AOPA Pilot Magazine - August 2018 - 62

Countinued from p. 60
115 horsepower. This will result in roughly the same
power-to-weight ratio as the Cessna 152. Seimens has
quickly become the electric propulsion leader in development programs. The Sun Flyer's motor is one of
many projects the company is working on, with power
applications ranging from 30 kilowatts (40 horsepower) to more than a megawatt. The motor Siemens
developed for Extra Aircraft's technology demonstrator had a 5:1 power-to-weight ratio, something piston
engines can't touch. And Siemens' SP70D, to be used on
the Sun Flyer, weighs only 26 kilograms (57 pounds).
Then there's the batteries. Whereas the weight of fuel
is an ever-changing variable that gives pilots an infinite
range of potential loading options, battery weight is fixed.
And the batteries will be heavy. Bye Aerospace is quoting 10 packs totaling 880 pounds. Thanks to lightweight
construction materials, Bye is saying to expect a "crew
weight" of 440 pounds. Even with such a light motor,
the batteries will be dispersed both in the cowling and
behind the cabin, indicating that their weight is a primary design consideration.
Relative newcomer EP Systems is providing the
battery packs for the Sun Flyer. Part of what gave Bye
Aerospace confidence to go with the California-based
start-up was its work with NASA's X-57 project, an allelectric test aircraft. It takes a Tecnam P2006T, strips
the engines, and bolts on a new wing and a host of electric motors. EP Systems is the battery pack provider,
and the batteries the company is providing to the Sun
Flyer are similar.
Aside from weight, fire safety is a major consideration of carrying around hundreds of pounds of batteries.
Teslas seem to be spontaneously combusting on the road,
Boeing had fires on the 787, and earlier this year a Magnus
eFusion electric aircraft crashed in Hungary with news
reports saying fire may have been a cause.
Bye Aerospace CEO George Bye said the safety protocol around the batteries is threefold. First, you design
a robust monitoring system. Then you incorporate a battery management unit that can isolate any problems-and
finally, you build in physical containment. NASA said its
tests of EP Systems' batteries showed the fire mitigation
system worked well enough to prevent and contain any
potential fires, a key point in the battery testing process.
Pipistrel claims a 1.5-hour endurance on the Alpha
Electro. Bye is claiming an endurance of more than three
hours, and says that number is today's reality with no
technological leap or improvement required. "It's not
magic," he said. The Sun Flyer's current batteries are
260 watt-hours per kilogram, a number some speculate
to be roughly equivalent to the latest batteries on a Tesla.
Strung together, the packs produce 92 kilowatt-hours of
energy, 73 kwh of which is usable when you factor in VFR
reserves and other buckets we shouldn't plan to dip into.
That's enough energy to run an average American home
for more than two days. With battery technology improving at an average of 5 to 8 percent every year, it's not hard
62 | AOPA PILOT August
PILOT
2018

REALITY OR VAPORWARE?
A look at current electric
projects
Any major leap in technology is
going to take some suspension
of currently held beliefs of what's
possible. It's good that the visionaries don't listen to the naysayers and all the others that try to
hold them back. But it's fun to try
anyway.

NASA X-57 Maxwell
With this technology demonstrator
and research test vehicle, the X-57
team is taking the unusual step of
mounting 14 leading-edge motors,
some of which will be engaged only
for takeoff.
Reality. This is NASA. If it can land
us on the moon, it can make electric
motors break the surly bonds.

to imagine a future where electric aircraft get
well beyond the training market and enter
the world of GA utility.
Bob Hepp, the owner of Aviation
Adventures in northern Virginia and one of
the first Sun Flyer position holders, is interested in how the Sun Flyer will help his flight
school. Hepp paid a deposit of $10,000 each
for his two Sun Flyers, a not insignificant
amount for a private flight school. "I've been
watching electric for a long time, knowing
the issues with 100LL," he said. "Ten years
after Sun Flyer makes it to market there will

AOPA Pilot Magazine - August 2018

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