Pitch transfer noise

[Gerd]

Are the bearings of the tailshaft ok? Please check them careful.

[rossk]

Originally Posted by Gerd

Are the bearings of the tailshaft ok? Please check them careful.

I just tried to pull the tail shaft out to check the bearings, the shaft would not pull out, was only inserted a couple days ago, and only bench run.
After much effort, I got it out, damaging the tail shaft, the tail case, and the tail gear.

The fin side bearing is 100%, the rotor side bearing is cactus, hard to say if it was cactus before or after the tail shaft difficulties.

I have another tail case here, but the bearings in it feel about 80%m slightly notch(1 flight, 1 crash).

I have ordered more parts, new tail case and collar, to exclude them.

So now I will have a completely new tail on its way, hoping to get this fixed soon...

[rossk]

I replaced the entire tail assembly with new parts, including a 'built by Gerd' tail hub.
I also tensioned the belt by hanging it, this def puts more tension on it then I have ever had before.

Bench tests are looking good, 2100rpm no vibes at all.
Going past 2250 created some vibes, but no where as bad as before.
So I think flying @2100 with peaks up to 2150, should be fine.
Will do some flight test tomoz, hoping for the best...

[helicraze]

Ross i got new diabolo kit and have same problems, above 2000RPM with silver pulley sounds like it will explode! I check everything and it looks fine

[lcheli]

I had the same problem 2 months ago on my new kit as well. did the same bench test as Ross had the same result. I gave up and just stay under 2100 head speed.

ROSS which part that fixed your issue?

Thank you
LC

[rossk]

I replaced everything, so I can't say which part fixed it in the end.
Biggest help in the end was rail 96's

[helicraze]

I cant even get above 1800rpm with silver pulley. New tail bearings as well

[smsodhi]

I had a similar problem going to 2200 with silver pulley, I had 115 tails on which were probably too much. That is what I put it down too. Anyway I am happier at 1900 with the red pulley. It sounded like the gearbox was going to explode.
What size tail are you using? Maybe try smaller blades and see if it improves?

You should be able to get well above 1800 with silver pulley, try red pulley and see if it happens at 1800?? If there is a shaft bearing issue it should be worse at the higher RPM, if not ? blades, ? balance of blades. Play with the tail pitch grip arm, change it from leading edge to trailing edge, I fly with trailing edge with no issues.

[helicraze]

Ive tried both pulleys and even without tail blades on tail shaft can be seen vibrating and grips going out of track

[rossk]

Have u run it without the hub on, just shaft?
This will eliminate everything up to the shaft

[helicraze]

Yep seems fine with just shaft in

[lcheli]

I had narrow down to the tail grip hubs. without just the tail grip hubs bench test up to 2300 HS were still very smooth. Once I install the Hubs onto the tail assembly the vibration starts from around 1900 HS and goes up as the HS increases. And thats without tail blades. My tail hubs spin very smooth on the tail assembly. had no idea why the tail grip hubs create the vibration.
current setup on my tail its with silver tail pully with 110 CY blades and 2100 HS. she flys good lol ...

[helicraze]

I seem to have same issue.

Gerd is helping me fix this

[smsodhi]

Originally Posted by helicraze

I seem to have same issue.

Gerd is helping me fix this

Any news? I had vibrations at 1900 today with red pulley, in the tail.
I recently changed the tail rotor shaft, hub and all tail bearings.
Problem started after the replacements.

[helicraze]

Gerd is sending me some replacement.

for you i guess put the old parts back lol

[Gerd]

Replacement is perhaps not the right term. From measurement nothing bad is to find on this parts. So we send new parts for finding the reason with changing them part for part.

[smsodhi]

Problem sorted.
I went through the tail with a fine tooth comb, in the end it was bad motor bearings.
The vibes would be responsible for my boom clamping shoes coming loose in flight as well.

[ChadL]

How did you go about isolating the issue to the motor bearings? One reason I like Vbar is the spektrum analysis for isolating such things.

[smsodhi]

Process of elimination, I did however, think how nice it would be to have vib analysis.
The fact that the vibes got worse in a particular RPM region got me thinking.
After I changed the motor, the heli felt so smooth , right upto 2300.

[jcflyer]

Satnam,
Back when I use to fly Skookum I learned about vibes and the like, the Sk720 has the ability to track down vibes through out the heli once you learn how to read the graphs. After learning this and discovering that if there wasn't some kind of event to cause a new found issue such as a vibe, most of the time you could be sure it was a bearing somewhere or bearing related!!!