Vibrations

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Home › Scale › ✈️Aircraft › Scale Heli › Scale Helicopter Main Discussion › Vibrations

03-10-2014 05:32 PM 6 years ago

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ssmith512

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Indianapolis, IN USA

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Vibrations

OK, so I maidened the pod and boom Trex 600N (converted to electric with the clutch) over the weekend. Did not have the tail boom supports mounted and no tail fin (basically flew it exactly like it will be in the fuse except installed the landing skids). Using Spin 620mm asymmetrical blades (first time I have ever used these). Stock Trex 600 3G head with the Align red dampers (the softest). Main blades are spot on CG and weight wise. I am noticing a decent vibration in the skids and the tail boom has a vertical up and down vibration to it. I tried 3 head speeds (1480, 1570 and 1650) and the higher head speeds looked like it caused the frequency to increase but the amplitude of the vibration to go down (just visual observation here). I removed the main blades and spun up the head (tail blades still installed) and the boom did not have the same up and down vibration as it did flying with the main blades. Tried a set of Rail 606mm (3D) blades, and saw the same basic vibrations as the Spin blades. Main shaft is true, head seems to spin true. Tracking is within a half turn (can only go full turns on the pitch links).

I am at a loss as to what I should be checking to track down my vibration. All of my 3D pod and booms (which obviously are running much higher head speeds), I have never encountered vibrations that I am experiencing with this model and these lower heads speeds.

Can dampers (too soft) be causing my wobbles? Do I need more flights at higher head speeds to "work the dampers in"??? Looking for some advice on what to check as I am in a new realm with these lower head speeds, soft dampers and asymmetrical blades.

Thanks in advance.Steve

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03-10-2014 05:57 PM 6 years ago

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Keygrigger

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Mississauga, Ont. Canada

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Steve:

There is a difference between a vibration and an oscillation. If your skids are buzzing, then there is something out of balance causing that to happen. It might be a gear out of round, a slight bend in the tail shaft, or a misplaced bearing in the torque tube housing. Don't rule out the motor, either. If the tail is oscillating up and down, which is quite common with standard two blade heads, then the dampeners might be too hard or your gain could be too high for the elevator in the gyro settings. I just finished an Airwolf that I had put soft dampeners in it but the tail still bobbed a bit up and down at a hover. A small adjustment was done to the gain for the elevator and the tail settled down very nicely. Hope this helps.

Don

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03-10-2014 06:02 PM 6 years ago

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coptercptn

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Mesa AZ. USA

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I would also install the boom supports! Lost one that way because of insufficient tail support.. Your tail rotor may be trying to bend (Flex)the boom sideways (Torque) and gyro trying to correct causing an oscillation.Home of the "Sea Cobra".....

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03-10-2014 07:14 PM 6 years ago

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Mojave

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Palos Verdes, Ca. USA

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X2^^^ I had this same issue flying my Rex550 without the boom supports. There is a LOT of flex in the boom support. You would think that running without them is the same as a scale fuse, but it's not. When the mechs are installed in the fuse, the fuse tailboom supports the tubular inner boom. Also, I think your dampers are too soft. But what I would do is install the boom supports and see if the vibe goes away. If it doesn't, then start looking for other issues, like dampers, blade balance etc. The problem could be as simple as the clutch adapter not running true on the motor shaft, or the tail blades are a little out of balance.
BarryAll helis and planes have an expiration date stamped on them...you only find it after you crash!!

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03-11-2014 03:38 PM 6 years ago

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doorman

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Sherwood, Arkansas

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X3^^^^

Put the boom supports on and then try it...
As mentioned, the boom will be inside the fuse tail boom and attached which basically replaces exactly what the supports were doing..

Let us know if that shakes the problem out (HA, made a funny!!!)!!

Stan

AMA 2918-Team Spin Blades,,Castle Creations, Unique Aircraft

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03-12-2014 02:28 PM 6 years ago

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ssmith512

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Indianapolis, IN USA

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Ack. Stupid weather. We went from 65 degrees and sunny yesterday to sub 30 degrees and snow storms today. I am not kidding. SO, I am grounded again for a while.

I appreciate the suggestions. After replaying the flights in my had, I am pretty sure it is a vibration and not an oscillation. One thing while I am imprisoned by weather is I am going to check the run-out again on the clutch/clutch adapter, as that is the only thing I can think of that might be causing the high frequency buzzing I am seeing. What is an acceptable amount of runout? And if it is out of spec, I am not even sure how to "adjust" it. I am using a Great Planes adapter, it simply set screws onto the motor shaft and then the Trex600N clutch hub center bolts to that and it also has pinch bolts, it kinda self aligns I think.Steve

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03-12-2014 07:32 PM 6 years ago

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Mojave

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Palos Verdes, Ca. USA

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The prop adapters are a good way to adapt the clutch, but they don't always fit the motor shaft as snugly as they should. So, when you tighten the grub screw it forces the adapter to one side of the shaft. I wouldn't want to see more than .002 run out on the clutch adapter.

But the first thing I would do is back the pinion away from the main gear and spin the motor up. This way you can observe/feel any run out. If it's excessive, you will definitely feel it in the airframe. If you narrow it down to the motor/clutch set up, then you can pull the motor and check the shaft separate of the clutch adapter. If the motor runs true, then you have narrowed it down to the adapter. Also, wiggle the motor can and see if the bearings are tight. A loose bearing will allow the shaft to move laterally and this in turn will cause the motor can to vibrate. A main gear that doesn't run true will also produce high frequency vibes. On my align based mechs, I switched to KDE main gears. They run very true and are well worth the money spent. But, I wouldn't go there until you narrow the problem down. You might be throwing good money over bad

BarryAll helis and planes have an expiration date stamped on them...you only find it after you crash!!

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03-16-2014 03:43 AM 6 years ago

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ssmith512

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Indianapolis, IN USA

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Thanks for all the suggestions. Today was a nice day and was able to look at things. Checked the balanced of the head with blades and it was dead on. Took the motor and clutch back out and checked runout, it was a whopping ten thousandths at the clutch. Redid everything and the best I could get was 4 thousandths. Reassembled everything, installed the tail boom supports and was rewarded with a smooth running bird. No more skid buzz, no more tail buzz. Yea! So lesson learned, details details details.

Thanks again everyone!Steve

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03-16-2014 06:17 AM 6 years ago

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Mojave

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Palos Verdes, Ca. USA

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I love it when a plan comes together...

Glad it worked out for you.
BarryAll helis and planes have an expiration date stamped on them...you only find it after you crash!!

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03-16-2014 06:42 PM 6 years ago