To Kamm or not to Kamm...that is the question

[hat_man]

I have started my aerocap and the frame is done. It is changeable at this time and I have another question.

I have seen these Kammbacks on other vehicles. I assume they are to help get a cleaner air separation at the rear. With my cap being vertical and nearly flush with the tailgate (red line), could I benefit from adding something like this (green line) at the tail end of my cap? Or does the cap in general constitute a Kammback and maybe add nothing.

It was just a thought and wouldn't be all that hard to add if I would see any more benefit. Or if the benefit is too small maybe it's not worth doing?

[Xist]

As long as you follow the template, the longer the better, although you receive diminishing returns.

[mikeyjd]

Originally Posted by Xist

As long as you follow the template, the longer the better, although you receive diminishing returns

Agreed and fixed . There is a graph somewhere showing the diminishing returns to give you a better idea of what length to aim for to best suit your needs.

[ChazInMT]

Uh, Yeah, No. Longer is good, but if you're overhanging it could be problematic. Unless you plan to extend the whole thing down to the bumper like a8ksh4 did on his Taco, I wouldn't go any further than you have it now. I think those little spoiler kamm things you mention are meant to ensure a clean separation of the air, just an abrupt 77° thing you have going now at the back will work great, no need for a spoiler thing unless you like it cosmetically, but I wouldn't go more than 3 inches or so with it.

[freebeard]

The full bellypan and wheel spats should come first.

[hat_man]

Thanks for the info everyone. I think I will just leave it alone for now. Sometimes I get to fiddling with stuff and end up taking a good project and hurting it.

While I do agree that a full belly would be very beneficial, that's a bit of work. I am hoping to see pretty good gains from this cap and it was easier to fab up than I think a belly pan would be. As for spats, I don't think the gains I would see from them would be as great as the cap is hopefully going to be. But hey, what do I know. I haven't researched a belly pan yet. I have plans for a 2"-3" drop in the front and a 4" drop in the rear. That coupled with a larger airdam might negate the need for a belly pan. That is in the future though. I am contemplating wheel arch gap fillers and some form of pizza pan covers or something similar, but for now I have to get the cap finished.

I tried to find a thread on here for the process of tuft testing this cap. Is there a set of "rules" to do this or is it something like place 6" pieces of yarn equally spaced at 8" intervals all over the cap then drive and film?

This has been a fun project so far and I am happy that the shape has been so well received. But it is no where near complete and I have to figure out how to skin it yet. I have some ideas but I want to try them on a smaller basis and then see if they will work for the entire cap.

[freebeard]

While I do agree that a full belly would be very beneficial, that's a bit of work.

You get my point. There's a lot you can do before you get down to that fine tuning. The rest of the ¶ shows you have a handle on the issues.

...tuft testing this cap. Is there a set of "rules" to do this...

One thread had the poster using a bigger square of paint friendly tape and a smaller square of something to hold the yarn to the first piece. I'd add—that could be hot melt glue before you cut a strip of tape into squares.

...and only half the cap needs to be tufted. A grid is a good start, but if you suspect separation, or worse—backflow, use longer yarns. A reconfigurable boom that gives a top rear view means you don't need a chase vehicle, although you could use one as well.

I'd skin it with Polymetal. Think strong as 5/8 plywood and light as coroplast. I haven't done a whole project with it, but I have tested samples. I could shear and roll it, but to brake an edge, I think you'd have to crush it along the line first. A 4x8' sheet is approx. $100 wholesale and $150 retail.

[Xist]

What about shorter tufts on one side and longer on the other?

[ECONORAM]

Originally Posted by freebeard

The full bellypan and wheel spats should come first.

Why is that? I don't understand the order of precedence. Bigger returns on investment or effort?

[freebeard]

I left off the

Marginal gain. It's at the end of a long smooth curve.

The aerocap is the thing that gives the greatest gain. On a pickup the underbody comes next. Time and effort would be better spent on the rear view mirrors.

All IMHO, of course.

Maybe this would be more apropos: