1/64th plywood over balsa lay-up

[SAC of MMMSClub]

Hi All,

I had a bad experience with the sticker paper over balsa fins, I had good luck with it for several rockets and then on a Semroc Omega the sticker paper just went all to Heck! I had the build complete and was in the Prime/Paint stage and the sticker paper bubbled and then began to peel at the edge of the fin and over night just curled up on one fin. With very little coaxing it came right off of the fins back down to the fillets and that is where I trimmed it off. I can think of several reasons why it might have done this, mostly to do with solvent in paint. The sticker paper was burnished on good. But there was some down time in the build, so it may have weakened over time??? Change in type of stickum on the paper? Who knows.

I was at Michael's Craft store for some 3 mm plywood and spotted the 1/64 thick plywood. So I gave it a try, with some 60 min. epoxy. It makes nice fins almost as smooth as the sticker paper.

Per instructions I gave the fins a quick fine sand, mostly just to make sure nothing is on the surface.

Cut free from the scrap and the tabs on the TTW fins of the Semroc Omega were masked and will hang over the edge of the plywood when epoxied.

The epoxy is spread thin and then the fins are placed and given a twist and smish to fill, expel excess, and make good bond. Then grandma's old stove irons go on top.

The result can be cut free and will be sanded down to just shy of the balsa and then the other side is laid-up.

 

[Rich Holmes]

Interesting, keep us posted on how it turns out.

 

[aerostadt]

I have done this on several occasions using 1/4" balsa as the sandwich filler and it has worked fine for me. I have done it for a parasite glider wing going up on the side of a booster powered by a J-motor. The tail fin was also the same material on the glider. This composite material is much stronger than 1/4" balsa and not as heavy as aircraft plywood, plus it is easier to cut than aircraft plywood. The 1/64" plywood can be cut with scissors and the 1/4" balsa with an X-acto knife.

 

[SAC of MMMSClub]

Interesting, keep us posted on how it turns out.

It looks real nice not the first set of fins I have done this to. They are not much heavier than just the balsa, and they are going to wear better than just balsa. I figure if you are going to build a rocket and work and fuss to make it look really nice, it should last more than a broken fin.

 

[aerostadt]

Yes, you are right they are heavier than just straight balsa, but not that bad. I would say the composite material is in-between balsa and aircraft plywood with regard to weight. I don't bother to air-foil these kind of fins, but if someone wanted to make the fins with a rounded edge, I would suggest making the 1/64" ply a little bit smaller than the balsa and then sand the balsa. The 1/64" plywood is tough and I don't think it sands well.

 

[AlfaBrewer]

I've done a similar thing with 1/32" basswood over 1/8" balsa. I made sure to criss-cross the grains, with the grain of the balsa going with the leading edge of the fin. Turned out a very stiff, but light fin that was easy to finish. Including sanding in nice rounded edges.

I just used regular wood glue, instead of the epoxy.

 

[GDJ]

I've done both Balsa and Basswood with the 1/64" birch glued on. Both work extremely well and are far stronger than the base material after everything is finished. Also I found that the rigidity of the fins is phenomenal. I'm not going to jump up and down and say that these combinations are stronger than G10, but they are pretty strong and tough.

Use the Balsa/birch combination if you want to save some weight, but the Basswood/birch combination is the best combination for lighter weight but strong as heck fins.

As for the glue, I use the yellow carpenters glue or Gorilla Wood Glue.

 

[SAC of MMMSClub]

I've done both Balsa and Basswood with the 1/64" birch glued on. Both work extremely well and are far stronger than the base material after everything is finished. Also I found that the rigidity of the fins is phenomenal. I'm not going to jump up and down and say that these combinations are stronger than G10, but they are pretty strong and tough.

Use the Balsa/birch combination if you want to save some weight, but the Basswood/birch combination is the best combination for lighter weight but strong as heck fins.

As for the glue, I use the yellow carpenters glue or Gorilla Wood Glue.

I like the 60 min. epoxy, or as I am now using West systems epoxy, about 12 min in pot, but more than 40 in thin film.

 

[GDJ]

I like the 60 min. epoxy, or as I am now using West systems epoxy, about 12 min in pot, but more than 40 in thin film.

That'll work. Plenty of grabbing power there.

 

[aerostadt]

At different times I have used both epoxy and wood glue. I have also put the 1/64" ply over 1/2" styrofoam on both sides for a larger parasite glider. It works good.

 

[GDJ]

At different times I have used both epoxy and wood glue. I have also put the 1/64" ply over 1/2" styrofoam on both sides for a larger parasite glider. It works good.

I admit I have not considered styrofoam as a core material. I'm going to have this a go.

 

[TheAviator]

I admit I have not considered styrofoam as a core material. I'm going to have this a go.

The airplane guys have been doing 1/32" balsa over white styrofoam for a while. If you're creative, you can do curved ruled surfaces like the fins on a WAC Corporal, Aerobee-Hi, or similar or the diamond airfoil like a Nike Smoke. Finish with Tissue, Silkspan, Iron-on covering, fiberglass, or standard fill and paint. The finished product is very strong, and small dings can be removed with a kettle and some steam. See George Gassaway's page here for info: https://georgesrockets.com/GLIDERS/CUDA/CudaFlap.htm