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

aeppel_cpm 12-18-2018 09:30 PM

Looking for tips: unwarping a glider body
 
Iím working on a 2.28x Tercel, and Iíve noticed the body has picked up a bend.



Itís a 3mm bend.

The construction is basswood over foamcore. Iím planning on capping the laminate with balsa. Iíve only done the nose so far.

Any suggestions for straightening this thing out?

Jerry Irvine 12-18-2018 11:06 PM

Moisture and a press/books. If it turns in flight that is a good thing and requires less wing clay.

Just Jerry

LeeR 12-18-2018 11:46 PM

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 donít have a heat gun, you can get them for as little as $10 at Harbor Freight, using a 20% off coupon.

Ez2cDave 12-19-2018 12:15 AM

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.

astronwolf 12-19-2018 05:21 AM

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.

This. I'll add patience to that.

Maybe if you used something to anchor the glider to your work table in the position shown in the photo, like a book or somekind of weight. Use a rubber band to deflect the boom aft of the wing's trailing edge so that it's straight. You'll have to rig something up to do this. Moisten the boom in the area just aft of the trailing edge of the wing. Don't get the wing wet. Allow to dry overnight, and check for straightness the next day. Repeat if necessary.

aeppel_cpm 12-19-2018 08:40 AM

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. 1/32Ē balsa, ammonia shaped.

ghrocketman 12-19-2018 10:02 AM

If you moisten wood with ammonia water (Ajax, BoPeep, etc) the wood flexes much easier than with plain water.

Ez2cDave 12-19-2018 09:37 PM

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.

ghrocketman 12-19-2018 10:23 PM

I don't think ammonia would attack any foam.

Ez2cDave 12-19-2018 11:43 PM

Quote:
Originally Posted by ghrocketman
I don't think ammonia would attack any foam.


I wasn't thinking about the Ammonia attacking the foam. I was thinking that since the wood was bonded to the foam, the Ammonia would only penetrate the wood and, as a result, not allow the wood to remain straightened if the foam is causing the warping.

Dave F.

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.

aeppel_cpm 12-22-2018 02:27 PM

Do you fly at Bong? It will likely fly there.

aeppel_cpm 01-29-2019 08:18 AM

Some update pictures. I will countersink and cover the nose weights eventually.




Ez2cDave 01-29-2019 10:40 AM

Looking good . . . When is the first test flight going to happen ?

Dave F.

aeppel_cpm 04-08-2019 08:03 PM

I guess I built too heavy. I can't get her to glide in hand-toss testing. She just flops. Doesn't seem to be unbalanced - just doesn't fly.

Ez2cDave 04-08-2019 10:38 PM

Quote:
Originally Posted by aeppel_cpm
I guess I built too heavy. I can't get her to glide in hand-toss testing. She just flops. Doesn't seem to be unbalanced - just doesn't fly.


Can you shoot some video of what's going on ?

It could be diving, stalling, or "mushing" . . . There might be a wing loading problem ( too heavy) or an "incidence" ( alignment ) problem involved.

Dave F.

aeppel_cpm 04-09-2019 11:30 AM

I'll think about it Dave, maybe I won't give up just yet. I went looking for my wing loading notes, but I can't find them. I'll re-estimate and re-weight and post. Because it may be too heavy to be worth the effort. I thought I was ending up in Estes Sweet V territory, but I might have miscalculated.

I think it's neither diving, nor stalling. (Had to think about the grammar I wanted for a second.) It looks like it has a left yaw that I wasn't able to trim out. Could be that blasted warp. And a left roll. I'll have to revisit the left-right balance (I was focused on the Cg previously) or maybe use clay (eek, more weight) if there is a dLift/dY. And, now that I've looked it up, I think 'mushing' is a good description of what it was doing.

Ez2cDave 04-09-2019 11:58 AM

Charles,

Here is more about "mushing" . . .

https://aviation.stackexchange.com/...a-mushing-glide

Dave F.

aeppel_cpm 04-09-2019 12:02 PM

Yes, I found that article, too.

jetlag 04-09-2019 02:53 PM

Charles,
I balance all my airplanes a bit nose heavy; slight nose heavy is your friend!
R/C, glider, sailplane, boost glider all get the following treatment:

I find the recommended cg location and screw in a small screw eye dead center (left-right) at that point. Then, I hang the model from a string. This way, one can see left/right as well as front/rear balance in one easy step. Adjust counterbalance as needed.
Never fails.
With the warpage, you may then need to build in some aileron influence. Sometimes, a stiff piece of tape to one wing to make an aileron is all that's needed. Just trim the tape to get desired effect/influence.
I suspect your glider to be tail heavy, too. I'd bet a $1 on it!
Do the balance first, then see how she does. You might be pleasantly surprised!

Pretty glider! Looks like a great finish!
Allen

ghrocketman 04-09-2019 04:26 PM

+1 for placing a bet on "tail heavy".
Roll can be balance or warp related.
Yaw is usually caused by fin/rudder misalignment, but could be due to an extreme tail heavy condition or not enough rudder/fin area.

aeppel_cpm 04-09-2019 06:01 PM

Okay:
Mass = 200g
Wing area ~110 sq. in.

Here's the fore-aft balance, suspended from the CG in the Tercel instructions. It's upside down, but still a little tail heavy.



And here's the left right balance after a repair to the wing attachment. It looks to me like the wing isn't on the fuselage square. I'm going to redo that.


ghrocketman 04-09-2019 06:34 PM

That's quite a bit tail heavy.
Always error on the opposite of that. If it was nose-down that much it would probably glide, albeit fast.

Ez2cDave 04-09-2019 07:57 PM

9 Attachment(s)
Useful information . . .

aeppel_cpm 04-09-2019 08:17 PM

I'm at ~9 oz.sq ft, when it looks like hand toss gliders are under 2. I wonder if it's worth trying to save.

jetlag 04-09-2019 08:29 PM

Absolutely!
It will just set up in a fast glide, but you can still get an exceptional sink rate. Fix the tail heavy state, go slightly nose heavy, and it will fly.

Allen

tbzep 04-10-2019 08:59 AM

Quote:
Originally Posted by ghrocketman
+1 for placing a bet on "tail heavy".
Roll can be balance or warp related.
Yaw is usually caused by fin/rudder misalignment, but could be due to an extreme tail heavy condition or not enough rudder/fin area.

Pitch/Yaw can be due to off axis thrust with regular rockets, and once I got my hands on a good DSLR I found that off axis thrust is extremely common. It might be a factor on rear engine boost gliders also, but probably not as much on a front mounted motor. After burnout, it would cease to have any effect anyway, and that's the majority of the ascent with most models.

ghrocketman 04-10-2019 11:53 AM

The OP stated these were hand tosses.
It wasn't yawing under power.

tbzep 04-10-2019 12:14 PM

Quote:
Originally Posted by ghrocketman
The OP stated these were hand tosses.
It wasn't yawing under power.

10-4. I think I mention it would really affect his model anyway. ;)

aeppel_cpm 04-10-2019 12:29 PM

I did check to see if the earlier warp had returned, and it hasn't. The fuselage is still straight.

We're in for a few days of crappy weather, so I won't be able to make much progress for a while.

I'm thinking that I'll go out to the range on an off weekend and do a test flight before flying at a club launch.

aeppel_cpm 04-21-2019 07:28 AM

Ok,
12g of additional nose weight and 7g on the right wing tip and I can get level, if not great, glides.

Hanging from the frame, she looks left-right balanced. I must have accidentally made the aerofoil unsymmetrical to have such a large left roll.

On to test launches.


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