Best adhesive to fix foam jets?

[Bill Sanford]

Well my EFlite Viper hit a bump during takeoff this evening on our bumpy grass field and jumped up prematurely and rolled over on its back and went in due to insufficient airspeed. Fortunately it's easily repaired. It cracked my canopy and also cracked a glued joint in the fuselage just ahead of the intake duct.
The fuselage crack is very structural so I need a strong bond. What glue do you recommend? CA? Epoxy? Bob Smith Foam Cure? Other?

Trailing link struts already ordered from EBay. I should have grounded it until I got them. Live and learn...

This is an AWESOME flying jet other than the landing gear. The wire struts and rock hard wheels may be good for smooth runways, but sucks on grass...

Also, add some fiberglass and epoxy to the inboard corner of the flap cutout on both sides of the wing to strengthen the wing so it won't crack by the wheel well due to the stress the landing gear put on the wing when landing. If you read the Viper thread, you will see that this is an issue for everyone... Do it BEFORE it cracks...

All this said, the Viper flies like a champ and I've been getting 6:30 flights with a 3300 with mixed flying. You can't beat this jet once it's in the air! It's fast and sips power compared to most EDFs.

[Alpha]

Hi Bill,
For cracks along structural fuselage joints on EPO type foams, I recommend Gorilla Glue White, Beacon Foam-Tac, or epoxy, but each have their Pros and Cons. The trick with repairing cracks is that all of these adhesives are additive. The short answer is that for any of these adhesives, you're best served by augmenting their adhesive contribution with tangible reinforcement such as carbon rods or bamboo skewers. This is because the energy upon landing requires that area of the fuselage in front of the intakes to have a bit of "give". Adhesive alone may not give you that kind of energy transfer --it will just shear again at the original crack eventually.

The Gorilla Glue expands like a hard foam, which is good for refilling in the gaps of torn out retract mounts where original material was lost, but in a crack unless you poke holes in the two faces with a bamboo skewer to provide space for the glue to expand, it will just expand outside of the crack and marr your finish without truly reinforcing the bond.

The epoxy alone is also problematic because if you use a thin enough epoxy bead that doesn't wick out of the crack, you run the real risk of not having enough of a bond to hold the foam together across the necessary range of forces. But, reinforced with a thin strip of carbon rectangle oriented in "portrait", it should work well. Orienting the carbon rectangle in this way absorbs the vertical load upon landing. Bamboo skewers are more flexible in all radial axes, but they are much easier to install (poke the skewer into the foam wall face to create a hole, pull out, insert dab of epoxy into hole, reinsert skewer, join both halves) and would probably be sufficient for a 70mm jet such as yours.

I wouldn't recommend CA for a joint at that high shear force area.

[Bill Sanford]

Thanks for the detailed information Alpha! I also asked this question on RC Groups and one post suggested that they had the same issue with the Viper and also added some thin FG cloth and epoxy over the joint in the battery bay. I like this idea in addition to gluing the joint and think it would forever solve the issue.

FYI: I also fly my Avanti S on this grass field and between the trailing links and better wheels, it's a champ and floats over the bumps on take offs and landings.
Great design! Good job!! :)

[xviper]

I use FoamTac on almost everything now. I've even put aside the Loctite in favor of FoamTac on metal threads. I may use 5 min. epoxy on some areas like motor mounts. I even make FoamTac hinges for repairing all foam hinges. Foam hinges usually break with a jagged edge. With FoamTac, it follows the edge. No need to cut them straight.

[Alpha]

Agreed, FoamTac is really versatile stuff. It's easily our highest selling adhesive on our website.

Bill, CG cloth works, just be mindful that sometimes the grip isn't the best between foam and epoxy/FG combo, especially if it's such a thin smear to avoid gunking up your battery bay. Every model is different, but just to throw in another idea for consideration is a strip of wide fiberglass-reinforced tape. On a flat surface where I'm just trying to reinforce a glued joint and distribute load across a wider area that's not the easiest to access with more traditional surgery, a strip of this kind of tape often suffices.

[TiredIronGRB]

Agreed, FoamTac is really versatile stuff. It's easily our highest selling adhesive on our website.

You're welcome...;)

[xviper]

You're welcome...;)

You could almost get "lei'd" with that.

[TiredIronGRB]

You could almost get "lei'd" with that.

At $9 a bottle I already have ;)

[xviper]

At $9 a bottle I already have ;)

It's over $12.00 a bottle in Calgary. I must have way more expensive taste in high end call .............. I mean glue, than you.

[Bill Sanford]

At $9 a bottle I already have ;)

You guys crack me up! LOL

[Tom]

LOL. George, I love the lei !!

[TiredIronGRB]

LOL. George, I love the lei !!

I wish I had thought of it before I threw the first 20 or 30 away, Hangar Days take a toll on Foam-Tac :Silly: