Commercially produced aerodynamic pickup bed cap

[freebeard]

I know in the Darko wind tunnel they put a metal mesh upstream that affected the attachment through the throat.

[aerohead]

Originally Posted by freebeard

There's got to be a line somewhere between what works and what doesn't. So -- 1/4 to 1/5th for air and 1/8th for water?

If anyone here has Hucho with them, he made a comment regarding the development of the Vanagon.
Minimum leading edge radii required to guarantee attached forebody flow on the scale model were found to be excessively large when in full-scale, even though they had the Reynolds number dynamic similarity covered.

[aerohead]

Originally Posted by freebeard

I know in the Darko wind tunnel they put a metal mesh upstream that affected the attachment through the throat.

My thought is that, the mesh was just there to protect the flow-straightener egg-crate from damage, should some random jetsam get in there.

[freebeard]

The guy running it said some thing about attached turbulence in the test section before they added it.

[aerohead]

Originally Posted by freebeard

The guy running it said some thing about attached turbulence in the test section before they added it.

Seems like any turbulence attributed to the screen would be insignificant compared to the turbulence created within the deep, egg-crate flow straightener at the jet.
Gary Eaker could probably tell us about that.

[aerohead]

I went back through Hucho.
What I was remembering, turned out to be about the 1951 VW microbus, compared to the 1969 Vanagon.
Pawlowski published on minimum leading edge radii requirements in 1930.
Lay's research in 1933 confirmed the efficacy of Pawlowski's work.
M'o'ller, in 1951, did not use Pawlowski's geometry for the VW bus.
It turned out that, the 1951 design would have had no greater drag, if the front radii had been just a fraction of what was used.
--------------------------------------------------------------------------------------
With respect to scale models:
Hucho suggests that anything below 1/4-scale would be good only for 'qualitative' investigation. You would not be able to do 'quantitative' work below that 'size'.
In the United States, the typical minimum model scale is 3/8ths, as of 1986.
Hucho said that 1/4-scale results are identical to 1:1-scale.
In 1991, Texas Tech University was using 1/24-scale in their small water tunnel, for food coloring-injected flow imaging. Only.
For underwater tow-testing and actual drag measurements from an overhead gantry bridge- supported sting, they used a 3/8-scale model, and SCUBA divers for close observation and image capture.
Ford paid $ 68,000 for a highly accurate 3/8-scale Ford Taurus model, with clear plastic hood ( bonnet ), complete with all engine bay structures, to develop CFD code. Model velocity was 2-mph.

[tomi_k]

Tapes are just to give visualization where a tailgate split could be vs. how side wall would blend in.... tape measure is probably closer to a shape planned (from sideview)....

[California98Civic]

In the second image, I think the tape measure line might be at a too-steep angle in the aft portion and could produce separation sooner than you'd prefer. Do you have the means to build a prototype, possibly of cardboard for tuft testing? You could build it, tuft test it, modify it, tuft test it, and by that means get a better sense of the most likely shape.

[freebeard]

I would have gone with 'the left and right don't match'.

I also see something that arcs from the separation line on the back of the cab into a plastic crate on the tailgate. Possibly to hold the arc line?

I would consider the Camper World race truck spoilers. And other aerocaps that have a flat truncation about half their height.


https://www.nascar.com/wp-content/up...in-625x340.jpg

Another example:



...and an L-shaped hatch like the Dodge Magnum for access to the bed.

[tomi_k]

Lol... the plastic milk box was simply to hold the tape measure in place... The arc, formed by tape measure is just to visualize that the cap will not be straight (as the tapes are). Prototype of the cap with detachable extension is under planning.... with tuff test and ABA tests... these are just initial captures of the cap idea.

I have traced trucks cabin exterior shape and extrapolated it and surprisingly, an arch goes pretty close to end of the trucks bed... the extension piece will be made exactly same arch as the cabin and the cap....