Tail Vibration

[Boomkidd]

Well, I'm just curious, I have a belt drive trex 450 w/ the silver head. I'm pretty sure I'm getting vibration from the rear when she spools up. If you're hold it while spooling (I know, safety), you can feel the tail doing a high speed vibration. If you look closely, it is vibrating quickly. Could my bearings be done? Maybe 1 too many crashes? (The bird is all good now except that mild, high frequency vibration.) The blades are not bad, nothing is too loose/ too tight, etc.
Any known problems w/ the tail? I removed that silly tentioner pulley. Does that reduce vibrations or something?
Or do i need bearing, shaft, maybe the hub the blade grips screw in to?
Thanks all!

[bigdawg86]

1.) Bearings
2.) Tail Rotor Housing Bent
3.) Tail Shaft Bent
4.) Loose Rotor Grips
5.) Offbalance Blades
6.) Belt Drive Pulley Bearings
7.) Belt Tension
8.) Main Bearings
9.) Etc... It's a one by one troubleshoot. HAVE FUN!

[Aussie_phoenix]

is the vibration up and down or side to side?

[Boomkidd]

Everything is adjusted/ configured properly back there.
I didn't know you can balance tail rotor blades (I don't think that is actually possible.) However, I changed the slightly beat up carbons w/ fairly new ones. I even weighed them to see if they're the same- which they are. The belt is a new, yellow one. Everything in the rear is tight and properly configured (except the belt tentioner pulley, which is removed.) I am putting it back on.
I took the main blades off to spin it about half stick and you can feel it in the entire bird but mostly from the tail (as you slide a finger down the boom towards the tail.) When it's vibrating slightly like that, if you look at the tail, you can see it vibrating if you look closely.
It doesn't fly abnormally (no bobbing or anything.) I just don't want to have a tail failure it the air due to something I can fix now. I think the belt drive shaft which drives the tail is slightly bent but I can't tell by looking at it. It has a very tiny bit of play when you try to wiggle it up/ down. It also moves in and out slightly @ the drive pulley in the tail...are there supposed to be shims back there?...it seems when I put pressure from my fingernail on the outside tip of the spinning shaft (esentially taking that movement away), the vibration subsides. Am I being picky and this is how these tails are? The bearings don't feel 'gritty' when I spin them while holding them. Are those bearings possibly shot? It's also what I suspect. Any precision bearings shouldn't have any play once they're installed. (But, the rear has very slight play.) I'm thinking of simply filing down the 3 spacer bars in the back about 1-2mm's to tighten the gap a little...is this a wise move?
Well, I'm broke until Friday as far as heli funds go so, I just hope it doesn't have failure due to something like a bearing or 2.

[FurryTrex]

take the main shaft out and see if its straight that was my problem

[flerpie]

Loosen the tail boom - let the tension off the belt.
Spin her up - but not full speed.
Does vibe go away?

You could also have some sort of resonance effect.
A small vibe at the head and a small vibe at the tail
at the same time. So loosening the belt helps to isolate
which end, if not a little on both ends.

[wrstew]

If you have play in the tailrotor output shaft, that'd be my first suspect. That thing is hauling rpm when in flight, and any play (read looseness) would be hi freq vibration. I would pull the tailcase apart and put a 1/2 drop of thick ca on the bearing support surface and put back together. Or a paper shim, something reversible to find if the bearing looseness is really the culprit. You should not have in and out play, if you can temp stop that, It would be beneficial. Pull the t/r drive belt and spin the mainshaft, see if the drive gear is really wobbling......that would load and unload the belt in use, also bad. Are the fins vibrating at hover?