Maybe a bent torque tube Mark

 

I've got one on order. I've checked everything else and replaced enough stuff, so It has to be the TT. The bird has never been crashed, so I don't know how the heck the TT could have been bent.

 

Ive bent them in flight on my 500 I had a sudden vibe problem.
Turned out the tt was a S shape

 

Feral, the TT looks very straight to me, and I've got a pretty good eye for that sort of thing. The heli feels fine until it gets near the head speed for stunt one and two, and then the boom supports vibe so badly they are just a blur.

 

Dude that odd real odd

Have you replaced the mainshaft @Mark Mickels

 

The main shaft is running true. The blades have never touched the ground. The V-bar Vibe analyzer shows a vibe of 79 with the TT out at stunt one, and when I put in the TT it jumps to 1300. It has to be the TT because everything else has been checked and replaced if needed.

 

Thats where id be putting my money on mate

 

IT has to be the TT. The V-bar vibe analyzer says the frequency equates to around 11,000 rpm.

 

Wow

 

It has to be twisting under load mate

 

If my friends remember to bring the parts to the field tomorrow, I should know. It's stuff like this that is really hard with this hobby!

 

I think it might be the bearings on the TT, either flogged out or let go from the TT (or the rubber). A extra bearing in there might stop it twisting if that's the issue
With the vibe at 11K it's somewhere in the tail drive for sure
Good luck

 

The tt bearing feels fine, and there is no lateral play in it that I can notice. I'll probably take it to work with me and put an indicator on it to check for runout.

 

and when you find the issue, post it so the pain is spared for others, thanks for taking one for the team
Simon

 

Thank you Sir Simon! I will indeed post when and if the issue is ever resolved. I feel like I'm chasing a phantom at the moment.

 

feathering shaft in tail and tail bearings also worth a look
Simon

 

I've had bearings that feel fine by hand but when under load go... swap out the tt bearing even if you think it feels fine.. I mean you have already got the tt out.. no extra effort and piece of mind it's not that

 

Just bought a new complete tail assembly. All new bearings, shaft, and hub and that didn't cure what ails me. It either has to be the TT or the boom, but like I posted this bird has never been crashed or even landed hard.

 

I agree, but I'm going to throw a whole new TT assembly in it at this point. I'm tired of messing about with it.