
A German Car That Was Ultra-Aerodynamic and Totally Impractical - jacquesm
http://www.wired.com/2014/09/german-aerodynamic/
======
colanderman
Drag coefficient alone is almost meaningless for passenger cars. Aerodynamic
drag is proportional to _both_ the drag coefficient _and_ the frontal cross-
sectional area. This product (typically named CdA) is what's useful to
compare.

For example, the Prius has a frontal area of about 2.3 m², giving a CdA of
0.58 m². The Schlörwagen has a frontal area of closer to 2.8 m² (thanks to its
nearly 7-foot width), giving a CdA of 0.42 m². Still better, but not 40%
better like Cd alone would lead one to believe. (The original Insight, for
reference, has a CdA of 0.47 m².)

~~~
grecy
Are you sure?

The wikipedia article [1] mentions the "reference area" is part of the
equation to calculate Cd.

My understanding was the the Cd _is_ taking into consideration the area in
question, that's why it's a "coefficient" [2] If it's not taking into
consideration the area, surely then it's not a "coefficient" of anything, it
would just be "drag".

Also worth noting that a scale model of something (plane, auto, whatever) has
the same Cd as the full-size version, showing that Cd does take area into
consideration.

[1]
[http://en.wikipedia.org/wiki/Drag_coefficient](http://en.wikipedia.org/wiki/Drag_coefficient)

[2]
[http://en.wikipedia.org/wiki/Coefficient](http://en.wikipedia.org/wiki/Coefficient)

~~~
colanderman
_Also worth noting that a scale model of something (plane, auto, whatever) has
the same Cd as the full-size version, showing that Cd does take area into
consideration._

We're not disagreeing; we understand English differently. You say "Cd does
take area into consideration" to mean that area has been divided out from drag
measurements to produce an area-agnostic number; I say "Cd does _not_ take
area into consideration" to mean that Cd does not vary based on area (because
area has been divided out).

These are the same statements. Both underscore my point that CdA, which is (by
definition!) proportional to both frontal area and to drag force, is the
worthwhile figure of merit for passenger vehicles (where lesser drag _force_
translates directly into fuel savings).

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cstross
The Germans were _really_ keen on aerodynamics for surface vehicles in the
30s; trains too! Here's some video footage of the Schienenzeppelin (propeller-
driven diesel train) during it's preliminary 1930 test runs:

[https://www.youtube.com/watch?v=E-ID_ktSoLY](https://www.youtube.com/watch?v=E-ID_ktSoLY)

(Part two of the video:
[https://www.youtube.com/watch?v=ZY7PIIV0nIs](https://www.youtube.com/watch?v=ZY7PIIV0nIs)
)

It later set a 143mph land speed record for a petrol-powered train, although
it didn't exactly catch on (in no small part due to safety concerns concerning
the passenger-mincer at the back). More here:

[http://en.wikipedia.org/wiki/Schienenzeppelin](http://en.wikipedia.org/wiki/Schienenzeppelin)

~~~
cc439
They really advanced the automotive arts in that era.

Here's another great example, the Mercedes T80:
[http://en.wikipedia.org/wiki/Mercedes-
Benz_T80](http://en.wikipedia.org/wiki/Mercedes-Benz_T80)

It was designed and built in 1939 to achieve 750km/h and very likely would
have if it the war hadn't interrupted its development. It had rudimentary
traction control and wings that generated downforce using the ground effect!

That 750km/h design target wasn't surpassed by a wheel driven vehicle until
2001!

~~~
jacquesm
I love this thread. Did you notice that it has spoked wheels?

------
ams6110
This car would have the same problem as early Saabs that had covered front
wheels: when driven in the snow, the snow thrown off of the wheels will pack
in and fill the cavity around the wheels and you won't be able to turn when
you need to.

------
pbhjpbhj
The profile reminds me a lot of the Citroen Xsara Picasso¹ (older model) but
in reverse; the front fender [bumper] is very like the Ford Ka's rear² too.

1 - [http://thumbs2.ebaystatic.com/d/l225/m/mWFPlYob-
ONd0k2waRJ1j...](http://thumbs2.ebaystatic.com/d/l225/m/mWFPlYob-
ONd0k2waRJ1jsw.jpg)

2 -
[http://www.theaa.com/images/allaboutcars/testreports/2005076...](http://www.theaa.com/images/allaboutcars/testreports/2005076_ford_ka_detail.jpg)

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m_mueller
Quite impressive how they managed to get .15 drag coefficient in 1939 without
modern materials and wind tunnels. I wonder whether modern materials and
construction techniques wouldn't allow this again while still maintaining a
road legal and practical design. The fact that the Tesla S has pretty much
beaten all cars in their class shows that there must be quite some room for
improvement in that area. Not requiring a certain brand shape for image
reasons seems to be pretty helpful.

~~~
jdietrich
>The fact that the Tesla S has pretty much beaten all cars in their class
shows that there must be quite some room for improvement in that area.

The gains made by the Tesla S are mainly due to the form factor - it is
uniquely advantaged by being a large all-electric sedan.

Longer vehicles have a significant aerodynamic advantage, because they can
more closely approximate a perfect airfoil than a shorter vehicle. The Tesla S
has a very smooth underbody because of the flat battery unit and because it
requires no exhaust system. Air intakes are kept to a minimum, because it does
not need to dissipate the copious waste heat produced by a combustion engine.

I don't mean to detract from the marvellous engineering efforts by the Tesla
team, but the Model S is in a class of one. Large sedans from mainstream
manufacturers come very close to the aerodynamic performance of the Model S,
but the use of internal combustion puts them at an inherent disadvantage.
Competing all-electric cars are predominantly cheaper and shorter vehicles,
designed for the European city car market. The high price of the Model S
allows Tesla to use a lot of trick aero features, like the bladed mirror
mountings, active inlet vents and retractible door handles.

I have no doubt that the traditional manufacturers could match the aero
performance of the Model S if they were to produce a car with a similar form
factor and price; The Mercedes CLA BlueEfficiency exceeds the aerodynamic
performance of the Tesla S, as one of the few large and expensive cars that
have been optimised primarily for efficiency. Volkswagen manage a drag
coefficient of just 0.159 with the XL1, but it costs $146,000.

~~~
m_mueller
The XL1 is exactly the kind of thing I mean. Only because it costs 150k
doesn't mean this can't be produced cheaper, especially using all electric
components once batteries become cheaper thanks to mass production. From what
I get, the main reason why the Tesla S doesn't look similar to the XL1 is
because they wanted it to appear 'normal' so people wouldn't feel estranged by
it.

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digikata
"For example, the car is remarkably sleek head-on and moves through the wind
almost effortlessly, but the car is so tall that a stiff crosswind could send
it careening to the side."

This statement in the article is odd to me. It's no taller than many modern
vehicles, nor is the frontal aspect ratio as bad as say, a SUV. It seems like
the side stability has more to do with the wheel placement or suspension, or
maybe weight balance.

~~~
qbrass
It's a light, tail heavy car, with a shape that generates a lot of aerodynamic
lift. At speed, it was probably hard to keep on the road even without a
crosswind hitting it.

It was certainly not because it was too tall.

~~~
Gravityloss
Because the wheels are faired, they have to be placed closer to the centerline
of the vehicle. Especially the front wheels as they need to have space to
turn. This makes the vehicle more susceptible to side wind tipping moment.

------
imaginenore
It's not surprising that a prototype-type of car has a drag coefficient of
0.15. Does it have AC, airbags, comfortable seats, audio system, power
windows, ABS, etc?

Volkswagen XL1, a production car, has a drag coefficient of 0.189.

If you look at the modern experimental cars, they have much lower drag
coefficients, like Aurora 101 is 0.08.

~~~
smegel
> Does it have AC, airbags, comfortable seats, audio system, power windows,
> ABS, etc?

How do any of those things affect aerodynamics? Maybe power windows require a
slightly different window design...but even that seems unlikely.

~~~
imaginenore
Because you can't shape the car any way you want, you have to fit all these
things in, while still being bound by box-like constraints (for driving on
normal roads, parking, stability while turning, etc) and having to be slightly
elevated to drive over bumps and small rocks.

It's pretty damn hard to build a practical and safe car with a very low drag.

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josephlord
Drag coeffiecients are not absolute amounts of drag created so some things
that improve the coefficient may increase the drag of the total car if they
increase its size. It seems to be relative to surface area rather than cross
section area so longer cars have an advantage in drag coefficient.

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nonick
Have a look at this earlier design by Romanian inventor Aurel Persu:
[http://en.wikipedia.org/wiki/Aurel_Persu](http://en.wikipedia.org/wiki/Aurel_Persu)
It had a drag coefficient of about 0.22.

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po
Focusing on aerodynamics is important because they dominate the efficiency at
high speeds but you can get pretty far without going to this extreme. For
example, the Honda CR-X HF was getting over 50 MPG in the early 1980's and it
was a very nice looking car, mostly because it was small, well shaped and had
a small efficient engine.

 _The original 1.3 liter car (chassis code AE532) had an EPA Highway mileage
rating of 52 miles per gallon (MPG)in 1984 and was reported to often achieve
over 70 MPG in favorable driving conditions_

[https://en.wikipedia.org/wiki/Honda_CR-X](https://en.wikipedia.org/wiki/Honda_CR-X)

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tim333
The Acabion is pretty cool along those lines for a contemporary aerodynamic
somewhat mad (300mph, Swiss) vehicle:

[https://www.youtube.com/watch?v=yGNaEDAooBI&feature=youtu.be...](https://www.youtube.com/watch?v=yGNaEDAooBI&feature=youtu.be&t=20s)

~~~
m_mueller
As a Swiss I like how you use 'Swiss' as an example for why it's mad ;-).

~~~
Gravityloss
With Swiss wages...

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jkneale
I love it. So slick.

The Italians used a similar concept (forward control, teardrop shape) for
their Fiat 600 Multipla.

Smaller and not quite as aerodynamic, but nevertheless it was shipped, and
widely used as taxis which proves its versatility.

Not sure why, but I just love the teardrop concept. No matter how flat and
squared the front of the vehicle, add a taper to the rear and all's well with
airflow.

