Wing joining tubes/rods

[StephenB]

My upcoming build of the Cliff Charlsworth SF-33 motor glider requires 10mm OD wing joiner tubes. I have 10mm OD carbon tube which is 8mm ID. The problem is I cannot find anything to fit in it, carbon tube or rod is 8mm OD so too tight, can't find piano wire that would fit, I guess I need something around 7.5 - 7.7mm to slip in fairly snug.

Any suggestions??

[Peter Balcombe]

Stephen,
I found that the Sussex Model Shop 8mm Carbon rod fitted nicely in their 10/8mm Carbon tube, but I understand that not all tubes & rods fit so well.
You could try easing an 8mm Carbon rod using emery paper, slowly working from one end until you get a fit.
Peter

[terry white]

Hi Stephen, just some thoughts out loud if you intend to use carbon as a wing joiner. It seems to me that an 8 mm carbon rod is very thin to use as a wing joiner (if I am reading you correctly.) even a 10 mm un- sleeved carbon rod would make me wince a little.Your problem is that the carbon tube has a wall thickness of 1 mm therefore reducing the thickness of the joiner bar by 2 mm.
My suggestion would be to go to E bay and find a 10 mm O.D. thin walled alloy tube that fits correctly into a 10 mm I.D.thin walled alloy tube.They are about. The thin wall is only about .25 mm allowing more meat to the joiner bar itself.
Into the 10 mm O.D. tube either sand to fit or inlay it with carbon tows and epoxy a good quality carbon 10 mm bar. This will give you the lightest weight wing joiner you can get. BUT please never use a carbon tube or rod without it being sleeved with an alloy. After a number of landing loads it could (and they do) eventually hairline crack just outside the fuselage tube.The alloy sleeve takes this sheering force away from the carbon.
If you don't happen to notice it ,it becomes spectacular on your next loop. hope this helps Terry

[StephenB]

Peter, I had a go at fettling an 8mm carbon tube but an awful lot of sanding achieved very little other than a lot of black dust. I was hoping if this worked to insert steel rod that I have of the correct size. I've got all these tubes and rods but none of them fit together!

Terry, I was intending to put a carbon tube inside the larger tube but also insert (and maybe glue) either an aluminium tube or piano wire to make the joiner. It's a relatively small model at 2.5M wingspan. The problem I have is that the laser cut ribs are designed for 10mm OD so I want to try and work with that. The other problem I have is either finding suitable material here in Hungary or, if it's available from the UK, I'm often faced with huge shipping costs or they won't ship overseas.

[Jilles]

a tip how to sand carbon rods. Had to do a couple for my Nimbus vintage glider
fit the rod in your electric drill, set to slow rpm. Sand surface water and 240 grid wet sand paper. make sure to keep it very wet all the time
Advantage is that you sand the complete surface evenly and no dust will travel through you workshop or in your nose. Regular wiping the surface with a cloth.

[StephenB]

Thanks Jilles, I'll have another go using your suggested method.

[Jilles]

Don't go too heavy on the sanding, before you know you take off too much with this wet sanding. Check at regular intervals