My right foam wing has a crack just behind the phenolic wing tube after a crash. The bottom balsa sheeting is split along the same place and the crack extends 50 % into the foam core but not right through. The split stops right where the phenolic tube ends in the wing. The phenolic wing tube is glued to a balsa box with triangle pieces filling in the corners. This assembly is then glued to a slot in the foam wing. There is no damage to this wing tube retainer. The crack is just behind this box.

I am thinking that I could apply a strong epoxy ( or gorilla glue) along the crack and clamping the wing between the original foam core saddles . When cured , I could strengthen this joint by applying fibreglass mat over the cracked section ( top & bottom) .Will this be enough strength ?

Any other ideas?

Tks

Use the Gorilla glue. It's stronger than the existing foam, and lighter than epoxy. Be aware that it will expand and widen the existing crack if you don't make arrangements to keep it clamped shut while it cures. If you're able, you can run bamboo shishkebab skewers wetted with the same glue through the joint to reinforce the repair. I would likely not use glass/epoxy over the repair, but if you have any doubts about it, I would just lay some .7 oz glass cloth over it and bond with polyurethane varnish like Varathane or Minwax. I have an 8' span plane going together now that uses 1/2" pink foam fuse construction, skewered joints and the same glass/PU covering, and it's very rigid & strong.

I dont have room to apply the bamboos skewers because the phenolic wing tubes are in the way . The tube is only about 3/16 inch from top and bottom surface of the wing . Other possibility is to add some carbon fibre strips across the joint on the wing surface . What you you think of this?

By the way , How do you apply gorilla glue into a crack that can be perhaps pried open by 1/16 inch ? Gorilla glue need some water to cure , so I am not sure how to apply glue on one surface of the crack and mist of water on other Tks

It's the sheeting which provides the strength to the structure. This is what you need to repair.

I would definitely use fiberglass (maybe 3-4" wide, wider for a very long wing or long crack). .7 oz is probably fine.

If the foam has not cracked all the way through, and the foam still mates, I wouldn't even bother to glue the foam since it doesn't contribute much strength. It's simpler that way, and you don't have to worry about polyu oozing out, and sanding, etc.

The next question is how is the phenolic tube held in place. I always use false ribs that the phenolic has to go through to give the wing strength.

If there is a false rib and it is broken, it won't do any good to just fix the sheeting as the phenolic tube will break through the sheeting with high g forces. If you built the wing, then you would know if a false rib was used or not.

In answer to getting the glue in the crack, go to eckard, wallgreens or some local pharmacy and purchase some 10cc syringes and some 23-25 guage needles. You may have to do a little explaining. At any rate, put the glue into the syringe and push the plunger as after you position the needle through the wing skin.

The syringes work better than anything for Robart Hinge Points also, especially if using epoxy. The Gorilla glue I used had a spout that could go into the hole nicely also.

Good luck

ed

[Deleted by Admins]