Herr Schlör's "Göttinger Ei" had a Cd of 0.186.
 

http://www.göttingen.de/magazin/arti...p?artikel=3281
Aerodynamik des Automobils ... - Google Books

The oft-cited 0.125 figure seems to be a bit of an EcoModder myth. That figure only applies to a scale model of the Ei.

I believe the .186 figure is consistent with its appearance:
http://www.göttingen.de/pics/medien/...608300260.jpeg

Yes, the 0.13 number was a model or mock up earlier in testing. They also adjusted the ride height to get the optimum drag: too low increased it (due to increased pressure underneath?) and too tall also increased it (probably because more tire was exposed?). We have gone over this, and gotten a lot of pictures, including in the wind tunnel; here's my collection of Schlörwagen "Pillbug" pictures including the Mercedes 170H chassis it was built on:
http://img.photobucket.com/albums/v7...file-Large.jpg
http://img.photobucket.com/albums/v7...-FrontView.jpg
http://img.photobucket.com/albums/v7...ndtunnel-2.jpg
http://img.photobucket.com/albums/v7...TheRoad-01.jpg
http://img.photobucket.com/albums/v7...0140887100.jpg
http://img.photobucket.com/albums/v7...-Propeller.jpg
http://img.photobucket.com/albums/v7...ug/mbo3225.jpg
http://img.photobucket.com/albums/v7...r-Interior.jpg
http://img.photobucket.com/albums/v7...-OnTheRoad.jpg
http://img.photobucket.com/albums/v7...ug/old-van.jpg
http://img.photobucket.com/albums/v7...2667_94688.jpg
The 0.18 number is for the actual working car, with cooling set up, etc.

http://translate.google.com/translat...n&hl=&ie=UTF-8

Man, imagine if THAT was the VW Beetle that made cars affordable to Europe... what a different world it would be today.

Beautiful set of pictures Neil, thanks!

Got any pics of the underside of this vehicle?

It does not appear to have wheel fairings or spats, which would help.

And, gap between vehicle and ground relates to interference drag. There is an optimum height, as noted in Hoerner's Fluid Dynamic Drag book with cites of external stores of bombs, fuel tanks, etc. in aircraft. Too close means a bit of savings from less wetted area of pylon, but more than offset by too much interference of flows around wing and bomb. Too far apart means less interference drag, but increased pylon drag. So, there is a sweet spot in gap adjustment. I think Citroen with its adjustable height also dealt with this issue.

No, there are no pictures of the underside -- all the pictures I know of are here:

Schlor Pillbug pictures by NeilBlanchard - Photobucket

Yes, wheel strakes would help a lot. From the wind tunnel tuft test picture you can see the main problem area: from just ahead of the rear wheels and behind them, the air is swirling up. The tail may need to be broadened and flattened, to improve things?

The other main issue with the Schlörwagen is the width: it is 2.1m (6'-11")which is very wide, indeed. They made it wide so that the front wheels could be fully enclosed, even when they are turned fully. I think that some system of articulated/moving enclosures would keep the advantage, while greatly improving the CdA.

pill
 

Yes,didn't Hucho say that while he was at VW,that they threw a full-scale version in the tunnel and come up with this value?

I think VW tested a scale model, and they got 0.15, if I am not mistaken.

Plus so they could claim the lowest Cd of any passenger car of the era. Let us not forget, the easiest way to improve a vehicle's Cd is to make it bigger. "the .186 figure" for a 6'11" wide car would translate to a .257 figure for a 5' wide car with the same total drag. I suspect (cynic that I am) that modern car companies tout their low Cds (or is that "low Cs of d"?) because it looks better than quoting the CdA when promoting a big car. For example, the Cadillac Escalade boasts a "segment-best aerodynamic drag coefficient of 0.36 " which looks pretty cool compared with (for another example) a Mazda Miata at Cd 0.38

Agreed, but let's give credit where it's due. If the Göttinger Ei was 7' wide and 5' tall, it had a CdA of 5.53ft². That puts it on par with the CRX, which only seats two.

The VW Beetle had a CdA of 9.3-9.5ft².

Is there a handy link to a story about the prop-driven experiment?
For stability issues, it is a pity that a front-engined chassis was not chosen, but that was part of the learning curve. Streamlining was slow to catch on even for racing because it often caused lift, and unevenly at that.

:confused:

Cd is non dimensional right?

:confused:

Hi Bob,

I think the prop experiment is to test the props themselves -- look at the cable restraining the movement of the car. I think the Schlörwagen merely provided a good platform for this.

I agree that the rear drive Mercedes 170H chassis was a flawed choice, but it doesn't negate the brilliant basic design.

A lot of the width comes from the need to cover the front wheels without doing anything "active". If the front wheels were covered by articulated skirts or pivoting shrouds, then the side overhand could have been reduced by 25-33% overall -- and this would have necessitated the rear wheel track to be narrowed; which would have meant that they could not use an "off-the-shelf" chassis.

Along with improvements like wheel strakes and fixing the turbulence around the rear wheels (broadening and flattening the tail?), I bet the Cd could be at least as good as the 0.13, maybe as low as 0.1 or 0.11, and the CdA could be well under 3 sq ft.

The second last paragraph of the article from Göttingen.de discusses the propellor thing:
"After completion of driving tests in Göttingen, the Schlör car was unveiled at the 1939 International Motor Show in Berlin to an astonished audience. But the Second World War destroyed any plans for further development of passenger cars. In 1943, the Schlör car was equipped with a propeller from the Russian war booty with 130 hp. On a test drive in Göttingen, the unusual design caused a stir."

The article also reports that there is no trail of the vehicle after the war. "Whether it was seized by the Allies and taken to England, landed in a scrap yard, or perhaps still is in a shed in Göttingen, to this day remains a mystery."

That's a quote mark, not an "inches". He's got it right.

RobertSmalls wrote...

> Agreed, but let's give credit where it's due.

Oh I do! I think it's a remarkable car, but it was impractically wide and for no reason than to get the Cd down. I agree with Neil that...

>A lot of the width comes from the need to cover the front wheels

...but I think that was more of a side effect, since there's more than a foot of extra body width past the front wheels that's not doing anything but streamlining...and increasing frontal area, which makes the car look good on paper because...

...and equivalent drag area divided by frontal area = Cd. So to reduce Cd you can either reduce drag, or increase frontal area, and Göttinger appears to have done both in pursuit of a low Cd number. As far as actual drag goes, it's no better than a Honda CRX.

Now a CRX only seats two, which makes the Ei far superior if it were being used as a school bus, but as a road car...excuse me a second:

Okay, I'm back. I just now watched the first 50 cars go by on Hwy 99 and not one of them had more than two people in it. Two seats are sufficient for the great majority of drives. Now where was I.

...as a road car it's an impressive styling exercise. I'd be more likely to take inspiration from it if it had used space better, even at the cost of Cd.

Now if the Ei had a front engine and a pickup bed (covered in back with the existing body shape but flip-up like the AeroLid) and cargo boxes in the side pods and alongside the driver, I'd be totally wowed. A delivery truck with huge cargo volume and a Cd of .186, now that would be something!

The frontal area of the bug has nothing to do with the Cd...

and everything to do with the CdA.

The whole bug could be downsized 25% or 57% or 81.4% and the Cd would remain unchanged.

IMHO they had a shape they wanted to use and simply scaled it so that it enclosed the mechanicals and interior capacity parameters they wanted.

They (or someone) acknowledge that there is excess width due (solely?) to the bodywork enclosing the front wheels.

Why they didn't simply articulate some front skirts to knock that width/frontal area down is beyond me... :confused:

Bicycle Bob -

I know this would probably be a band-aid sin, but how about two small "training-wheels" behind and outside of the front wheels? I know that would add to the Cd, but it might allow the frontal track to stay narrow and therefore keep the front wheel-skirts. Maybe the little wheels would be on +-15 degree castors for grins, I don't know.

CarloSW2

articulate
 

That was my thought when I read of the rational for the width.They could have done as basjoos has with AeroCivic.
And that's real easy for me to say with decades of hindsight.