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Old 09-25-2012, 03:10 AM   #21 (permalink)
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It looks like it's got a lot of taper in plan, and the lower nose seems to be handled well; but yeah, that's not a number.

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If you'd like to depart from the 'Template,' you might want to find out all you can about Wolfgang Klemperer's 'minivan' of Cd 0.16 (in naked model form) which he tested in 1921...This 'minivan' is what VW used as the basis for the VW 2000 concept car.
I'm familiar with the VW Auto 2000 concept; but I'm not finding much on Klemperer. I searched on combinations of 'Wolfgang Klemperer 1921 windkanal minivan', etc. Google points to page 25 of the Aerodynamic Streamlining—Part C thread but the trail goes cold there.

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If you weren't interested in going below Cd 0.16 it would be a good way to go.
I'm stumped, I can't decide if I am interested in sub-0.16 territory. While I'm dithering, how valid do you think the reported Cd of 0.17 is for the Volkhart-Sagitta:

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Old 09-25-2012, 06:04 PM   #22 (permalink)
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Cd 0.17

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Originally Posted by freebeard View Post
It looks like it's got a lot of taper in plan, and the lower nose seems to be handled well; but yeah, that's not a number.



I'm familiar with the VW Auto 2000 concept; but I'm not finding much on Klemperer. I searched on combinations of 'Wolfgang Klemperer 1921 windkanal minivan', etc. Google points to page 25 of the Aerodynamic Streamlining—Part C thread but the trail goes cold there.



I'm stumped, I can't decide if I am interested in sub-0.16 territory. While I'm dithering, how valid do you think the reported Cd of 0.17 is for the Volkhart-Sagitta:
It would help to know where the number came from.Just shooting from the hip,I don't have a problem with it.All the leading edges have generous radii.The windscreen has nice curvature as well as it's header and A-pillars.
The full wheel skirts are a plus.And the side mirrors are well formed and pushed forward into slower air away from the A-pillars.We could presume a full bellypan?
It's very similar to Ferdinand Porsche's personal car of 1939 with which he commuted between Stuttgart and Berlin.
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Old 09-25-2012, 06:20 PM   #23 (permalink)
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That's the way I see it, too.

The up-kicked cowl on the Talbot-Lago T-150-C was a styling gimmick, here it serves the aerodynamic need. And it has a single wiper. I picture those skirts having the one Dzus fastener at the top and then they could rotate out 90° and pull out of a slot in tube restraints at the bottom corners.

My understanding is that 2 were built, now there's one in a museum. It was a 4-passenger high speed Autobahn cruiser for the Luftwaffe.

VW reproduced the Berlin-Rome racer and characterized it in a wind tunnel. I'd like to see that done here. Imagine if in 1974, someone had re-popped that in fiberglass and sold them as a kit car.
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Old 09-25-2012, 06:50 PM   #24 (permalink)
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kit car

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Originally Posted by freebeard View Post
That's the way I see it, too.

The up-kicked cowl on the Talbot-Lago T-150-C was a styling gimmick, here it serves the aerodynamic need. And it has a single wiper. I picture those skirts having the one Dzus fastener at the top and then they could rotate out 90° and pull out of a slot in tube restraints at the bottom corners.

My understanding is that 2 were built, now there's one in a museum. It was a 4-passenger high speed Autobahn cruiser for the Luftwaffe.

VW reproduced the Berlin-Rome racer and characterized it in a wind tunnel. I'd like to see that done here. Imagine if in 1974, someone had re-popped that in fiberglass and sold them as a kit car.
If Fibre Fab had done exactly that in '74,I would have been all over it.I'd just read Crisis Fighter Pinto by Don Sherman and purchased a crashed Karmann Ghia to restore and replace my El Camino as commuter car.
I'd seen Fibre Fab's Valkerie at a North American Rockwell facility in Palmdale,CA where we were working with the B-1 Bomber.They could make anything out of composites! And nice stuff!
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Old 09-25-2012, 10:09 PM   #25 (permalink)
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You and me both. I was headed toward a Sterling or Amiga kit car until the world changed around me into something I wasn't expecting (still does that); I got as far as the PolyGlas F60-15s on 8" wide rims (front and back, on gravel you could turn or brake, but you couldn't turn *and* brake).

The nice thing about today is there is software that will produce a 3D model from a few 2D pictures. One could recreate and 3D print the Volkhart-Sagitta to within a few tens of microns accuracy.

=============

Oh, and this:
Karmann Ghia Station Wagon in France - Fake Volkswagen

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Old 09-28-2012, 05:03 PM   #26 (permalink)
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3D

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Originally Posted by freebeard View Post
You and me both. I was headed toward a Sterling or Amiga kit car until the world changed around me into something I wasn't expecting (still does that); I got as far as the PolyGlas F60-15s on 8" wide rims (front and back, on gravel you could turn or brake, but you couldn't turn *and* brake).

The nice thing about today is there is software that will produce a 3D model from a few 2D pictures. One could recreate and 3D print the Volkhart-Sagitta to within a few tens of microns accuracy.

=============

Oh, and this:
Karmann Ghia Station Wagon in France - Fake Volkswagen
With Scaled Composites 5-axis router,a full-scale rendering could be done from which tooling could be generated for wet layups or a chopper gun.
If you shaved the chrome and integrated the bumpers
n stuff,the Volkhart- would appear to most as quite modern.And with seating for 4,more 'practical' than Porsche's speedy little 2-seater of '39.
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Old 10-01-2012, 12:51 AM   #27 (permalink)
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Since you're dropping names like North American Rockwell and Scaled Composites; I'll just say—somebody needs to do it and I don't think you should wait for me.

I need to catch up on some promises I made in another thread, but I've been thinking about modelling the V-S in 3D, by extracting the cross-sections from the 2D pictures manually in Photoshop. I use a box modeler instead of a subdivision modeller, but the smoothing function can yield the compound-curved surfaces needed.
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Old 05-29-2013, 05:51 PM   #28 (permalink)
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Quote:
Originally Posted by freebeard View Post
My understanding is that The Template is a half body of revolution to insure that air doesn't want to move laterally because of pressure differentials between the top and sides, which leads to vortex generation.

If that's the case, wouldn't a half-square cross section serve as well, given equal cross-sectional area? If air is not wrapping across the edge, would no vortexes be created?

Here are three aeroforms, a cylinder, a superellipse and a square. Would their Cd be equivalent?


(These are not dimensionally highly accurate; I just eyeballed the proportions against The Template)

The next question: If the height/width proportion changes, what happens to the respective tapers? If the half revolution form is 7' wide, then it is 3 1/2' high. If the height is proportionally greater, does the side taper increase or relax?

TIA
Did you ever develop this line of thought and exercise further?
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Old 05-29-2013, 09:44 PM   #29 (permalink)
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Were you talking about this thread in the other thread?

Where I'm at currently is a 6-frequency octahedral symmetry geodesic dome. The octahedral symmetry puts 90° corners at the center of the top/bottom, sides and front/rear. Increasing the frequency approaches a smooth compound curve and the geometry can be calculated to any arbitrary precision.



Big ol' windshield with skylighting in the living area. I have a donor vehicle and tools, but not the shop space and budget. The basic sphere is 'prolated' front to rear and above the equator and 'oblated' and truncated below the equator. 30/70° split front to rear. As such:

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Old 06-06-2013, 08:55 PM   #30 (permalink)
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Quote:
Originally Posted by ERTW View Post
dang you! I came on here to post my pics of my latest CFD testing. I'm trying to replicate the box fish, which MB used to shape the bionic car. My very first iteration, which was 80" long from peak to the kamm back, came to 0.143. My second iteration is 120" long, and came to 0.101. MB said the box fish came to around 0.005 with excellent yaw stability.

I used a convex rectangle section with rounded corners, approximating Morelli's later designs, instead of the "X" type shape of the box fish (I actually took a video of one at the local aquarium today). I was surprised how easily it obtained such a low Cd, considering how much more work I did to get Aero's template to 0.092. The body falls away from the streamlines much quicker, yet there's no delamination.

This answers my question of whether we "need" the tear drop shape for a low Cd. A box is certainly roomier, and easier to fit/hide wheels, and it's much shorter than the template.

Note that any body will work better with a rounded bottom - not flat - and generous fillets on the rocker panels, and a raised tail. Anything to equalise pressure around the perimetre of the body helps prevent vortices. Morelli discusses elliptical shapes to minimise wetted area, hence, skin drag.

discuss amongst yourselves
Interesting stuff, I would love to see more of these studies.

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Where I'm at currently is a 6-frequency octahedral symmetry geodesic dome.
And now that I know about your dome background, this is all becoming clear.

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