Nylon bolts and CA warning
 

I experienced a wing bolt failure on my new profile plane the other day and wanted to warn others of a potential problem. The profile features bolt on wings that attach by threading a block in one wing panel and running the bolt through the other wing's root rib, through the fuse, then into the threaded block. This usually requires the use of some sort of tool to tighten the bolt. What I've been doing is gluing a stud into one wing and using a wing nut to tighten everything down. It has worked well in the past for me and doesn't require any tools to assemble the plane.

When I originally glued the stud into the wing, I used white Gorilla glue. But after a few times assembling and disassembling the plane on the bench, the glue turned loose, allowing the bolt to spin. Without thinking, I picked up the thin CA and ran a little onto the bolt, then hit it with kicker. Worked like a charm....

Until the maiden flight. About 3-4 minutes in, I pulled up into a wall and my spotter heard a small 'pop'. I didn't hear anything, and we chalked it up to the wing settling. A couple of minutes later, at about 100 feet up, I started a roll and the right wing separated from the plane. (This was fortunate because the battery was in the left wing!) All I could do was slow the descent by spinning the plane to the ground. Amazingly, very little damage occurred. Both wing panels were perfect, and the fuse was only cracked in a couple of places.

Post mortem determined that the nylon bolt (1/4x20) had sheared off, allowing the wing to come off the wing joiner. But what made the bolt shear was unclear. Initial tests on other bolts showed the shear force to be much greater than one would see on the plane. So, I did an experiment where I drizzled CA on the bolt and hit it with kicker. Waited about 2 hours and tried to bend the bolt. To my surprise, it snapped off easily where the CA was applied. I tried breaking the same bolt in another spot without CA and could not break it. Another modeler I know tried it also without using kicker and achieved the same results, but it took about 2 days for the bolt to become brittle enough to snap. It seems that kicker accelerates more than just the CA cure!

Apparently, CA and/or accelerator changes the chemistry of the nylon making it very brittle. So be very careful if you are using nylon bolts and need to glue them in! NOTE: This happened with the WHITE nylon bolts you can find at Lowes or other H/W stores. I have not tried it on the black ones.

RE: Nylon bolts and CA warning
 

Interesting...

Thanks for the info Joe.

RE: Nylon bolts and CA warning
 

Very interesting. I have used CA on nylonscrews for years without issue. I knew that accellerator on nylon is a bad idea. I wonder if the brand of CA or the place of origin of the nylon screws has anything to do with it? After seeing this I'm going to take a good look at the tail wires of my Laser. They are .070 CF rod with a nylon clevis CAed to the rod. They have held of over a year now with at lest 300 flights but one can not be too careful

RE: Nylon bolts and CA warning
 

That's a good think to check. I've seen carbon fiber high altitude pressure vessels almost completely disintegrate during testing because a supplier used a different paint than the spec called for. Solvents and oxidizers can quickly change the strength of some materials.

RE: Nylon bolts and CA warning
 

I know I've used CA on nylon parts in the past without problems. I don't know if there is a difference in chemistry between various nylon parts. You would think they are all the same, but you never know. Maybe a few more people could try a test to see if their results are the same.

RE: Nylon bolts and CA warning
 

Same here.

I'm thinking it must be the accelerator. I'm very careful on what I use on my nylon bolts. I don't doubt that some chemicals can weaken the nylon, but regular CA has not been a issue yet with me.

Thanks for the " Heads Up."


Pete

RE: Nylon bolts and CA warning
 

On that same subject. I had bolted a new outrunner motor to my planes nylon motor mount. The bolts came through the holes in the mount from the back and into the motor. I applied a little Great Planes Blue threadlocker to the bolts. In doing so some of the locker ozzed out onto the nylon motor mount. The next morning my motor was laying on the table below the plane. The Blue threadlocker had turned the nylon into something on the order of bread crust. It would crumble between my fingers. Anyway, Just thought I would pass that on.

Tom

RE: Nylon bolts and CA warning
 

Its probably the heat of the CA and kicker combination that is making the nylon brittle. I was told by numerous members 15-20 years ago when i started that you never use any type of solvent on a Nylon fastener. Because it will either melt-it or make it brittle.

RE: Nylon bolts and CA warning
 

This is certainly surpriseing but very intertesting. Will hopefully remember this before doing it myself!!!

RE: Nylon bolts and CA warning
 

This is a copy/paste from page 19 of the Tower Hobbies Uproar 60 manual.

17. Screw the 1/4" - 20 nylon bolts through the holes in R2
and glue them to the ribs with thin CA.

RE: Nylon bolts and CA warning
 

invertmask may have hit upon the reason when he mentioned it may be the extra heat generated by the kicker that does the damage. I haave used CA on nylon before without problems, but it was obvious that the CA and kicker DID have an affect on this particular bolt.

RE: Nylon bolts and CA warning
 

The only way to know for sure what occurred would be a series of experiments to establish the conditions under which the bolt could be affected. You'd have to use multiple types and brands of CA, different types of accelerator, and different brands of nylon bolts to create a test matrix. Testing would be CA alone, accelerator alone, then CA plus accelerator. Each brand/type combo would have to be used on each brand of bolt to get valid results. Wouldn't be cheap or quick, but would definitely be interesting to see the results.

RE: Nylon bolts and CA warning
 

It would definitely be interesting, but I don't have that much time (or ambition) and I've already convinced myself that I won't use CA and kicker anymore on nylon bolts! ;)

RE: Nylon bolts and CA warning
 

It may be easier to take one bolt. Cut the head off to where you have an all thread. Then thread a block onto each end. Use CA on one end and CA with kicker on the other. I have a shop day planned for Wed. I may try it myself.

David

RE: Nylon bolts and CA warning
 

Oh, that's nasty! I know one thing, Blue Threadlocker or Loc-tite is good for removing paint. Don't ask!


Pete

RE: Nylon bolts and CA warning
 

it is the accelerator that is drying out the nylon.
there was a thread about it here at one time with a list of the accelerators that would and would not destroy nylon.

it's always best to use old nylon parts during a build where you use accelerator, then use brand new nylon parts when doing the final assembly.
accelerator really should only be used in a situation where you need to tack glue, or stop glue runs.
accelerator really weakens any joint as the CA is not penetrating.

RE: Nylon bolts and CA warning
 

I agree . Put a drop or two of CA on your finger and hit it with the kicker , you'll quickly see why this theory is plausible . ;)

In all seriousness , don't try this at home , if you haven't already "accidentally" done this to yourself . Unless of course you like pain . After all , pain just let's you know you're still alive . :)

RE: Nylon bolts and CA warning
 

You'll never learn how much is too much until you've scorched the back of your hand with thin CA that's wicked off of the assembly you're holding together.