Carbon Fibre Pushrods - Central Hobbies

Central Hobbies sells carbon fibre pushrods. How to I attach these to the standard 3/32nd hole on the my control horn. There was an ad in Stunt News a while back of someone manufacturing one of those "whatchamacalls". Can anyone give me a hand on this one and get me the name and phone number of that person?

I've started using the Rocket city ball links. THese accept a 4-40 threaded rod and attach to the horn with a supplied cap screw. Replace the standard nut with a nylok nut and this all results in an adjustable, low free-play system. The 4-40 threaded rod can be epoxied into the CF rod, or one of the standard rod-end filler pieces can be attached first. Be certain to rough-up both pieces first and use a high-strength epoxy mix. I just wax a screw, and epoxy that. It ends up depending upon the same epoxy interface to the CF rod.

I'm planning to set up a right-hand, left-hand system on the next plane so the rod becomes the center of an adjustable turnbuckle-style link. So it will adjust without detaching an end.

Hope this helps.

I'm sure others will have other details to suggest as well.

I just wanted to correct the terminology I used in my original reply. I dont believe standard "ball links" are acceptable for our CL applications. The things I use are reallly "spherical rod ends" They are made for model car steering and suspension systems. The bolt goes THRU the ball.

DuBro also makes a version of these.

They DO NOT snap apart like the ball links.

Since your question is how to attach those standard 3/32 inch hole horns to your carbon rod, the fast answer is to attach 3/32 wire ends to the rod. Unless you have a take apart system, you don't need ball links, and if you build the rod, then adjust the location of the stabilizer--forward/back--to line everything up square, you don't need adjustable length, either. A little "tweaking" can always be done afterwards IF needed. The key is to build it as square as possible to begin with.

To attach the wire ends, cut your rod about 4 inches shorter than the total length you will need. Then cut two 4 inch pieces of 3/32 wire and put a 1/4 inch right angle bend in one end. Cut two one inch long dowels of the same size as the inside diameter of the carbon push rod and put a 3/32 notch down one side of each dowel. Drill a 3/32 inch hole in the side of the carbon fiber rod one inch from each end, insert the short wires with the angle bends sticking out those holes, and wedge the wood dowels with epoxy on them into the ends of the carbon rod to hold the wire ends securely in place.

Now you have a carbon fiber rod with wire ends. Bend these ends to the final length that you need, centering the carbon fiber portion as evenly as possible, and attach the wire ends using washers and solder as you would a full length wire push rod.

Dave brown makes some neat plastic ends that he includes with his carbon fiber rods, and these ends are available separately (one rod is long enough for two planes), but the wood/dowel method works just fine. The total weight is no greater than a standard 3/32 inch pushrod and there is no bending, flexing, or fairleads needed.

After someone lost an aircraft at Huntersville due to the attachment of the 3/32 wire failing, Tom Morris had a brain storm and this is what he came up with as a possible/probable solution to this problem. Take the 3/32 wire for the control rod and cut it to the approximate length needed. Then slip about a 6-10 inch piece of carbon fiber rod over this (the thinnest variety), it's only slightly larger than 3/32 inside diameter. Secure the carbon fibre rod centered between the flap and elevator horn with JB Weld. Of course this is not as light as using just the tubes terminated at the ends with the 3/32 wire, but there certianly cannot be a failure of this system if it is engineered properly so that the carbon fiber tube cannot slip forward or aft even if the JB Weld lets go (highly unlikely).

For what it's worth

How did the pushrod fail in the instance that you cited? Certainly JB weld is an alternative solution, but in the method I cited, the 3/32 rod exits the side of the carbon fiber push rod and is held securely even if there were no glue holding the dowel in place. Of course, the glue is there to keep the dowel, itslelf, in place, and should never be omitted.

I just don't see how the "standard" method of attachment can fail, unless there was not enough wire protruding through the side hole, or the side hole were eliminated entirely. (Or did the wire, itself, break?) Let's face it, a lot of people using "advanced" construction methods do not always read or have instructions before them. If they try to build using other, unsound, methods, then failure can and will occur. Everything in the system must be made bullet proof.

There are alternate good and bad solutions. Certainly Tom's method should work. If you have other alternate systems, by all means post them. We all learn in the process. (And sometimes we learn what does and does not work.)

Len,

As I was told, when the CF rod was drilled for the 3/32 rod, it apparently created a slight crack in the inside of the rod that went unnoticed. Vibration took it's tool on the crack and caused the CF to break and allowed the pushrod to come loose. I understand that the rod was not wrapped with wire or string and epoxied on the outside past the point that the wire exits as I do the ends of mine. I have never had one of mine come loose yet! Knock on Wood!

Here is where the Dave Brown rod ends might come in handy. With the wire going down the center of the plug, it can't break out. The rod end again goes through the hole to the outside, but for it to come loose the entire plug would have to come loose as well. I put one together with epoxy and tried to take it apart again and could not. I not only would have had to destroy the carbon fiber pushrod, I would have had to destroy the end plug as well.

I guess a second consideration is the source and integrity of the carbon fiber rods themselves. A lot that are called carbon fiber are really fiberglass. Carbon fiber rods cost considerably more, but are stiffer and lighter. If the rods were made with lengthwise tow only, or if they were of too thin a material, I could see where they might split quite easily. Then if the wood plug method were used, it could allow it to split out. If the ends are wrapped, however, as you suggest, or the Dave Brown ends uses, I think this would eliminate any problems, even with a lower quality rod.

I have used arrow shaft pushrods and am familiar with the attachment. With the Central hobbies units there is a 4/40 insert which goes into the small but ridged shaft. I need to find connector which has 4/40 threads and will not fail in stunt application. So far model car ball links seem to be the ticket. Thanks for the help.

I use the Dave Brown inserts but rather than wrapping with thread or whatever I put 2 inches of heat shrink tubing over the pushrod ends. No failures so far.
Nils

I doubt that with the Dave Brown inserts you would have failures anyway, since the rod goes through the center. As I mentioned, once you get those plugs in, I don't think you would ever get them out.

All the methods suggested above are fine...here's just another variation. "The test" he refers to is once the threaded rod is
"BlackFlashed" into the CF tube, you can hit the open end of the tube with a hammer and drive the threaded rod through a 2X4 without loosening it in the tube - pretty convincing!

http://www.darrolcady.com/Carbon_Fiber/carbon_fiber.htm

I'm sure you're right Leonard but I like the finished look the shrink tubing gives.

Ok, I'll admit it, I also just like to play with shrink tubing. I like shrinking Ultracoat with a heat gun too. Simle pleasures for simple minds...
Nils