Box van rear end mod

[aerohead]

Originally Posted by Engeu1

There's also another great report by Maragno & Visser, May 2003 with a lot of plots.

Comments then please on a vane system, 3 or 4 sides of box, say 6 in / 15 cm radius, no inset, v.g.s?

90 degree, 90 degree perforated (after first 10/15 degrees), or increase the radius and reduce the arc length?

Other combinations?

Hucho tested vanes and measured no benefits. Only box-cavities and boat-tails made any difference.
No 'aerospace' technology has ever improved road vehicle aerodynamics.

[aerohead]

Originally Posted by freebeard

Look into Coanda nozzles.

Not to pick on Coanda, but his ' Coanda nozzle' airplane never flew.
Blown slots require more energy to power, than they save through drag reduction.
Aircraft operate in two-dimensional flow, trucks operate in three-dimensional flow.
If you had an 'over-unity' power supply available, I'd say 'go for it!'
But then, you'd have a 'jet' truck anyway, with free thrust.

[aerohead]

Originally Posted by freebeard

I recall an example of putting round holes instead of horizontal slots in cattle trailers and how it reduces suffocation of the livestock!

It's on EcoModder somewhere. I don't trust Google to find it though.

Speed holes

https://i.kinja-img.com/gawker-media...jzd2eihqoc.jpg

Cattle haulers have Cd 1.15. If you cut holes in a car or truck, that will be your reward.

[freebeard]

Not to pick on Coanda, but his ' Coanda nozzle' airplane never flew.

The way I got the story was that it flew once. With it's tail on fire.

[j-c-c]

Originally Posted by aerohead

Cattle haulers have Cd 1.15. If you cut holes in a car or truck, that will be your reward.

The holy jalopy pictured, I believe is a prime example of enthusiastic all out weight reduction, not any early learned aero drag reduction, but I may be wrong.

[Engeu1]

Originally Posted by aerohead

Hucho tested vanes and measured no benefits. Only box-cavities and boat-tails made any difference.
No 'aerospace' technology has ever improved road vehicle aerodynamics.

Was that in his 1987 book?

Your Ragatz and Thornton post is also interesting helpful.

[Engeu1]

Originally Posted by freebeard

The way I got the story was that it flew once. With it's tail on fire.

But the principle got used in several fielded design.

[aerohead]

Originally Posted by Engeu1

Was that in his 1987 book?

Your Ragatz and Thornton post is also interesting helpful.

Yes, you'll find it in his chapter on commercial vehicles, if memory serves me.
The work on the Ahmed Body will also be of interest. There's a full development of drag and vortex drag as a function of angles, boat-tailing, and diffuser geometry, all combined into a single graphic.
Graduate student Mark Funderburk, along with Professor, Dr. Carvin, at Texas Tech University's College of Engineering picked up on the Ahmed body research, along with General Motors, who'd come up with an 'OPTIMUM TAIL' investigated in the Texas Tech 1/10-scale model wind tunnel.
GM's OPTIMUM was a spitting image of the 25-degree/10-degree/10-degree Ahmed tail, with all-edge radii added to kill any chance of vortex formation. This tail, however, was optimized for a 'box' or 'van' which already had upper edge radii, something not seen typically in commercial vehicles, due to the intrusion into the cargo volume. GM's tail is probably the best thing that can be fabricated without compound curves, as in Fachsenfeld's inflatable boat-tail, developed next door to Daimler-Benz at the FKFS, in Stuttgart.
Fachsenfeld's is the best I've ever seen. Hucho has a depiction of this in his bus section.
I tested an inflatable tail on my Toyota truck back in the 1990s, and along with partially stuffing the open truck bed, allowed a 4-mpg improvement on the highway. And it was deformed so much under inflation pressure, that it didn't even resemble what it was tailored for in static form. ( don't ever use expandable Naugahyde for inflatables!)

[j-c-c]

Originally Posted by aerohead

As far as I know, the DOE/ DOT will allow up to 60-inches of rear elongation if it's for fuel economy.

In Florida the applicable wording regarding specified overall vehicle length limits is: "but exclusive of safety and energy conservation devices approved by the department for use on vehicles using public roads."

As of 2019 Florida Statutes 316.515.

Now what is "approved" or how or why, is beyond me. This restriction has been added, but I am unsure when, which really doesn't matter now.

[aerohead]

Originally Posted by j-c-c

In Florida the applicable wording regarding specified overall vehicle length limits is: "but exclusive of safety and energy conservation devices approved by the department for use on vehicles using public roads."

As of 2019 Florida Statutes 316.515.

Now what is "approved" or how or why, is beyond me. This restriction has been added, but I am unsure when, which really doesn't matter now.

here, we see exemptions for loggers pulling over-length pole-trailers, wind turbine blades, oil and gas pipeline components, manufactured housing, sometimes they'll move vintage and historical homes for restoration and display.
When they moved Howard Hughes' 'Spruce Goose' out of Long Beach, California, I'll bet they had some kind of special 'approval.'