Box Cavity for a pick-up truck

[JeffD]

I decided to try a box cavity for the rear of my pick-up. It's about 4" deep which compares with the 100mm I've seen, but the rear bumper sticking out might not help the situation (filled the space between the bumper and the tailgate with pipe insulation). I was going to make it deeper, but didn't want to block too much of the rear tail lights. Think it'll help?

[Frank Lee]

I'm not seeing how that will do anything.

[California98Civic]

Originally Posted by Frank Lee

I'm not seeing how that will do anything.

A study by somebody named Hussain Ali at a conference on aero at Coventry found that a 4" (100mm) rear box cavity could yield a modest gain. But a diffuser at a slight angle (2*) was also needed. I tested a box cavity, without the diffuser, and had inconclusive results: http://ecomodder.com/forum/showthrea...tml#post376489

[Xist]

Originally Posted by California98Civic

A study by somebody named Hussain Ali at a conference on aero at Coventry found that a 4" (100mm) rear box cavity could yield a modest gain. But a diffuser at a slight angle (2%) was also needed. I tested a box cavity, without the diffuser, and had inconclusive results: http://ecomodder.com/forum/showthrea...tml#post376489

It looks like that refers to pages eleven and twelve of this:

http://www2.warwick.ac.uk/fac/sci/wm...ionvehicle.pdf

[ChazInMT]

The Audi that the box cavity was on already had a very low Cd. So it was dealing with what was fairly smooth airflow. The area behind the tailgate of a pick up is deciedly less than smooth.

[t vago]

Trucking companies are beginning to equip semi trailers with box cavities. It's been suggested that these cavities could net as much as 9% improvement in fuel economy, over stock. Can't hurt to try.

[Frank Lee]

Those trailer "box cavities" make sense as they are quasi-boattails that extend the aft surfaces and are "Kamming" the flow ("quasi" in that they lack endcaps).

The vertical fences on this one appear to reside in the turbulent bubble. I could see them helping if they were deep enough to intersect the free stream flow- like a Bonneville spoiler only vertical. These look too short and/or too far inward towards centerline to me.

I can imagine some benefit to extending the tonneau like that though.

[kach22i]

I found this image the other day, maybe it can be applied to the back of a tailgate.

Automotive Aerodynamics: Drag Area – Size Matters

[freebeard]

^^ That's a cool find, too bad the trail goes cold in the comments section at that link.

They wired in the third brake light but didn't put taillights in those cat-eye shapes in the lower corners?

I think the bottom should be dropped 6" or so:

[aerohead]

Originally Posted by JeffD

I decided to try a box cavity for the rear of my pick-up. It's about 4" deep which compares with the 100mm I've seen, but the rear bumper sticking out might not help the situation (filled the space between the bumper and the tailgate with pipe insulation). I was going to make it deeper, but didn't want to block too much of the rear tail lights. Think it'll help?

To have the best chance for success,the airflow coming to the box would have to be perfect.So some major work would be required over the bed.