Glassing Balsa Fins

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Well-Known Member
Jan 25, 2009
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Hi all,

Can I glass both sides of a balsa fin at once before they are attached? How would I do this?

What I have done is to glass one side, lay them on wax paper, glass the other side, more wax paper, and then lots of books. I hear using panes of glass on both sides will make for a smoother finish.
yeah the glass panels are what I use with mylar to prevent the epoxy from sticking to the can even spray paint the mylars first and impart color to the finsihed galss balsa ......
Mylar, now that's a new one on me. I usually just use wax paper between the fin and the glass.

OBTW this technique can also be used on plywood fins for LMR and HPR rockets. I use 1/4" plate glass put 50# of lead shot on top of the glass to compress the fins.

Ken Holloway

I used to do the wax paper too and still do when I don't want any color....I learned the mylars technique(the painting part) from Kevin Kuczek. He learned it from a video and people in model gliders.
I use the pink foam from Lowes, lay a peice of acetate down, then two layers of fiberglass, dry, then add the resin and get it good and wet and free of bubbles, add a layer of balsa, more glass, more resin, another layer of acetate, then the foam, and as much weight as i ca throw on top. Turns that crappy paperthin brown balsa that bends like paper stiff in no time...

Scott McNeely
the ways mentioned here are very good, I have even just taken a whole bunch of scrap fiberglass (those 3"x3" trimmings) and layed it on a board, then some wax paper, then the glass with some resin, another peice of wax paper, another board and some clamps or heavy objects, nice peice of G10
someone clue me in...

won't the balsa eventually crack under the glass?.. what is the benefit of using such a brittle core? weight? I don't get it
as in why not just make fins from ply or g10?
Balsa is not really that brittle - why is it going to crack?

The balsa core is just there as a filler to keep the skins separated. The real strength comes from the skins. The resistance to bending relys on the compression and tension strength of the material and its distance from the center of the beam being bent. i.e. the bit in the middle does almost nothing.

I have used 1/16" balsa fins surface mounted and then tip to tip glassed them with a couple of layers of 2oz cloth. They are very stiff and this model is 24mm minimum diamerter. It has flown on D12s without any problems but is designed to take an F39.
Off topic a little but to illustrate how stong the fiberglass / balsa / fiberglass composite construction process is take a look at some of the fishing boats in the 16' to 35' range. Some of them use balsa blocks glued together and sanded to shape for the core of their hulls. The balsa is then fiberglassed inside and out resulting in an extremely strong hull to which the boat's superstructure is attached. The 22' and 30' "SISU" boats were made this way and they are still one of the favorite hulls in use by New England lobster fishermen.

Ken Holloway, NAR #78336
thanks for the replys .. so basically the balsa's sole purpose is a form for the glass..