Trebuchet03's JettKamm (2000 VW Jetta)

[trebuchet03]

So approximating 2 yd's of 50" wide cloth per layer... Minimum of two layers (top and bottom).

17oz biaxial weighs about 47oz. taking 50/50 resin/cloth ratio (and assuming 1fl.oz. of resin = 1oz by weight - assumption from the supplier), that's 94oz per layer - 188oz for two layers... Which is ~11.75lb in cloth/resin.

Add the weight of foam and glue which I'm estimating ~ 5lb. that brings me up to 16.75lb. Slightly over budget on my weight goal at a cost of $34 in cloth plus shipping.

If I move down to 12oz cloth - that's a weight of ~8.33 lbs - plus ~5lb in foam/glue -> $13lb... Which is within my target of >15lbs at a cost of $33 in cloth plus shipping.

BUT, 12oz cloth is disproportionally more expensive.... I'm wondering if I should "go for broke" with the heavier stuff. I feel either of these weights will be more than strong enough because of the geometry I'm forcing, but I'm not entirely sure....


My decisions analysis says....
Foam Template/Core - Biaxial cloth - Epoxy Resin....

This weekend I'm home for thanksgiving, then it's the week before finals.... Then it's finals week.... Then I go home for a month.... I need to see what my finals load is this semester - if it's not too bad, I might start building late next week. Worst case, a few weeks.....

I've settled on 18.25 degree profile taper.... Now I'm looking for an optimal bird's eye taper. It's proving difficult because of the angles the rear of my car presents. A small lip spoiler and some styling should help it "fit in" with the rest of the car. I'll have a 3d model of the Kamm soon, but I've got a "test" of sorts to study for at the moment

[Christ]

hence the reason I never build parts that have to be structural as a rule... I don't feel like figuring all that crap out, I just like brushing on the resin!

[trebuchet03]

Nah, this isn't structural It just needs to hold it's shape.... Well, I guess it needs to support a small amount of load where it hinges - but that's about it

[Christ]

Oh, in your weight analysis, did you count the moulded in mounting locations, etc.?

I would assume a nice delrin composite flange moulded between the two layers would be sufficient.

[trebuchet03]

Nope - I didn't include the weight loss from the windshield cutout plus the weight of the windshield itself.... I don't know what I'm doing for that just yet, so I can't speculate. Not 100% on the hinge part either, I need to mock up things first.

[Christ]

Just for kicks, you should run a quickie of the kamm with a 2 or 3* upturn not more than 3 inches out.

[wyatt]

I was looking at the "unique spoiler", and if you said with cfd it showed a net gain of about 2%... I wonder how much better (if any) it would do if there was a second spoiler inverted and added to the bottom bumper. The lift/downforce would offset each other, so you could shape the lower one different to keep the downforce if that's desired. Either way, you might be in the 4 or 5% gain area. In practice, these could be added to the sides of the car also to help just a little more (unless they blocked the brake lights too much). Something to think about.

[Christ]

I think I understand what you're saying, wyatt, but would really like to see some kind of sketch or something to make sure that I fully understand.

[wyatt]

I'll see if I can make one tomorrow... But you probably have it pretty well figured out.

[Christ]

I think I do, I just want to physically see that what's in my mind is what's on yours. It's better for me (And several others) to verify an idea by seeing it.