First Electric van boat tail

[JohnForde]

Current drawings illustrating Zevo's wake size.

[aerohead]

Originally Posted by JohnForde

Current drawings illustrating Zevo's wake size.

1) If choosing, I'd go with less than 14-degrees.
2) And it would integrate into the 'cuff' itself, where the local tangent angle agrees with the design slope angle.
3) If the slope begins on the 'yellow' perimeter, all the flow will have already been lost on the cuff, wherever the tangent angle reached 25-degrees.
4) If you must begin on the yellow line, then you're looking at a box-cavity technology, instead of a boat tail.
5) The extension panels would just go 'straight' to the rear, perpendicular to the rear of the box, with their trailing edge falling along an imaginary
streamlined path, capturing locked-vortices between the 'cuff' and the trailing edges.
6) And whether a boat tail, or box-cavity, the surfaces where they attach and adjoin each other. must be 'airtight'.
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Please look at #62 (permalink ).
This is a 'Cliff Notes' version of Boundary-Layer Theory, $75,000 if you want to get in college.

[JohnForde]

I might be able to install these and try them Thursday or Friday.

[freebeard]

Once your done prototyping, it might help to replace that cuff completely.

[JohnForde]

A guy can dream. I should have numbers in a week.

[aerohead]

Originally Posted by JohnForde

I might be able to install these and try them Thursday or Friday.

I located a citation online, from a 2013 Lawrence Livermore National Laboratory piece on Semi-trailer boat tails, starting on page-12 from the top of the report.
Of special interest is 'Tail 2' a straight, 11-degree EBLA tail, top and sides, with horizontal floor.
Tail 2 produced the lowest Cd of four tails tested, @ delta-26% for a 48" , 3-sided tail, and delta-26.1%, for a 32", 4-sided tail.
If extrapolated to full-length, Tail 2 would be 263.3" in total boat-tail length, longest of the four.
The trailer's 'box' was only streamlined, starting with a wake of 80.75-sq-ft, and reducing to 67.372-sq-ft/ 62.19-sq-ft, respectively; a 16.56% / 22.97% wake reduction, respectively.
Qualitatively, a 4-sided, 48" tail would provide a delta 36.2% Cd.
It's worth a 'long' look!https://www.energy.gov/sites/prod/fi...ari_2013_o.pdf

[aerohead]

Originally Posted by JohnForde

A guy can dream. I should have numbers in a week.

Please look at #76 ( permalink )

[Joggernot]

Originally Posted by aerohead

https://www.energy.gov/sites/prod/fi...ari_2013_o.pdf

I'm not able to open the file. Can download the file (done twice), but get an error. Tried another way and got "file not found" error.

[JSH]

Originally Posted by Joggernot

I'm not able to open the file. Can download the file (done twice), but get an error. Tried another way and got "file not found" error.

The uploaded file does not open for me. However the link in the body of the post works fine and goes to the same document.

EDIT: This is likely the most interesting page



And I liked this plywood prototype:

[JohnForde]

It is rarely this hot here in MN. I had hoped to build today but will soon.
My plan is a rounded cuff of 1.5m radius followed by a hinged door at 14-18 deg. It might make sense to put vortex generators right in from of the hinge.