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Spectrum Analyzer questions
https://www.spirit-system.com/phpBB3/viewtopic.php?f=20&t=391		 Page 1 of 1
Author:  nougiw [ Thu 18. Dec 2014 19:05:11 ]
Post subject:  Spectrum Analyzer questions
Could someone please explain to me the diagram for vibrations? The peaks I see in the diagram do not keep up with the single value on the right. The peaks always seem to be way higher. Like this example in the photo where peak seems to be at ~58 while it says OK=46

Attachment:
DSC_0068.jpg
DSC_0068.jpg [ 1.13 MiB | Viewed 1161 times ]


Also I'd like to know how the Hz on the X axis correspond to rpm's. I mean, ok, apparently from manual someone understands that if you can see vibrations up to 500Hz or 30,000 rpm, the one I see here at ~220Hz should be around 13,200 but what are these 500Hz? What do they correspond to and why 500Hz is 30,000 rpms?
Author:  ZeXx86 [ Thu 18. Dec 2014 19:20:54 ]
Post subject:  Re: Spectrum Analyzer questions
Hi,

1Hz = 60 Revolutions Per Minute. You can point with mouse to the peak to get RPM value.
From RPM you are able to determine such vibrating part.

Right bar gives you information about total vibration amount, while graph can tell you what part of the model is problematic and what amplitude it has.
Normally amplitudes lower than 50 are fine.

From the graph I can see, that there is peak in 210Hz (12600RPM) so it will be probably tail issue.
If you divide 12600 / 4.5 = 2800. 4.5 is gear ratio between main and tail rotor. So from this calculation you know that if your head speed is 2800RPM, then 12600 must be rudder.
Author:  tdeane [ Thu 18. Dec 2014 19:22:34 ]
Post subject:  Re: Spectrum Analyzer questions
The easy part. Hz, means cycles per second. 1 Hz = 1 cycle per second which = 60 cycles per minute.

So 500 Hz = 500*60 = 30,000 cycles per minute.

One cycle = 1 revolution, so purely arithmetically 500 Hz = 30,000 rpm.

So if you know your head speed as well as your tail rotor speed, then you can probably accurately figure out the general area where the source of your vibrations comes from.

This link
http://www.rcuniverse.com/community/heliwizard.cfm

Can help you determine the rough head and tail rotor speeds that you would expect.

I hope that this helps.

Trevor
Author:  nougiw [ Thu 18. Dec 2014 22:30:34 ]
Post subject:  Re: Spectrum Analyzer questions
tdeane wrote:
The easy part. Hz, means cycles per second. 1 Hz = 1 cycle per second which = 60 cycles per minute.

So 500 Hz = 500*60 = 30,000 cycles per minute.

One cycle = 1 revolution, so purely arithmetically 500 Hz = 30,000 rpm.

So if you know your head speed as well as your tail rotor speed, then you can probably accurately figure out the general area where the source of your vibrations comes from.

This link
http://www.rcuniverse.com/community/heliwizard.cfm

Can help you determine the rough head and tail rotor speeds that you would expect.

I hope that this helps.

Trevor


Oh God, I was totally absent and I forgot it is rounds per MINUTE. That's why I couldn't find out what's going on. LOL!! Thanks anyway...
Author:  nougiw [ Thu 18. Dec 2014 22:33:23 ]
Post subject:  Re: Spectrum Analyzer questions
ZeXx86 wrote:
Hi,

Right bar gives you information about total vibration amount, while graph can tell you what part of the model is problematic and what amplitude it has.
Normally amplitudes lower than 50 are fine.



ok, so according to the manual which says that up to 50% is normal, should I go out and fly because it says OK=46 or should I take some bench time since the graph shows ~59%
Author:  ZeXx86 [ Thu 18. Dec 2014 22:44:01 ]
Post subject:  Re: Spectrum Analyzer questions
It should work fine.
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