Tail vibration

[ianjh123]

I have had a problem with a tail vibration since new. At about 1800rpm you can see the tail shaft form a cone of about 10mm diameter at the tip as it vibrates (very noisy). Increase the rpm and it smooths out. Drop rpm and it starts again.

I had the same problem with the original tail hub and now with a thrusted trex600 tail hub. I have balanced the blades but it makes no difference. I put new bearings and shaft in still but makes no difference. Any suggestions before I try trex600 blades, and after that a whole trex600 tail?

[tornet999]

I had similar problems earlier, was getting crazy, changed everything like complete new tail, new head etc and I never got rid of the tail vibrations. BUT then I moved to another controller (align 75) and everything worked so fine, not a single vibration, it turned out to be the stock ESC creating this, the motor was not running smothly. No idea why, not long time ago I tried same ESC on my second Hurricane, and same problem. Of course the probabilty of you having same problem is small.

It took while to find out anyway ...

[ianjh123]

Thanks, but I use a Quark 65 ESC, so I don't think that is the problem (I hope). Interesting find though.

[ianjh123]

Further news - changed the tail case - no improvement.

I think this is a problem with the whole helicopter acting as complex system and a harmonic vibration occurs in the tail at a certain frequency. To test this I strapped a tool onto the tail near the tail rotor to act as a damper. This was enough to change the system and the vibration stops. I will modify the length of the tail stays and this may give the same result. Or else I will mount the tail servo on the boom near the tail rotor.

[ianjh123]

A bit more to the story. I removed everything from the main shaft - no change. I then changed the gearing so the motor ran much slower - no change. So guessing the problem is in the tail itself I pulled it off. There is no way I could get it to run smoothly, even with all new parts, so I guess it is the problem. I think a Trex 600 cnc tail is on the way!

[Phoinix]

How tight was your belt? Did you check the bearings? I found two bearings on hurricane with almost half a milimeter slack in turning.

[ianjh123]

I used new bearings which seemed OK. The shaft was new but had a slight run out. The plastic pulley is slightly out of true and seems to be able to interfere with the case depending on how the case is pulled together (this seems to be the big problem). Maybe I'll have one last go and put the pulley and shaft in my lathe and true it up.

[ianjh123]

Well, finally an end to this story. I glued the two haves of the tail pulley together. With the pulley mounted on the shaft I used the lathe to reduce the pulley diameter slightly and skim a small amount from the outside walls. The tail vibration is now gone. Finally.......

[Phoinix]

Well, finally an end to this story. I glued the two haves of the tail pulley together. With the pulley mounted on the shaft I used the lathe to reduce the pulley diameter slightly and skim a small amount from the outside walls. The tail vibration is now gone. Finally.......

Something new for all of us to learn. Good work!

[joskibob]

way to go man... thats gotta feel good.

[tungym]

I have had a problem with a tail vibration since new. At about 1800rpm you can see the tail shaft form a cone of about 10mm diameter at the tip as it vibrates (very noisy). Increase the rpm and it smooths out. Drop rpm and it starts again.

I had the same problem with the original tail hub and now with a thrusted trex600 tail hub. I have balanced the blades but it makes no difference. I put new bearings and shaft in still but makes no difference. Any suggestions before I try trex600 blades, and after that a whole trex600 tail?

I got the exact problem recently. I go the thrusted and non-thrusted tail vibrate heavily on a certain rpm. On bench test it happens very violently then the tail gear box is about to explode. No vibration at all if the tail blades are not put on. Repeatedly blade balancing exclude any imbalance.

I am quite certain 100% that is due to RESONANCE, as the vibration went away completely if I hold the tail boom 5cm distal to the original boom support. I end up putting on the longer Trex 600 boom support and it reduce the vibration 80%.

I am still curious why this resonance happens. May be the tail gear box becomes flexible on aging, thus allowing the tail shaft to cone itself.

[ianjh123]

Tungym, I spoke too soon. After I "fixed" the tail I had to split the frame to replace a seized bearing on the one way shaft. When I had it back together and tested it the tail vibration was back. I agree it is due to resonance. I think I will try the Trex 600 cnc tail box and stays to try and change it enough that the resonance is at a frequency that doesn't cause me any problems.

I don't think it is the tail case going soft as I put a new one on and still had the problem. I think the new frame from Rotorworkz (when it is out) will fix it!

[mbigby2]

I wonder if some kind of dampener between the boom and the frame, or between the boom and the tail case would help? Perhaps a layer of clear tape? I would think that if the problem is resonance, wouldn't a stiffer (CF) frame make it worse?

[tungym]

Changing a new tail gear box, pulley bearings, shaft, blade does not cure the resonance.
I want to keep using the Align thrusted tail grip and hence I did not test the old Gaui grip set.

Finally, all resonance gone after I replaced with an old Align tail gear box. Weird!


[Supplementary]
Subsequent repeated test shown that the vibration comes from unbalance tail blades (despite using a blade balancer), as a new pair of Align white carbon blade cures the rest of the vibration. Conclusion: vibration and resonance somehow related and exagerated by multiple factors.