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  #1  
Old 12-18-2018, 09:30 PM
aeppel_cpm aeppel_cpm is offline
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Default Looking for tips: unwarping a glider body

I’m working on a 2.28x Tercel, and I’ve noticed the body has picked up a bend.



It’s a 3mm bend.

The construction is basswood over foamcore. I’m planning on capping the laminate with balsa. I’ve only done the nose so far.

Any suggestions for straightening this thing out?
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  #2  
Old 12-18-2018, 11:06 PM
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Jerry Irvine Jerry Irvine is offline
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Moisture and a press/books. If it turns in flight that is a good thing and requires less wing clay.

Just Jerry
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Old 12-18-2018, 11:46 PM
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Another option is a heat gun. It works well, with moisture, to get parts straight. If clamping is difficult, you may even be able to hold it for a few minutes in the correct position long enough for cooling to cause it to set in its new position.

If you don’t have a heat gun, you can get them for as little as $10 at Harbor Freight, using a 20% off coupon.
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Old 05-04-2019, 02:38 PM
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Quote:
Originally Posted by LeeR
Another option is a heat gun. It works well, with moisture, to get parts straight. If clamping is difficult, you may even be able to hold it for a few minutes in the correct position long enough for cooling to cause it to set in its new position.

If you don’t have a heat gun, you can get them for as little as $10 at Harbor Freight, using a 20% off coupon.
Yes--model HLG (Hand-Launched Glider) and catapult glider books recommend using the hot steam (which is really hot water vapor--the true steam is the narrow, invisible portion of the plume closest to a spout) from a tea kettle's spout, combined with gently bending (or twisting, if that's the problem) a warped balsa or basswood part in the direction opposite the warp, until it is straight. (*Deliberately* steam-warping fins has also been recommended for clustered-motor models, to induce a little spin--which evens out slight thrust line misalignments and/or thrust variations between the motors--during powered ascent.) Also:

Stove-top--for gas or electric stoves--tea kettles with narrow-aperture, whistling spout lids (which are opened for pouring out the hot water using an included finger "trigger" on the kettle handle) provide a narrow stream of steam and (above the steam) hot water vapor, which is ideal for such work. If the area of warpage is larger, the stream from the kettle is wider farther from the whistle aperture; one can use whatever height above the aperture that "blankets" the warped area. If the warp is very long, it can be 'steamed and straightened' in sections, until the entire warp is straightened out.
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  #5  
Old 12-19-2018, 12:15 AM
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Quote:
Originally Posted by Jerry Irvine
Moisture and a press/books. If it turns in flight that is a good thing and requires less wing clay.

Just Jerry



I'm concerned that it might "spiral" or "corkscrew", during boost.

Dave F.
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  #6  
Old 12-19-2018, 08:40 AM
aeppel_cpm aeppel_cpm is offline
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Quote:
Originally Posted by Ez2cDave
I'm concerned that it might "spiral" or "corkscrew", during boost.

Dave F.


I'm also more concerned about boost than glide.

Thanks for the suggestions, gents. I'm hoping the capping - turning the laminate into a box - will help stabilize it - but I'd like to get it straight first. I'll try heat before moisture, as I suspect moisture got me into this pickle in the first place. Laminated with TBII.

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


And the capping around the nose. 1/32” balsa, ammonia shaped.
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Old 12-19-2018, 10:02 AM
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If you moisten wood with ammonia water (Ajax, BoPeep, etc) the wood flexes much easier than with plain water.
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Old 12-19-2018, 09:37 PM
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Quote:
Originally Posted by ghrocketman
If you moisten wood with ammonia water (Ajax, BoPeep, etc) the wood flexes much easier than with plain water.




The use of Ammonia & Water would work on an all wood fuselage, but he used a foam "core" for the fuselage, with Basswood sides bonded to the foam.

On an all-wood fuselage, Steam could also be used, but I am concerned about how the foam might react to the heat.

I'm wondering if the warping was either caused by a reaction between the foam and the adhesive used or if the fuselage was un-clamped too soon, before it had fully dried / cured .

Dave F.
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Old 12-21-2018, 11:25 PM
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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.
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  #10  
Old 12-22-2018, 08:16 AM
aeppel_cpm aeppel_cpm is offline
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I think you’re 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, I’ll 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. I’m putting the edge balsa on now.
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