All right then, I've spent the last 3 days thinking hard about this, and have come to a few realizations.
1st, I no longer feel that the vacuum created by the large area of the tailgate is the number 1 enemy.
2nd, it seems the main thing to avoid is turbulence. The energy which goes into making air swirl about or spin like tornadoes behind the truck are really what we need to be aware of.
3rd, a clean release line at the back of my cap/truck is preferable to a radius style release.
I have made 40-50 movies using Flow Illustrator to test out my theories and to check on what the going wisdom I have seen on the site look like.
My idea of extending my roofline down would be valid if I had a 2d truck, almost no turbulence is seen at the rear with a very clean release. But as fate would have it, the GMC Sierra pick up which I own, is indeed, part of the 3d world.
One of the things which had me seriously second guessing the "Leave the sides sticking up in the back" theory was the idea that the air on the outside rear of the bed would be getting sucked into the low pressure area created on the inside rear, this is a set up for some major vortex creation. I got to thinking I could add spoilers to counteract this down inside the box like the wing tips on airliners, then I remembered, I'm a freakin amateur, trying to design these things is beyond my capabilities. So In order to keep it simple and still do myself some good, I have decided on keeping everything above the box. I still want it to be as low as possible at the top of the tailgate, and I want the front facing profile to match the back of my cab.
Now I have come to consider the details. One of the things that just seems not quite right with Bondo, Sepp, and Fubecas builds are how the sides remain fairly vertical all the way to the back of the truck. This creates a large down sloping area on top of the cap, with long boundary areas on each side. Even in some of the tuft test images I've seen the side air wanting to roll up to the top. If this is generating a vortex or turbulent flow on the back corners, it is certainly an efficiency robbing problem. Even Bondo reports dirty air here. I’d be curious to see how paper party streamers (think “Just Married”, pop cans tied to strings optional) or longer strands of yarn would behave at highway speeds if they were taped to these designs on the top of the caps above the tail lights.
So, in my laying awake trying to combine things that I believe to be true, on image popped into my head. How do we taper in the sides? Keep the profile tight on the front? Try to account for the vortex generation on the corners? Certainly someone has thought of all this?
Enter:
So this is what I’m basing my design on. The air coming from the side window areas can taper into the center a foot or so along the side, this allows that air go where it wants to without having to leap over the edge to do it. Any vortex creation that tries to get started on the corners will be stopped dead be the horizontal triangle areas in the rear corner areas of the cap.
Obviously, since my need for downforce generation at high speed is nonexistent, the rear wing thinga mahjig has to go….maybe I could sell it on ebay.
My trick now is going to be in the production side of this. I really like Fubeca’s construction techniques. I have a similar set of woodworking tools. My only questions are how readily will the thin plywood will accept compound bending and how do I get the shrink wrap plastic to hold into the concave area where the horizontal triangle area meets the fastback hump?
I’m really not thinking at all about fiberglass because of the expense and my never having messed with it. I have been a builder for 9 years and am quite the finish carpenter so I think I’ll stick with the wood.
Has anyone tried to incorporate these ideas into an AeroCap before?
Does anyone have any other ideas on how to protect the wood?
Also, what did Fubeca use as a heat source to shrink the plastic?
I plan to make this as 1 piece and keep the weight down through engineering.
I’d add a LED strip 3rd tail light in the area under the tailgate and above the bumper to address any legal concerns regarding covering my 3rd stop light.
So, What do you think???? Any and all suggestions or comments at this point are welcome.