First Electric van boat tail

[freebeard]

How do you propose to create the curved panels?

[JSH]

Originally Posted by 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.

I'm curious why you are planning curved panels when testing in a full size NASA wind tunnel by a national lab showed better results for a simple straight panel.

Seems like a lot of work for less return.

[JohnForde]

Originally Posted by freebeard

How do you propose to create the curved panels?

Coroplast 24"L with gorilla tape at both ends and 2 spacers to define the curve.

[JohnForde]

Originally Posted by JSH

I'm curious why you are planning curved panels when testing in a full size NASA wind tunnel by a national lab showed better results for a simple straight panel.

Seems like a lot of work for less return.

Placing a straight door right at the break point actually seems harder. The cuff breaks at 19 degrees and has shown to be too steep. Placing something at 11 degrees or 8 degrees from the cuff seems too hard. I will just tape coroplast over it with a gentle bend and 2 spacers.

Thanks for asking. More drawings soon.

[aerohead]

I made photo-enlargements of 'Livermore's' work.
1) It appears that they're using 'effective' angle in a different context as 'Effective Back-Light Angle' ( EBLA ).
2) Tail 1 is 3-sided, achieves a 'tangent' angle of 14-degrees, a wake area of 78.1259-sq-ft, and a 'system' drag reduction of 24.8%, at 48" length.
3) Tail 2 (A) is 3-sided, achieves a tangent angle of 11-degrees, a wake area of 76.3516-sq-ft, and a 'system' drag reduction of 26.0%, @ 48" length.
4) Tail 2 (B) is 4-sided, achieves a tangent angle of 11-degrees, a wake area of 84.693-sq-ft, and a 'system' drag reduction of 26.1%, @ 32" length (the lowest drag of all tails ).
5) Tail 3 is 3-sided, achieves a tangent angle of 27-degrees, a wake area of 69.985-sq-ft, and the 'worst' 'system' drag reduction, @ 21.9%, @ 48" length.
6) Tail 4 is 3-sided, achieves a tangent angle of 22-degrees, a wake area of 67.488-sq-ft, and a 'system' drag reduction of 23.0%, @ 48" length.
7) Tail 2, as a 4-sided, 48" tail, qualitatively, might produce a drag reduction in the neighborhood of 39.94%.
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8) So, the 'largest' wake had the 'greatest' drag reduction! ( having a 'floor' in the boat-tail made all the difference )
9) The 'shortest' boat-tail also had the greatest drag reduction. (for the same reason a #8 )
10) An 'all-curved' tail of 2.66 meter radius ( 104.72") had no advantage, as it reached 115-degrees of arc from the virtual forward stagnation point, and 22-degrees tangent, prematurely, initiating eddy rollup and flow separation, even though it is actually 'longer' than the other three tails.
11) If the 48" Tail 2 was given a 'floor', to block the transverse pressure adulteration from below, it would likely take top honors for drag reduction.
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I've got one more thing to investigate, but it'll require a few more trips to the copy machine and light table.
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It's unfortunate for us that 'Livermore' lumped three different aerodynamic technologies into a 'system' ensemble. Untangling the drag reduction attributions for each of the three devices creates a real 'migraine.'

[JohnForde]

Today I was able to use spacers to adjust the 'bones' of the Zevo's Whaletail (WT). Both the top and sides are at 14 degrees. Tomorrow I will fill in the coroplast cuff.
I am confident the top and sides will maintain attached flow.
Friday morning I leave on an 800 mile drive.
Questions:
1 Should I attach lower portions on the doors 1/4" x 2' x 4' plywood. Easy. I am planning on it. They will not cover the tail lights. This will lose attached flow but it does 'stuff the box' on the lower third.
2. Should I install a floor making the box '4 sided'?
3. Should I cover the rear with a panel. The aperture or 'wake' is exactly 48" wide so using a sheet of polycarbonate would be easy.
Eager for comment as I must do any additional construction tomorrow.
Thanks
John

[JSH]

I would do a horizontal bottom instead of a cover on the rear. See the picture above of of the plywood prototype.

[JohnForde]

Implementing today

[aerohead]

Originally Posted by JohnForde

Implementing today

Try and get some rest!
Adding the floor is a big plus.
NASA registered a 1.9% drag improvement, 'stuffing' the wake turbulence with a full-separation stinger. Perhaps the lower mods will do something.
----------------------------------------------------------------------------------------On the off-chance that some motorist, on your 800-miler, should point there phone camera at ZEVO, and share it somewhere where we'll find it later, if someone were to help you tuft just one half of the rear, we might be able to 'see' the flow, by 'default' some day.
Travel safe.

[JohnForde]

First test. No success. 30 miles each way.
1.55mi/kWh northbound
1.85 southbound.
Stock Zevo averages 1.85
Pictures