Greetings,

Here's a SketchUp model of an aerodynamic cap for a pickup truck, that could be made out of foam (hence the pink color!) with the Phlatprinter to make ribs, and then form 1/4" foam to form the surface, and then fiberglass over that.




Uploaded with ImageShack.us

Here's a video animation of this:
http://www.youtube.com/watch?v=pEEzbnT5dKs


If you would like a copy of the SketchUp file, I'd be happy to email it to you.

 

It was done all in SketchUp. The truck itself is from the 3D Warehouse, of course, and I scaled it to be close to the size of someone on EcoModder, who is building a cap for his truck. He is using foam ribs about 12" apart, and then 1/4" foam skin. If it works aerodynamically, he'll then fiberglass it.

If it does work aerodynamically, it can save a lot of fuel -- several other folks on EcoModder have saved 10-20% with similar caps.

 

I wonder how much of an improvement this would actually make. Don't trucks form a sort of bubble in the bed behind the cab? I remember reading somwhere that having the gate open actually increases drag because it changes the shape of the bubble that forms.

I suspect that a greater improvement would come from lowering a pickup closer to the ground and flattening the windsheild angle.

 

Lowering might help, but windshield angle means very little. Yes, pickups form a pocket, but aero caps help a lot -- like 10-20% in fuel economy. Check the threads on this over at EcoModder.com. My design might be a bit too steep of a taper, for pickups with short(er) beds, anyway.

The trailing shape of a vehicle is actually where most drag is created or avoided. The angle/arc of the taper is determined by atmospheric pressure pushing the air back, and also a "springing" compression generated by the front of the vehicle. The localized higher pressure helps to close the air back together. And if the trailing surfaces can maintain attached air flow, then it avoids turbulence and a low pressure pocket on the back that actually pulls on the back of the car.

This is a very low drag design from 1938 called the Schlörwagen, that illustrates a close to ideal shape (though not perfect):




Also, check out my CarBEN EV open source design. It may well be as good or better than the Schlörwagen, and it will have a much smaller frontal area. The front wheels are able to be covered at highway speeds, but then the hinged panels allow room for the wheels during sharp turns.

 

Here's a revised version of the aerodynamic pickup cap that is probably better suited to the mid-size pickup it is based on.

http://imageshack.us/photo/my-images/828/screenshot20120321at922.png/



The darker area on the back is the face of the previous design.

 

There are several folks over at EcoModder.com who have made aero caps for pickup trucks and they usually get 15-20% fuel economy.

My earlier pink model is probably too steeply sloped. The later blue one is probably much better.