I need help with the vibration on my XCELL ST that I can't get rid off. You can see the vibration mostly on the tail boom especially when you are at a hover or about to take off.
I am already so frustrated, I need advise .......

If I read you correctly, you mean the boom itself is moving around.

If this is the case examaine the following (not nec. in the given order).

1. Main blades out of balance (try to borrow a good set of glass blades to rule this out very quickly)

2. Bent mainshaft (check the main shaft bearings while you're at it)

3. Major bend in the blade axle

4. Markedly out of balance flybar.


If possible, try to be as specific as possible in the description of your problem (for example, is the whole boom moving or the tail fins on the boom) and cover what you've tried to fix the problem. Doing so will allow us to offer you more specific suggestions.


Ben Minor

Actually I noticed this after the crashed. I have replaced the main rotor blade, new flybar and paddle, new spindle, main gear and tail boom. Flybar are equal in length between the paddle. I also tried to re-aligned paddle. Main blade are balanced and have the same CG.
The whole tail boom is shaking up and down and you can notice this upon take off and while hovering. It seem to decrease once in forward flight. What else have I missed or do. I appreciate you taking time to help out.

Did you check the main shaft for straightness ( I didn't see it listed as a replacement)? Did you check the main shaft bearings for notchiness? I have never had a crash where the brades hit the ground that I did not bend the main shaft, blade axle, and destroy the main shaft bearings. Also check TR shaft and hub for bends.

I should have included that I have also replaced the main shaft. I took the main rotor apart today and double check. I found out that the replacement spindle is bent so I will bring it to the hobby shop to point this out to them.
I appreciate it very much to all that responded to my plea for help. Thank you !!!!

IF the blade axle is bent the blades would not stay in track. You could track them and have them in track , but soon as you pumped the collective couple of times they would be out of track again .
They would be continously going in and out of track if the blade axle is bent.
How did you determine the replacement axle was bent?
Also usually a bent blade axle does not cause the vibration your describing except when the blades are out of track.

Just trying to help.

David

Well, when I took the rotor head apart, I check both the main shaft and the blade axle against the glass of our dinning table. The main shaft roll smoothly while the blade axle wobble. I am also considering the possibility that the wood blade I am using myabe warp. As far as if this may totally eliminate the vibration, I don't know. At this point I am just doing the process of elimination and taking in all that is recommended by those of you that give me advise. Definitely I need it.... Thank you.

Hey David,

It has been about a decade, but I have seen a boom shake from a bent blade axle. Like you, I'll agree that it doesn't seem to add up as a boom shake causer like a bent mainshaft would, but this guy's X-Cell 50 shook like a wet dog until that axle was replaced.

Like Cliffy says, "Something to do with metaphysics". <g>

Ben

Ben,
Yeah I agree it can cause a shake. But also I would think he would have trouble keeping the blades in track also.
Now he mentions blades that may be warped, I think we are dealing with some serious metaphysics here now <G>


David

Since my skill level is intermediate, I'd rather not invest on those expensive fiberglass/carbon fiber blade. I am currrently using AEROTECH woody's. Is there another way to tell if the blade is warp aside from visual. Do you think I have covered all the areas that my cause the vibration? Well, I can't wait until the hobby shop open so I can get the part and put the heli together so I can test it. Thanks.

You can spot a simple unidimensional bow in a blade by sighting down the leading and/or trailing edge.

To find a twist, first set both blade grips STATICALLY to the same pitch by matching all control rods. Next mount up the blades and pick a side from which to start. Beginning at the root of one blade, use your pitch gauge and measure pitch at the root, midblade and at the tip. It makes no difference what the numbers are; they should be consistent if the blade is twist free and NOT of a washout design. Flip around to the other blade and repeat the measurements. The numbers you get should pretty well mirror the ones from the first side. If the pitch readings are consistent across the blade yet different from the first side, the blade reinforcements are on differently.

Given the fact that a decent set of glass blades can be had for about $80, and you can't trust that the wood baldes you have are good (plus the flying time you're losing screwing around with this stuff), you can see why so many guys just don't bother with wood blades anymore.

Ben Minor

You know I belong to a very small club here in Suisun City California. We only have 14 members and I am the only one flying helicopter. The advise I am getting from our memebers are basically on the care and adjustment of engines. I rely mostly on people from the internet that are kind enough to share their experience and knowledge on helicopter. There are other clubs in the area but I enjoy the people I fly with. Again, I appreciate the information and you guys taking the time. Thank you.

You're most welcome.

Please follow up and tell us how things worked out, because we learn too about which pieces of advice lead to a solution to a problem.

Ben Minor

Huh !!! finally I'm back in the air VIBRATION free. I have replaced the feathering shaft in the main blade that is bent. A little adjustment to get a good tracking in the main blade and it's sweet !!!!
I want to thank Ben and David on their advise. THANK YOU !!!!!!

Cool.

That's nice to hear.

Enjoy your model!


Ben Minor