
Axial stack battery design could unlock the era of supersonic electric airliners - adius
http://newatlas.com/axial-stack-battery-supersonic-electric-airliners/45537/?amp=true
======
WalterBright
> But the airline industry is still roughly as slow, and noisy, and expensive,
> and inefficient and dirty as it has been for the last 40 years

This is not true. Dramatic gains in fuel efficiency have been made. Such gains
are the primary driver of new airliner designs. The 757, for example, had (if
I recall correctly) 35% more efficient engines, and a more efficient wing. The
787 has something like another 20% less fuel burn - again, due to better
engines, wing shapes and weight reduction.

You also don't see the black smoke trail anymore that was normal for the 707.
The engines are much cleaner.

There is a limit to how far this can be pushed, but Boeing and the engine
makers have done an amazing job in improving the situation.

~~~
nraynaud
you have to remember that a lot of gain come from economy of scale, making
bigger planes, the gains are realized only if passenger traffic increase
(hence total pollution).

~~~
WalterBright
The 757 was about the same size as the 727, but 35% less fuel burn. The gains
I cited were for the same size aircraft. (I worked on the 757 engineering.)
The gains are real, and the airliners fell all over themselves to replace the
old, inefficient jets with the new ones, because the operational cost savings
were immense.

Ever notice the little vertical "winglets" on the wing tips? They increase the
wing efficiency. They worked so well that Boeing produced kits so older
aircraft could get them, too. They're just one example. The plastic skin used
on the 787 is for weight saving, another example of reduced fuel burn.

------
anexprogrammer
This proposal seems to ignore so much.

Like the intense friction, and heating, supersonic flight produces. Concorde's
service speed was limited by heat limits place on the aluminium alloy to
ensure a decent service life. They were always white as that was part of the
spec - dark colours would have taken heat absorption out of limit!

Wing roots varied by >100C each flight if I remember right, and _fuel was used
as a heat sink._ Are we going to use the batteries?

If the outer surfaces are conductors, what are we doing about icing
conditions?

Concorde, or likely most SST, engines put out a _lot_ of thrust in a very
fighter-like profile (they were a continuation of a fighter engine, and had
reheat). Electric fans aren't going to work efficiently in that profile and
would probably be large diameter, which isn't very supersonic friendly.

How are we now handling taxiing and subsonic? Edit: To expand the last point,
Concordes were horribly inefficient subsonic, and burnt something like 2t of
fuel to get to the runway. Reheat was used at takeoff and going transonic.
They pumped tonnes of fuel after reaching supersonic - for weight and balance
and reduced drag. They were basically really big fighters.

~~~
msl
> They were always white as that was part of the spec - dark colours would
> have taken heat absorption out of limit!

Interesting. The SR-71 Blackbird was dark (almost black) in order to radiate
heat efficiently [1]. Then again, the Blackbird flew much higher (at around 26
km compared to Concorde's just over 18 km) so maybe convection plays a bigger
part in Concorde's thermal management.

[1]
[https://en.wikipedia.org/wiki/Lockheed_SR-71_Blackbird](https://en.wikipedia.org/wiki/Lockheed_SR-71_Blackbird)
(Although my primary source is the book "Skunk Works" by Ben R. Ritch and Leo
Janos.)

~~~
anexprogrammer
Fascinating. Now I want to know why! Maybe at mach 3 more heat's coming from
inside than being absorbed.

Concordes were specced with Anti-flash White (high reflectivity as used by US
and UK nuclear bombers), and the main reason I remember is there was some
publicity when France painted one Pepsi blue (not wings) for a sponsorship. It
had to have speed restrictions.

Wikipedia has a little more (not much), but says the white finish reduced the
skin temperature by 6 to 11 degrees Celsius.

[https://en.wikipedia.org/wiki/Concorde](https://en.wikipedia.org/wiki/Concorde)

~~~
msandford
The sun adds 1000 watts per square meter, and black body radiation is the
fourth power of temperature difference. If you're heating the skin say 5000
watts per square meter due to friction or compression, then the 1000 watts
from the sun isn't bad. But if it's only say 500 watts, well, then the sun
dominates. They operated at different speeds and altitudes so it's not
entirely surprising to me that they had different strategies.

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nickff
This 'proposal' seems to assume that the rest of the aircraft would be almost
unaffected by the change, which is very unlikely.

Existing engines are designed to compress air, combust fuel, and recover
energy from the exhaust to push air (to propel the aircraft) then compress
more (to keep the cycle going). Once you are no longer combusting fuel, all of
that compression is simply wasted energy. An electric aircraft is much more
likely to have single-stage axial fans, with a much larger diameter than jets
like the Concorde (because larger and slower fans are more efficient). This
difference in propulsion will probably affect various other elements of
airframe design.

As an aside, Elon Musk has mentioned VTOL as a possible feature of electric
aircraft, and this makes a lot of sense. If the fans can be tilted (to provide
part of the 'lift' for takeoffs and landings), it means that the airplane
could have very small wings, which are usually good for efficiency, but cause
problems while landing conventionally.

~~~
etwigg
> Once you are no longer combusting fuel, all of that compression is simply
> wasted energy.

Not true. Instead of burning fuel, you can use electricity (something like an
arc welder) to generate heat. And the efficiency with which that heat is
turned into mechanical power will be dependent on the compression ratio,
regardless of whether the thermal energy is coming from electricity or burning
fuel.

Thermal energy in chemical fuel and the potential energy in a battery or a
raised weight have the same units, but there's actually a difference. You can
turn energy in a battery or a raised weight into mechanical energy with 100%
efficiency - not achieved in practice, but there's no theoretical limit.

When you turn thermal energy into mechanical energy (via Otto cycle in a car
or Brayton cycle in a jet), the peak efficiency you can achieve has a
theoretical limit based on how much you can compress the working fluid (air)
before injecting thermal energy (burning fuel or an electric arc).

So if you've got electic energy that you can turn into mechanical energy in a
fan with 100% efficiency, why would you take the thermodynamic losses of
"burning" that electricity? Because we don't know how to go supersonic speeds
with a fan or propeller - the only way we know how, for now, is with a jet
running on the brayton cycle. And all the advances we've made in high
compression fuel-burning jets would apply to electric jets just as well.

If you're okay limiting your top speed to ~Mach 0.7, then you're correct
spinning a large propeller using electricity is absolutely a better way to go,
and you can make that propeller a lot bigger if you're able to tilt it.

Karem Aircraft has done extremely interesting work on figuring out how to tilt
rotors, and much of their research would apply to electric motors as well:
[http://karemaircraft.com/](http://karemaircraft.com/)

~~~
hx87
> Instead of burning fuel, you can use electricity (something like an arc
> welder) to generate heat.

Why go through all the trouble of using electricity as the heat source in a
Brayton cycle engine instead of the obvious solution, using electric motors?
Your statement that "we don't know how to go supersonic speeds with a fan or
propeller" is clearly wrong, since supersonic aircraft have been flying with
turbofans and no afterburners for almost five decades now.

~~~
etwigg
When a jet engine burns fuel, some energy goes into turning the fan, and some
energy goes into creating thrust.

At low-mach, the fuel burn is primarily producing torque which turns the fan.
This fan could be turned by electricity.

At high-mach, the fuel burn is primarily producing pure thrust, and the fan
portion hurts the engine's performance.

Supersonic turbofans are a compromise that have to produce thrust from takeoff
through to high speed. I may be incorrect, but I don't believe we have ever
built a ducted fan which can use pure torque to generate supersonic thrust,
although I guess I don't see why it wouldn't be theoretically possible. We can
put megawatts of energy into a fast-moving flow using thermal energy and a
brayton cycle. In order to put megawatts of energy into fast-moving flow using
rotors would require a totally new design - nothing like the supersonic
turbofans currently in production.

~~~
nickff
You have to distinguish the conventional (high efficiency) cycle of a jet
engine at low Mach, from the reheat (low efficiency) operation usually used
for high Mach.

No engine (of which I am aware) has air flowing past the fan blades at
supersonic speeds, because the trans-sonic transitions tear engines apart.
There is one prototype aircraft (a naval derivative of the F-84) which did
have a supersonic propeller, but it was very inefficient and loud. All jet
engines compress sub-Mach 1 flows, then expand them at the very back of the
engine to produce supersonic exhaust.

~~~
etwigg
> You have to distinguish the conventional (high efficiency) cycle of a jet
> engine at low Mach, from the reheat (low efficiency) operation usually used
> for high Mach.

Exactly. At high mach, almost all of the energy being put into the flow is
from expanding combustion gases - not the compressor stage. If you wanted to
go at supersonic speeds using only spinning fans, you will need a heck of a
lot of fans. Maybe we could do it! But we haven't so far.

~~~
hx87
I suppose one way to do so is to build an electro-thermal equivalent of a low-
bypass turbofan, with a jet section to deliver high-velocity thrust and a fan
section to deliver low-velocity thrust.

------
bArray
I had to squint to look at the images on that site. The designs may or may not
be a good idea, but if we can't read them then it doesn't matter. Bit of a
poor show from whoever published the article.

Looking at the accompanying text, there are some problems with his ideas. Some
of that "supporting" material is also about fail-safe design and heat
distribution. A copper plate running through the middle of a battery will draw
the heat out nicely. These batteries are all good and well until they fail, at
which point you have a huge problem. With fuel, you can dump it. What do you
do with you battery wing?

One of the massive problems is energy density, but that's not the only
problem. With the batteries embedded into the wings, you need you to figure
out how to effectively charge them too. Planes can't afford to sit for hours
on the ground between flights and swapping wings over is not going to fly with
safety regulations very well.

The intentions are good but I'm not convinced there is something viable here.

~~~
jcfrei
> I had to squint to look at the images on that site. The designs may or may
> not be a good idea, but if we can't read them then it doesn't matter. Bit of
> a poor show from whoever published the article.

Remove the ?amp=true from the URL and you'll get the proper desktop version.

~~~
bArray
I don't understand why that's set, but thanks.

------
PaulHoule
Too dangerous.

If the wing got smacked up a little and got bent, thus the positive and
negative surfaces touch, you would have a massive short circuit, then heat-up
and very possibly ignition of the electrolyte with a fire that is worse than a
jet fuel fire.

------
Animats
Not a better battery, just one with slightly less packaging. That's nowhere
near enough for aircraft.

"Breakthrough" articles in the battery and "nanotechnology" (usually surface
chemistry) fields need to be viewed with extreme skepticism. Those two fields
seem to generate a high fraction of overhyped "breakthroughs".

------
myself248
I can't imagine how this would deal with damage. A large amount of Tesla's
safety comes from each cell having a micro-fuse connecting it to the module
bus, so a failed cell simply disconnects itself. Large single battery plates
might be lower-resistance, but they'd be incredibly susceptible to damage.

~~~
ethbro
High performance, low maintenance and supply, fragile. Military hypersonic
UAV, anyone?

------
jpm_sd
This is unbelievably stupid. (1) Supersonic airplanes get incredibly hot, just
by flying. Largest battery fire the world has ever seen? (2) It would be
impossible to manufacture. (3) It would be too heavy to fly.

~~~
digerata
I don't believe he was intending the plane to fly supersonic. Instead he was
talking about using the design of the wings because they have a larger volume.

~~~
triplesec
What's the use of a supersonic plane that doesn't fly supersonic? Edit. It's
unclear what your defence of the concept using this tactic achieves. The whole
article talks of this as for supersonic flight. There are fewer issues with
subsonic flight for this idea, though many (see above and below) remain.

------
lj3
Luke Workman. Why am I not surprised to see that guy's name in this article?
He took Zero Motorcycles from a battery pack that only went 40 miles to one
that goes 120 miles while making the battery pack physically smaller. His work
never ceases to amaze.

~~~
dogma1138
>He took Zero Motorcycles from a battery pack that only went 40 miles to one
that goes 120 miles while making the battery pack physically smaller.

And what did he actually do? lithium ION batteries have been increasing in
capacity over the years and quite considerably, 18650's are now nearly 4 times
the capacity they were introduced in. I can't find anything he actually did
other than hack batteries together to make "custom" packs, while this is some
sort of an engineering achievement this is quite far from designing an actual
battery.

~~~
ryao
Those "packs" are batteries. The thing that he did not design are
electrochemical cells. The term battery pack is a misnomer invented by people
who do not understand the difference between a battery and an electrochemical
cell.

------
dogma1138
Luke Workman is "some guy" who works for zero motorcycles and hack's EV's
together.

"Some guy" is the best description I could come with because he isn't a
scientists/researcher, he hasn't published a single paper, I can't find even a
trace of his record as far as education or engineering achievements go besides
soldering a couple of batteries and putting them in a motorcycle.

All records I could find of him and his company are pretty much from News
Atlas (their sources and references link to their own articles) or it's
affiliates.

~~~
flyinglizard
I've met plenty of researchers and paper publishes who're full of crap. The
most prolific people I know have no papers behind them. If you do science,
you're a scientist; and education in its own is no more of an achievement than
raising VC money is. It's just a tool.

~~~
dogma1138
Your dismissal of actual science is quite absurd. I would still not count
anyone who takes of the shelf batteries and soldered them together a
scientists, maybe an engineer in the broadest sense of term. I've seen nothing
of this guy that makes me think that he is even remotely qualified to design a
battery that would go into an aircraft.

~~~
oldmanjay
I'm finding some humor in your accusation of dismissal considering that you
are the only one expressing dismissal in this conversation. It's a very human
sort of foible.

------
digerata
Wings flex while in flight. Either the cells need to handle that stress or the
wing needs to be super rigid. Neither is particularly easy to achieve.

~~~
dogma1138
Wings can't be rigid, the fluttering would shred them to pieces or worse
transfer to the main body and shred it pieces (tho at 35-40K ft it doesn't
really matter what breaks apart ;)).

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kldavis4
The article mentions grid level power storage but I don't see any comments
around that. What would the feasibility of creating one of these batteries as
some kind of fixed structure be?

~~~
ars
What would be the point? For land power storage you don't care about weight
(or volume). Just cost.

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jsprogrammer
What if the battery terminal/wing is hit by lightning?

~~~
dogma1138
You don't need to worry about lighting the contraction/expansion from pressure
and thermal differences alone is going to be interesting to see, put a battery
in a low pressure chamber and see what happens to it. I'm also wondering how
they are going to deal with the temperatures and other aspects that can affect
the batteries.

Solar Impulse flew at 15,000ft, a subsonic or transonic jet would be flying at
around 35,000ft, the pressure at those altitudes is about 22-23 kPa and the
temperatures are around -55 to -60c, and if he's aiming for supersonic he'll
have another issue which is the fact that the temperatures of the aircraft can
reach several 100's degrees C from the forces of friction alone.

