Weight of fin papering

[neil_w]

In another thread, @boatgeek asked about the weight penalty of papering fins with label paper. Here is a breakdown.

1. My Avery label paper weighs 0.003 oz/in^2. Because you need to paper both sides of the fin (unless you're really weird ), that comes out to 0.006 oz of paper per square inch of fin. Note that this includes the "glue". In my case I only lightly CA the edges, which I deem to be negligible in this calculation. If you soak the whole fin with CA after papering then you'll need to factor that in.
2. Balsa density varies enormously, but let's say that typical medium-density stock runs 0.1 oz/in^3.
3. Let's say typical basswood density (also quite variable) is 0.3 oz/in^3

So:

Fin material and thickness	Fin weight / in^2 (oz)	Label Paper weight / in^2 (oz)	Paper weight penalty
1/16" balsa	0.0062	0.006	97%
3/32" balsa	0.0094	0.006	64%
1/8" balsa	0.0125	0.006	48%
1/16" basswood	0.019	0.006	32%
3/32" basswood	0.028	0.006	21%
1/8" basswood	0.038	.006	16%

Conclusion: for balsa fins especially, the weight penalty for papering this way is quite steep, although I can't say how it compares to other methods. For this reason it is important to include some sort of estimate of this additional weight in your sim models, it really can make a difference in CG location.

If anyone wants to fill in this sort of information for their own preferred papering technique that would be great. Any method that includes significant amount of glue requires weighting a bare fin and then a fully papered fin to see the additional weight of paper, which should be relatively constant per unit area regardless of the fin thickness or material.

 

[lakeroadster]

I rarely use balsa for anything anymore. But here's some data I gathered for basswood back in April of 2022. I also did a strength test and found about an 8:1 increase in bending strength.

https://www.rocketryforum.com/threa...er-1-16-basswood-with-a-strength-test.172313/

​

 

[mh9162013]

I paper my balsa fins for added strength and to get a better surface finish for painting, sure. But I also do it because I enjoy the process and it's oddly one of the more satisfying parts of LPR rocket building for me personally.

 

[neil_w]

I paper my balsa fins for added strength and to get a better surface finish for painting, sure. But I also do it because I enjoy the process and it's oddly one of the more satisfying parts of LPR rocket building for me personally.

Me too!

 

[asm109]

Wow, 61 pound photo paper. Way to go big or go home! I love the data. data is always good.
Wonder what the strength would be if you used 20 pound copy paper. (about .003 in thick)

 

[Steve Shannon]

The first paper that I learned about for papering fins was the tissue paper used to wrap around men’s dress shirts. Simply brush on white glue and then lay the tissue on the surface of the balsa like fiberglass and brush on more white glue to smooth it out, not unlike laminating with fiberglass. I don’t recall if the glue was thinned or not and I never tried it. It doesn’t take much to strengthen balsa like that.

 

[neil_w]

There are a hundred ways to paper fins, each yielding a different balance of
1) strength
2) smooth finish
3) effort
4) weight

Label papering, which is my preferred technique the vast majority of the time, is very strong on #2 and #3, medium on #1, and a bit weak on #4... although not necessarily weak compared to some alternatives like glue-papering with cardstock.

I would suspect that tissue-papering is weaker on #2, which is one of my primary reasons for papering in the first place.

 

[tsmith1315]

The first paper that I learned about for papering fins was the tissue paper used to wrap around men’s dress shirts. Simply brush on white glue and then lay the tissue on the surface of the balsa like fiberglass and brush on more white glue to smooth it out,

I recall being told to do that with Aero Gloss dope many moons ago.

 

[bjphoenix]

I was papering 3/32" and 1/8" balsa fins with printer paper and titebond. I did some rough weight checks and what I recall was about 50% increase over the balsa weight itself.

 

[sr205347d]

I have been covering fins (and body tubes) with colored packing tape because it is lots easier and quicker than painting. I never considered the weight. Here are some examples:



To figure out the weight, I cut a square of foamboard, weighed it, covered both sides with tape, and weighed again:



Results: 0.117 g/in^2, or 0.00413 oz/in^2. There would be a little more required to fold over the edges, but the added amount would depend on your fin size and shape.

This is less than the label paper. Since there is no painting required, there is more weight savings. Surely it adds stiffness too. The yellow, black, and blue in the above photos are all tape (except for the 3D printed bolt-on fin brackets and the nose cones).

 

[Blast it Tom!]

I think the great thing about the tape, and many of these other methods, is that it puts a layer of non-direction dependent strong fibers (or polymer, for the tape) on the outside edges, largely negating the strongly directional-dependent strength of balsa - which is why we run the grain along the leading edge as well. The packing tape adds a lot of toughness as well; I like it. But ya gotta have the right color for your project!

 

[SolarYellow]

I’ve been using Monokote/Econokote. Like it overall. It’s shiny and smooth at a micro level, but at a macro level, it shows through the waviness of the surface of the body tube. Have made some improvement by blocking the tube flatter before covering, but it’s a work in progress. I need to commit some tubes (and more importantly, time and attention) to finishing technique development without saddling the project with a whole rocket build.

 

[sr205347d]

I liked UltraCote back in the day when you built airplanes from balsa kits.

That shrink wrap stuff is tricky to work with though.

 

[Dane Ronnow]

Despite being .125 plywood, and not really needing paper for reinforcement, I used Avery label paper on these to give a better surface for painting. Easier than filling the grain and sanding. I don't know what the difference in weight is between label paper and wood filler, but weight is not super-critical on this build.

 

[neil_w]

Despite being .125 plywood, and not really needing paper for reinforcement, I used Avery label paper on these to give a better surface for painting. Easier than filling the grain and sanding. I don't know what the difference in weight is between label paper and wood filler, but weight is not super-critical on this build.

View attachment 579663

13% weight penalty for 1/8" birch ply.

 

[MidOH]

Which is no worse than my papering. By the time it's all sealed, sanded, and smooth, it's heavy. Never again.

I'd rather just repair balsa fins as needed. A little CA on the trailing edge, and they're plenty strong. Need stronger go ply. Then fiberglass or carbon.

 

[Alan15578]

The question should be, how much weight can you save by papering fins. this assumes that you are building fins to take the same loads, but using thinner or lighter core material for the papered fins.

 

[lakeroadster]

The question should be, how much weight can you save by papering fins. this assumes that you are building fins to take the same loads, but using thinner or lighter core material for the papered fins.

I think most of us are just trying to keep from busting fins. Unless your competition flying your primary goal isn't making all components minimal.

 

[BigMacDaddy]

I assume that you are comparing to solid basswood (not basswood plywood).

Why do people usually go to basswood instead of thinply / plywood (birch or basswood based)?

According to OpenRocket basswood is .5g/cm^3 vs. plywood at around .63g/cm^3 (sorry do not have pieces of both here to actually weigh). When it comes to breakage, flex, etc... I would think that the advantage of plywood would be worth the 25% additional increase in weight over solid basswood.

 

[neil_w]

I can cut basswood with a hobby knife is the main thing. Although I haven’t tried with birch ply.

 

[tsmith1315]

Why do people usually go to basswood instead of thinply / plywood (birch or basswood based)?

It’s in the same display as the balsa at the hobby/craft store, same size pieces, and similar price.

Answering for a friend.

 

[BigMacDaddy]

I can cut basswood with a hobby knife is the main thing. Although I haven’t tried with birch ply.

Good point about cutting ease - it is definitely harder than balsa to cut by hand but not sure how it compares to basswood.

I think cost-wise thinply plywood is also very hard to beat (around $1 to $1.50 per 8.5"x12" sheet).

If you want 2mm / 3/32" - https://www.amazon.com/Basswood-Plywood-Unfinished-Burning-200x300x2MM/dp/B09XV3CM2H
If you want 1.5mm / 1/16" - https://www.amazon.com/gp/product/B08RJ2LRWQ/

This is 3 layer and has a grain direction (basically top and bottom layers go in same direction and middle filler layer is not as strong). Not aircraft grade by any means but it is very durable in my experience to falls, 2mm works for very large fins (see my R1 for example), finishes well, is pretty light, etc... Also, it can warp if you let it dry without weight on it.

 

[Bill S]

I can cut basswood with a hobby knife is the main thing. Although I haven’t tried with birch ply.

I've been using a crosscut saw, and in some cases an Xacto hobby saw, on 1/8" plywood.

 

[SolarYellow]

Try a Zona saw for this stuff if doing it by hand. The pull-stroke-cut of the teeth is nice.