Vibration analysis on Logo 500

[Joce]

Hello, I recently got a used Logo500. I'm still flying at medium rpm because of new lipos.
Heli flies nice and rescue is ok.
I have a concern with vibrations. I could see in logs a notification of very high vibration.
I made the vibration analysis on 3 axes.
On Y axis at 1800 rpm I can see that high vibration that I suspect related to main blade balancing. But I also have a high level at 3600rpm and at 8340. This last one is the tail (ratio is 4.6 on this heli). But the one at 3600 I can't explain.
Could you please help in understanding this graph ?

[ZeXx86]

Hello,

the biggest issue is the first spike which is very high and should be really from main rotor or its bearings.
8340RPM is from your tail.
3600RPM could be main wheel that is too close to the pinion and is touching at two points somewhere.

[Joce]

Thanks Tomas for your answer, this makes sense. I will try to figure out the source of vibrations and give you feedback.

[Joce]

Hello, i made different tests. First without blades, then only tail blades. Vibration level on Y axis stayed below 14.
I checked the cg of my main blades, was near perfect. I also statically balanced them.
Then with main blades on, big vibration comes back.
,Back to the desk, I noticed a very slight oscilation on the main shaft.
I ordered a new one and will see if it improves things...

By the way, I tried to dynamically balance the tail blades. Adding tapes on one blade, oscillations were going up to 25. But on the other blade the effect was not clear. Will try again with new main shaft.

[kmaluo]

Your main shaft bearings might be ruined if you shaft was not perfectly straight. Make sure they're not notchy under load. I would replace them just to be safe.

[btheli]

Hello, i made different tests. First without blades, then only tail blades. Vibration level on Y axis stayed below 14.
I checked the cg of my main blades, was near perfect. I also statically balanced them.
Then with main blades on, big vibration comes back.

I had this same behavior on one of my helis and it was slop in the main grips. The two grips are connected to each other with the spindle shaft. Because of the slop I was able to slide the grips back and forth in the head about 1 mm. When I would spin up it would slide to one side and create a huge vib. Shimmed it out and now perfect.

Sent from my SM-G920P using Tapatalk

[Joce]

Thanks btheli, I'll check that asap !