Material choice for slip joints. - RC Groups
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Feb 04, 2013, 11:51 AM
Registered User

Material choice for slip joints.

So here's my question of the day. The project I am working on will have a couple slip joints. I am assuming these joints will receive some pretty good side loads. At this point I am planning on using braided sleeves to lay them up. What materials should I use. The joints will be about 3.5" long. The wall thickness of the female tube will be about .05" at the opening then increase to about .2". The wall thickness of the male tube will be in the neighborhood of .065" From what I see on this forum it looks like it's common to use Kevlar fabrics on female parts like wing tubes, and carbon for male parts like wing rods. Let me know of you need more info.

Thanks again
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Feb 04, 2013, 12:01 PM
I'm All Thumbs
AirBornOne's Avatar
Hey Bruce,
I think the most experience composites engineer would need to know more about your needs to be of any help.
What's the project?
Spar,chassis,mast,torque tube???
How are the loads applied?
Tangentially,axially,constant,intermittent,all the above???
What is the expected max load?
Ya know,that kind of stuff.
Feb 04, 2013, 08:12 PM
Registered User
I can see that by including a few specific details about my project I have made it difficult for you all to give me the kind of general answer I was hoping for. I will try again.

From what I see on this forum it seems like it's common to use Kevlar fabrics on female parts like wing tubes, and carbon for male parts like wing rods. Am I seeing this correctly? If so, what properties do these materials have that lend themselves to the tasks?

Feb 04, 2013, 09:23 PM
Cognitive dissonance
kcaldwel's Avatar
CF is used for the joiner (male part) because it has high bending strength and stiffness, which are the primary loads that a wing joiner has to carry. There is also a shear load, which CF is also pretty good at, but it is usually less critical for a wing joiner.

The sleeve (female part) is sometimes made from Kevlar, I think primarily because it makes a very light part. Kevlar is low density compared to glass. I just made some Kevlar wing sleeves at 3 grams a side. The loads on the sleeve are usually transferred into other structure right away, so the tube really only acts as the interface to the CF joiner, and the structural requirements aren't very big. I've had gliders where there wasn't a sleeve at all. The CF wing joiner just went through holes in ribs at the joint and 100mm inboard.

I'm not at all sure how that applies to your part requirements.


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