push rod question
 

<div id="post_message_19331443">while im not brand new and have built several kits. I have a newb type question.
building the midwest superstearman and the plans call for a 3/8 by 3/8 home made push rod with 2 2/56 rods bent at weird angles to operate the elevator. I was going to use sullivan flexiable rod in rod but even the angle is too severe. ideas? will the homemade one for the plans work with the 1.20
4 stroke im using?
thanks.</div><! / message >

RE: push rod question
 

I assume that the pushrod on the plans is made of wood? I suppose that would work but I would rather use the Dave Brown fiberglass pushrods. They are stiffer and stronger than wood. If you wanted you could even make them with 4/40 wire ends and be certain that they are strong enough.

Another option would be to build two elevator servos into the aft end of the fuselage and drive each elevator half with a short 4/40 pushrod. The servos in the tail might even help to balance it with the 1.20 engine on the nose.

RE: push rod question
 

One of the nice things about the Sullivan push rods is that they are flexible and slide very cleanly through their tubes. I have used both Goldenrods and their carbon fiber rods. As long as you secure the tubes in several places along their route, they work just fine. If you don't secure them right or in enough places (like at each former) with epoxy (rough up the shell at the point where you would apply the epoxy), and at both ends, you can get them in some pretty ackward places.

CGr.

RE: push rod question
 

Don't forget that you can always use a combination of both methods

RE: push rod question
 

Hi!
But best is to use fishing wires (steel)!

RE: push rod question
 

Pull-pull using cables is by far the preferred system for ultimate reliability. It is lighter and can be guided quite easily by proper nylon bushings at exit points.

RE: push rod question
 

the pull pull might work best. as the golden rods will not bend out of the fuse as called for on the plans.
thanks everyone.

RE: push rod question
 

Pull Pull is great if you have a direct and straight line access to the elevator and/or rudder.

Minnflyer has the right idea.

CGr.

RE: push rod question
 

I used basically the same as the plan except that I used a carbon fibre rod instead of the 3/8 square. Did this on both elevator and rudder. Can't remember how I fixed the wire to the rod, however the plane is 10 years old so must have worked.

If I was doing it again I would use the DB fibreglass pushords as someone suggested earlier.

Terry

RE: push rod question
 

You do not need a straight line access, I use pull-pull on all my large models and many do NOT have a straight line to the servo. You can use nylon guide tubes well anchored where they touch structure, and do some amazing routing with no detriment to functionality. I have some large bipes that use this technique that are now 15+ years old with no problems in control on both elevator and rudder. Again, the secret for reliable operation is to have a slight amount of positive Ackerman built into the system and have the cables just snug enough at neutral to not have any sag. Now, straight line access is best and easiest if you can get it but is NOT MANDATORY.

RE: push rod question
 

Personally, I find Pull-Pull much more trouble than it's worth.

If you feel like going through the extra work, by all means have at it. And I'll do it if the plane is specifically designed for it and comes with the setup, but I wouldn't bother adapting a plane from a pushrod setup to pull-pull.

But that's just me.

RE: push rod question
 

The midwest Stearman tends to come rather tail heavy without adding servos to the tail. Even with the 1.20 . I haven't decided what to use for elev push rods on the one I'm building now, but I do plan to use 2 servos on the elevator(mounted up front) and Pull-pull on the rudder.

RE: push rod question
 

the pull pull seems ok at first but the angles are somewhat sever at the plan located exits. and I belive even with exit guides they will cut thru in time. Some of the other ideas may work betterlike the golden rod with the bend in the threaded rod idea.

RE: push rod question
 

Threaded rods are very weak as compared to music wire, especially if bent. Far better, if you use push rods, is to use music wire in the area that is bent and solder threaded couplers on the end for a clevis. I would not trust any threaded rod that has been bent. You can get solderable threaded couplers at the hobby shop, they have a cupped end to solder the wire into with the other end threaded. You can get them for either 2-56 or 4-40 threads.

RE: push rod question
 

I just looked through the manual ( the planes are in the box and I'm not digging ) and I don't see where there is a problem . Just do it like the manual & plans call for, Mike wouldn't have designed it that way if it wouldn't work.

You could make up some rods like Minn showed in post # 4, just be sure and support the flex rods about every 6 ". ENJOY !!! RED