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Thin foam wings-how to spar?

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Thin foam wings-how to spar?

Old 01-31-2007, 04:10 PM
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wsmalley
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Default Thin foam wings-how to spar?

Any suggestions as to how to spar these thin wings. Each panel is 4' 2 3/4" long, 1 1/2" thickest point. Fuse weighs about 2 1/2 lbs. Figure all up weight about 8 lbs. I should add these are my first foam wings!
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Old 01-31-2007, 04:25 PM
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khodges
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Default RE: Thin foam wings-how to spar?

Can you find a source for carbon fiber tubing, or bar stock? A hobby store that sells high-performance kite stuff might have what you'd need. Something like 3/4 wide by1/8-3/16 thick, if imbedded in the foam core, should be plenty strong, along with the strength that the wing skin will add.

Is that a TR-1? Gonna look awesome. You gonna use the centerline main gear with wingtip bogies?
Old 01-31-2007, 05:38 PM
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Default RE: Thin foam wings-how to spar?

I'll check into the carbon fiber-hadn't thought about kites. Yes, a TR1, retract center line mains and steerable tail wheel. all scratch built. Started it long ago, in a far off place! Built it around a Turbax/Rossi, took that out, decided to build a Schreckling turbine-couldn't get that to run right-, decided to try an electric DF this time.
Old 02-01-2007, 08:43 PM
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Default RE: Thin foam wings-how to spar?

MikeSell and I used Kevlar fishing line to spar a 15-foot heavy lift wing, by making ply wing roots & tip caps, then grooving them at about 7 even intervals, and wrapping snugly with the line before glassing the wing. This would work fine with sheeting, also, is cheap, and weighs almost nothing. The wing was extremely rigid, even though we only used one layer of 1.5 oz cloth on the bottom, and two layers on top.
Old 02-01-2007, 10:10 PM
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Default RE: Thin foam wings-how to spar?

Interesting idea! I guess you used a single winding for each of the 7 loops. Did you put it under tension? What weight line? Bill
Old 02-02-2007, 10:17 AM
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Default RE: Thin foam wings-how to spar?

We used one continuous strand of 60-lb (I think, it might have been 40-lb) spiderwire, ca'd at each end. You don't want to make separate loops. The line has a kind of woven texture to it, so the epoxy can get a grip. We simply drew each strand slightly taut as we made each turn. The stuff has zero stretch, so the opposite surface of the wing gives tensile support to the bending moment, hence the double layer of glass we put on the top surface. We were adding (perhaps unnecessarily) some extra compressive strength to the surface we intended to put the most load on (perhaps as much as 40 lbs). I'm experimenting with a sailplane wing right now by using a continuous x-pattern of 15lb line to replace the shear webbing. It will either work, or saw through the ribs & spars on the hi-start...

You could PM MikeSell or Taylorcraft1947. They might have a pic or two. I took some, but gave them to them.
Old 02-02-2007, 12:18 PM
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Default RE: Thin foam wings-how to spar?

Thats gonna be a sharp looking plane, I like it. I'd never heard of a tr-1 before today.

Never thought about reinforceing a wing with fishing line.. Very cool.
Old 02-02-2007, 01:09 PM
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Default RE: Thin foam wings-how to spar?

Think of the TR1 as the 'stretch limo' of spy planes! As I recall the U2 didn't have convential main spars anyway. I wonder, however, if these big 'glider' wings need some flex-or do you think they should be rigid? Maybe that's a question to pose up in the 'aerodynamics' section.
Old 02-02-2007, 01:41 PM
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Default RE: Thin foam wings-how to spar?

Run 3 or 4 peices of strapping tape on the bottom of the wing. Works great and its easy.
Old 02-02-2007, 02:53 PM
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Default RE: Thin foam wings-how to spar?

Another idea I hadn't thought about!

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