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Sleeve for carbon fiber pushrod

Old 04-21-2015, 05:12 AM
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Default Sleeve for carbon fiber pushrod

All of my smaller (kit and ARF) aircraft utilize micro or 2-56 metal pushrods to maintain control surface positions. I would like to convert the metal pushrods to carbon fiber in certain locations because I'm getting too much deflection in the rod.

One example: I have a Mini Ultra Stick. I removed the tailskid located below the elevator tail and installed a tail wheel connected to the rudder. This added more resistance to the control surface and the micro pushrod is deflecting too much. First, I reinforced the tubing, but the metal pushrod has too much resistance inside the tube. There is a lot of friction between the pushrod and the plastic sleeve. Also, the metal pushrod is still deflecting.

I purchased .060 carbon fiber rod and installed as needed. The setup is complete, with one problem. The carbon fiber rod is installed in the same knock out locations within the interior formers as the original tubing. The carbon fiber is rubbing against the interior holes of the wood formers. I'm concerned the carbon fiber will be damaged as it continues to reciprocate within the former holes. I want to install the carbon fiber within a tube. I installed some K&S round aluminum tubing but it's not perfectly straight. I still have some resistance within the aluminum tubing.

I did some testing and discovered the .060 carbon fiber rod moves freely within a carbon fiber tube. Can I use this application or will the carbon fiber rod and tube deteriorate as they rub against each other?

I may install Sullivan Gold-N-Rod sleeves and install the carbon fiber rod within the plastic sleeve (discarding the metal rod) OR installing the rod "free air" (without additional supports).

I'm new to carbon fiber. I've done my homework reading about gluing, tying and wrapping clevises and other hardware to the carbon fiber rods. My problem is protection and placement.

I could install a pull-pull system, but I want to learn more about carbon fiber applications and installation techniques.

Any suggestions are greatly appreciated.

Thanks!

-PD
Old 04-25-2015, 02:43 AM
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Just use short sections, 1/2" long maybe, of the sleeve tubing at the formers,, that will reduce the friction dramatically and the over all weight

good luck
Old 04-26-2015, 05:39 AM
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With a CF control rod, if it is flexing then it's too small. Broadly speaking, there are two kinds of control rods for RC planes: stiff rods that don't need support, and rod in a tube systems that rely on a sleeve. CF lends itself well to the stiff rod setup, as does cedar wood. Steel and plastic are good for the rod in a tube setup. Which is best depends largely on the fuselage structure you are working with. If you can support a plastic tube every 2-3 inches, the rod in a tube setup will usually be lighter for the amount of strength you get. But sometimes you can't, so a stiff rod is necessary.
Old 04-27-2015, 05:35 AM
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Thank you for the replies. Scale only 4 me, I arrived to the same conclusion and will install several 1/2" sleeves to provide support and proper direction where the CF pushrod travels through the formers.

Jester_s1, I do not have any flexing of the carbon fiber pushrod. The problem was with micro wire pushrod flexing at my rudder control horn. I wanted to replace the metal wire with .060 Carbon Fiber rod. It is working wonderfully now, no flex.

Thank you for the help!

-Clear Skies
Old 04-27-2015, 03:15 PM
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If there is no flex, then you don't need the support tubes. And yes, there could be a problem caused by them. I couldn't say if the rubbing will be an issue, although I would worry about it. But probably more concerning is the rod binding against those guild holes where it rubs. It doesn't take much binding to slow down your control response and cause inaccurate centering. IMO, a stiff rod setup needs to not be touching anything besides maybe the fuselage exit. 2 or more points of contact is a chance to bind, which is a chance for problems to develop.
Old 04-28-2015, 05:21 AM
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I attached some pictures identifying the problem and the materials I'm working with.

I am not going to use the aluminum tube or the micro wire.

I am unable to install the CF pushrod without touching the wood frame; I don't have an unobstructed straight / direct path between the control horn and the servo arm . The only way to accomplish this would be to modify the wood formers.
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Old 05-02-2015, 06:13 PM
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I would use nylon tube as guides. It would be best if you can run a guide tube the full length. Using some carnuba wax on the CF rod will make the interface really free. When setting up a model this small I don't bother with the threaded couplers. I have found that I can slide a nylon clevis into place, set everything to nuetral and a drop of CA will secure the clevis to the CF rod. Do not use kicker and clean the ends with acetone befor applying glue. The clevis will never pull off but can easily be cut off if needed. Do not use those quick connectors with CF rods, the screw clamping down on the rod will create fractures.
Old 05-04-2015, 06:09 AM
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I tried nylon tubing with the CF rod. I'm having a difficult time matching the I.D. of the nylon tubing with the O.D. of the CF rod.
The quick connectors you see in the photos are from the original installation with the micro metal pushrods. The quick connectors are discarded and I'm installing Sullivan clevis to the control horn.
I'm still working on the best fit for this application. I'm not in a hurry to complete this. It's important to me the installation is solid and worry free.

Thank you for the help!

-Clear Skies

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