Friction in Push rods
 

I have completed my Falcon III, built to print and covered. I have noticed that there is a certain amount of friction when I manually push the pushrods. The push rods pass thru mylar tubes that are glued in place. The tubes were installed as per the plans from Goldberg. I think it is friction on the side walls at the curves where the tube makes a shallow curve. Is there anyway of reducing this friction without re- laying out the tubes? The plane is covered. Is it possible to spray some sort of lubricant into the tubes?
Your advise on this would be greatly appreciated.

Friction in Push rods
 

The only way I know of to reduce the friction is to make the pushrod runs straight. I recently had a problem with a Decathalon that wouldnt center reliably on the rudder and elevator. Turned out to be the pushrod setup. This was in a 10 year old plane. Had to strip the covering off to fix it. Better to do it now, unless the plane wont last that long.
Edwin

Friction in Push rods
 

Have you tried lightly sanding the inner tubes with fine sandpaper? This has worked for me.

Re: Friction in Push rods
 

There is ALWAYS going to be a certain amount of friction. If it's not too bad, don't worry about it. Without actually feeling it ourselves, we can't tell you if it's normal or too much. If you're really concerned about it, find a local builder who can check it out for himself. (and try to get someone who's opinion you trust, maybe get two opinions)

Friction in Push rods
 

If the servos don't buzz, there's not enough friction to worry about.

The friction may not be in the pushrod... I've often found friction at the clevis or hinge.

Friction in Push rods
 

I had the EXACT same problem with my GP US40+. I releived the aft-most edge of the opening with a round file, that helped some, but much to my surprise, the friction all but vanished when I pulled the aft ends of the pushrods out from the fuse 1/16" or so. I plan to install the elevator cortrol horns so that they hold the rods away from the fuse like this. Almost no lateral pressure is required to accomplish this and the change in resistance on the control rod is amazing. Being a newbie I was in a panic about this untill I showed it to a very experienced modeler - he showed me the light!

Re: Friction in Push rods
 

I agree with MinnFlyer that it's hard to tell from your description if it's normal or not. But in general, they should move pretty easily with your fingers. There's no point wasting your battery on fighting friction. I've not actually tried this, but perhaps you could take out the rods, and spray silicone lubricant on them.

Friction in Push rods
 

DON"T LUBE THE RODS!

As the rods live in an environment that is not sealed, any lube you apply will, in a fairly short time attract all manner of gunge, making your problem worse!

Fix the problem correctly and the fix will be permanent.

Friction in Push rods
 

Thanks for all your input guys.
Last night I opened the sides of the covering - (much wailing and nashing of the teeth I might add) removed the pushrods and re-ran them in a straighter line. I removed the nylon tubes and drilled a new 1/8" hole through the aft pushrod exit forward through the bulkhead towards the servo area. Had to use a 5" long drill, but it did the trick I guess. The friction is significantly less. I am not sure if the original configuration would have worked, but at least now it has a better chance.
I wonder how the original configuration would have worked. According to the plans, the pushrods are run with a much smaller curve. When I laid the pushrod over the plans and followed the curve, there was significant friction and binding when I tried to move the wire within the tube. I cleaned the wire, and made sure the surface was polished, but the binding was still significant.
I wonder what the advantages of this type of pushrod system are? Intuitively, I would have thought that it would allow the path of the pushrod to follow some arbitrary curve, but this does not seem to be the case. If the wire is too flexible, it would only properly work in tension, and would buckle when compressed. Should I have substituted a smaller gauge wire? Was I missing a step?


Troubled in Toronto

Cable /pushrod lube
 

David 99% right If you go with lube try powered graphite that is sold for locks --it won't collect dirt. :D :D

Friction in Push rods
 

Smark, It's tough to say what went wrong, or what could have been done differently without seeing it first hand. But that is all water under the bridge now. I would like to congratulate you on a sucessful surgery! I can relate to gritting your teeth and breaking something loose, but sometimes it's the best thing to do!

Friction in Push rods
 

I had the exact same situation in my plane. I think that the holes that were die-cut in the aft-most former for the push-rods to go through were in the wrong place.

Friction in Push rods
 

I keep a few 12" long drill bits in the 1/8" to 1/4" range for just such purposes. I also have a the same dia bits in a 6" length. These are just too handy to not have around. A lot of my planes lately have been swapmeet planes that are in the bones or I just modify them to match my prefered setup methods. One of the problems with binding is that over the years you end up with a re-centering problem. Some planes dont care. But my Decathalon and warbirds generally dont like it.
Edwin