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  #11  
Old 03-17-2017, 06:14 AM
BillL BillL is offline
 
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Quote:
Originally Posted by Electrogunner View Post
It is attached with hinges. Per the advice I think I will do a layup on the inside across the widest area to stiffen it up a bit. Thanks all for the advice and ideas.
Without some core material, it will not be very satisfying. Painting on resin does nothing. One layer of glass is difficult to measure. 2mm Soric and one layer of glass is dramatic. If the price of Soric is too much, take 1/4" thick pink styrofoam and make a strip with it. That work just fine. Even 2" wide. Also dramatic. Cut some triangles 1/2" on a side, get some depth. There is a reason floor joists are placed on edge and not flat.
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Last edited by BillL : 03-17-2017 at 06:18 AM.
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  #12  
Old 03-17-2017, 08:55 AM
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erich weaver erich weaver is offline
 
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Quote:
Originally Posted by BillL View Post
Without some core material, it will not be very satisfying.
One layer of glass is difficult to measure.
I can assure you that one ply of FG is both easily measured and adds considerable stiffness to the wing tips. I know because I did it. If even more rigidity is desired, add a 2nd ply, but I didn't find it necessary.

Erich
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  #13  
Old 03-17-2017, 09:54 AM
Bill Boyd Bill Boyd is offline
 
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Is this an application where carbon fiber would be useful?

Obviously not where antennas will reside in wingtips, but otherwise?
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Last edited by Bill Boyd : 03-17-2017 at 10:12 AM.
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  #14  
Old 03-17-2017, 10:04 AM
BillL BillL is offline
 
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Quote:
Originally Posted by erich weaver View Post
I can assure you that one ply of FG is both easily measured and adds considerable stiffness to the wing tips. I know because I did it. If even more rigidity is desired, add a 2nd ply, but I didn't find it necessary.

Erich
Good to know, I only did the bench test. It was with 4 layers 8 oz, then 2-core-2 in the photo. I later did a 2-core-1 test that "seemed" as stiff as the 2-core-2, but only tested it for strength. The 2-C-1 piece was cut to expose the core to see if it would fail in shear, it didn't. Also, the pict was an infused piece. I got the Soric for plenum covers.


It seems the tips may only have a couple of glass layers, at least from my measurements the rest is gel coat. So, if a single layer works excellent! If more stiffness is desired a core will give much greater stiffness per oz, but it also has weight, probably equal to another glass layer. All in the expectations, I suppose.

Edit: Lets add some numbers. Deflection is inversely proportional to the moment of inertia. 2 layers of 8 oz is about .020", 3 is .030" So, one additional layer - Proportionally 1.5X^4 ~5X stiffer. With a 2mm core .020 becomes .070 thick and ~150X stiffer. Conclusion: 5 is pretty good (but not for a plenum)
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Last edited by BillL : 03-17-2017 at 10:19 AM. Reason: more definitive comparison.
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  #15  
Old 03-18-2017, 09:39 PM
bob888 bob888 is offline
 
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Did you have a problem with the surface of the wingtip deforming at all when you stiffened it with the layer of bid glass? Is one layer enough, or would you do more if you had it to do over? Thanks for your advice as I'm also concerned about the flexing after paint.
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  #16  
Old 03-18-2017, 10:20 PM
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No deformation at all. Not sure why that's a concern.
One ply was adequate for my -7a tips

Erich
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  #17  
Old 03-19-2017, 05:31 AM
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Steve Melton Steve Melton is offline
 
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a guy leaned on my wing tip early on and "pow", a big delamination. I repaired it by removing the delaminated material and adding big pieces of glass to stiffen it. then I added the same to the other side. I added the glass an then immediately attached it to the wing tip to cure. no deformation.
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