For a year and a half, I have been trying to figure out why my Shark 45 will not turn insides. Outsides are fine but the insides are scary. On inside maneuvers, the plane seems to hesitate or simply not want to turn the corner. I have tried every trim trick imaginable, without success. As you can imagine, trying to turn the corner during an inside square, as you heading straight down, and the plane does not want to respond to the control handle is to say the least, unnerving. (And not desirable.)
So for some history. After I finished the plane, I took it to the Golden State contest in October of 2012, and flew it in Classic. It did not want to turn insides. The greater the speed or wind, the worse it was. I talked to a number of really good flyers and builders about the problem. One of the better builders was kind enough to spend some time with me trying to figure out the problem. We tried a number of things, including, at his suggestion, testing the plane for a flexing pushrod. He and I pushed, pulled, prodded and otherwise abused the control system and concluded that the problem was not a flexing pushrod.
So over the next year and a half since then, I have continue to fuss with the plane trying to figure it out. At this point, it was not so much that I had some emotional attachment to the plane but I wanted to understand what was going on.
So fast forward to a Fun Fly in Salem, Oregon a few weeks ago. I tried another “adjustment” that had no significant effect. I was talking to another experienced flyer about it and he said, “Maybe the pushrod is flexing.” I started to say that it could not be the pushrod flexing because I had already looked at that possibility early on. But the more I thought about it, the more the turning characteristics matched those of a flexing pushrod. So again, back to pushing, pulling, prodding and otherwise abusing the control system. I still could not detect any flexing. But it made so much sense that I decided to “bite the bullet” and hack into the fuse and replace the pushrod. After all, I tried everything else and I was ready to hang up the plane in utter defeat.
So I replaced the pushrod with a carbon fiber one. The previous pushrod was a 4-40 threaded pushrod. The plane is powered by an Evolution 60 and weighs 74 oz. (It’s been through a “war.”)
That absolutely fixed the problem. The plane looks like a wreck but now flies quite well.
I share this story for 2 reasons. The first is to let you know how very subtle the flexing pushrod problem is. You cannot necessarily feel the flex in the pushrod under static conditions, even when you “push, pull, prod and otherwise abuse the control system.” I would say that if your plane exhibits the inside turning problem I described, nothing seems to make it better and you do not have a carbon fiber pushrod, take a good long hard look at the pushrod setup and consider replacing it with carbon fiber.
The second reason for sharing this is that this is my first time using a carbon fiber pushrod and I have heard of some failures with glue joints in a few pushrods. I assembled mine borrowing from my fishing rod building experience. Here is how I did mine. I would like to hear from others on how they do their pushrod assembly.
First, my pushrod inside diameter is slightly larger than the outside diameter of the wire used for the bellcrank or control horn attachment. See the pictured below. That was intentional so that I could insure that I was able to get a good amount of JB Weld around the wire when it is inserted into the CF rod.
Next I cut a very narrow width piece of masking tape to wrap around the wire to be inserted. I will wrap a narrow band of tape at each end of that part of the wire that will be inserted into the carbon fiber rod. Picture is below.
The next (hopefully these are in the correct order) I show how the tape is being used like a collar to center the wire in the hollow carbon fiber rod. There is, of course, another band of masking tape at the extreme end of the wire that is already inserted into the carbon fiber rod.
At first blush, it may appear that the masking tape will not be adequate to support the stress on the wire but in reality, the tape only centers the wire in the carbon fiber rod hole and helps capture the JB Weld. After the JB Weld cures, of course, the masking tape is no longer a factor, just along for the ride as it were.
I used a small file to rough up the inside of the carbon fiber rod so the JB Weld can get a better grip. I also used a cutting blade on a Dremel tool to gouge and rough up the wire to be JB Welded in place. See picture below.
I pushed some JB Weld into the carbon fiber rod then inserted the wire until the first masking tape collar disappeared into the rod. I then spread JB Weld liberally between the two masking tape collars and pushed the wire further into the carbon fiber rod. I pushed the wire in until the second tape collar disappeared. I then tried to squeeze in more JB Weld behind that and to form a small “blob” at the front of the wire where it exits the carbon fiber rod.
The last picture shows the finished end. I think with this extra attention to the JB Weld and all of the mating surface preparation, I should not have any of the failures I have heard about.
Again, please share how your carbon fiber rod is constructed and any related stories.
Mike
Topic: Does Your Plane Turn Insides, or Not (Read 4932 times)