At wits end on with tail vibe

[bstanley72]

I’ve been trying to get rid of a tail vibe and have had no luck. I’ve got over 200 flights with this bird (Trex 500, esp style, belted tail) logging vibes under 2, now they’re through the roof and I can’t figure it out. This is a really starting to sour my enjoyment of the hobby and shake my confidence going forward. I really want to build a Goblin 500 when they come out but his is making me question my skills. It is a mechanical issue, I can feel the boom buzzing when I spool it up. Here is the log:

http://www.filedropper.com/log81

I’ve replaced everything in the entire tail, some things multiple times, here is what I’ve gone through trying to sort this out:

6 tail shafts
3 boom drive pulleys
2 belts
3 tail cases – 2 plastic and 1 metal
3 pitch sliders
3 sets of tail blade grips
3 rotor hubs
2 booms
2 boom blocks

Please, anybody, I'm pulling my hair out here.

[Slyster]

I've solved this issue on a few helis.. most notably my ex Trex 500 ESP.

Put a 1/2" of black electrical tape around the leading edge 1 tail blade. Measure vibes. Better? Worse? With a little trial and error I've completely dialed out vibes as bad as yours.

[TBur]

Didn't see tail blades in your list, but I assume you did try that ?

[dee cee]

Yep try another set of quality tail blades. How's your tail servo after 200+ flights.
Ensure the boom supports and fins are all loctited in, vibes are known to come from when these are loose. Hope you sort it and enjoy flying again. Luck...

[Feeback]

Why is the plot cut off at about 500hz?
I'd like to see what your motor is doing. That should be up around 600hz.
You are running about 2950 on the main rotor right?

Also, check the tail fin for cracks.

[bstanley72]

To answer a few of your questions and share some more info:

On the log above the tail blades aren’t on the bird and the push rod is off the tail servo, so it’s not them.
If I take the tail rotor off and run the log the vibes are under .5 (point 5).

If I pinch the belt and rotate the head the belt pulses, or gets a little tighter then loose then tight etc. I think this explains why the vibe is mainly for/aft. I think if the rotor was unbalanced then it would be a combination of similar intensity for/aft and up down, right?

My original thought for the for/aft vibe was a bad pulley, but I’ve tried three of them. So that leaves the tail shaft, tried 6 of those. I can see the tail shaft move slightly when I rotate the head. It does it with every shaft I’ve tried. I thought maybe the tail case was off and was causing this, I’ve tried two plastic and a metal one. Still the same.

My latest theory is I have hit a bad bunch of tail shafts. I bought them all from the same place, all within the last month. SO I’m thinking that they had a run, or part of a run that produced shafts that aren’t true and those ended up at the place I purchased them from.

Any other ideas? Because I’m all out. I’m even considering converting it to torque tube, so I know I’m getting desperate.

[Feeback]

One thought is that when there's a bad belt, there are often a lot of them and since they aren't so popular anymore, might take a long time to run the inventories out. Can you see if the pulleys are running out of true? That would explain your finding with the belt getting tight/loose.
It doesn't seem to be the belt because you say the vibe is gone when you remove the rotor. Did you try it with just the hub with the grips off?
Any chance you could take a video of the tail shaft moving as it turns. This sounds like your problem. And yes, it is quite possible a lot was made that's out of whack.

[Luvmyhelis]

Wow, I wish I could help.

But I am myself fighting almost identical looking vibes in a new Warp build I am trying to sort out. Like you, I replaced everything. Even going so far as to integrate another brands tail assy onto the tail shaft. And like you, if I take off the hub assy leaving the shaft bare. The vibes disappear. I even changed the slider! And went through 3 sets of new blades in different brands. My tail shaft is also arrow straight. And for the first time ever. I am stumped.
I just posted here as misery loves company?

[Slyster]

If the tail shaft is straight.. I'd still put on tail blades and try the tape method. It has worked for me many times.. my 500 was so bad it actually hurt to touch the boom spooled up without main blades and tail link off.

[jcflyer]

B where is the sk unit located on the heli and which heli???

[wis1]

Maybe try the chinese weight mod, some decent youtube vids on it. Might be worth a shot.


wis1

[bstanley72]

Here's a video of the tail. You can see the shaft wobble both at the end where the rotor goes and around the pulley. All the shafts I have do this. So it's either something I haven't thought of yet or I have a bad batch of tail shafts (or drive pulleys).

I’m actually thinking of doing something I haven't done before, and that is buy clone parts. Maybe I'll pick up a Tarot tail shaft and drive pulley and see what those do. At least I know they aren't from the same run as the parts I have.

It is frustrating. I've had tail vibes before. Once it was a bent shaft, the other time the bearings were shot. Both times I just replaced the bad part and it was then butter smooth.

[ame]http://youtu.be/CClyZrED3I8[/ame]

[TBur]

Wow, yea one would to after the shaft and bearings. Is the pulley removable ? Could always just roll the shafts on glass to see if they are true. Are you using stock bearings or ?

[Feeback]

That shaft is bent. No two ways about it. And, on top of it, the pulley is not mounted true on the shaft. The bigger issue is the shaft being bent.

[Larry227]

It also looks like there's slop in the left bearing or the spacer is out of round, unless that spacer is part of the pulley.

[Larry227]

Also a couple other things I noticed on my 500 ESP. Even though mine is still TT it's something to check. When I was chasing tail vibes on mine I ended up finding the right bearing was spinning in the case. Once I solved that the vibes got better but I still had to fine tune it with a piece of tape on a blade like Slyster mentioned in post #2. Ever since then I always play around with adding some tape on a blade.to get the vibes as low as possible.
Sometimes I wonder if the grub screw in the hub is enough to throw the whole assy off balance and that's why tape helps. If you think about it, everything else on the assy is pretty much symmetrical except for that single grub screw.

[bstanley72]

Originally Posted by TBur

Wow, yea one would to after the shaft and bearings. Is the pulley removable ? Could always just roll the shafts on glass to see if they are true. Are you using stock bearings or ?

Originally Posted by Larry227

It also looks like there's slop in the left bearing or the spacer is out of round, unless that spacer is part of the pulley.

Pulley and spacer are part of the shaft. The stock bearings are in there now and they are smooth, I have a set of Bocas I put in, no difference.

[snaaakeey]

Know how your feel! I have a 7hv with an unpalatable vibe issue after a minor bonk! Replaced most bits to no avail! Good luck.

Sent from my GT-P3110 using Tapatalk HD

[bstanley72]

Here's another video with a different tail shaft. Watch the belt move on the back side the pulley, how bad out of round it is.

[ame]http://youtu.be/tZ_OTlI-wuY[/ame]

[TBur]

What is just to the right of the left bearing ? Is that a spacer, part of the pulley ? Whatever it is, shouldn't it sit flush to the bearing ? It's very different than your earlier video.