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Strange logs, main rotor high vibrations
https://www.spirit-system.com/phpBB3/viewtopic.php?f=20&t=775		 Page 1 of 1
Author:  Ben M [ Wed 01. Jul 2015 1:04:51 ]
Post subject:  Strange logs, main rotor high vibrations
I have two helis that flew fine until recently. Both are on v1.20.

Last week, after a uneventful first flight, my X3 started to tilt over during spoolup on the second flight. I disconnected and then restarted and then it flew fine. This occurred again today. The first flight was fine, then on the second flight it started tilting on spoolup. I downloaded the log last week after the first time this happened and it is very strange. I am not sure whether the log was from that flight or not because when the heli was flying well, I did not check the logs, so this log may be from another flight.

I thought it may have been a vibration issue because a vibration analysis showed over 90% vibrations at the main rotor frequency in the aileron axis. The main shaft, feathering shaft, and main gear looked fine but I replaced them anyway. The vibration analysis still was just as high. I then took the rotor head and swash off and redid the test with only the motor, main gear, and main shaft, and tail rotor in place. The vibration level at the main rotor frequency was still very high. However I cannot remember the number.

Today I also had a strange crash of my 300cfx that I think was caused by mechanical failure. I checked the Spirit log anyway and the log looked nearly identical to the X3 log. Again I do not know whether the log was for the last flight or some other previous flight. I replaced the main and feathering shafts and main gear and did a vibration analysis. Like the X3, the analysis showed over 90% vibrations at the main rotor frequency in the aileron axis. After I removed the head and swash, the vibration was less but still very high, and this is with only the motor, main gear and shaft, and tail rotor in place. I noticed that the main gear was slightly out of round though.

So I am not sure what is happening or what to do as there are not many main rotor drive parts left in the system and I still have high vibrations. The motors on both are fairly new.

As far as the logs are concerned, I do not have governor activated, nor have I had any flights with low battery voltage or loss of signal that I am aware of. My X3 has two satellites and my 300cfx has one.

Attachments:
spirit-log-2015-06-30-095625 300cfx.pdf [29.43 KiB]
Downloaded 100 times
spirit-log-2015-06-26-110413 X3.pdf [29.44 KiB]
Downloaded 84 times
Author:  ZeXx86 [ Wed 01. Jul 2015 17:21:57 ]
Post subject:  Re: Strange logs, main rotor high vibrations
The log seems to be partially corrupted, but the main information is still there.
You are probably running the software from wrong directory or you have moved EXE file somewhere else so there are also missing icons.

It seems that log data are valid until approx- 1:00 minute in both cases. Second log was probably caused due to Low Voltage event. On the helicopter that this log was recorded you can try to start BEC test to be sure there is no issue.

90% vibration level shouldn't be a cause for crash. Unit can fly even with 400% level, but during flight it can be much worse when bearings are hotter. So the level can increase gradually with time.
Author:  Ben M [ Wed 01. Jul 2015 19:52:39 ]
Post subject:  Re: Strange logs, main rotor high vibrations
Thanks for the quick reply and help.

I reloaded the software so now it is not corrupt. Icons now show up in the log.

With both helis, I did the bec test and both passed.

With the X3, I removed the tail grips and the vibration level at the main rotor frequency dropped dramatically. Since the highest vibration was at the main rotor frequency, I did not suspect the tail rotor system. Now I know what was the cause of the vibrations.

My concern with the X3 was the tip over at spool up. Maybe that was caused by the high vibrations from the previous flight?

With the 300cfx, removing the tail grips did not reduce the vibrations. I suspect it is the out of round main gear. I will try another gear and hope to find one that is not so out of round and check again.
Author:  Ben M [ Thu 02. Jul 2015 1:34:02 ]
Post subject:  Re: Strange logs, main rotor high vibrations
An update:

The X3 y-axis main rotor frequency vibration ( a very distinct narrow spike) with the tail grips removed actually lowers and raises cyclically, with a period of several seconds. The spike seems to range from about 55 to 100, and vibrations from 43 to 55.
Author:  ZeXx86 [ Thu 02. Jul 2015 14:39:22 ]
Post subject:  Re: Strange logs, main rotor high vibrations
When lifting off and motor is already running make sure that you do not move with the sticks.
In this case helicopter will try to get into inclination that was set on the sticks as when it is flying - this is different in each FBL system and very different from flybared helicopters.

When motor is not running you can move with the sticks in any way.
Author:  Ben M [ Thu 02. Jul 2015 15:23:09 ]
Post subject:  Re: Strange logs, main rotor high vibrations
No, I did not move the sticks at all. My hands were off the sticks and the motor was in the process of spooling up.

I have also had a couple of incidents where after landing safely and after the motor motor was turned off with hands off the stick, the heli tipped sideways while the blades were still spinning. The heli was in a stable position before I took my hands off the sticks. Then after I turned off the motor, while the blades were still spinning it tipped over.

This has all happened recently, after the v1.20 upgrade, although the timing may be just coincidental. Prior to these recent events, there had been no issues.

I will be replacing the tail blade grip mounting hub on the tail shaft as one of the tail blade grips does not appear square to the shaft. I will also be installing a new motor. I hope that will reduce the vibration.

Is it possible that high vibrations could have caused the tip overs?
Author:  Ben M [ Thu 02. Jul 2015 15:31:22 ]
Post subject:  Re: Strange logs, main rotor high vibrations
After rereading your reply, I think it may possible that I was moving my sticks during landing to make sure that the heli landed level. It may have been possible that the sticks were moving slightly just a the moment or just after the heli touched ground. Could that possibly cause the tip overs after landing? The heli was stable for a couple of seconds though before it tipped over.
Author:  ZeXx86 [ Thu 02. Jul 2015 15:41:38 ]
Post subject:  Re: Strange logs, main rotor high vibrations
Tip over due to vibrations is unlikely, especially when landing. Problems caused by vibrations could happen just in the state where helicopter is in exceptionally bad condition when it is destroying itself.
There were no changes for very long time that could affect it due to firmware upgrade.

If stick is moved to even small extent but for longer time, it will try to maintain new position (when motor is still running). So after some time it can overcome skids force and tip over if stick was held.
Author:  Ben M [ Wed 08. Jul 2015 5:49:28 ]
Post subject:  Re: Strange logs, main rotor high vibrations
After spending many hours replacing the main shaft, feathering shaft, main gear, and motor on my X3, and testing and prodding, the vibration at the main rotor frequency was frustratingly still there. And then it finally dawned on me what was causing the vibration to show up in the vibration analysis.

The Spirit is mounted on my X3 with the connectors facing forward. The extra lengths of servo wire were bundled together in front of the Spirit. What was causing the vibration to be sensed by the Spirit was that the bundle of wires was contacting the heli frame and the Spirit. The bundle of wires was conducting the vibrations from the frame to the Spirit. After moving the bundle of wires so that it no longer contacted the Spirit, the vibration analysis finally showed reasonably low vibration levels in all axes.

On my 300cfx, the Spirit is mounted with the connectors to the rear. The extra lengths of servo wire were tightly bundled behind the Spirit. I suspect that the tight bundle of wires were a stiff connection between the frame and the Spirit and was conducting vibration to the Spirit, although not at the same level if there was direct contact. I have loosened the bundle of wires to reduce its stiffness to lessen the possibility of it transferring vibrations. I suspect that that may be a cause of the high vibrations that I had managed to reduce but not get rid of. At this moment I have not taken the blades off to do a vibration analysis.

So be careful when wiring up the Spirit. Make sure that there is some flexibility in the wires connected to the Spirit so that they do not transfer vibrations to the unit.
Author:  ZeXx86 [ Wed 08. Jul 2015 10:20:02 ]
Post subject:  Re: Strange logs, main rotor high vibrations
Thank you very much for the update.

You are right that all moving things on the helicopter can create additional vibrations. It depends how cables can transfer vibration or how are they mounted on the helicopter.
It is also very important that the unit is mounted as hard as possible so it can't flex to any side. If it is on a soft tape then it can create additional vibrations too and also nothing is touching the unit.
The unit itself can start oscilating on the pad or things around as well.
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