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Old 08-03-2015, 07:05 AM   #631 (permalink)
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I will let Aerohead answer, but you should note there is more than one Aerodynamic Streamlining Template that he has posted over the years. I utilize the second one that was posted, which is labeled AST-II. I cannot tell from your photo which one you are using, but I think it is the first one.

Also if you look really closely at the template versus the streamlined body diagram, I believe the front of the template (not the boat tail) has been stretched out to be deeper than necessary for minimum drag. I believe this was a practicality measure to have more usable interior volume for the Template vehicle.

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Old 08-03-2015, 06:17 PM   #632 (permalink)
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conflicting ratios

Quote:
Originally Posted by 3-Wheeler View Post
Hi Phil,

I'm not trying to be picky, even though it could come across this way, but I do see some conflicting length/width ratios for the minimum airfoil shape posted at EcoModder.

The link below has some information that I will present below, and discuss.

Aerodynamic Streamlining Template: Part-C

The image below has sections of several minimum drag sources that show length/width ratios.

Starting from the top of the graphic, the minimum L/W ratio seems to be 2.5:1. I did not scale the graphic closely.

The second graphic shows a ratio of 1.0/.255 = 3.92 L/W

The third graphic clearly shows 2.5 L/W ratio

The C-version Streamlining Template shows a ratio of 4.72/2 = 2.36



I've looked on-line and did not find any other L/W information for subsonic winglets, and minimum drag, so this type of information may be limited to Hucho and other rare sources.

I do recall that you have mentioned that the minimum drag occurs at a L/W ratio of 2.5 many time before, yet some of the other sources do not match this, including the Streamlining Template.

Thanks, Jim.
*Hucho is using Hoerner's research,and if you look at the source you find that 2.1:1 produces the lowest drag.This was from early NACA airship coastdown testing in New York.The enormous surface area of the airship envelope produced a thick turbulent boundary layer,which when sloughing off the rear tended to fill in a phantom tail area,built up from the shedding torroidal boundary layer.This dead air traveled along with the airship,effectively increasing it's L/D ratio.
*I think it was the 1929 ZMC 'tin bubble' metalclad airship which was built to one of these low ratios.It had very good speed for its power and frontal area but made the crew seasick,and you find airships built longer for flight stability.
Here's the 'tin bubble' at the bottom

*The 2.1 ratio is low drag,but for a bluff body it exceeds Mair's 22-degree contour slope maximum and also Buchheim et al's 23-degree slope maximum.
*So as a half-body,in ground proximity,we need to stay near 22-23-degrees to protect the turbulent boundary layer from rapid pressure increases which trigger separation.
-------------------------------------------------------------------------
*For struts and airfoil sections the bottom of the friction drag/pressure drag 'bucket' occurs at L/thickness= 3.92 (also from Hoerner).So for mirror stalks,suspension fairings,wheel fairings,etc.. Also,we find that 3.92:1 has also been used successfully on record cars with plan-taper of the body only.The 1957 MG EX 181 uses it.

Here's the 'template',4th from bottom

Here is the strut/wing section research,published by Horner,from Goldsein's research

Also,we could theoretically use elliptical bodies of revolution as a basis of automobile bodies as their drag behaves exactly the same as streamline bodies EXCEPT that the windshields would be too steep to see out of,so we default to the 'bulbous','bug' nose equally low drag to get something we can see out of with glass.Hucho used the elliptical body L/D ratios in his drag example of the 1966 VW Beetle 1300,which again,show the drag minimum @ 2.5:1.

On the Aerodynamic Streamlining Template-II I used a 'faster' rear contour,closer to Buchheim et al.'s,from my college fluid dynamics text.It's close to a 2.5:1 L/D streamline body also,just a little more aggressive early in the contour,then actually more conservative at the end,with 21-degrees maximum slope.

Here is the Buchheim et al. contour,developed in the VW wind tunnel.We shouldn't do anything more aggressive than this or we lose the game.

I kept the 'Template' conservative,as members are looking at maybe 800-man-hours to create an aft-body modification,and after all that you sure don't want to see separation back there.
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Last edited by aerohead; 08-03-2015 at 06:29 PM.. Reason: add Franzini
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Old 08-03-2015, 06:30 PM   #633 (permalink)
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Indeed not!
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Old 08-03-2015, 09:09 PM   #634 (permalink)
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What about the rounded tail of the Schlorwagen/Volkhart-Saggita/Dymaxion compared to the sharp pointy object that it The Template? Better to truncate it like the Cobra Dayton coupe?
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Old 08-04-2015, 02:01 PM   #635 (permalink)
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Quote:
Originally Posted by aerohead View Post
I kept the 'Template' conservative,as members are looking at maybe 800-man-hours to create an aft-body modification,and after all that you sure don't want to see separation back there.
Well said Phil !!

Thanks for the clarification above. I really appreciate it!!

Jim.
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Old 08-04-2015, 02:13 PM   #636 (permalink)
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Before I start the big trailer project, I want to prove out materials and methods on a trailer for the new beetle. Since it is foam and glass and a bit large, my concern is how it will do in winds. It will be very light when empty, and about 4' tall by 11' long by 5 1/2' wide.
I hope to follow the template accurately in profile, and have some of the body of revolution aspects of it, but the plan taper will be somewhat limited for practical purposes.
This is still by far the best shape to combat side winds and stay put behind the tractor, right? A light trailer plus side winds plus lift is a bad day.
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Old 08-04-2015, 04:33 PM   #637 (permalink)
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I found 5th wheel design, but is the New Beetle trailer a new announcement? Because this is, as they say, relevant to my interest.

I will repost this here:



Simple curves, but approximates to The Template. The door is moved to the truncation so no extra framing is required on the side. Built on a 4x12 sheet of plywood. The frame is copied from the 1952 Silver Streak I used to own, a Central tube, C-channel crossmembers (each with a carriage bolt at the ends) and a strong connection to the wall so the whole thing is s stressed monocoque.



For a 5th wheel, you could have a curved arm to the hitch:



Instead of exposed wheels like a teardrop, maybe follow this with curved side-boards:



The rear entrance again.

/I don't even have a trailer hitch.
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Old 08-04-2015, 04:53 PM   #638 (permalink)
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I'll start up a new thread on it, but the question was really as design relates to the template, and the property of reducing lift and hopefully minimizing crosswind mayhem. Without a load in it, the trailer will be around 500 pounds, and safety is a primary concern at all times. I'd hate to think it would need sandbags
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Old 08-04-2015, 10:58 PM   #639 (permalink)
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A foamy? I'll watch for a new thread. Can you drop a link here?

The cardboard model follows The Template except there is no taper in the rear elevation. What that does might add some rudder effect. Today I'd probably use a Gothic arch, like this:



I think the tandem axle (rubber torsion trailing arms) with 10" wheels would add stability compared to a single axle with 15" wheels. And some horizontal fins might damp out any 'porpoising'.
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Old 08-04-2015, 11:25 PM   #640 (permalink)
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That is too cool for school man. Love how it will fold up. Does it have a window in it for engine access and also cooling flow when either up or down?

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