I'm working on finishing my G-202, and have put together a carbon rod for elevator control. I'm just not convinced that I should trust the set up.

I cut the rod to length (less than a foot) and used a liberal amount of JB Weld to simply glue a 4-40 threaded rod to the inside (centered with JB Weld all around) of the tube. I stood the rod up on end to have the JB Weld run down into the threads as much as possible. With the commercial set-ups like this, there is a fitted end that is pretty tight in the rod, and the JB Weld is minimal.

I pull on the ball link on the 4-40 rod, and it is strong, but will vibration and/or age cause a failure?

The complete set-up is a Du Bro Super Heavy servo arm with a 4-40 ball link to 4-40 rod. This is on both ends of a short length of carbon fiber tubing (3/16 I think). The control surface end is connected to an MK bellcrank via a 4-40 ball link.

Would you trust such a set-up on your plane?

After I made my post, I see you have a 4-40 all-thread all the way thru your CF tube?? If that's the case and you are just using the CF to stiffen the rod, you should be OK as long as you don't get stress fatigue where the threads meet the tube. The set-up I use below has a short piece (1 1/2" or so) of 4-40 rod glued into each end of a CF tube, with the factory threaded inch or so sticking out of each end. My rod doesn't go all the way thru the tube, just glued into each end. Original post below:

I run identical set-ups on all kinds of planes. The only thing I do differently is I score the 4-40 rod pretty good with a pair of diagonal cutters to give the JB Weld something to bite into. I also make it go up into the CF tube about twice as far as the Central Hobbies titanium thread pieces. Never had a problem, and I'm running them on a Whiplash that has a lot more vibration than most planes will ever see, at pretty good speeds. The set on the current Whiplash has even been thru a crash (45 degree angle into hard dirt at close to 200 mph). I also run them on my profiles, just easy to make up a pushrod with no soldering. Same set-up on the 4-40 ball links, everything. I know it's overkill on a profile, but it is slop free, light, and looks neat. One other thing...I take a brass ferrule that goes thru the rubber grommet on a servo and slide it over the 4-40 rod and into the CF tube while the JB is still wet. That gives me a nicely finished end. Looks neat and keeps a wad of JB from being on the end of your rod.

Thanks Chuck, but my 4-40 rod is only about 2 to 3 inches long Each piece has about an inch sticking out of the CF tube. The threaded rod is not all the way from end to end. There is a separate piece on each end of the Carbon rod.

I like the idea of the brass on each end whenever the rod is visable. That looks much nicer than what I have, which is a tapered glop of JB Weld.

You should consider putting a short piece of aluminum tubing over the end of the CF rod to prevent the rod breaking under side loads. CF pushrods are extremely light and stiff but do not hold up well to side loads.

Aluminum tube is sure a great addition, but I also have wrapped the end of a splitting tube with SpiderWire and CA and that will stop the splitting. Aluminum tube sure looks better!

This is how I've set up my pushrods.....



This is not my model but I have used the exact same principle - VERY rigid.

What would cause a side load?

This is on a Great Planes G-202 46. The elevator servo is in the center of the fuselage and so is the input side of the MK Bellcrank. The elevators are built oversize, but I do not see a huge load there as I do not fly at a hundred miles per hour.

As short as the rod is, there shouldn't be much problem, but I'm worried about the JB Weld cracking due to vibration, or just letting go (losing adhesion) of the inside of the carbon fiber tube.

The picture of the aluminum with carbon set-up is nice. For giant scale, that would be the way to go.

Taitwister,
I've used the same system you're describing on helicopters (lots of 3D) and never had a bit of trouble. I think it will be just fine.