Superroc Coupler Question

[cbrarick]

I figure this is the place that the people in the know about superrocs hang out...
I'm doing a superroc that's a bit upscaled.
I know that couplers tend to be failure points, but have a odd question
IF full length couplers weren't possible, and the longest you can get is 3.5x the body tube diameter.
My material is linen phenolic, so it's stiff and not going to bend the way paper does.
would it be stronger to epoxy the coupler into one of the tubes at 1.5 or even 1 body diameter, and use the rest for the slip joint, which I'll use 4 rivets to hold in place, or is the standard "put half in each side" stronger?

 

[cbrarick]

Wow! 52 reads and no responses!

 

[Sandy H.]

I'm bummed that you didn't get a real answer from someone, but my feeling is that it would be best to put less in the glued side and more on the slip joint side. The glued side (epoxy/whatever) will definately be more strong than any slip fit.

I think Superrocs can often fail in buckling, so I bet the failure could be right below the glue joint or right above the slip joint. I suspect the slip joint, but I could be wrong, as stress concentrations right below the glue joint could lead to the buckling failure while the slip joint might have less stress from a buckling standpoint. . .

If I was doing an LPR Superroc with a limited coupler length, I would do 1/3 glued, 2/3 slip ratio as a start - just a gut feeling. If it was an MPR/HPR Superroc, I would do a lot of testing before running the power up.

I'm pretty sure that someone here has the simulation tools to give you a better approximation, but if they don't respond, you just have to do the experiment yourself, I guess. . .

Sandy.