Aerodynamic Streamlining Template: Part-C

[freebeard]

KamperBob -- I'm not sure how to respond. I'm getting

I'm fascinated yet puzzled. This



looks like a series of "torpedo" upper-half cross sections (taken lengthwise from apex to rear) from the left side of this.

and

So then my brain wants this



to be "boxfish" sections from the right side. Where did my brain make a wrong turn please?

with my illustration in between. So I'll just describe what's in the picture.

On the left is the minimal aeroform. On the right is an equal area square section. In the middle the section is a Squircle (my new favorite word).

HTH

Edit: Oops, I repeat myself

Tesla -- When you start that thread I want to post a picture of a boattail with clamshell doors and a neat little retractable loading ramp.

[Tesla]

Originally Posted by freebeard

In the middle the section is a Squircle (my new favorite word).


Edit: Oops, I repeat myself

Tesla -- When you start that thread I want to post a picture of a boattail with clamshell doors and a neat little retractable loading ramp.

Vote 1 for the Squircle, I had a bit of a look at it the other day.

I'm thinking maybe just start a generic trailer ideas thread, it's a common issue that many try to tackle, would be good to have a thread to put the ideas together with links to previous threads and ideas.

[KamperBob]

Freebeard, thanks. Your pic in fine. You should've seen it sandwiched between two pix (#1-2 of 3) from Tesla's post #463. Those pix show for me (Win Vista, Firefox). Others? Especially Tesla: I'd prefer to understand your math.

[Tesla]

Originally Posted by KamperBob

Freebeard, thanks. Your pic in fine. You should've seen it sandwiched between two pix (#1-2 of 3) from Tesla's post #463. Those pix show for me (Win Vista, Firefox). Others? Especially Tesla: I'd prefer to understand your math.

It's been an evolutionary process, in summary:
I started looking for an equation to solve the template curve so I could calculate boattail dimensions at any point along the length rather than just the 10% increments.

Set up excel spreadsheet to plot template and compare different equations.

Stumbled onto the NASA symetrical airfoil equation and after a bit of jiggling found the 0039 profile was close enough to the template for my needs.

Then exploring how the template needed to be applied in plan view, then the penny dropped it needs to be applied in a radial fashion not just vertical or horizontal.

Re plotted points with the radial calculations, the distortion from corners is due to the diagonal being the largest radial dimension, hence setting the longest tail profile and gentler curve than the shorter dimensions of height or width.

Main point being when building a boattail, consideration needs to be given on how the height and width of vehicle compare to the radial measurement to the corners, most vehicles are slightly rounded over the top, so not too much of an issue, but for those that have a taller and more square profile there is greater risk of seperation at the corners if they are tapered too quickly.

The 0/0 point is ground level vertical centre to measure the radial distances to relevant vehicle points, the roof corners will usually be the longest dimension.

There are many other things to consider and I am still putting it all together.

[Vekke]

I have done some overlayes conserning my roof chopping and this is bothering me this is correct overlay and its way off:

If I put it about 250-300mm too toward the front it layes perfectly:


So the guestion follows:
If you put the template too much in front of the picture is still layes perfectly ok to the shape. So can I do the same in my lupo and still get nice flow. My own estimation is that when you are at the max roof camber you can make that first few degrees pretty rapidly like those pictures prove or what do you think?

This may be true only if you begin the cambering at the max camber point etc?

third option:


Now template aligned at car underside lowest level and its quite nice match on the roof. Note that sidesills are lower than the cars underside, because its better aerodynamically that way.

Plan is to begin the rood chopping this weekend so would like to get some feedback. My own estimation is that the xl1 roof camber is streamlined in wind tunnel and there is attached flow...


On the 2009 vw L1 model the roofline is according to the template so VW has finded somenthing after that...

[hotrodfeguy]

looks dam good to me, also consider that the winshield agle may have some effect on the rear angle as well.

[HydroJim]

Remember, it's always better to error on the side of less steep than too steep. The template is about the minimum that can be achieved with good flow attachment. I'm sure with good flow upfront, your initial angles can be slightly more steep, but the 22 degree max remains constant.

When you chop your roof, I'd make all your angles using conservative measurements in order to ensure attached flow.

[aerohead]

Originally Posted by Vekke

I have done some overlayes conserning my roof chopping and this is bothering me this is correct overlay and its way off:

If I put it about 250-300mm too toward the front it layes perfectly:


So the guestion follows:
If you put the template too much in front of the picture is still layes perfectly ok to the shape. So can I do the same in my lupo and still get nice flow. My own estimation is that when you are at the max roof camber you can make that first few degrees pretty rapidly like those pictures prove or what do you think?

This may be true only if you begin the cambering at the max camber point etc?

third option:


Now template aligned at car underside lowest level and its quite nice match on the roof. Note that sidesills are lower than the cars underside, because its better aerodynamically that way.

Plan is to begin the rood chopping this weekend so would like to get some feedback. My own estimation is that the xl1 roof camber is streamlined in wind tunnel and there is attached flow...


On the 2009 vw L1 model the roofline is according to the template so VW has finded somenthing after that...

*The 'Template' should be positioned only as originally intended or we run the risk of jeopardizing boundary layer attachment.
*I've done a comparison of the 2009 1L car and got the same thing.Online,there is the original concept sketch of the 1L car and it is dead-on the 'Template.' Rear visibility may have been a factor in running the roofline a bit faster.I don't know.At Cd 0.195 the 2nd-gen car has higher drag than the 1st-gen of Cd 0.159.
*One of the members posted a color photo of maybe the 3rd-gen 1L in the wind tunnel under smoke.It looks very good!
*Hucho's associate at VW,Rolf Buccheim (sp?) reported that we could go as steep as 23-degrees.If you can morph the 'Template' to include a max tangent angle of 23-degrees within the 1st 80% of the aft-body,you'd probably have a strong confidence for success if you wanted to try it.

[sgtlethargic]

I started an offshoot of this thread called "Aerodynamic Streamlining Template 3d Models".

http://ecomodder.com/forum/showthrea...tml#post354542

[aerohead]

*I've been working with a 'modified' 'Template' since early year.
*It is based on the upper half of Daugherty and Franzini's 2.5:1 teardrop published in their FLUID MECHANICS text of the 1970s.
*I posted it on page 37 of this thread at #366 (permalink).
*If you rotate the image counter-clockwise,then use only the upper half (Upper and lower halves are asymmetrical),this upper half becomes the basis for the 'new' 'Template.'
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*This 'new' contour addresses some of the criticism of the primary curvature of the 'Template,' and after working with dozens of comparisons I'm now confident that it is an 'improved' version,allowing,as you'll see,a bit more radical slope in the early stage of roof down-slope,which puts a more flattering light on the aft-bodies of many production automobiles and pickups.
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*Everything else remains essentially the same.
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*I'll scan the new image an post this coming Saturday.For those of you computer-savvy members,you can just overlay the new contour onto the existing 'Template.'
P.S. As always,we're concerning ourselves only with the aft-body portion of the contour as a means to prevent flow separation where it's most prone to occur.