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| vibration with gas engine https://www.spirit-system.com/phpBB3/viewtopic.php?f=20&t=389 |
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| Author: | The Mechanic [ Wed 17. Dec 2014 4:17:57 ] |
| Post subject: | vibration with gas engine |
My new build; 700n DFC Helibug G290RC, Spirit FBL, ProModeler 420 in-oz brushless cyclic servos. I mounted the Spirit with the supplied 3M tape, the really good black rubbery stuff not the white foam stuff. I'm concerned about the Spirits ability to handle what I believe is a normal amount of vibration for this gas engine helicopter. I'm running it up for the first time today without any blades resting on a rubber mat on concrete. At idle engine speed all is normal. At about 30 to 35% throttle (0-100% is linear from full closed to full open); don't know the RPM the left cyclic servo starts to oscillate moving the swash ball up and down about a quarter inch; maybe a half. The other servos don't move. Also when I just start an engine run the bailout keeps the swash level when it engages. After about 10, maybe 15 minutes of running the engine, stopping the engine, adjusting the carb (I have to tip the model to do this); restarting and just running the motor at different speeds while I check the carb adjustment... then when I engage the bailout instead of the swash just lifting up level it tilts to the left even though the model is level as it was when it was initialized. On the vibration analyzer in the Spirit software it reads just under 50 at idle and says it's OK. At 35% throttle it reads 110 (off the chart) and says extreme vibration. The main frequency in the elevator channel is about 240 Hz. It's about 120 Hz at idle. My question... is the bailout not going to work because it seems to be drifting in a short time? Is the Spirit gyro going to work in this environment? I can't think of anything I can do different short of mounting the Spirit on a pillow. I'm pretty sure the airframe vibration will be less once the blades are installed and the helicopter is off the ground but I don't know how much or if it's safe to fly in this condition. |
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| Author: | ZeXx86 [ Wed 17. Dec 2014 8:52:47 ] |
| Post subject: | Re: vibration with gas engine |
Hi, bailout should work well with gasser heli too. For imagination of vibration amount - if you can see extreme vibrations it is approximately two times more than for example Microbeast can handle in normal operation, so they are really extreme. With Spirit you can fly even with 300% vibrations, but for Bailout extreme vibrations are not good. But flying with extreme vibrations will surely lead to some mechanics malfunction that even loctited screws will unsrew soon so it can be dangerous. Fortunately you can enable Extended signal processing parameter that is perfect for such operation and should help you. But if possible vibrations should be lowered. |
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| Author: | The Mechanic [ Wed 17. Dec 2014 14:40:00 ] |
| Post subject: | Re: vibration with gas engine |
Thank you for the response. Up to 300%; that is good to know and gives me some confidence. Do you know why the left cyclic servo may have been moving when the center and the right were not? |
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| Author: | ZeXx86 [ Wed 17. Dec 2014 14:54:39 ] |
| Post subject: | Re: vibration with gas engine |
This can be caused by such extreme vibrations which confusing automatic geometry correction. Do you see it with Extended signal processing enabled too? |
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| Author: | The Mechanic [ Wed 17. Dec 2014 16:22:29 ] |
| Post subject: | Re: vibration with gas engine |
I didn't try Extended signal processing but that is a good idea. I will try it next time I run. If I engage the bailout after initializing the helicopter and the swashplate goes up evenly; and then later engage the bailout and the swashplate tilts left, is that an indication that the gyro has drifted? |
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| Author: | ZeXx86 [ Wed 17. Dec 2014 16:32:27 ] |
| Post subject: | Re: vibration with gas engine |
Yes, it is likely. Mentioned parameter should help a lot in this case. Make sure you have mounted the unit precisely so vibrations are symmetric from each side. I guess the highest vibrations will be in Y axis - Aileron. They are sometimes much higher than for Elevator and Rudder axis. So if you didn't checked it, you can do it. Still I recommend to check source of vibration since it can cause major mechanics malfunction during the flight. Vibrations that are 90% and higher are very dangerous because any part of the helicopter can fly away. |
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| Author: | The Mechanic [ Wed 17. Dec 2014 18:30:20 ] |
| Post subject: | Re: vibration with gas engine |
Well... the source of the vibration; I hope; is that I'm running the helicopter on a rubber mat laying on concrete. Once I get the blades on and get the skids off the ground (aircraft in flight) I'm hopeful the vibration level will be much less. Other than that it's a one cylinder gas engine with no balance shafts of any kind that weighs 4.5 lbs bolted to a helicopter that weighs about 7 lbs. As they say it is what it is. Thanks for letting me know about the bailout swashplate behavior. I can use that as a test in the future. |
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| Author: | ZeXx86 [ Wed 17. Dec 2014 18:40:50 ] |
| Post subject: | Re: vibration with gas engine |
No problem, in case of any issue you can ask me. |
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| Author: | The Mechanic [ Sun 21. Dec 2014 1:33:26 ] |
| Post subject: | Re: vibration with gas engine |
Hi Tomas, I enabled Extended Signal Processing and did another test run today. It didn't make a difference as far as the left servo jumping so I switched the signal wires for the left and right servos and the problem stayed on the left servo. So I don't think the Spirit is causing this problem. I didn't have time to test how the Extended Signal Processing may or may not help keep the Rescue feature from drifting from vibration. It may be a long time before I can do that. Probably next spring when I start flight tests. I do have a question. Are there any negative effects from enabling Extended Signal Processing and will it prevent the Rescue orientation from drifting from level during an extended 20 minute flight? |
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| Author: | ZeXx86 [ Sun 21. Dec 2014 11:37:27 ] |
| Post subject: | Re: vibration with gas engine |
Thanks for your info. You check check if there are no high voltage EM pulses that are affecting servos - wires should be as far as possible from the ignition. EM noise could be also reason why the rescue is not holding precisely position. Such pulses are very similar to electrostatic discharges. With extended signal processing it could be little bit harder to tune tail performance, but normally the difference is very small/insignificant. |
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