Integrity of epoxy connections
 

I was discussing an in-flight failure at the field with a fellow pilot in which the epoxy bond between push-rod tube to the fuse failed during a high-speed maneuver. He was able to recover his plane. I have to believe this type of failure is quite common with planes that have lots of hours.


In thinking about this, I wondered how someone could check all glued connections during pre-flight. I suppose you could check tension by gently prying a screwdriver up against the connection. If something is to fail, then better while the plane is on the ground.

In discussing this with someone at work, the idea of using a tension meter (with springs) could provide a robust means of accurately determining bond strength. If you know how much tension any given connection is required, you can measure for it, hopefully in a non-destructive way. Maybe it is not possible to know what the exact numbers, but perhaps general guidelines based on wing loading, or some other method. Or maybe I am over-killing this issue, and this degree of checking is not required.

I didn’t find anything in Google, but I have to believe someone has already established something similar that works.

Any thoughts on this?

RE: Integrity of epoxy connections
 

If I am understanding this, you are talking about securing the pushrod outer sleeve to the fuse? Also, apparently this was done by putting epoxy over the sleeve to glue it to the fuse? If my understanding is close, the problem is failure to construct a physical connection such as a ply connector between the sleeve and the fuse. Glue alone is not all that secure. If I am not understanding this correctly, kindly disregard this transmission. ;)

RE: Integrity of epoxy connections
 

The pilot in question is very experienced and has many years, so I'm pretty certain he built his plane correctly. I never saw the inside of his plane or witnessed the incident. (It wasn’t my plane, I don’t think I will ever have the skill this guy has) The failure resulted in little elevator control, and the picture I had in my mind all this time, conversation was a while back, was that the tube came loose inside the fuse. Whether or not there was ply, I don’t know, but given the pilot, I would assume the build was solid.

RE: Integrity of epoxy connections
 

If you have several thousand dollard to spare you could put strain guages with instrumentation on all the areas in question as we did in the ! to ! scale a/c flight test world.

RE: Integrity of epoxy connections
 

Just do like Jim said and make secure glue joints and you should not have a problem.



Buddy

RE: Integrity of epoxy connections
 

Great, thx for the replies.

RE: Integrity of epoxy connections
 

To be perhaps a little more helpful, the cause of that failure was undoubtedly not following directions and not understanding the materials that are being "glued" together. The material used in outer pushrod sleeves is a slick plastic through which the inner tube will slide easily. The material is so slick, in fact, that the manufacturer of the pushrods specifies that the surface of the tube be roughed up with course sandpaper before attempting to glue it. (Experience will also tell you that CA sticks to it a lot better than epoxy does.) If the fuselage was fiberglass, it is also necessary to clean off all wax, mold release and overspray before gluing anything to it.

Making adequate glue joints, like anything else, requires reading and following directions, paying attention to what you are doing and making sure that the result is satisfactory. If it is, continued testing can only be counter-productive.

Jim

RE: Integrity of epoxy connections
 

i've found that polyurethene glue ( Gorilla Glue, for one) works better than epoxy for this type of usage, and as stated before clean and roughened up. A gentle tug once in a while never hurt anything, either;).
Mike

RE: Integrity of epoxy connections
 

In the above, the statement " The failure resulted in little elevator control " leads me to wonder if maybe the bracing for a flexable control rod let loose causing only partial control due to flexing. Usually if a glue joint on a control rod fails ~~ IT FAILS !!!

ENJOY !!! RED

RE: Integrity of epoxy connections
 

I have some older airframes and noticed that some epoxy glues over many years will become brittle and start chunking off, if stressed and pried with a tool.
If your glue is 10 years old and yellowed alot,I'd bet that its ready to let go,and unreliable.

RE: Integrity of epoxy connections
 

Nitro,
The type and speed of the epoxy has something to do with old joints that are "peeling" away. The longer cure time epoxy usually penetrates a lot better than the 5minute and 15minute. Five minute almost doesn't penetrate at all compared to the others, and 15 doesn't do half as good as 30. And that'll make or break the joint over time. It's good enough reason by itself to not use 5minute for any construction, and to not use 15minute if you've got 30minute available.

"make or break the joint"..... hmmmm is that a pun? ;)