AOPA Turbine Pilot Magazine - November 2013 - 12

LETTERS

FROM OUR SEPTEMBER 2013 ISSUE

Where Do We Go From Here? Battery Power
In the conclusion of our three-part series on the future of propulsion, Editor at Large
Tom Horne looked ahead to the possibility of an electric future.
As a pilot and airplane builder
with an MIT degree in aerospace engineering and a career
in the defense industry, I have
been watching with interest the
development of electric vehicles
for three decades.
While I understand this
article is intended as a glimpse
at a possible future for aviation,
I feel compelled to point out
some technical shortfalls. The
biggest issue, which I find to
be encouraged by advocates
of electric vehicles, is confusion of measurements. Energy
is not measured in watts any
more than it is measured in
horsepower. Both are measures of power. Statements in
the article such as “lead-acid
batteries put out about 11 watts
per pound” and “at 5,500 watts
per pound, gasoline” are meaningless without also specifying
the time. An ordinary lead-acid
battery can easily exceed 100
watts per pound while cranking a starter, but will be dead in
a matter of minutes. Power multiplied by time yields energy. For
most of us in aviation, a more
intuitive measure of energy
would be horsepower-hours
or horsepower-minutes. We all
have a pretty good feel for what
100 horsepower can do when
applied to our propellers for
one hour.
Expressed in these terms,
one pound of gasoline burned
in my Lycoming O-360 will
provide two horsepower-hours
of usable mechanical energy
to the propeller (less time at
full rich, full power; more with
careful leaning at cruise). One
12 | AOPA PILOT November 2013

PROPULSION / ELECTRIC

WHERE DO WE GO
FROM HERE?

BATTERY POWER

EXPLORING THE FUTURE OF
GENERAL AVIATION PROPULSION
(THIRD OF THREE PARTS)

THE eSPYDER’S

carbon-ﬁber propeller
is custom designed by
Helix Carbon GmbH of
Germany. Prop diameter
is 70 inches.

Our editors explore the future of general
aviation propulsion technologies

any scoff at the notion of electrically
powered aircraft. After all, what do you
do when the batteries run out?
Short-sighted, I say. Already, battery-powered,
light two-place airplanes have the potential to ﬂy
for three hours or more, which would satisfy the
aviation ﬁx for many pilots. Such airplanes aren’t
quite ready for prime time, but soon they will be.
More practical applications for electric propulsion may include a hybrid approach that uses
on-board generators to drive electric motors that
drive propellers. Such generators might even be
internal-combustion engines or perhaps fuel cells
in the future.
Regardless, most futurists believe we are entering an all-electric age, where internal-combustion
engines will be phased out in favor of more efficient
and simpler electric motors. Aviation is unlikely to
be an exception to that movement over the long
term.
We explore the short- and long-term possibilities in this third and ﬁnal part of our series on
the future of propulsion. Share your feedback via
comments on our Reporting Points blog and our
Facebook page.
—T O M H A I N E S, E D I T O R I N C H I E F
THE eSPYDER is powered
by a Yuneec Power Drive
brushless motor of 24
KW (32 horsepower).

62 | AOPA PILOT September 2013

www.aopa.org/pilot AOPA PILOT | 63

The example electric aircraft in the article are also so
far removed from the proven
practical GA archetype as to
make fair comparisons impossible. Motorgliders and the very
lightest LSAs and ultralights
are good pioneering applications for electric propulsion
because they need very low
amounts of total energy with
relatively high (but brief )
peak powers—a perfect electric motor application. I might
someday find myself experimenting with such a design,
perhaps as a post-retirement
project, but I certainly would
not expect the resulting aircraft to be good for much more
than a Saturday morning buzz
around the patch or over to the
neighboring airfield.
This technology is much
further from being competitive
to replace gasoline in everyday applications than any of
the advocates would have us
believe.

“Before we get all rhapsodic about electricity and its environmental friendliness,
we should acknowledge that the battery
stores energy, it does not create it. If you
follow the electric lines from your charging station, they will eventually lead you
to a coal- or gas-powered generating plant.
While the electric airplane does not generate any pollution here, it does generate it
there. It may be that solar is the only truly
Allen Burke
AOPA 674335
clean energy, and it is so diffuse as to be
Orlando, Florida
of little real use. In the short run, I’m still
ADS-B
hoping for a solution to the avgas problem. I read Dave Hirschman’s
“Dogfight: ADS -B AbomMy Cherokee is calling and I must fly.”
Mike Bonsal
AOPA 1115732
Rio Rancho, New Mexico

pound of the best lithium polymer battery performance claim
I can find on the Internet, using
the efficiency Yuneec claims for
its new 81-horsepower motor on

its website, will only provide 6.9
horsepower minutes. That’s 17.4
times more energy per pound
from gasoline compared to the
best battery I can find.

ination” article and I agree.
Why can’t the FAA drop its
signal blocking? They should
broadcast all traffic information. I have Foreflight with
Stratus 2 so I only receive
glimpses of the complete traffic picture when there is an
ADS-B Out aircraft nearby. To
improve flight safety, I should
always be receiving this traffic
information.

http://www.aopa.org/pilot

AOPA Turbine Pilot Magazine - November 2013

Table of Contents for the Digital Edition of AOPA Turbine Pilot Magazine - November 2013