Time Pilot

I've read some debate on this and would like the reasoning behind it.

Why is it recommended to glue wing halves together with epoxy? I thought that wood glue soaked into the wood and formed a stronger bond than the surounding wood. On a tight joint, I would assume the wood glue would make a stronger bond.

(The wing root is NOT fiberglass reinforced.)

I also need to glue 3 pieces of 1/8" plywood together to make a firewall (Tower Trainer .40). Instructions say to use epoxy to glue them together. I'd rather use wood glue as it's easier to work with and clean up. I will fuel proof the firewall when it's all together, but why use epoxy? Will the wood glue fail because of vibration in this application?

On another note, I'm ticked at myself. I put a dehumidifier in my work area to deal with humidity issues while the laundry is being done, but I didn't think of what it would do to my 2 fuselage sides! They are slightly warped now. Not enough to matter, I hope. I have weighed them down in hopes that all will return to normal as the wood reabsorbs moisture. All that care and attention to building perfectly straight.... [] If I'm going to bend or break it, I want it to be spetacular!

MinnFlyer

My Feedback: (4)

Epoxy will help to fuel proof the firewall. Should fuel soak into one area, the epoxy will act as a barrier to keep it out of the next.

As far as the wing goes, most times it is not possible to clamp the joint. That is where epoxy is better.

Time Pilot

Makes sense. Thanks.

Rodney

TimePilot, I often use wood glue instead of epoxy, even on the quarter scale types. If you have a good fitting joint and use a good glue, the joint will be stronger than the wood and work as well as anything else will. Epoxys are better when it comes to being fuel proof; but, if you do a good fuel proofing job you can get by just as well with the wood glue. In fact, depending on the epoxy used, the wood glue joints will usually be much more resistant to shock loads than the epoxy joints. Now if you are taling about 5 minute epoxy, most anything will be better than that.

Time Pilot

Rodney,

That is good to know. If it works on quarter scale, then it will definitely hold on my .40 trainer.

I am aware that I need a good joint and wouldn't rely on wood glue to fill the gap.

When it comes to certain things like putting these kits together, I tend to be a bit anal (my wife would say a lot, but who asked her, right?). It will be fuel proof.

khodges

My Feedback: (1)

Epoxy has a much better fatigue strength than aliphatic glue (Elmer's Carpenters Glue, TiteBond) and since it is fuel proof it just make sense to use it on the firewall. Most kit instructions you will find strongly recommend epoxy for the firewall. 5-minute does not penetrate the surface of the bonded sufaces sufficiently in its short cure time, so use 30 min. epoxy.The longer cure time epoxies(longer than 30 min aren't really any better than 30 min. for bonding parts so they are a waste of time waiting for them to harden or cure. They are better for thinning and finishing surfaces or using with fiberglass cloth. Aliphatics may have advantages in shock strength because they remain slightly flexible when cured so their use for bonding parts that may need to flex is advantageous (wings)

Time Pilot

Thanks. I've already laminated two pieces of ply together with wood glue. I'll do the last one, the one between the engine and the pieces I've already glued with epoxy. Not looking forward to it, especially. Messy stuff to work with.

Thanks for the info, though. I definitely will glue the whole piece in with epoxy when I'm done though, including 'painting' the engine compartment with it too.