I need some ideas on how to fix a "poor planning" problem I have with a Midwest AT6. The pushrods recommended for the tail surfaces are the Dubro laser rods. Without thinking I bought a few of them and installed the outer sleeve in the fuse (not glued yet). The problem is that the actual pushrod is a clear plastic tube and I'm a little concerned with whether they will be strong enough for a plane like this. I'd go ahead and use a carbon fiber rod, but the guide holes in the fuse formers don't make a straight line to the rear. Does anyone have any ideas on what kind of pushrod I might be able to use that will be stronger than the dubro's, but flexible enough to make a few minor bends over the length? Thanks!

Ben

The laser Rods will work fine, just be sure to have metal ends that go from the Fuse Exit to the control horn.

Minnflyer,

You don't think the metal rods will pull out of the plastic rod? Even threaded in 1/2" or so, I don't have alot of confidence in the plastic holding the threads at the bottom of a high speed dive. What about temperature changes affecting the rod length, I image the plastic they use for these things is pretty stable? I'm probably just being paranoid, but I'm used to using short metal or carbon rods where the servo is a few inches from the surfaces. Even the 40 size stuff I had a while back used 2-56 metal rods in a plastic sleeve.

Thanks,
Ben

I'm using this setup for years now without any problems on a 3D plane......BUT.... one flex tube goes into another flex tube of slightly larger diameter....Right? Ok....I fed them through a hobby brass tube of slightly larger diameter than both and shaped it with slight bends to where I need to hook up. Works fine for me. Recheck your CG though.

I use a cut-off wheel to make very small nicks around the metal rod to give the glue some tooth. Also, be sure to brace the outer tube every few inches inside the fuselage.

No problem Ben, I have been using them for years without problem. I don't know Kaz, and I don't doubt his word a bit, but if you know Caffeenman, you'll know that he creates superior airplanes. If he can trust it, (as I do) you need not worry.

Try this:

1 Thread a rod into a plastic tube

2 Pull it out

I think you'll agree that this method works well. In fact, My retracts use flexable pushrods, and on a few occaisions when they have been ripped out on a bad landing, usually the inner rod breaks before the threads pull out.

Thanks for the tips, guys. I think I'll go ahead and use the plastic rods. The only thing I was concerned with was the metal seperating from the plastic, but I'll just thread the metal ends in as far as I can with a little epoxy. The sleeves are supported through the fuse formers every couple inches so they shouldn't flex at all. I've used a laser rod for the tail rotor on a scale heli for a while with no problem, but it doesn't see much stress.


Ben

These pushrods are the same design that comes with the Sig Somthin Extra. I am on my second plane and have absolutely no problems with them pulling out. and trust me, I put a lot of strain in the pushrods. My advice would be to not worry about it, they should be ok for your use.

MinnFlyer,
I was taught to install the threaded rod in this manner, does it look okay to you?

Just so you'll sleep better why don't you do a stress test? Setup a rod like you will be using on your plane then put some kind of scale on it like a fish scale maybe? Then keep putting presure till it breaks. Then you'll know how strong it is and can be confident that it'll work.

I thought about doing a little stress test, but I don't think I would get much info from it. I don't know how much stress the rods would see in flight, I also wouldn't know how the effects of temperature/time/repeated stress would affect the materials. The experience of others is plenty of reassurance. I did call a friend of mine who used to have a Midwest AT6 and he said that he used the plastic rods without any problems.

Ben

The most serious problem you will find from bending is if you fail to support the outer tube at several places in the fuselage. There shouyld be a balsa suppor at least every 3" to 4".
Minnflyer gave you the best solution. Thread one end in about 3/8" and then try to pull it out.
I'll take bets on whether you or the rod wins the tug of war.

I wouldn't worry about it. The rod will work fine. If you want to do a stress test, build something similar to the elevator and then push and pull on it. If the elevator breaks before the rod, then the rod is ok.