Vibration Issue AGAIN (Fury Extreme)

[cdrking]

Am running out of ideas.

Fury Extreme
YS91 (about 50 flights) IMO tuned correctly
SB-16FH
CP30%
GY601

Etc,etc, etc,

I have done all the usual.

Runout less than .001
Fan balanced
Alignment (better than it's ever been) Spent a lot of time with this.
Balanced tail blades

I WAS cracking rear vertical channels (3) and that seems to have gone away. But at a Fun fly last weekend I broke a landing grear bolt. This is the first time since 2003(since new) that it's happened.

The ONLY thing I can "see" is that the rear delrin tail coupler seems loose. I am going to change it. But how much will this really contribute to vibration?

Please tell me I should have checked something else. I can't figure this D%#$ thing out.

Thanks for the help.

Jeff

[Alfred]

Jeff
I would ignore the broken landing gear bolt
Either the bolt was faulty, was too loose (hammering in the lower metal frame) or too tight.
It sounds like that you removed the original problem, but other parts have suffered from the original vibs. So I would keep an eye on parts for any other that were damaged in the original hassles and are now giving out due to fatique.
Just using logic (guessing) the loose Delrin coupler would cause shockloads to the tail drive system everytime the RPM changes and when you go through load/no load changes.
So, yes..I would change it no matter what.

[Wyn]

I had a vibration at the tail that turned out to be from the torque tube for the tail drive. It had a slight bow in it. With the tailbox off, spin the crown gear and watch how much the tube runs out. Reverse the torque tube in the boom to check the other end for run out. It doesn't have to be perfect, but <= 1mm works for me. Mine was pushing 3mm and had enough vibes to annoy, but not enough to stop flying.

Just a thought, and it's easy to check while your working on the coupler. Best of luck.

[WayneBrown]

the delrin cup doesn't really have a large affect on the vibrations, the tail is always under a load. (been there, done that. Flew great)
While you have the gearbox off to check the torque tube, rotate the output shaft with the slider all the way out. If the bellcrank moves at all, the tail output shaft is bent.
If you were still cracking channels, I'd suggest looking to see if the crown gear is warped, allowing the pinion to run loose-tight-loose...

[cdrking]

I should have mentioned a few other things with my original post.

I have checked many, many things on the heli. Here's a list, probably can't remember everything though.

Checked the following.

Main shaft
Crown gear shaft
Put a new tail output shaft (wasn't bent but upgraded to the new shaft for the open box)
Torque tube (as per MA it's less than .006)
These were checked with a dial indicator with V-blocks.

Changed many things also.

Crown gear
Metal beveled gear that drives tail rotor
Main gear
Torque tube (tried a couple of different ones)
Swash plate
Added new flybar cage
Clutch stack is new

Balanced tail blades using a Koll balancer/CG checker.

Crown gear mesh is set really nice as far as I can tell.

I called and talked to Tim at MA and he suggested that the delrin couplers could contribute to vibs. I don't completely understand that but I am going to change them if they are really loose.

Thanks for the suggestions though. I would really like someone to look at my machine and tell me that I've done something wrong. I've had several others look at my heli and they can't find anything either.

I'll keep flying it and see what happens.

Jeff

[Alfred]

If the Delrin Couplers are loose, they might not want to centre and actually wobble.
That certainly would cause a lot of vibs.
You might have a nusty harmonic in the heli.
Last ditch resort:
Loosen all the frame spacers and carefully do them all up again, you might have got a very slight offset in the frame from the last crash and the components are now under tension all the time.
Replace the Head Dampers with the normal soft "O" rings, just for testing
Remove all everything of the tail except for the gearbox + output shaft. Run heli up to below liftoff (obviously have some weights on the skids.
Loosen and re-position your Boom steady clamp by a few milimetres..1st one way then move it a few milimetres the other way.
Any of these should give you a real clue where the problem might be.
Good Luck