Adding fin strength

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Well-Known Member
Oct 9, 2002
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I am looking to add some strength to my Flis Kits Praetor. I am going to seal the fins with 20 minute Finishing Epoxy. I have had good results in the past. Is there anything short for fiberglass cloth I can use to add a little strength?

I don't want to add too much weight. I want to fly a D13 it and want the fins to be a little stronger. Would something along the line of tissue paper be worth it?

Cover the fins with copy-machine paper, or for even more strength, use card-stock paper.

Cut the paper to fit both sides at once by folding to wrap around the leading edge and leave excess paper hanging over the edges. Get everything glued/wet, slip the paper wrap over the fin, slip this between sheets of waxed paper, and put underneath a heavy telephone book (or equivalent). When the epoxy is cured, trim the paper around the tip, root, and trailing edge, and proceed with assembly.

Adds a lot of strength, makes a great surface to begin sealing and painting, simple, cheap, and fast.

Lots of folks here on TRF have posted their results with this approach, you can find a bunch more info using the 'search' button.
I glassed the fins on my Praetor. It was easy and added a little weight, but that little bit of weight is perfect! She'll easily eat up a box of C6-3's if I had enough money to BUY a box of C6-3's!

Here's a few pix. This one is of the fins being glassed:


And here is the finished product!


I have used tissue and epoxy to form a type of "glass." I don't recall the name of the tissue, but it is very tough. It is sold at hobby shops for covering model aircratft wings. I used finish epoxy and pressed between plate glass, weighted with 25 lb.
I was just going to start a thread on fin strength but you beat me too it.
I have a love hate relationship with Launch Pad kits,
As most people will tell you that have built them the balsa stock for the fins is less than adequit to cut them out properly. You find yourself cutting fins with the grain running the wrong way.
TLP suggests that you apply a coat of thin CyA.
My first attempt at this ended with strong fins but a rough and difficult to sand finish. My second attempt was to coat with epoxy, this sealed the fins but did not add any stregth.
Finally on my third attempt I got it right.
I applied thin CyA to one side of each fin ,BEFORE mounting the fins (this caused the fins to warp and scared me, but after applying to the other side they straitened out nicely) after applying to the opposite side I was able to lay the fins on a flat surface and sand them smooth.
These fins that where very week to start with are now rock solid and a good smooth sealed finish.