What is the strongest way of building a quarter inch thick horizontal stabilizer? The stab on my Canard Stick folded in flight. The stab span is 22 inches and made of quarter inch sheet balsa with the middle 6 inches fiberglassed. It cracked and folded at the end of the fiberglass. Any suggestions on the best way to make it stronger?
Thanks

Sounds like the fiberglass created a stress point. If the fiberglass hadn't been there then the stab may have been able to flex rather than break. But this is just Monday morning quartebacking.

You could use a 1/4" spruce or basswood spar in the middle of the stab.

The strongest stabs are built up and sheeted. It's more work, but they're stronger and lighter.

What was the plane doing when it folded? Was it a high-G pullout from a power dive or something?

CafeenMan,
I had just leveled out from a highspeed turn when the stab folded. With the stab only being a quarter inch thick, would a stick built and sheeted stab be strong enough? Seems like the sticks would be pretty small and the sheets pretty thin. The hardwood spar down the middle sounds like it may work. Anyway, I appreciate the info.
Weez

I would make it thicker at the same time. Guess I forgot to mention that. It should fly better having an actual airfoil.

The way it works is that the thicker it is the stronger it is. If you make an airfoiled stab 3/8" to 1/2" thick the plane will probably fly better and the stab will be stronger. The only reason we use flat slabs is for convenience - not for better flying qualities.

I would use a 1/8" x 1/4" hardwood spar centered in the ribs or perhaps a 1/16" x 1/4" spar top and bottom as a conventional wing. Then sheet it with 1/16" balsa. Make the leading and trailing edges 3/8" wide by whatever height is necessary. You would be hard pressed to fold it.

Then again, I have to admit I'm amazed you managed to fold a 1/4" balsa slab. I don't know much about canards, but considering the small span there either had to be some kind of stress crack already or it was under a lot of G's.

Run a fiberglass arrow shaft down the middle. It'll be plenty strong.

You probably had soft balsa in your stab.

Another way with sheet is to CA on a 1/2 inch wide strip of carbon fiber tape on either side. I did this for years on built up stabs and never had one fail.

Build it per plan, don't add anything. Those were strong enough that way. If you add stuff, you add more possibility of it failing like it did.

Flyboy,
It was built the first time according to the plans and it failed. Why should I build it that way again?
Weez

I didn't remember the fiberglass. I will have to go look at it again.

I wouldn't glass the center. Maybe run 3 strips of 1 inch fillament tape lengthwise on it to allow it to flex, but not break. I have done that on many wings and they can flex like crazy and not break.

I just got a new set of plans for that plane. I will look at it again tonight. I didn't remember there being glass in the middle when I said that.

did it break inside or outside the fuse?

glass joints are bad news, almost everyone lays the tape and glasses it, then you've got a sudden change in material strength and a weekness waiting to strike, the way to do it propperly is to lay a diamond shape so the glass tapers out, then the epoxy should go a bit beyond that. personaly i dont glass, i use cloth medical bandage and PVA, its thinner, lighter, almost as strong, and much easier to cover over.
For this plane i think i may lay a 1/4x1/4 "spar" down the centre of the cannard

Flyboy, it broke outside of the fuse right along the end of the fiberglass.

Thanks for everyones help and tips. Tonight I will do a little cutting on the plane and see if I can see anything else that might have caused the failure. I will probally use a combination of the suggestions offered when rebuilding the carnard.

Just so everyone knows, it flew great for about 5 to 6 minutes prior to the canard failure. Looks a little strange, because it looks like your plane is flying backwards.

Again, thanks to everyone.
Weez