vjarnot

What's minimal? Got any tips?

Thanks.

Antonov

7-8mm strip in the foam core, few layers wet layup/vacuum bag

mikegarrison

Foam core isn't used a whole lot in aeronautics, because its strength-to-weight ratio is not as good as a semi-monocoque design. But in this case, it's not likely to end up being a significant difference.

mikegarrison

ps. Jack, what was the thickness of the aluminum you used for your skin?

JackOlsen

c32b, Thanks. Unfortunately, I don't know what the APR lip is. My splitter would be lower in a perfect world, but it's as low as I can make it with my body roll and the height of most track berms. I tried flexible curtains coming down even lower on a previous iteration, but they would just get ground off in real world use. It's not perfect, but for really effective underbody aero you need super-stiff (like 2000#) springs.

petawabit, that is the flag station in turn 4 at Willow. Luckily, I didn't hit the concrete or anything else in that spin.

vjarnot, please keep this thread updated with any progress you make on using the foam insulation. I'm interested in trying to make a wing with that stuff.

The airfoil I went with:



I built it so that it could come apart into two pieces and fit inside the car for the drive to the track:




More details:



Construction:

A - Ribs are Alloy 3003 .02 inch, folded over to 3/4 inch tabs

B - Anchor rib: Alloy 6061 .9mm
Rear leg doubled up with same material
Front leg doubled up with 1.1 mm by 3/4 inch bar, L-shaped to meet up with 1/2 tube, secured with clamp and glue

C - Spars are 35" each Alloy 6061 T-Section 5/8" X 1/2" X 1/20" Thk
Spars are bridged with 4" rectangles of Alloy 3003 .02 inch

D - Main tube is Alloy 38.5" 6063 .625" Od, .527" Id,
with inserted 36" Alloy 6063 .500" Od, .370" Id

E - Rear tube is 14" 6063 .625" Od, .527" Id,
with inserted 7.5" Alloy 6063 .500" Od, .370" Id

F - Skin is '0.86 gauge' Aluminum flashing material

Also:

Gurney lip is made with 35" each 1/2-inch L-shaped Alloy 6063 1/16" thick

Where tubes meet ribs, the junction is reinforced with a snap-on piece of PVC pipe, about 1/3-1/2 inch, secured all around with adhesive.


What I would (will) do different next time? The core of my wing's strength is two-fold. The I-beam that runs the length of it provides its rigidity, and next time I might use thicker aluminum between the top and lower T-shaped pieces, maybe reinforcing those with rivets. The 'anchor' of the whole thing is a path that goes from one upright, to the cross tube, and back to the other upright. This is the part that shouldn't fail even if the wing kinks and bends. Next time, I may do two complete tubes to double this strength.

Also, the aluminum I'm using for the skin is probably too thin. I love that it's light (and was cheap, since it's roofing flashing ($40 for 50 feet of 24-inch wide aluminum). It's not a structural problem, since it's strong. But it dents too easily -- almost like fabric on the old biplanes.

No flutter or resonance problems that I've been able to detect.

innovation

its like building the airplane wings but for a car

mikegarrison

Thanks Jack. I'm working on a wing design of my own, but I was thinking of using thicker aluminum for the skin. I didn't know how thin I could get away with.

Thicker aluminum is going to be more costly and harder to bend. Should be stronger and (I hadn't thought too much about this) more resistant to denting.

It may end up depending on what I can find.

JackOlsen

If you want a sample of the stuff I'm using, I'd be happy to send you some. Its light weight is great, but rock hits leave marks on it. If vjarnot is able to get those Texas foam cutters to make a wing for him, then I'd think the flashing material would make a nice skin to put over the foam.

vjarnot, let us know if you move forward with those guys. I'm still interested in seeing how that type of design could be made to work.

mikegarrison

If the flashing material is cheap enough, you can always just reskin the wing every so often, unless the design is such that it's a real PITA.

vjarnot

[QUOTE=JackOlsen,Jul 9 2008, 04:29 PM]If vjarnot is able to get those Texas foam cutters to make a wing for him, then I'd think the flashing material would make a nice skin to put over the foam.

vjarnot, let us know if you move forward with those guys.