Another warped fin fixit question, Bow up or Down?

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El Cheapo

El Cheapo

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I've been working on and off on a 1.33 Mercury Invader up-scale for my daughter. The fins are 3/16 balsa laminated with Xmas gift box material. They're amazingly light and strong. Total combined weight of all four is 2.4oz.

Either in the process of laminating or the time they have not been under weight or installed on the airframe, two have developed a slight bow. As suggested in another post, I'm going to try wetting them out with an ammonia based product (Windex) and allow to dry. I've got a special treat over and above my usual 1989 Suburban brake rotor. These little biscuits are going to get the rotor and an bare 4cyl head I've got lying around.

So the question is does the bow go up or down?

I'm not sure if you can even tell by the pics but here they are.

Thanks as always

IMAG0132.jpg

IMAG0133.jpg

IMAG0134.jpg

IMAG0135.jpg
 
Are you stacking them on top of each other? OR are you pressing one at a time?
 
El Cheapo said:
I've been working on and off on a 1.33 Mercury Invader up-scale for my daughter. The fins are 3/16 balsa laminated with Xmas gift box material. They're amazingly light and strong. Total combined weight of all four is 2.4oz.

Either in the process of laminating or the time they have not been under weight or installed on the airframe, two have developed a slight bow. As suggested in another post, I'm going to try wetting them out with an ammonia based product (Windex) and allow to dry. I've got a special treat over and above my usual 1989 Suburban brake rotor. These little biscuits are going to get the rotor and an bare 4cyl head I've got lying around.

So the question is does the bow go up or down?

I'm not sure if you can even tell by the pics but here they are.

Thanks as always
Click to expand...


Is this a trick question?
Are we going to be tested on this later?

I can't see that it would make any difference, since the same amount of pressure is going to be applied reguardless of their orientation to a flat surface.
 
When I did the laminate, they were set next to eachother, snug as a bug in a rug but not stacked one on top of the other.


bradycros said:
Is this a trick question?
Are we going to be tested on this later?

I can't see that it would make any difference, since the same amount of pressure is going to be applied reguardless of their orientation to a flat surface.
Click to expand...

Nah, no test. I think it might have something to do with reversing the spring, bow, memory or however you put it.

I'm not sure it matters either but I've heard to put the bow this way or that and just can't remember so I figured I'd give it a try because I really don't want to have to re-cut these. This rocket has 2.6" interchangeable mount and will fly on single 24mm APCP, dual BP/APCP, triple bp, quad bp as well as 29mm. I really don't want it ripping itself apart if it starts to spin too aggressively on a little H motor. I don't think it could handle much more than an H-128 or H-165. Just have to wait and see.
 
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This is dry fit next to its little sister. Picture is from around Xmas time. Tells you how long its been in the "crap I have to finish this pile". This one will be called Kat's Growl with the same Gum Drop Krylon and up-scaled vinyl from Stickershock.


picture.php
 
El Cheapo said:
When I did the laminate, they were set next to eachother, snug as a bug in a rug but not stacked one on top of the other.




Nah, no test. I think it might have something to do with reversing the spring, bow, memory or however you put it.

I'm not sure it matters either but I've heard to put the bow this way or that and just can't remember so I figured I'd give it a try because I really don't want to have to re-cut these. This rocket has 2.6" interchangeable mount and will fly on single 24mm APCP, dual BP/APCP, triple bp, quad bp as well as 29mm. I really don't want it ripping itself apart if it starts to spin too aggressively on a little H motor. I don't think it could handle much more than an H-128 or H-165. Just have to wait and see.
Click to expand...


When a piece of wood is warped, one side has contracted and the other side has streched. Soaking the wood with a 4:1 solution of water to ammonia causes the fibers of the wood to expand and relax. As the water/ammonia solution slowly evaporates the wood fibers go back to their natural state of stiffness. Between a rock and a hard place there is nothing the wood fins can do but dry out flat.

Again, I can't see that it would make any difference, since the same amount of pressure is going to be applied reguardless of their orientation to a flat surface.

Seal them after you get them flat again.
 
The problem is I can't exactly soak them as it'll delaminate the delamination and that would put a serious hitch in my giddy-up :horse:

I was thinking of wiping on enough to dampen the laminate material but not enough to make it come apart. maybe even set between dampened paper towels while weighted?
 
El Cheapo said:
The problem is I can't exactly soak them as it'll delaminate the delamination and that would put a serious hitch in my giddy-up :horse:

I was thinking of wiping on enough to dampen the laminate material but not enough to make it come apart. maybe even set between dampened paper towels while weighted?
Click to expand...


Murphy's Law:

If it breaks while your trying to fix it, it needed replacing anyways.


I'm not suggesting you soak them over night. But the solution needs to penetrate the wood fibers, a few minutes soaking will probly do the trick. The cardboard is going to be under the same pressure as the wood and dry flat. The wood glue used for the lamination will dry out and be as good as new.

The problem I see is the cardboard sticking to the surfaces it's being pressed with. To avoid that I'd use a small sheet of plastic wrap so the cardborad has nothing to stick to. Remember, moisture still needs to escape. Use only enough plastic to cover the cardboard.

The edges of the cardboard might come out wonky, but wood filler, a file and sand paper should fix that.

If that doesn't work, remember Murphy's Law.
 
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The edges have all been sealed with CA so they should be fine. I have always used wax paper to keep things from sticking. Never thought of using cling wrap, cellophane or whatever one calls it. Thanks for the tips, Ill give it a whirl and let it set under weight for a good week.
 
El Cheapo said:
The edges have all been sealed with CA so they should be fine. I have always used wax paper to keep things from sticking. Never thought of using cling wrap, cellophane or whatever one calls it. Thanks for the tips, Ill give it a whirl and let it set under weight for a good week.
Click to expand...


Let us know how "Project Sqwish It" turns out.
 
How long ya think I should weight. Typically I let a laminate dry for 48 hours but that's not soaking the whole fin. This evening will be five days. I've also heard from someone on here to relieve some of the pressure but not all for around 24 hours to let it relax a bit to avoid it from snapping back to shape.
 
El Cheapo said:
How long ya think I should weight. Typically I let a laminate dry for 48 hours but that's not soaking the whole fin. This evening will be five days. I've also heard from someone on here to relieve some of the pressure but not all for around 24 hours to let it relax a bit to avoid it from snapping back to shape.
Click to expand...


I think the wait is over. Lets see what ya got.

I can't think of any reason to relive some pressure.

Was any explanation or facts given as to why?
 
the reason was if there was any memory left in the wood to avoid it from springing back to shape if all the weight/pressure was relieved at one time.

I'm going to put them back under weight regardless because I won't be able to put the fins on in the next day or so. I'm just curious. I've got a fuel pump to put in first. Oh, Joy!!!! :rolleyes:
 
El Cheapo said:
the reason was if there was any memory left in the wood to avoid it from springing back to shape if all the weight/pressure was relieved at one time.

QUOTE]


Well... I don't belive that none. That's what the ammonia solution and pressure were for, to work their mojo on the memory in the wood!

Are you gonna tell us if their flat?
Click to expand...
 
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Copy that.

Curiosity got the best of me. All fins came out great except the tip on the forward leading edge has a bit of a bow in it. I think I can get the fin mounted to the central 2.6" with fillets and then tack that forward tip in place with a medium weight CA to get her all lined up. Surprising to me is the laminate remained very smooth with no wrinkles.
 
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the law of flat paper lamination fins .... avoid glues that "shrink" when they dry
 
El Cheapo said:
Copy that.

Curiosity got the best of me. All fins came out great except the tip on the forward leading edge has a bit of a bow in it. I think I can get the fin mounted to the central 2.6" with fillets and then tack that forward tip in place with a medium weight CA to get her all lined up. Surprising to me is the laminate remained very smooth with no wrinkles.
Click to expand...


You can do them again if you want. Move on from "Project Sqwish It" and camense "Operation Sqwash It".
 
Lol...they're back under weight until I can get them mounted. Thanks for the help.
 

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