Help track down a tail vibe! *SOLVED*

[Relisys190]

The kind of tail vibration that makes you say " I WILL SELL YOU AND BUY AN UPGRADE HELI MODEL" lol

Okay so here's the deal. Today I put on some SWITCH tail blades, I've been running eco power (Amain). The switches are considerably bigger and 4 grams heavier (which could induce or magnify vibes).

Today during a flight I broke a rudder pushrod support. Just snapped rigg off, it was brand new with the boom I just put on after a crash 3 weeks ago. The heli was making a strange sound and tail was vibrating violently.

Now back on the bench at home, main blades off because even the sound is a high freq (high speed) vibration resonance. I spin the heli up while tail blades are on and I'm holding the boom/push rod disconnected (Don't try that at home)

Here's what I've done:

New tail shaft
New tail shaft bearings
New tail rotor hub
Two sets of tail blades each balanced.

Using a magnetic balancer i dynamically balanced the tail rotor assembly using blade balancing foil tape

I mean this thing is spot on balanced. YET... When spun up on the bench with tail rotor installed its a wicked vibration that makes it difficult to hold the boom (high speed vibration)

Sorry for the long winded. I just want my reliable 500 back.

Thank you,
-Markus

[AKPhill]

I don't know what type heli you are flying but if it is tt check your torque shaft bearing location
It might have moved one way or the other

[SumOFparts]

Have you tried sticking different kind of blades on it and if there's a difference???

IS everything smooth if you drop the blades all together??

-
And these are the blades you filed the roots down -
I found if I sanded the kbdd blade roots on my 450x's - it would create a stress point - and thereby shortening their life considerably - but watching yours according to that other thread...

[Relisys190]

It is a trex 500 belted tail.
I've tried two sets of tail blades and dynamically balanced both with a magnetic prop balancer.

Oh the frustration lol.

[Relisys190]

I'm considering replacing :

I2 tail grips

I am going to order some "pro" tail grip assembly and see if that helps.

Still by dynamically balancing the assembly, it should be smooth.


Everything else that rotates on the tail has been replaced.

No, there is no vibration with the tail assembly removed. With just the tail shaft spinning with belt attached, it's smooth as butter.

[Relisys190]

Holy crap guys. I just spent another 4 hours meticulously checking every rotating part. So you wanna know what it is?

poor quality control on new parts.

The belt pully that is manufactured into the tail shaft is out of round. I can literally see it moving 1mm forward and backward when I spin the head by hand.

I cannot believe this would cause such a huge vibration!

I just ordered another one, this time from RonLund. Really hoping to get a good true unit.


On the plus side, my tail assembly is balanced like a humming bird.

I'll update as soon as my new part comes in.

[AK65]

Considering that the tail rotor is spinning at 12000 rpm +, any small unbalance becomes an extremely big deal. Also with the wind loading of the tail rotor blades and the inertia of the tail grips also, they would tend to amplify the wobble of the rotor shaft. Throw in some bearing play and a resonant frequency, and you've got real problems.

I hate the tails, they are the real weak spot of these machines imho.

I had one issue when one of the stub shafts coming out of the centre hub was slightly out: (bent from a crash) it did not show up without the tail blades on (just tail grips). But once the blades were on, since it affected the tracking, it made the machine totally unflyable. This was on a 450 btw, but the 500 would have the same basic weaknesses.

Then there is my recent post regarding tail 'notchiness'. Either the grip bearings (which are subject to huge centrifugal force) or the pitch control slider were failing under load when the tail got up to speed on my 500 (took me a long time to figure it out) - the standard check you would do would be to disconnect the tail servo and check the slider under static conditions: smooth as silk - the problem only came about under working headspeed. I bought tarot tail grips and hubs for my 450's, which use thrust bearings which can handle the outward loading that the fast tail rotor speed generates. I have also bought cheap chinese grips in the past where the bearings actually started to disintegrate due to the centrifugal loading. After one flight, the bearing was almost in pieces.

I think the tail is one area where you really want the best, because the margins are so small. A bit of slop on the main rotor head is not amplified as much due to the far slower headspeed.

For those of you guys running fast headspeeds of 3000+, I don't know how you do it. But then, I assume that that's where the difference between Aligns and clones like HK makes the difference between flyable machines and endless frustration on the bench trying to 1. identify the actual issue, and 2. trying to fix it.