First Electric van boat tail

[JohnForde]

One problem is the cuff of 1/8" HDPE flexes. I think that ruins the flow attachment.
Tomorrow or soon I will replace the cuff with 1/4" Plywood. I will also replace the doors with 1/4" Plywood and reduce the angle of the top to 10 degrees or less. I will then angle the new full height doors at 11 degrees.

I hope this produces a measurable result.

[JohnForde]

Cuff & doors all at 11 degrees. Total length 84" (10" Cuff, 8" step bumper, 48" wood doors & 18" polycarbonate twin wall extension)

[JSH]

Originally Posted by JohnForde

Cuff & doors all at 11 degrees. Total length 84" (10" Cuff, 8" step bumper, 48" wood doors & 18" polycarbonate twin wall extension)

The top at 16 degrees is too steep.

Your vortex generators may be hurting instead of helping. They do help some if done right on a bare trailer but I don't know of any industry testing that combined vortex generators with a trailer tail. If they helped I would expect we would see them sold as part of a trailer tail kit.

Here is a paper on the topic:
https://scholars.csus.edu/esploro/ou...57830972201671

[aerohead]

Originally Posted by JohnForde

Seeking advice.
Today I thought for sure I would see an appreciable decrease in drag. My sample was only 15 miles but any improvement was negligible. I have a 4 sided box 66" long at 16 degrees. The entry cuff is curved HDPE at about 11 degrees. The top is 16 degrees. There are vortex generators on top & both sides.
The Zevo is 84" W. The WT doors 'aperture' @ 50"W.

I cannot do a tuft test because I do not have a partner/chase vehicle.

Included are 6 photos and a video. Thoughts?

https://photos.google.com/photo/AF1Q...YZmJw5oCr5sSsJ

* The VGs just may not be capable of inducing reattachment onto the 16-degree slope.
* A study of the Mitsubishi Lancer Evo's effective back-light angle would 'tell' us something about their VG's capability to reattach flow onto the boot/trunklid of that vehicle.
* Vortex-drag is the most 'powerful' type of drag known.
* A 'squareback' trailing edge already produces vortex-drag.
* From Bearman's research on angled aft-bodies, a 16-degree slope would have increased vortex-drag by over 300%, compared to the 'flat' roofline.
* Another 'unknown' has to do with the exposed, down-facing 'winglet' formed from the upper panel.It may be behaving as a 180-degree out of phase 'capping plate' that you'd find on the wings of an Indycar, or Formula One. Very 'draggy'!
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* If we presume that ATDynamics wind tunnel, or CFD tested ( or both ) their 'Trailer Tail,' then observation informs us that they weren't willing to push their aft-body slope angle beyond 12.5-degrees. This may be the 'GO, NO GO' for a simple body type. And we're not led to believe that Trailer Tail has 'attached' flow over it's 48-inch span, only that it's tearing edge has 'intercepted' the 'reversal point', where the flow just barely reattaches before it reaches the trailing edges of the tail.
* Shooting from the hip, I'd be inclined to ignore everything between 16-degrees and 12.5-degrees, and go straight to 12.5-degrees for a re-test.
* The result would would be instructive either way. ( aerodynamicist Alex Tremulis referred to this as conducting 'pick and shovel work').
* If you saw 'pay dirt' at 12.5, you could always 'back off' until the drag trend 'reversed', indicating the slope 'limit.'

[freebeard]

Permalink #119:
ecomodder.com/forum/showthread.php/measuring-aerodynamic-pressures-40081.html
I hope you didn't miss that. Data over conjecture.

[freebeard]

Dropping into random pages in the Random Aerodynamic Oddity of the Day Thread can be entertaining. I was looking for a reference to 4-bar linkages and found this instead:

ecomodder.com/forum/showthread.php/random-aerodynamic-oddity-day-thread-35653-3.html#post581029

10-07-2018, 06:18 AM -- #88 (permalink) -- kach22i

One study conducted in 1989, “Turbulent Flow Separation Control,” explored controlling airflow—flow separation—to decrease energy expenditure and weight in airfoils, inlets, and diffusers and improve aircraft control and decrease drag. The study employed vortex generators, aerodynamic surfaces protruding from a body that draw faster moving air to the surface of the vehicle and disrupt the slower moving boundary layer air around a vehicle, the use of which can be traced back to research conducted by the National Advisory Committee for Aeronautics (NASA’s forebear) in the 1950s. The generated vortices “energize” the slower-moving boundary layer and thereby reduce drag and, in aircraft applications, increase lift.

Maybe you're not using enough of them?

(Also found this, but that's another story:

the Pontiac Vivant....using Pontiac parts sourced from a junkyard, including a Tempest transaxle, full-size Pontiac Bonneville alloy eight-lug wheels, and a Pontiac 370-cu.in. V-8.

I'd like to see that setup in a Model T center-door sedan.)

[JohnForde]

Thank you JSH, Aerohead & Freebeard.

I have purchased 1/4" plywood with which to do the cuff properly and build doors with an 11 deg downslope.

My measurements are approximate. I have been using a "rise over run" webpage to plan.

I will get the cuff, doors and top all between 11 deg ( 5 over 1) & 12.5 deg (4.5 over 1).

I will test at 11 deg before removing the VGs.

Aerohead - the exposed down facing winglet is what allows me to adjust door angle while in development. I think with doors at about 11 degrees the winglet is all swallowed up. It will be sawed off when I am done.

[freebeard]

1/4" plywood will take a curve. Open ribs would be punk, or dope, or whatever kids-these-days are saying.

[JSH]

Originally Posted by freebeard

Maybe you're not using enough of them?

If that actually worked we would do it at the factory.

[freebeard]

The :rolls eyes: was to signal that I wasn't serious. I understand there needs to be downstream opportunity for reattachment.

The breadcrumb leading to NACA was the point. I hate explaining jokes.