This past weekend I flew my Ziroli Corsair with Brison 5.8 at the HOTMAC Warbird flyin in Waco Texas. During my last flight I pulled into a big loop. All was well until I began to pull out of the loop. I used full up elevator to come out about 10' above the ground. The push rod broke during the loop. The plane has about 60 flights. I used 4-40 rod epoxied into a 5/16" hardwood dowel.

Talk about having a free airplane...WOW.

When I put in new push rods, what suggestions do you have to prevent this from happening again?

Ken

gee you were very lucky. You could try a setup I have on my 1/4 scale Cub.

I use fiberglass arrow shaft. Use the 4-40 rod but what you do is trill a 4-40 hole about 1 1/2 " back from the end of the shaft. Put a 90 degree bend in the 4-40 rod with about 1/2" on the bent end.

Next you take a piece of wooden dowl that will fit inside the shaft snuggly. dremel out a channel so that the 4-40 rod can recess into it.

You then put the bent end of the rod in through the hole in the shaft, then epoxy in the dowell.

Should solve your problem.

cheers
Peter

Peter, the steel rod broke near the end of the dowel rod. The dowel did not break nor did the steel rod pull out of the dowel. Your method sounds good but I don't think it will solve the problem other than maybe change the resonance frequency.

A friend suggested a possible fix. Use several layers of heat shrink tubing on the steel rod to build it up near the diameter of the dowel and then put a length of heat shrink tubing over the dowel and the rod. This combo should give a shock absorbing effect to the assembly to keep down the resonance vibration.

Ken

I found out that by seperating the elevators each with their own pushrod it minimizes failure. I use fiberglass rods (Dave Brown) with aluminum inserts and joined them @ the servo. I used Dowels 2'' in length as a bearing guide for the pushrod as it passes thru the sheeting.
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paradiserceer, the elevator is separated and driven by two separate servos. Here is a little different view. The elevator servos are on the outside and the servo in the center operates the rudder in pull-pull.

Ken

sounds as though you are getting some sort of elevator flutter to cause a rod to be experiences those sort of vibrations. I would be looking in that area for astart and also looking at some sort of pushrod guide so that it can not flex about too much.

cheers
Peter

I think you are just the unlucky (no so badly so) bearer of bad luck. I have used the shaft that Oz speaks of for years. I had a 12 year old plane and they never broke. You may have gotten some softer pushrod by chance. Another thing to do is to support the rod closer to the servo output arm. This will minimize flexing...especially under a load. I actually use 1/8 welding rod and tap that 4-40. It makes for a little thicker material. You can get it at a welding shop for about $4.00 for 5 three foot rods. Also, a 5.8 Sachs is quite a shaker of a motor, so I would support at the servo and each fuse former location. Vibration is a killer.

I like to reenforce the 4-40 rod itself by slipping it into a brass tube. Then I sweat solder into the tube. I can't imagine anything breaking the rod using this set up.

Ken,
It looks like you have a good set up but the steel on the rod was too soft?? Central sells Titanium 4/40 rods for pushrods, I'm sure those will withstand the stress.
JG

Actually you only need enough build up on the 4-40 rod to allow the the heatshrink on the dowel to be able to grip the rod diameter. The failure looks to be a classic section transition type of failure.
As others have said vibration damping and a higher strength material will also help. Gradual section transition will be the easiest approach.
Sure a lot easier than a rotating counterbalance design for the Sachs.
The ten ft. high pullout looked more like 6 ft. or less to me. The landing however was as the smoothest Xwind touchdown that I have seen.

First of all I want to thank you all for the suggestions. There are some good ones. I have no way to get in the fuselage to brace the rod without major surgery. Here is the transition based on Gremlin Castle's suggestion in person. The steel rod area is filled with heat shrink and one layer goes over the ball joint fitting tail end. The final red heat shrink goes over the dowel and over the fitting. I think this will sufficiently dampen the high frequency vibration. I'll do the other side the same way.

The pull out probably was at 6' but I was so puckered up at the time that I wasn't judging height above the hard deck effectively.

Ken

Ken, Back in my full scale training they told me that pucker does not create lift..possibly they were wrong?? Better check that transmitter stick too..it's probably bent back.
Sure happy to hear the ending was good!

In reply to post #5. Ken I have a picture of what I am describing, But not sure how to get it to you. It will help even though you already have the elevator on seperate servos....

Randy, I really believe pucker factor was working for me. Once I found out that I still had a little elevator left then I relaxed and the landing was no problem. Running separate servos is the only thing that saved it. They surprised me with a nice plaque for Best WWII and one for Spectators Choice.

Randy tell me you are back working on the B-25.

paradiserceer, I sent you an e-mail.

Ken