First Electric van boat tail

[JohnForde]

Keeping my door slopes no steeper than 19 degrees and with extension limited to 48" behind the bumper, reducing the aperture and drag from 42 sq ft to 18 sq ft gives me a reduction of 58% in drag.

[JSH]

Originally Posted by JohnForde

4 pics of the Zevo's 'cuff' and gap

It looks like you can close that gap just by extending the plywood forward past the hinge. At least for the mock-up / test.

[JohnForde]

Originally Posted by JSH

It looks like you can close that gap just by extending the plywood forward past the hinge. At least for the mock-up / test.

Even the much up needs to hinge. I will fill the gap with coroplast. I will do my best to be precise.

[aerohead]

Originally Posted by JohnForde

Before I cut the very expensive aluminum and polycarbonate I decided to do a plywood prototype. I am glad I did. It helped me think thru top corner intersections and attachment mechanisms.

Here are 5 pics. The angle on these is 28 degrees. I am aiming for 22.

1) According to W.A. Mair's reporting, the boundary-layer would not survive the flow deceleration of 22-degrees until an elongation of 81.1" was obtained, and that's predicated upon all of that 81.1" constituted a lead-in curvature from the rectangular-cylinder 'box' body, necessary to maintain attached flow.
2) If using Mair's contour, your 'full whale-tail' would be 157.75" in total length.
3) Walter Korff of Lockheed Aircraft Corp. gives 156.24" total length.
4) GM's 1980 'OPTIMUM' tail gives 158.2" total length.
5) None of these tails exceeds 22-degrees on 'top'.
6) None of these tails exceeds 22-degrees on their sides.
7) 'Diffusers' run from 15-degrees, to zero.
8) NASA's curvilinear 'Shoebox' tail, at 45", was separating at 22-degrees.
9) ATDYNAMICs' 'Trailer Tail', positions it's tearing edge at an EBLA of 12.5-degrees @ 48" elongation
10) The Ahmed body achieves lowest drag at 9-degrees EBLA on top, the 'tail' portion constituting 21.5% of total body length, which would occur at 67.0" elongation on the ZEVO.
11) Paul Jaray's 'whale-tail' is the shortest, @ 115.6"
12) Walter Lay's, the 'longest', @ 211.4".
13) Lawrence Livermore National Laboratory never exceeds 15-degrees, their 'best' tail is limited to a EBLA of 11-degrees.
14) Renault chose 5-degrees for top/sides/ and diffuser on their V.I.R.A.G.E.S. semitrailer.
All the tails must be considered with respect to their particular geometries.
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The wake area/ delta-Cd relationship is valid only with attached flow.
Nothing but 'curvilinear' tails, known not to produce flow separation, can perform this hat trick.
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If you cannot stomach the 'curvilinear' construction, try to place the top, sides, and diffuser tearing edges where the 'curved' path would have been located. This dates to Dr. Hermann Burst, with his PORSCHE 911 RS ducktail spoiler, presently used on the Hyundai IONIQ 6, and M-B Vision EQXX, Lightyear Zero.

[freebeard]

https://www.acronymfinder.com › EBLA.html
EBLA - Definition by AcronymFinder
6 definitions of EBLA. Meaning of EBLA. What does EBLA stand for? EBLA abbreviation. Define EBLA at AcronymFinder.com

[JohnForde]

Here is more detail on the Zevo project. I need to keep the tail lights visible from directly behind the van. I will cover the lights with lexan and the rest with coroplast. The light issue necessitates a slope of 19 deg for 18 inches.
After that 48" doors can angle anywhere from 4.4 degrees up to 20 deg and beyond.

Could the necessary 19 deg slope might be maintain boundary flow by adding vortex generators? If so, where?

Thanks in advance.

John Forde

[freebeard]

Trailer lights?

[JohnForde]

Zevo is not designed for trailering and the manual says do not tow. It will be technically difficult to get a 'pigtail' connector ($500?) but I will have to do it soon.
OTOH I will only need to do it when my WT extends more than 48" behind the step bumper, (59" behind the tail lights) so that is what I am working on with the plywood prototype.

[JSH]

Originally Posted by JohnForde

Zevo is not designed for trailering and the manual says do not tow. It will be technically difficult to get a 'pigtail' connector ($500?) but I will have to do it soon.
OTOH I will only need to do it when my WT extends more than 48" behind the step bumper, (59" behind the tail lights) so that is what I am working on with the plywood prototype.

If you put a second set of taillights on the back of your aero tail your angle issue goes away. They can be as simple or complex as you want to make them but your are compromising your aero trying to keep the stock taillights visible from the rear.

You could do something as simple as trailer lights on a swing out extension wired to a trailer pigtail. Plug them in when the tail is extended and remove them or fold them back when the tail is folded.

[JohnForde]

I agree tail lights solve a great deal. To get at the wiring requires removing the cuff. I am working on getting info how to do that. I will have a pro do it and it will be expensive.

KEY QUESTION: Am I safe in assuming the stock "cuff" of 19 deg for 11" is designed to hold smooth flow? (diagram 1)

Extending the exact 19 deg angle for 10" more over lexan seems reasonable to me.

I can then experiment with door angle. I would love it to adhere at the same 18-19 deg. At the maximum legal distance of 48" behind the step bumper that would leave an 'aperture' of about 40", cutting aero drag in half from the 84" stock width.

If I cannot get flow to adhere one option would be to add tail lights, put the hinge an inch or two further to the side and build a rounded shallower cuff. That is a big project I am hoping to not have to do. (diagram 2)