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spar placement in a foam wing?

Old 03-16-2010, 05:50 PM
  #1  
Popriv
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Default spar placement in a foam wing?

Cutting another wing and still questioning the best way to add spars.

Here is what I've tried so far.
I made the spars from a select pine board. ripped down to about 1/4" x 3/8" x 6' long.

The pink wing has a long spa cut on top. Right about on the CG. it stops about 5" from the wing tips. It also has a 16" spar cut in on the bottom. I thought this would be to weak but I've flown it and it held up to easy flying. this wing with servo = 1.14lb

The middle blue wing is heavy. I cut 2.5" back from the LE of each wing half and splice in 1/4" pine and glued the LE back on. ( so these spars do not cross the wing joint in the middle) Then I joined the two halfs with a 18 inch spar on the bottom. This made the wing very stiff. its also a little bigger. this wing with servo = 1.68lb

Now I have a 3rd wing and wondering whats best....

I's a little flex a good thing?

I've looked at the 3/16" fiberglass driveway marker rods but they are only 4' long.. is that enough? also the pine is lighter..

I'm thinking 1/4" x 3/8" pine, cut into the bottom, around the CG, the full length of the wing....thats it.. I do have some light fibergass strips wrapped around the wing joint.. Keep it light till it fails then go stronger???

steve
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Old 03-17-2010, 11:03 AM
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Lnewqban
 
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Default RE: spar placement in a foam wing?

Not exactly what you ask, but check these out:

http://www.charlesriverrc.org/articl...ersheeting.htm

http://www.charlesriverrc.org/articles/supra/supra.htm

http://charlesriverrc.org/articles/d...rengthcalc.htm

http://charlesriverrc.org/articles_foam_vac.htm

http://charlesriverrc.org/articles/c...webcutting.pdf
Old 03-17-2010, 11:31 PM
  #3  
Crash Campbell
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Default RE: spar placement in a foam wing?

Hi Steve,

From the image these appear to be one piece wings? If so you can get by without a spar. Cover the blue foam in epoxy and micro baloons then lay on two layers of light cloth with the weave in the first layer at about 33degrees to the span and the second layer the reciprocal angle of the first layer. This makes an incredibly light and very rigid composite structure. If the wing is in two pieces joined to the fuse by a spar it should be on the CofG and around half the length of the span, CF tube is ideal for this purpose. Adjustable pins at the leading and trailing edges will help to tweak the incidence and confirm the alignment.

Cheers,

Colin

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