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Vibration analysis question
https://www.spirit-system.com/phpBB3/viewtopic.php?f=20&t=1261		 Page 1 of 1
Author:  scrambled [ Thu 10. Mar 2016 21:27:33 ]
Post subject:  Vibration analysis question
While upgrading to V2.0.0 I also played a bit with the Spectrum analyzer. (Great tool.)

It gives me some vibs only on the Y-Aileron axis.
Why only on that axis?
Does that point in a specific direction for trouble shooting this issue?

Sometimes it goes a bit over "50" and it shows "increased vibs" or something similar.
The heli (Gaui X3) seems to fly fine to my knowledge. :mrgreen:
Should I worry or just go fly?

Thx.

Attachments:
File comment: Vibration analysis
IDL1.png
IDL1.png [ 103.41 KiB | Viewed 1997 times ]
Author:  scrambled [ Fri 11. Mar 2016 10:10:53 ]
Post subject:  Re: Vibration analysis question
Any directions on this ZeXx86 please?
Author:  ZeXx86 [ Fri 11. Mar 2016 10:20:48 ]
Post subject:  Re: Vibration analysis question
Vibrations are mostly transfered to the Y axis because of custruction of the frame.

Generally you can tell that helicopter is OK if any spike will not exceed 50% amplitude.
Unfortunately first spike is exceeding 100% which is not really good.

First spike is from the main rotor and it look like a bent main shaft, bad bearing is less probable because spike is very precise.
Second spike is coming from your tail mechanics. There could be same issue.
Author:  scrambled [ Fri 11. Mar 2016 10:42:45 ]
Post subject:  Re: Vibration analysis question
Thx.
Not sure why the peak is so high on the picture, the numbers only show slightly above 50.

After the last crash I replaced main and tail shaft.
I know they are perfectly straight.
Flying with a bent shaft I would certainly notice. (Not the case here.)

Could it be the steel pinion on the main gear (very hard plastic) transferring some vibs into the frame?
If I put my hand on the heli while spinning at high rpm, I don't feel much vibs at all.
Author:  ZeXx86 [ Fri 11. Mar 2016 10:51:04 ]
Post subject:  Re: Vibration analysis question
Yes, it can be main gear or anything assymetric on the mainshaft.
But in case that there was an accident when main shaft was bent, then in the most cases at least one bearing is often faulty too.
Some vibrations can't be sensed by hands too well since frequency is quite high.
Very often vibrations that you can feel in hands are not that bad as these that you can't feel - this apply especially for bearings.
Author:  scrambled [ Fri 11. Mar 2016 13:01:37 ]
Post subject:  Re: Vibration analysis question
OK, I always try to feel by hand if bearings are notcy or gritty.
That was not the case so I left them as is.

I'll replace anyway to see if it helps.

Thx!
Author:  ZeXx86 [ Fri 11. Mar 2016 22:11:42 ]
Post subject:  Re: Vibration analysis question
You can gradually dismount parts so you will see when the spike will disappear. If it will disappear, then the problem was very probably in the unmounted part.

You are welcome!
Author:  scrambled [ Sat 12. Mar 2016 13:52:04 ]
Post subject:  Re: Vibration analysis question
I'll do that on the first maintenance.

For fun I added a small piece of electrical tape on one tail blade.
Wow, amazing!
Spike is a lot lower. :mrgreen:
(On my first post tail blades are also connected.)
Tested with rudder servo disconnected and tail blades centered.

For the Spectrum analyzer it would be handy if it defaults to the Y-Aileron axis.
That page shows the spikes.
On other axis it's almost nothing.

Attachments:
File comment: Small piece of tape on one tail blade.
X3 vibs tail with tape.png
X3 vibs tail with tape.png [ 92.8 KiB | Viewed 1925 times ]
Author:  Coco66 [ Sat 12. Mar 2016 20:51:22 ]
Post subject:  Re: Vibration analysis question
You cannot trust mutch the vibes analysis with tail blades on.. it is tuned for without them.
Author:  ZeXx86 [ Sat 12. Mar 2016 22:51:30 ]
Post subject:  Re: Vibration analysis question
Actually you can use analysis also with the blades. The only problem are main blades - these are highly not recommended because of the safety and other possible issues. With the tail blades on you have to do measurement very carefully.
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