
Electric Planes Usher in the Second Great Age of Aviation - lelf
http://www.wired.com/2015/07/electric-planes-usher-second-great-age-aviation/
======
sokoloff
I drive an electric car and fly piston airplanes. I don't see electrics
replacing internal combustion in aviation in my flying lifetime.

Why? Weight.

The specific energy (energy per kg, edited per masklinn) of batteries sadly
lags the specific energy of gasoline or kerosene, and the airplane carries
that weight for the whole flight for an electric airplane. (My gas airplane
gets lighter and lands as much as 1000 pounds lighter than it took off,
meaning the landing gear, wing spar attachments, and brakes can all be
lighter.)

Many airplanes are certified for a ramp, taxi, and takeoff weight higher than
their approved landing weight. Electrics will be unable to take advantage of
this and must confine their takeoff weight to their landing weight.

I love that such rapid progress is being made in automotive, and I'd love to
see that adoption increase so we can reserve petro-based fuels for cases where
their energy density provides a compelling operational benefit, such as in
aviation.

~~~
nacnud
Surely the landing gear, wing spar attachments, and brakes all have to be able
to cope with an unexpected turnback and landing with most of the original
weight? (not to mention heavy landings in adverse weather conditions)

~~~
yread
No see
[http://www.caa.co.uk/default.aspx?catid=60&pagetype=90&pagei...](http://www.caa.co.uk/default.aspx?catid=60&pagetype=90&pageid=822)
or
[http://www.boeing.com/commercial/aeromagazine/articles/qtr_3...](http://www.boeing.com/commercial/aeromagazine/articles/qtr_3_07/article_03_1.html)

They are only certified to the maximum landing weight which typically is lower
than the maximum takeoff weight. When an overweight landing (ie. the weight is
higher then maximum landing weight) occurs engineers have to perform a
thorough inspection of the plane structure - landing gear, spars, wings,
wingbox

EDIT: thanks ForHackernews

~~~
ForHackernews
> the maximum landing weight which typically is larger than the maximum
> takeoff weight.

I assume this was a typo and you mean that the max landing weight is typically
_less_ than the max takeoff weight.

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simonsquiff
I read a piece by Elon Musk, who was saying that electric planes - whilst very
far away - are the future of air travel. Why? Because they will allow planes
to fly higher - increasing efficiency and speed. Apparently the normal 30,000
feet cruising altitude is not higher because the reduced oxygen levels at
higher altitudes impact the gasoline combustion too much. Even at 30,000 feet
the air is thick as soup at cruising speed, and that's why planes have not got
faster for the last 50 years. Go higher, as electrics could do, and you reduce
the air pressure further and could fly faster and more efficiently. Who knows
when battery technology will be advanced enough, but it sounds like a goal
worth shooting for (as well as the other benefits of noise reduction and
environment concerns)

~~~
srb-
Like most, I originally assumed that because batteries have poor specific
energy compared to fossil fuels, there was no point in considering them for
aircraft.

But Musk's assertion has made me reconsider. Has anyone here done the math?
What I think he's talking about is NOT a conventional plane with a battery
simply replacing the gas tank, but instead essentially a flying battery, where
90% of the plane's mass is battery.

This sounds ridiculous at first, but when you consider how cheap electricity
is compared to jet fuel, as well as the other benefits the OP mentioned, there
might be something to it (for short-haul flights.)

~~~
sokoloff
Electricity is not especially cheap compared to jet fuel.

Jet Fuel has about 128kBTU/gal and is available around $2/gal, so 64kBTU/$.

Electricity is about 3400BTU/kWhr and a kWhr is about $0.05, or about
68kBTU/$.

~~~
coryrc
Except, electricity will be about 85-90% efficient and a turbofan is about 30%
efficient [1], roughly tripling the cost advantage.

Fuel costs are about 35%[1] of operating costs, so only a ~20% cost reduction
is possible for fuel change, so your point is still mostly valid.

[1]
[https://en.wikipedia.org/wiki/Jet_engine#Energy_efficiency](https://en.wikipedia.org/wiki/Jet_engine#Energy_efficiency)

[2] [http://www.ajc.com/news/business/airlines-keep-adapting-
to-h...](http://www.ajc.com/news/business/airlines-keep-adapting-to-high-fuel-
costs/nQRrf/)

~~~
masklinn
> Except, electricity will be about 85-90% efficient and a turbofan is about
> 30% efficient [1], roughly tripling the cost advantage.

But then batteries store 1% the energy per mass fuel does so even assuming
triple the efficiency, the energy storage is 30 times easier (assuming
everything else stays constant which it can't because now your craft is an
order of magnitude heavier and your short-haul plane is as heavy as a 747)

~~~
srb-
Ah, thanks for putting some numbers out there everyone. Very interesting.
That's why I love HN.

Musk has said several times that if he wasn't working on space and EVs, he'd
be working on hyperloop or electric planes. Wonder what potential he sees in
the latter.

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thearn4
At NASA, we're very interested in hybrid electric propulsion. As an applied
math guy, it's a very interesting and surprisingly non-trivial design problem
to tackle. Even addressing the "does this really make sense?" question is
tricky.

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amalag
They could at least mention Hyrdogen fuel cell powered aircraft

[https://en.wikipedia.org/wiki/Hydrogen-
powered_aircraft](https://en.wikipedia.org/wiki/Hydrogen-powered_aircraft)

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soulsurfer
Reminds me of a german startup that designs a vertical takeoff and landing,
two seated electric plane with an interesting form factor: [http://lilium-
aviation.com/](http://lilium-aviation.com/) [Edit: no affiliation]

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gambiting
"In a statement, Pipistrel said Siemens prohibited the use of its motor for a
flight over water."

I am not sure how that could happen? Surely if they bought the engines they
could have done whatever they wanted with them? Unless they were leased from
Siemens or something.

~~~
alexhawdon
Maybe to get permission for your flight plan when using an experimental
vehicle you have to be able to show that the manufacturers of the major
components have confidence it will be able to complete the proposed route
safely?

~~~
pingec
Afaik both UK & French authorities gave permission for the flight to take
place. It were Siemens that wanted to prevent it.

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stillsut
Electric powered flight...probably best for blimps.

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mathattack
"Electric flight isn’t new—it can be traced to 1973 West Germany—but it’s not
about to dominate the skies either."

I think this says it all.

