aircraft flown today. (Image Credit: NASA/MIT/Aurora Flight Sciences)