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  #1  
Old 09-29-2019, 11:24 PM
vulcanitebill vulcanitebill is offline
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Default fin grain direction / fin paper

I've been in rockets for a long time and the conventional wisdom was always for the grain direction of the balsa to be parallel to the leading edge of the fin. I never questioned this until now. I'm building a HiFlyer XL (because I found a pack of D12-7 in my gear!). The HiFlyer XL has long narrow triangular fins so the fin grain ends up almost parallel to the fin root. Well I'm not a structural engineer for real (a rocket scientist just for fun) and since the fin is trying to cantilever from the fin root, the fin grain should be more perpendicular to the fin root and not parallel to the leading edge.

Balsa is pretty weak in bending perpendicular to the grain direction, and since I couldn't re-cut the fins I came up with another idea. I papered the fins to give more strength in bending in that direction.

Papering is a whole nother subject. I've done it before and I've watched people do it on youtube. I put wood glue on the fins with a small paintbrush, then stuck on the paper. The paper sucks moisture out of the glue and wants to swell and wrinkle. I rubbed down some of the wrinkles with a putty knife and then flattened the fins with a heavy piece of tile. The few remaining wrinkles I will cover up with fill n finish. I had the idea afterwards that if I had somehow moistened the paper first I would not have had the wrinkle problem. Maybe hold the paper in front of a steam iron for a few seconds. If I do papering again I might try this.
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  #2  
Old 09-29-2019, 11:37 PM
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LeeR LeeR is online now
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Lots of ways to paper fins, but I use 65lb. cardstock (feels like heavy typing/printer paper). I brush fins with Mod Podge, then apply paper and press this sandwich between glass plate for 24 hours to prevent any warping. Use a few heavy books for weight on the glass to keep them flat and wrinkle-free.
If I want tapers on leading edge, I sand balsa tapers, and use a one-piece fin cover folded at the leading edge.
My covers are cut slightly oversized and I trim once they are removed from glass press.
I seal paper edges with thin CA to prevent lifting.
Then glue to body tube, fillet as usual, and prime and paint as usual.
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Old 09-30-2019, 04:23 AM
Scott_650 Scott_650 is offline
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Iíve never used wood glue to paper fins - believe it or not my go to glue for papering is Elmerís School Glue. Lay down a bead, spread with on old credit card, lay on the paper, use a clean card to smooth out the paper, layer between a couple of dollar store plastic cutting boards then weight with as big a stack of books as you can. Let things rest that way for a day or two until dry, trim/sand the edges clean, touch up any loose edge spots as needed. Sealing with thin CA is a good option but sometimes I forget until after I already primed so that doesnít always happen. Iíve been papering my fins almost since I started my time as a BAR - going on ten years now...geez Iím old
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Old 09-30-2019, 08:47 AM
jetlag jetlag is offline
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All the papering jobs I've seen look like crap. There is no substitute for the old fashioned fill/sand method for a beautiful, long lasting finish. By the time one papers properly, one could have done it the right way in the first place. Papering doesn't like direct sunlight (heat), and it gets crappier looking with age. It adds very little strength. You want strength, wick CA into the woodgrain and sand, or use basswood. Don't give in to easy...it'll look like it!
Allen
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Old 09-30-2019, 10:25 AM
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ghrocketman ghrocketman is offline
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Agree with Jetlag.
Papering fins looks like crap...ALWAYS and is a cheap/quick lousy substitute for PROPERLY finishing balsa.
If you don't want to fill balsa in the traditional way on fins, use R/C aircraft MonoKote/Ultracote.
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  #6  
Old 09-30-2019, 04:05 PM
Scott_650 Scott_650 is offline
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Ok, from now on Iíll do my fins the right way...wait, no I wonít Iíll do it the way I like and not care how anyone else does theirs.

Thereís an old vaudeville bit about a guy who keeps bees in a jar as a hobby. His buddy asks if he punches holes in the lid to keep the bees alive - the beekeeper answers ďno, I donít punch holes in the lid, so what that the bees die - itís only a hobby!Ē.
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  #7  
Old 09-30-2019, 05:06 PM
jetlag jetlag is offline
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If you were going to do it anyway, why'd you ask the question?
You of course are free to do what you like. Papering does little to strengthen fins. Papering doesn't last, and to do paper to where it looks good, one has to put about the same labor into the project as one would the traditional way of filling/ sanding/repeat. Go ahead and time yourself. I think you'll find I'm right. If you don't care, well, good luck!

Allen
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  #8  
Old 09-30-2019, 05:54 PM
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LeeR LeeR is online now
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Papered fins looks like crap when you donít do it correctly. And when done correctly, it not only looks great, it does add strength. Iíve tested a papered fin to a plain balsa fin. Easy to snap balsa along the grain. Not as easy when papered.

Iíve seen recommendations to use Avery label paper, but I donít think the adhesive is sufficiently sticky to stay stuck to fins. I prefer Mod Podge since it looks like white glue, but it brushes on smoothly. Finally, I think the secret to getting super-flat, super-smooth fins when papering them, is to press them flat while drying. Papering fins adds moisture to the paper. Glass plates and plenty of weight helps eliminate any wrinkles, waves, or irregularities caused by the moisture.

Doing something the ďtraditionalĒ way does not make it better, it all depends on application. And should you think I paper all my fins, and therefore a ďpapering snobĒ, I only paper occasionally. Iím a huge fan of Brodak sanding dealer and use it 95% of the time to fill grain. I just like to try different techniques.

If you take your time, filling balsa grain on fins with sanding sealers, or papering your fins, can yield similarly excellent results. No one way is necessarily better, itís just different. Some builders, like John Boren of Estes, use Bondo Spot Putty to fill grain, and use lots of coats of filling primer, prior to painting. His finished models look pretty good.
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NAR 55948, L2

Projects: Super Sky Hook, Estes Saturn V, Astron Farside-X
Stuck In the Paint Shop: Estes Saturn 1B
Completed!: Painted Prowler! (ditched the pink tube wrap ...)
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  #9  
Old 09-30-2019, 11:15 PM
vulcanitebill vulcanitebill is offline
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I put on the paper to gain some strength, I wasn't so concerned about how it looks although I didn't want excess wrinkles. I papered some fins long ago and they came out well. The few spots on these current fins with wrinkles will be then treated with fill-n-finish like I normally do for balsa.

I don't recall a problem with moisture the last time I did papering. This time there was more wrinkle tendency than I remembered and later I thought of the idea to increase moisture content of the paper first. If I decide to try this again I'll experiment first.

I know more than a little about bending stresses and the properties of wood. I might have to do a test to see if I can quantify what it really does.
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  #10  
Old 10-01-2019, 12:12 PM
astronwolf astronwolf is offline
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I paper fins if I feel like it. I have a Red Max with papered fins that I did in the 1970's. Paper is still attached to the fins. The papering seems to have lasted over 40-years.

Add Paper Skins To Balsa Wood Fins To Make A Stronger Model Rocket

Tissuing glider wings.... papering balsa fins... these are ancient techniques for adding strength to balsa structures.

I wouldn't pay too much heed to these curmudgeons on this board. They are so "you are either with us, or against us" given to such STRONG opinions and absolutes. Chill out guys...
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Last edited by astronwolf : 10-01-2019 at 12:40 PM.
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