Low-drag automotive silhouettes

[aerohead]

Here's a thread I can add to over time which shows a historical development of low-drag automobile test models or actual 'running' vehicles.
I'll try and keep them in chronological order.
NOTE: Low-Drag is defined as Cd 0.25 or lower for the sake of this thread.Sorry I didn't make this qualification at first.
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1850,derigible,Pierre Julien,1st longitudinally asymmetrical (teardrop) body.

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1865,Air resisting train,Samuel Calthrop

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1922 'pumpkin seed',Paul Jaray,Zeppelin Works,Germany,Cd 0.13.Based upon a streamlined half-body.First use of a 'diffuser.'

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1922 streamline half-body,Wolfgang Klemperer, Cd 0.15

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1924,patent illustration for streamlined car.Persu.

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1933 wind tunnel model,Walter Lay,University of Michigan.Cd 0.12.

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1933 R.H.Heald,U.S.Dept. of Commerce,Bureau of Standards,Cd 0.20

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1934 Dymaxion Car,R. Buckminster Fuller, Cd 0.25 (estimated)

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1934-1/2 Chrysler De Soto Airflow test mule,Carl Breer,Cd 0.244.

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1935 (circa) 'Kamm' car,wind tunnel model,Baron Reinhard Koenig-Fachsenfeld

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1935 DKW Meisterclasse, Jaray-bodied,by Sighard F.Hoerner,Cd 0.245.

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1935-6 Elliott Gray Reid,Stanford University,Cd 0.15


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1937 AVA G'o'ttingen Sch'o'r wagen (pilbug car),Cd 0.186


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1938 Mobil Special,Reid Railton,Cd 0.18

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1938 AVA G'o'ttingen 'Lange' car,Cd 0.14-0.16 (1/5-scale smooth model with zero features)(Cd 0.16 by Hucho et al @ Volkswagen tunnel)

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1957 MG EX181,land speed record car,Cd 0.12

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1963 tractor trailer,Walter H. Korff,Lockheed, Cd 0.20

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1969 Composite wind tunnel model 'recipe' car,R.G.S.White,MIRA,Cd 0.245.

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1978 D-B M-B C-111 III,long tail, Cd 0.178

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1978 D-B M-B C-111 III,short-tail, Cd 0.195

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1978 D-B M-B C-111 III,no-tail, Cd 0.237

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circa 1980 NASA van,long tail, Cd 0.238

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circa 1980 NASA van,truncated tail, Cd 0.242

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2000- HONDA 1st-gen Insight, Cd 0.25

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Toyota Prius, Cd 0.25

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2006 Daihatsu UFE-III, Cd 0.168

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2012 Ford Probe-X ,Cd 0.152

[Cd]

Oh wow the 1938 Mobil Special,Reid Railton at Cd 0.18 ???

A full tear drop shape, fully covered wheels, a bubble canopy, and a smooth underbelly, yet point 18 ?

And then we have the Mercedes here at .22 without a boat-tail, no wheel covers, a gaping grille and rear glass that is too steep.



Air flows in strange ways.

[Vman455]

This is the BlueEfficiency version of the CLA, the model for which Mercedes claims Cd .22:





Notice the mostly-closed wheel faces, paneling under the engine bay (and I presume the rest of the underbody as well), and completely redesigned rear bumper area.

[freebeard]

Like a flat stone on water, you're hitting all the high spots. How about Rumpler, or the Josep Ganz's Maikäfer [1931]? Here's what I have. It's a silhouette not a glamour shot.

[ennored]

Fair to mention the Vixen Motorhome here? Circa 1989. Cd .31 (actual number - not a scale test).



To me, the lesson is (as has been stated before) round the front as much as needed (which isn't that much) and taper the rear as much as you can. Done.

The result? A brick that is more aerodynamic (relative to Cd) than most cars on the road.

[freebeard]

Nice for it's time. I saw one once.

Instead of those elephant ears behind the rear wheels, the lower rear should be like the upper rear of the VW GTTI-650 w12



...with the radiators in the corners like Porsche does in the front now. A surface development that would be completely lost in silhoutte.

[aerohead]

Originally Posted by freebeard

Like a flat stone on water, you're hitting all the high spots. How about Rumpler, or the Josep Ganz's Maikäfer [1931]? Here's what I have. It's a silhouette not a glamour shot.

I'm not including anything over Cd 0.25.It has been used in the past as the cutoff mark for low drag.

[aerohead]

Originally Posted by ennored

Fair to mention the Vixen Motorhome here? Circa 1989. Cd .31 (actual number - not a scale test).



To me, the lesson is (as has been stated before) round the front as much as needed (which isn't that much) and taper the rear as much as you can. Done.

The result? A brick that is more aerodynamic (relative to Cd) than most cars on the road.

I went back to the top of the thread and added a NOTE which I should have posted initially,that the cutoff for low drag would begin at Cd 0.25.Sorry!

[aerohead]

I've added 5-new images:
*1933 Heald car
*1935-6 Reid cars (2)
*Front and rear elevation views of the 1938 pilbug car
*1938 Lange car (influenced Porsche 911)

[aerohead]

I've added 7-new scans to the bottom of the table.