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Old 02-28-2013, 02:28 PM   #491 (permalink)
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Quote:
Originally Posted by aerohead View Post
.....I've ignored the 'noses' per se,as they are always discounted in Fluid Mechanics,and rather place the greater emphasis on the aft-body portion......
Phil,

Well, at first thought this statement makes sense. The exact shape of the "nose" may not be especially critical, since it's on the leading edge of our "aero" shape.

However when you look at the dimensions for length/width in the streamlining template, the "length" of the nose becomes part of the 2.5:1 length/width definition.

http://ecomodder.com/forum/358696-post490.html

So it seems that the nose shape is "critical" at least when it comes to understanding the ideal "wing shape" that you have proposed many times here.

Jim.

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Old 03-01-2013, 07:23 PM   #492 (permalink)
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dashed lines

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Originally Posted by sgtlethargic View Post
Aerohead,
Will you please take a few minutes and explain the dashed lines, especially the one I marked? I think I understand the other dashed lines to represent the top (plan) view.
The outer-most dashed lines define the forebody of the original 'donar' 2.5:1 streamline body of revolution in its entirety.
I 'reduced' the nose section to more of a 1/2 convex hemisphere,rather than the prolate ellipsoid original,as every reference I have for automotive streamlining effectively discounts the entire forebody.The 1/2-hemi 'bulbous'-nose has demonstrated lowest drag for crosswind conditions,so it became the 'default' forebody.
--------------------------------------------------------------------------
The premise for the 'Template' was the extremely careful handling of the airflow over the aft-body which prevents separation,which is what all aerodynamicists agree is THE target for streamlining.In this respect,the nose is of little import to us.
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Old 03-01-2013, 07:27 PM   #493 (permalink)
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"nose"

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

Well, at first thought this statement makes sense. The exact shape of the "nose" may not be especially critical, since it's on the leading edge of our "aero" shape.

However when you look at the dimensions for length/width in the streamlining template, the "length" of the nose becomes part of the 2.5:1 length/width definition.

http://ecomodder.com/forum/358696-post490.html

So it seems that the nose shape is "critical" at least when it comes to understanding the ideal "wing shape" that you have proposed many times here.

Jim.
Absolutely!
If we were doing a body in white,we'd need to consider the 'whole' vehicle.
The 'Template' was to be only an aid for aft-body streamlining,as I've no idea how we could modify existing production cars to mimic the 2.5:1 full nose.
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Old 03-01-2013, 11:46 PM   #494 (permalink)
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Quote:
If we were doing a body in white,we'd need to consider the 'whole' vehicle.
The 'Template' was to be only an aid for aft-body streamlining,as I've no idea how we could modify existing production cars to mimic the 2.5:1 full nose.
...existing production cars...

There's your problem.
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Old 03-02-2013, 01:45 AM   #495 (permalink)
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I couldn't resist putting that in Photoshop. Here it is with the rear track reduced 6-8" and the body pie cut.


I couldn't do a lot more with that view. It needs some curve to the drip rail and beltline. But here's a teardrop body on a COE.


The Type II doors have a separable window frame. So you could take that off and add a curve to the opening. In fact, you could bring the rebody right to the windshield header and eliminate the overhang, like a Barndoor bus.
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Old 03-02-2013, 03:55 PM   #496 (permalink)
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Aerodynamic Streamlining Template Gen-II

This Generation-II 'Template' was 'built' from a different L/D= 2.5 streamline body of revolution.I've identified it's source within the image.
*As a 'free-air' body,it would have Cd 0.04
*As a half-body in mirror-image ground proximity it would have Cd 0.08.
*Adding wheels would bump it up to around Cd 0.13
*Adding wheel fairings would lower the Cd.
---------------------------------------------------------------------------
*I'll show it as a full half-body with 'full' nose.
*And as a 'Template' with shortened nose.I added an extra side window to help distinguish it from the Gen-I 'Template.'
--------------------------------------------------------------------------
*As a 'Template' it is intended as an aid for separation-free aft-body streamlining only.
*From Hucho,"...the shape of a body in front of the largest cross-section has only minor influence on the total drag.The main contributions to the drag force originate from the rear part of the body.It is not important to find a proper shape to divide the oncoming flow but it is very important to design a rear body surface which brings the divided streamlines smoothly together.
...low drag can only be achieved when the separation at the rear is eliminated.
Shapes of this kind are aerofoils and 'streamlined' bodies."

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Old 03-02-2013, 05:00 PM   #497 (permalink)
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Thanks, I saved it as '-->Scan12' so I can find it again.

One would think the only caveat on the forebody would be that it not set up adverse streamlines. I need a word that means 'rotational around the axis in the direction of travel'. Or would those smooth out under the soothing effect of the afterbody?

Wasn't it Tesla that was trying to find a mathematical description of that curve?
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Old 03-02-2013, 05:35 PM   #498 (permalink)
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forebody

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Originally Posted by freebeard View Post
Thanks, I saved it as '-->Scan12' so I can find it again.

One would think the only caveat on the forebody would be that it not set up adverse streamlines. I need a word that means 'rotational around the axis in the direction of travel'. Or would those smooth out under the soothing effect of the afterbody?

Wasn't it Tesla that was trying to find a mathematical description of that curve?
*It's funny about the forebody.Hucho beat up on M'o'ller for giving the original VW van so much radius up front.
*He cites F.W.Palowski of 1930,who demonstrated that once the radius was enough to maintain flow attachment,that any further rounding returns zero drag improvement.
*He applauds the Vanagon and it's 'optimised' radius,which worked out at 0.045 X body width.He shows a drag curve which he probably created himself,which clearly shows no additional improvement in drag with larger radii.
------------------------------------------------------------------------
Their does appear to be a CAVEAT back in the commercial vehicle chapter,showing the bulbous nose to have the lowest drag in crosswind.
*GM published the same findings in the early 1960s.(there's a pictorial drag table of that work at the 'full-boat-tail trailer' thread)
------------------------------------------------------------------------
There would be a mathematical formula for these profiles.A visit to the Math Dept. at the local university might fill in that blank.Volunteers?
-----------------------------------------------------------------------
The streamlined bodies are a profile which is revolved around the longitudinal axis.
The noses are described as ellipsoid,and the tail is referred to as a prolate ellipsoid (NFL Regulation footballs are 'prolate-ellipsoids',Cd 0.055 average, while spinning in a perfect spiral pass)
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Old 03-02-2013, 05:41 PM   #499 (permalink)
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Photoshop

Quote:
Originally Posted by freebeard View Post
I couldn't resist putting that in Photoshop. Here it is with the rear track reduced 6-8" and the body pie cut.


I couldn't do a lot more with that view. It needs some curve to the drip rail and beltline. But here's a teardrop body on a COE.


The Type II doors have a separable window frame. So you could take that off and add a curve to the opening. In fact, you could bring the rebody right to the windshield header and eliminate the overhang, like a Barndoor bus.
I envy your command of the graphics software! I struggled here at Copy-Pro over a month of spare time on a single image,going pixel by pixel.
My hat is off to all you masters of the virtual french curve!
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Old 03-02-2013, 09:23 PM   #500 (permalink)
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I saw this picture below a few days ago, and did not know where to post it.

Random TRANSPORTATION pictures - Page 931 - Pelican Parts Technical BBS


With some glazing and flush wheel flares it could be a low Cd, right?

Needs a tail cone or something.

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