t_vago's compound curve foam board pickup aeroshell
 

This is what I originally came up with for my truck.

http://www.tom-viki.com/spgm/gal/Car...1010120001.jpg
Underlying frame

http://www.tom-viki.com/spgm/gal/Car...1010200002.jpg
Side view, right-hand side

http://www.tom-viki.com/spgm/gal/Car...1010200003.jpg
Side view, front facing rear

http://www.tom-viki.com/spgm/gal/Car...1010200004.jpg
Rear view

I waited too long to coat it, and it disintegrated during one of my commutes. Version 2 will be a bit less aggressive.

Looks great! :D

How much did that cost you? How did it disintegrate? Did you yarn tuft test it at all? How did you come up with that design?

I don't think I want to go that aggressive as I need to load/unload things from the truck bed...hence why I have a hatch on mine. I still have a few sheets of coroplast so I'm gonna stick to that material fer now...until I git the itch to use something else. ;)

Your compound curvature is outstanding. Absolutely beautiful. What thickness foamboard did you use? Any fabrication tips you can share? I don't see any burn marks for example. :)

Sorry it died. What MPG improvement did you quantify?

Keep us posted on Version 2.

Would love to see tuft testing of that as well.

Well, I formed the frame out of 1 inch thick FoamulaR insulation. The ribs and rails were initially cut using a jig saw, then fine-tuned using a finger-cutting knife (actually, one of those As Seen On TV knives that are supposed to cut anything from a ripe tomato to an aluminum can, but the knife I used couldn't cut cooked meat worth a darn but was excellent at cutting fingers - hence "finger-cutting knife").

The height and width of each rib were calculated using Microsoft Excel, based off of that paper written by that Naval PostGrad sailor, and my memories of how the snow formed itself on the tonneau cover of my truck last winter. I didn't want to bother with sharp edges, because they're harder to work with, with regard to being able to coat the exterior with fiberglass or something, so it was made as curvy as possible.

The ribs and rails were glued together with Gorilla Glue and a lot of water to ensure the foaming action necessary for the Gorilla Glue to work. The skin was made with 8 sections of FoamulaR 1/4 inch sheeting. Each sheet was partially cut, then partially glued onto the ribs, repeatedly until each sheet was completely glued onto the ribs. The sheeting was held in place by weights placed on the seams (things I had in the garage - spare crank pulleys, spare car radios, spare alternator, jumper cables, etc.) while the glue set.

The aerocap failed because the rear ribs and the side mounting rails were too thin to support the vibrational stresses imposed on the aerocap while the truck was travelling at speed. This was compounded by shrinkage of the rear 1/3d of the aerocap to the point where the rear was able to be wiggled by hand. The combination of the two causes caused the rear 1/3d ribs to fracture and separate from the mounting rails. The rear of the aerocap, no longer joined to the truck, caused the rest of the aerocap to break along the mounting rails, and then lift off the truck altogether. The aerocap flew upward about 10 feet, and luckily landed in the center divide of the highway, but the rear 1/3d completely disintegrated. I could recover the main part, but it was completely unrepairable.

I should have secured it more firmly at the rear, I should have used thicker ribs and rails, and I should have stiffened the skin with fiberglass. These will be applied to version 2.

I imagine that tuft testing would have revealed some turbulence around the rear of the aerocap, because I think the vertical slope was a bit too aggressive.

I was able to quantify a gain of 1 MPG from this aerocap. Incidentally, the same testing revealed absolutely no gain whatsoever from having a tonneau cover installed.

Very nice to have seen and read about. Hope to see more in version 2.

I have to tell you, I wish you had posted those when I still had my Ranger, I would have copied it (if you didnt mind, that is)

T Vargo, you need to separate your project out in its own link. It is very nice. I suspect you're right about the V1 cap being too aggressive, keep the same shaping ideas, but only taper down about 6 - 8 inches front to back and make the transition from rear of cab to cap very gradual, your V1 appears to dive right in.

My 2₵

Split this into its own thread. Good idea.

Awesome work! I really like seeing how well the 1/4" foam works on compound curved surfaces.

You have got me thinking very hard about going this route with my CarBEN EV design.

Are you going to skin it with fiberglass? Is Gorilla Glue and this glue compatible with fiberglass? If so, what sort?

FWIW, I'm told that urethane foam may be better from a chemical compatibility standpoint, as Gorilla glue is just liquid urethane. Further, since polystyrene foams are dissolved by polyester resin, you need to use more expensive epoxy with them, another reason to stick with urthane foam in the first place. Not hotwire-able due to toxic outgassing, urethane foam is nonetheless said to be easier to sculpt and shape with sanding, grinding, etc..

For compound curves, consider kerfing the back side of the foam.

I have a feeling, 2011 is the Year of the Boattail. :D

Yah, I think so, too. I might start work on version 2 this weekend. Tempted to use something more substantial for the frame than FoamulaR, though.

Oh, and if you do decide to use resin for your fiberglass shell, be sure to completely cover the exposed polystyrene with a good masking tape. It's as what Otto said - Fiberglass resin will very quickly eat FoamulaR (or any other polystyrene).

Polyester resin will eat styrofoam, and knock you out. Wear a respirator. However, epoxy resin produces lighter composites, evolves much less toxic vapor, and is compatible with foam. At $65/gal, it's twice the price of polyester, but it's money well spent.

Sorry for the confusion - I tend to call polyester resin "resin," and epoxy resin "epoxy."

At most home improvement chains you can get foil coated foam board in full sheets. The foiled (not in the Snidley Whiplash sense though) side should be eco(nomically as in polyester) FG resin friendly. The foil layer also provides radiant shielding so your truck bed under such a foam-glassed cap wouldn't become a solar sauna. :)

BTW, I've found TAPPlastics.com a good place to buy resin and hardner. Anyone have other recommended sources?

TAP Plastics
Instructional videos!! ;)

http://www.tom-viki.com/spgm/gal/Car...ldBedCover.png
Here was the final MS Excel workup for the old aerocap

http://www.tom-viki.com/spgm/gal/Car...ewBedCover.png
...and here's the workup for version 2

This will give an idea of what the completed version 2 aerocap will look like.

Are you gonna put in a rear window? Is this one gonna be hinged/have a hatch so you have access to the bed? ;)

t vago, what's the benefit of the tight-radius inside corners and flat tonneau-like surface between the raised portion and bed walls. I'm skeptical flow would attach that deeply into those gullies. Why not use larger fillets instead?

Eventually. The foam shape has to be made, and that will not have any of the functionality you mentioned. However, the foam shape can be removed in about 20 seconds, and can be lifted with 1 hand. Version 1 fit this requirement rather easily.

Hm... Just had the strangest idea for using my existing tonneau side rails to secure the aerocap, so that it could be removed in 2 seconds instead of 20.

Heh... See, now you're picking on my poor man's CAD program. There's only so much I programmed into that Excel spreadsheet. :p

You'll notice that the curves on version 1 were a bit gentler than in the Excel workup.

http://www.tom-viki.com/spgm/gal/Car...ldBedCover.png
Excel workup

http://www.tom-viki.com/spgm/gal/Car...1010200002.jpg
Real life 1

http://www.tom-viki.com/spgm/gal/Car...1010200004.jpg
Real life 2

That was one of the reasons I decided to use FoamulaR sheeting. It can be curved to form compound curves fairly easily, as long as the underlying frame shape can support the minimum bending requirements.

I tend to agree with Bob -- the trailing shape of the tailgate would be "cleaner" I think if the entire surface of the cap was tapered down; so the air flow over the truck as a whole was improved. Like the shape that others have done -- though I do like the look of this project. So, maybe a combination?

I'll attempt something is SketchUp -- which has an excellent free version, by the way. And, this would deepen the ribs nearer the back, too I think?

There's an engineer at work we like to pick on for doing all of his analytical work in Excel. But Excel as a CAD program? That's ... very MacGyveresque.

A spreadsheet is the Swiss Army Knife of application software. From poor man's database to poor man's CAD. Two plus decades ago I used spreadsheets to clean up the coordinates of industrial robots for example. :)

t vago, I wasn't picking at all. I would like to understand your motivation for gullies on the sides. Is the ole tear-back look an aesthetic goal for example? Inquiring minds want to know. :)

Neil, like this?

http://kamperbob.com/images/aero/Aer...cept%29.v3.png

I know, I was just trying to make a funny.

Anyway, I have noticed in the past, when my tonneau cover was covered with snow, the obvious thing that air wants to flow down from the roof of the cab. I also noticed that air wants to flow back toward the centerline of the bed from the sides. Who am I to argue with Mother Nature?

Also, from reading that other grad paper that was posted yesterday in this forum, I noted that the traditional 12 degree sloped aerocap was good for a reduction in C(d) of 16.2%. Sloping the sides, like what I am going to do, resulted in a reduction in C(d) of 19.8%. To me, the math makes sense.

http://farm3.static.flickr.com/2421/...fc475bbf45.jpg

This guy had a similar idea for his Nissan. I think, though, I could live without the huge wing.

And Ecomodder member ChazInMT had a similar idea, too.

http://ecomodder.com/forum/member-ch...-shot-side.jpg

The Nissan rally truck didn't always sport the rear wing...
http://www.nissanpress.co.uk/press_s...4/36716nis.jpg

I do like the look of the Nissan cap, and it may be fine aerodynamically -- only tuft testing will tell.

I made a quick attempt in SketchUp (after downloading a free quad cab model from the Google 3D Warehouse -- there is a Dakota there, but not for download), and it lacks the arch all the way back to the tailgate (a little more trial and error would get it there):

http://img522.imageshack.us/img522/1...10122at334.png

In my estimation, the departure angle of the whole trailing edge would be better with a downward slope.

That looks like a 2005+ Dakota quad cab. Nice!

Steep angle aside, you can see that if you were to look downward on Neil's drawing, that the sides kind of curve in toward the centerline anyway. I think I am going to go with my 12 degree sides anyway, though. Trying to do that drawing in real life looks to be beyond my ability.

Here's a slightly better version:

http://img522.imageshack.us/img522/6...10122at428.png
http://img717.imageshack.us/img717/3...10122at429.png

I could email you the SKP file and you can work on it -- there is a section tool that can show the surface contour.

When you reconstruct this, is your plan to skin it with fiberglass? Or, just toughen up the ribs, etc. so you can run it as foam and see how it changes the FE -- and then finish it?

The plan is to run it as foam and see how it changes the FE. Once I am satisfied with it, I'll likely use it as a mold for a fiberglass shell.

Just put a fiberglass layer on it.
The foam weighs so little it wont make much of a difference and it will add strength.

Just put a fiberglass layer on it.
The foam weighs so little it wont make much of a difference and it will add strength.

Neil, give up on making the cap end at the top of the lift gate, this is NOT an an optimal aero design, it is far too steep and departs radically from the "Ideal" template which is discussed, have a 1 foot tall lift gate. Look at current design SUVs for inspiration. Do curve in the sides, about 6" each gradually, and only drop the top 7-8". And the trailing edge should be sharp, not radiused.

T Vargo, tweek the sides of your V2 cap, you have fallen into the trap of creating a sudden change in air direction right behind the cab on the sides....do you see it? Just copy the line you have for the top (when viewed from the side) and put that line on the sides too, if looked at it from the top, otherwise, the top profile is GREAT. Keep up the good work. I like the flat area above the tailgate.

In the light of the Aero Cap Thesis thread, I'll try to do a 12 degree main slope with the 3D side taper, and see how that looks.

How long and how wide is your bed t_vago? (I wish the Dakota SU model was available, but the GM one I got will do...) I'll adjust it to be the right dimensions.

My bed opening is 53 inches across by 63 inches long.

Let's see what you come up with.