Fin skinning with 1/64" plywood

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icyclops

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I see your problem with using too thin of paper for heavy structured fins like what you show in your photos. I normally paper over flat structures or open flat fin builds Which is very different. Your teardrop or diamond shape finning is more like skinning an airplane wing. I have used epoxy or Spraymount with thin styrene plastic sheet (.020 - .030) for fins that require more dimensional stability.

I would agree that papering over dimensional fins like you show, thin card stock may not be the best...I would go with thicker Bristol board stock (very hard and tough card), 1/64” ply, or 0.30 plastic sheet would work better.
 

BABAR

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Personally, I am not a fan of papered fins over cavernous fin frames. Those tend to result in fragile fins that get damaged by sitting on a shelf.
However, I got into just such a mess with a recent TLP build (pics below). The frame is constructed out of flimsy balsa, and even 'painting' final product with epoxy still resulted in one fin cracking while being handled during painting.

View attachment 465737 View attachment 465749

The fins overall shape, however, is awesome. There is no way I would have been able to achieve a perfect diamond shape with custom trapezoid on top by any other means. I am now wondering if replacing paper outer skins with 1/64"-thick plywood would produce a more durable result.
Thus my two questions:
1). I don't suppose there is any readily accessible method for bending 1/64" plywood, is there?
2). Assuming "no" to the question above, what's the best compound for sealing the edges between plywood sheets?

I would expect to end up applying four (4) 2x2" 1/64" plywood sheets per fin, and ideally, the transitions between them should be invisible and perfectly smooth.



The price is exceedingly reasonable.

TIA,
a
Can’t speak for balsa.

I am guessing your fin injuries were the forward and trail edges, which from the two pictures are unsupported.

options would be adding a toothpick or other tiny rod crossing the front And rear edges, but that may be to thick.
Another possible better option would be a dental floss “stringer” across the forward and trail edges. Caveat, either will only be as strong as the end piece it is attached to.

just an idea.

I find dental floss to be stronger than most thread, plus it wicks up CA or other glues. Kevlar thread gets brittle with CA. Plus floss comes in a pack with a cutter on it, so I am not always looking for my scissors!
 

afadeev

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I see your problem with using too thin of paper for heavy structured fins like what you show in your photos. I normally paper over flat structures or open flat fin builds Which is very different.
Yes, same here.
This is the first time I ran into kit design that treats paper as a load bearing material. I think it is an all-around bad idea, and thus my interest in using 1/64th plywood as replacement.

TLP instructions called for "dipping" paper into CA, which I've done in the past and that does achieve some strengthening. I upped the ante and applied outer layer of West Systems epoxy, and the surfaces became almost firm-enough to be sanded (there is still some give, but not much). Still, these are pretty large fins, and at least one of them is guaranteed to take a whack upon landing. I have almost zero confidence that it can take it.

I would agree that papering over dimensional fins like you show, thin card stock may not be the best...I would go with thicker Bristol board stock (very hard and tough card), 1/64” ply, or 0.30 plastic sheet would work better.
I used cardstock that came with the kit, it's pretty firm. Similar to what Estes uses for bodies of Shuttle glider and Asteroid Hunter.

I am guessing your fin injuries were the forward and trail edges, which from the two pictures are unsupported.
Good guess, but no.
I had purposely allowed epoxy to puddle and drip-off the trailing/aft edges of fins while drying, to make them stronger. So something else had to give.
The model was laying on an outdoor table, waiting for a yet another layer of primer to dry, when a strong gust of wind blew it to the ground. I didn't witness the impact, but the results are as shown below. I think the trailing edge of the fin was the point of impact, and transferred the force to the fragile balsa frame of the fin.
Definitely repairable, and equally disappointing, and testifying to the frailty of the fin:
1621984329356.png
 

James Duffy

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Here's an update on the Citation Patriot project that was the genesis for this tutorial video. Construction and finishing are complete, and the rocket is ready to fly.
A6C91509-BB23-41E5-BB13-C3282C21046D.jpeg
To recap, the base kit was a copy of the new Der Big Red Max from Estes, with an additional 15.5" of 3" OD tubing. Laser cut fin cores came from Galactic Manufacturing, and the cut vinyl markings were sourced from Stickershock23. It will fly soon on a composite E or F somethingorother, perhaps at our local TARC finals next week.

James
 
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DigBaddy

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Here's an update on the Citation Patriot project that was the genesis for this tutorial video. Construction and finishing are complete, and the rocket is ready to fly.
View attachment 467219
To recap, the base kit was a copy of the new Der Big Red Max from Estes, with an additional 15.5" of 3" OD tubing. Laser cut fin cores came from Galactic Manufacturing, and the cut vinyl markings were sourced from Stickershock23. It will fly soon on a composite E or F somethingorother, perhaps at our local TARC finals next week.

James
Wow, that looks so good!
 

NOLA_BAR

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Here's an update on the Citation Patriot project that was the genesis for this tutorial video. Construction and finishing are complete, and the rocket is ready to fly.
View attachment 467219
To recap, the base kit was a copy of the new Der Big Red Max from Estes, with an additional 15.5" of 3" OD tubing. Laser cut fin cores came from Galactic Manufacturing, and the cut vinyl markings were sourced from Stickershock23. It will fly soon on a composite E or F somethingorother, perhaps at our local TARC finals next week.

James
Ok so what size is that Orbital Transport in the background?
 

James Duffy

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Ok so what size is that Orbital Transport in the background?
That's a 3x version of the Orbital Transport. You can read more about it in this thread:


James
 

aviserated

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Cool rocket! Roughly how high does it fly using E or F power.
 

James Duffy

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Cool rocket! Roughly how high does it fly using E or F power.
My guess is that the Citation Patriot flies to ~400' on the F42, and the C-47 Max is flying to about 250' on an E20.

James
 
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dpower

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Great technique James, thanks for the video. BTW, what’s an Estes Centuri Patriot? 😁
 

BABAR

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This weekend afforded the opportunity to fly two recent builds featuring 1/64" ply fin skins, and the flights were documented. You can see the video here:


Enjoy,
James
Nice fin alignment on the patriot, just about zero roll!
 

Tobor

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I've seen this ply at our regional home improvement box store, Menards. A bit more than online, but no shipping. Was thinking that they would be perfect for fin skinning when I first noticed them. They have a lot of other basswood and balsa in the store too.
Yeah, I know, late response....
Midwest Products produce really nice "Aircraft Birch Plywood". Aircraft plywood is a lot stronger then regular plywood and handles bending/shaping better. Their plywood is used a lot in the model airplane & model boat hobbies.
 

GlenP

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I skinned fins with cardstock over a cardstock core of variable ply thickness to drape in a crude stairstepped "diamond" airfoil on this cardstock 18mm power LPR model of the Alpha Draco. These are very thin, but you can see the layers of the cardstock core on the edge view and shadows on the surface of the fins. Cardstock fins are great lightweight fins for LPR. I used an Elmer's School Glue Stick, purple but dries clear.

 
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TigerHawk

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Here's an update on the Citation Patriot project that was the genesis for this tutorial video. Construction and finishing are complete, and the rocket is ready to fly.
View attachment 467219
To recap, the base kit was a copy of the new Der Big Red Max from Estes, with an additional 15.5" of 3" OD tubing. Laser cut fin cores came from Galactic Manufacturing, and the cut vinyl markings were sourced from Stickershock23. It will fly soon on a composite E or F somethingorother, perhaps at our local TARC finals next week.

James
James,
What was the overall length of your upscaled citation patriot?
 
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