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-   -   Looking for tips: unwarping a glider body (http://www.oldrocketforum.com/showthread.php?t=17638)

aeppel_cpm 12-20-2018 07:54 AM

I didn't remove the paper from the foamcore, some in some sense it's basswood-paper-foam-paper-basswood.

It's bowed so the middle arches away from the side against the rail during clamping. So the outer side is effectively slightly longer than the side against the rail. I'm wondering if I ran into some differential drying issue - the outer side drier faster?

I switched to laminating wing cores while I ponder the next step. For the wing cores, I'm using BSI 30 min epoxy and vacuum bagging - doing the bottom in one pass and the top in another. I left the paper on the lower side of the wing to help stabilize it - I find the foam warps all over if I take off both sides.

So far, they are behaving.

Jerry Irvine 12-20-2018 09:28 AM

I think we should overthink the problem. :D

aeppel_cpm 12-20-2018 09:40 AM

Anything worth doing is worth overdoing.

ghrocketman 12-20-2018 11:06 AM

Always use WAYYYYY more Epoxy than you think is required.
I prefer to build FLYING TANKS.
They almost never break upon landing.

Ez2cDave 12-20-2018 02:55 PM

Quote:
Originally Posted by Jerry Irvine
I think we should overthink the problem. :D


Hmm . . . Let's "underthink" it . . . Build a new fuselage !

Dave F.

Jerry Irvine 12-21-2018 03:59 PM

Correct.

aeppel_cpm 12-21-2018 09:13 PM

If I must, but Iíd like to have a better idea of what caused it, first.

Trying a counterbend tonight.

Ez2cDave 12-21-2018 11:25 PM

Quote:
Originally Posted by aeppel_cpm

How I did the body, clamped to a launch rail.


I have a theory as to what caused the warp . . .

In your pic, the fuselage is completely supported by the launch rail, on ONE side. HOWEVER, the clamps are providing uneven pressure ( at their contact points ).

As a result, they "pinch" the fuselage, likely compressing the foam core, and introduce a "pre-load" to one side of it.

I suspect that the 3rd clamp ( the Black one, 3rd from the left ) may be the "culprit", due to its location, although all uneven clamping pressure is the prime suspect.

Solution : When you build the next fuselage, use even support and clamping pressure on BOTH sides of it and make sure it is FULLY dried / cured before touching it.

Dave F.

aeppel_cpm 12-22-2018 08:16 AM

I think youíre on the right track - though the third clamp actually has the least grip. It must have a weaker spring. But the one sided part likely was the root cause. Since this was paper to wood, I used Titebond II. I suspect the moisture left at different rates on the two sides. If I ever do this again, Iíll try epoxy.

I tried an overnight bend. Wet with ammonia water, then clamp against the rail with a 1/8th spacer on the nose and a clamp on the tail and nothing between.

It worked. Iím putting the edge balsa on now.

Ez2cDave 12-22-2018 10:33 AM

Quote:
Originally Posted by aeppel_cpm
I think youíre on the right track - though the third clamp actually has the least grip. It must have a weaker spring. But the one sided part likely was the root cause. Since this was paper to wood, I used Titebond II. I suspect the moisture left at different rates on the two sides. If I ever do this again, Iíll try epoxy.

I tried an overnight bend. Wet with ammonia water, then clamp against the rail with a 1/8th spacer on the nose and a clamp on the tail and nothing between.

It worked. Iím putting the edge balsa on now.


Glad to hear you got it straightened out . . . Hope the glider flies well .

Merry Christmas !

Dave F.


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