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| Vibration Analysis Help https://www.spirit-system.com/phpBB3/viewtopic.php?f=20&t=2367 |
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| Author: | omarb [ Tue 02. Jan 2018 0:38:11 ] |
| Post subject: | Vibration Analysis Help |
Hi, need to trouble again. I test spooled my heli and the tail rotor spike is going all the way up. It's only showing as an extreme vibration on y axis although the spike is on all the axis. This is with tail blades off it's almost no vibration. This is a new set of tail blades. Heli is a logo 550sx about 16 flights since new. Had a mishap last year during training where my instructor had to take over and autoed it down. Damage was mains and tails and main shaft. Any ideas about what I should check? Sent from my SM-G920F using Tapatalk |
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| Author: | ZeXx86 [ Tue 02. Jan 2018 8:24:29 ] |
| Post subject: | Re: Vibration Analysis Help |
Hi, I guess that the problem could be tail shaft or a bearings of the tail shaft. Since tail grips are plastic they can bent in some way too. It depends on where it was hitted during impact. Could you post the plot please? I can review it and make sure that it is going from tail. In Logo it is easier, because there is just a belt so the problem is most likely just in the tail mechanics. |
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| Author: | omarb [ Tue 02. Jan 2018 23:49:04 ] |
| Post subject: | Re: Vibration Analysis Help |
When i tested the first time all the vibes were on the tail. No it's showing on the main rotor. The first time was on a table but i had a few folded table cloths on the table. This next time was on a carpeted floor. Images are in xyz order    Sent from my SM-G920F using Tapatalk |
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| Author: | ZeXx86 [ Thu 04. Jan 2018 8:26:24 ] |
| Post subject: | Re: Vibration Analysis Help |
Thank you for the plots. It is really looking like there are two issues. One at the main rotor and second at the tail rotor. If the tail rotor had no blades during measurement then it mean that the tail rotor vibration level will probably rise at least 2 times higher. What I recommend first is to disassemble tail rotor blade holders so there is just bare tail shaft. Then perform measurement again. In this way we will be able to see if vibrations will be still present or the spike will disappear completely. Main rotor could be not that bad with blades on under load, because sometime vibrations are caused just by the gears itself. When they are under a load, it can be better than now. But if helicopter crashed, then it is very possible that a main shaft could be bent, some gear can be missing or gears are too close to the motor pinion. If a shaft is bent, then usually also bearings are damaged. Radial bearings can be checked so that when you put there a shaft and rotate under a slight force out of the axis, they should always work smoothly. Without any crunching. Unfortunately to repair helicopter perfectly after a crash it is best to at least verify each part that somehow impacted with the ground. Even that there is nothing visible by eye damage is sometimes hidden. |
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| Author: | omarb [ Thu 04. Jan 2018 9:23:31 ] |
| Post subject: | Re: Vibration Analysis Help |
Thanks so much for the help. The main shaft was replaced and the tail blades were on. I can redo the plot with blades off again. When i did it blades of there was almost no noticeable vibes. Sent from my SM-G920F using Tapatalk |
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| Author: | ZeXx86 [ Thu 04. Jan 2018 14:33:18 ] |
| Post subject: | Re: Vibration Analysis Help |
If it is with blades on, then I think that the level is acceptable already. In that case spike of the main rotor could be a bigger issue. |
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| Author: | omarb [ Fri 05. Jan 2018 5:26:47 ] |
| Post subject: | Re: Vibration Analysis Help |
Yes it is with tail blades on. What must I check in the main rotor? I did turn the spindle bolts to see if the opposite end grips moved, and it didn't so I'm guessing the spindle is fine, I could be wrong though. Sent from my SM-G920F using Tapatalk |
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| Author: | ZeXx86 [ Fri 05. Jan 2018 8:24:15 ] |
| Post subject: | Re: Vibration Analysis Help |
I recommend to verify the main shaft if everything is straight. Looking at the rotor head you will not find any issue, until something is bent a lot. You can put it on a glass and verify if there is any inequality when rolling on it. |
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| Author: | omarb [ Sat 06. Jan 2018 23:32:18 ] |
| Post subject: | Re: Vibration Analysis Help |
As soon as I get a chance I'll do that. This is a brand new main shaft though. Could gear backlash cause this maybe? Sent from my SM-G920F using Tapatalk |
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| Author: | omarb [ Fri 19. Jan 2018 0:32:03 ] |
| Post subject: | Re: Vibration Analysis Help |
Hi, just an update. Checked the heli and realised I had the main blade bolts in the grips and one was loose. Removed it and vibes went away. Had a test hover and the log shows only good health messages and one with tail limits. Would it be safe to assume that can I use the rescue and stabilisation modes safely now? Again thanks so much for all the help. Sent from my SM-G920F using Tapatalk |
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