I have a Blade CX which I've been having a lot of fun with, getting to where I could hover pretty confidently including nose in, and fly around my office between the cubes.

Yesterday I broke the plastic hub which holds the upper blades, and replaced it with the metal repacement hub. At some point after that I noticed that the heli now swings around like a pendulum while hovering, rather than staying in one place. Specifically, if I take off and have the power set so it stays level, and then take my hands off the controls, the heli will gradually start to move in a circle, but with the nose pointing in the same direction. The diameter of the circle increases until it's about 5 feet. In forward flight I also notice that it seems to be gently lurching forward instead of flying at a steady speed. (For those that don't know, the Blade CX is a coaxial rotor chopper, and normally will hover pretty much hands off once it's trimmed.)

I have performed the upper blade tracking adjustment as described in the manual, but this didn't solve the problem. Does anyone know what else would cause the heli to behave this way? It makes it pretty much impossible to fly through narrow spaces like a doorway, which I was able to do before this started happening.

Adam

Check to make sure the the flybar moves freely. If you screw it too tight on the hub, it will make it stiff and your cx will hover poorly

Thanks for the suggestion duaneh1. Your suggestion is the first thing I thought of as well, but the flybar moved freely.

The problem turned out to be unbalanced lower blades. I thought that would have just caused vibration, but apparently not. I brought the heli to my LHS. The guy there flew it and agreed there was a problem, but didn't know what it was. When he held it up and spun the rotors at low speed, we could see the outer shaft wobbling. He thought it was bent, and recommended I buy a new outer shaft. After I replaced the outer shaft though, I could still see it wobbling, plus when I rolled the old shaft on a flat surface, it didn't appear to be bent at all. When I tried spinning the motors without the rotors attached, then the shaft didn't wobble at all, so I concluded that the rotors were the culprit. The blades were not damaged at all, but I had replaced the lower blades, and I guess the replacements weren't balanced. By adding some scotch tape to the tip of the lighter blade I was able to get rid of the wobble, and now the heli is much more stationary in a hover.

If the stabilizer bar is bent, it can cause that "toilet bowl" behavior as you described also. I've had that happen a few times following minor crashes that bent the bar a bit...