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Old 07-26-2010, 04:07 PM   #51 (permalink)
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Well, i'm glad to see that my reading of Hucho and others doesn't seem to have been wasted

I have become such an admirer of your work that I've pretty much given up on the idea of doing anything in cardboard. It is a vastly inferior medium to what you are doing, and the work and expense would ultimately be wasted. I think I'm going to just wait and see how yours works out. After all - according to the old joke - the early bird gets the worm, but the second mouse gets the cheese

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Old 07-26-2010, 06:12 PM   #52 (permalink)
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That's some serious remodelling job you're doing, Jim !
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Old 07-27-2010, 02:35 PM   #53 (permalink)
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Quote:
Originally Posted by jimepting View Post
.....I have become such an admirer of your work that I've pretty much given up on the idea of doing anything in cardboard......
I would agree as well!!

Actually, the same thing could be said of coroplast in my view. I can't count the number of times that I wondered how someone would be able to make the same shape with a non-formable sheet. If someone can do it, I would be absolutely blown away, and more power to them!!

I make enough bobbles that need fixing by cutting/removing/adding material in various areas of the foam build, that I don't think it would be attempted using other materials. At least not with my skill level.

I have heard of craftsman who can hammer sheet aluminum into some fantastic shapes however.

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Old 08-01-2010, 11:27 PM   #54 (permalink)
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Since the tail extension build is getting about two feet in length now, I decided it was time to ensure that the master template I made from AeroHeads Streamlining Airfoil was correct in shape.

To do this, I cropped his streamlining airfoil to a smaller size and placed it in a CAD program for analysis.

I drew several large diameter circles, as you can see in picture one.

For the first 60% or so, the circles seem to be a good match for the curvature of the streamlining airfoil. This is the portion of the curve that matters most to me since my tail extension will not be longer than this.



Here is a closeup of the two red circles as they fit above and below the streamlining airfoil.

It shows that my constant master template does indeed match this shape as I did my best to get this shape into a constant curvature.

This same master template is now ready to create the curvature of the remaining two feet or so of tail extension.



I think that there may be a rendering problem with the airfoil shape from 70% to 100% length. I made several larger circles (shown in forth picture with blue line) that hugged the airfoil from 70% t0 90%, then veered away from the airfoil from 90% to 100%.

The next picture shows how shallow the airfoil shape is in this region. If anyone has any ideas, please let me know.



This picture shows how the 90% to 100% line looks distorted in shape. Notice how far away the blue line is from the airfoil at 90%, but then suddenly gets much closer at 100%?

I tried extracting data from the airfoil and placing values in a spreadsheet, and that's when I noticed there was something fishy with the airfoil rendering. The angular numbers did not make sense from 60%, on.




Jim.
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Last edited by 3-Wheeler; 08-01-2010 at 11:50 PM..
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Old 08-02-2010, 07:20 AM   #55 (permalink)
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Quote:
Originally Posted by 3-Wheeler View Post
I think that there may be a rendering problem with the airfoil shape from 70% to 100% length. I made several larger circles (shown in forth picture with blue line) that hugged the airfoil from 70% t0 90%, then veered away from the airfoil from 90% to 100%.
If anyone has any ideas, please let me know.
That's normal for a trailing edge on a classic airfoil.

The upper and the lower airflow must meet up with as little turbulence as possible, so the angle between both flows is reduced when the flow reaches the trailing edge - both airflows are lined up.

On laminar flow and supercritical wings, you'll see "the circle" continuing on top, while the airflow line-up happens through an S-curve on the underside.
See :

(wing section from a Pipistrel light aircraft)

In this design the air flows downward when leaving the wing.
That's probaby also what keeps the higher pressure "bubble" on the aft part of the wing.

Some low-drag vehicle designs have already utilised this sort of airfoil section - but then the trailing edge is relatively high up from the ground.

When the tail is close to the ground a net downward flow will likely increase drag through its turbulent interaction with the ground.
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Old 08-02-2010, 01:50 PM   #56 (permalink)
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Quote:
Originally Posted by 3-Wheeler View Post
I think that there may be a rendering problem with the airfoil shape from 70% to 100% length. I made several larger circles (shown in forth picture with blue line) that hugged the airfoil from 70% t0 90%, then veered away from the airfoil from 90% to 100%.
The upper surface of the Aptera does the same BTW :

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Old 08-02-2010, 02:17 PM   #57 (permalink)
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Quote:
Originally Posted by euromodder View Post
That's normal for a trailing edge on a classic airfoil.

The upper and the lower airflow must meet up with as little turbulence as possible, so the angle between both flows is reduced when the flow reaches the trailing edge - both airflows are lined up.

On laminar flow and supercritical wings, you'll see "the circle" continuing on top, while the airflow line-up happens through an S-curve on the underside....
Hi Euromodder,

Yes, the bottom side of this airfoil is designed to create more lift. I'm after minimizing air drag, so the bottom "S-curve" may not apply in our road-going designs.



I still think that the streamlining airfoil shape from 70% to 100% needs some "adjustment".

Your airfoil still curves even if it is slightly, over that last portion on the top side of the wing.

Jim.
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Old 08-02-2010, 02:24 PM   #58 (permalink)
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Quote:
Originally Posted by euromodder View Post
The upper surface of the Aptera does the same BTW :

Hey, nice picture!!

That's got to be an early prototype of the car. Notice no outside mirrors and side reflectors?

I'll bet this is one of the early rear-wheel drive models.

Aero-wise on the Aptera, that top slope down the back window is way steeper than presented in the Streamlining Aero Template of AeroHead. I'll bet they are loosing a few Cd "points" due to that sharp angle.

As a styling statement however, I find it very attractive!! Thanks for the picture!

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Old 08-02-2010, 03:42 PM   #59 (permalink)
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Quote:
Originally Posted by 3-Wheeler View Post
Aero-wise on the Aptera, that top slope down the back window is way steeper than presented in the Streamlining Aero Template of AeroHead. I'll bet they are loosing a few Cd "points" due to that sharp angle.
Possibly. But the Streamlining Template is for a 2D body, or a car of infinite width. The Honda IMAS concept and EV1 also have curvature that exceeds the template, but only in regions where the sides curve inward as well.
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Old 08-04-2010, 02:32 PM   #60 (permalink)
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Just as a curiosity more than anything else, I placed a couple circles on this wing shape, and surprisingly the circles indicate the shape of the wing curvature past the major thickness, on the trailing side





Jim.

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