Tail vibration

[khigerd]

I've got a tail vibration I can't find. I've been chasing it for so long, I'm not sure if it's not normal. How much does your tail vibrate? I can see the tail fin vibrate in flight and it's causing the tail servo to dance. Everything from the tail boom back has been replaced along with the main and feather shaft. When I run it on the bench, i can feel a very fast vibration in the tail. Where else should I look?

Thank

[TomC]

Mine is very smooth and vib-free. Sounds like either a bent tail rotor shaft, tailcase bearings, or out of balanced tail blades. I replaced the stock plastic tail blades with radix 92mm ones and this smoothed it out even better.

Cheers,
TomC

[khigerd]

Thank for the reply Tom. I thought mine used to be smoother than it is now. Everything is new from the boom back. Hub, shaft, tail case and bearings, gears, drive shaft, and blades, all new. I've even tried 3 bearings on the drive shaft. Can something be transfering from further forward?

[TomC]

Maybe check your main blade balance? Try a small piece of tape on one blade at a time, run it up, trial and error, and see if this helps. I usually do this as a final step to make it all as smooth as possible.

Cheers,
TomC

[khigerd]

The vibration is still present while running without the main blades. I ordered a set of carbon fiber tail blades and give them a try.

[JustPlaneChris]

Long shot here: Are your torque tube bearings spaced equally on the shaft, or are they offset so you have unequal distances between bearings? You want the latter. If they are equal distances apart it sets up harmonic vibrations.

[SamIAm]

I had very nasty tail vibes when I first built mine, to the point where it bent the tail shaft while spooling on the bench. I swapped the Mavrikk 95s over to Edge 95s and it seems to have solved it.

[khigerd]

Originally Posted by JustPlaneChris

Long shot here: Are your torque tube bearings spaced equally on the shaft, or are they offset so you have unequal distances between bearings? You want the latter. If they are equal distances apart it sets up harmonic vibrations.

Right now, I'm back to the standard setup on the tailshaft bearing. I eye balled the bearings on the shaft so I'm not sure of the spacing with out measuring. Good to know. Thanks

[khigerd]

Originally Posted by SamIAm

I had very nasty tail vibes when I first built mine, to the point where it bent the tail shaft while spooling on the bench. I swapped the Mavrikk 95s over to Edge 95s and it seems to have solved it.

While waiting for the carbin fiber tail blades, I tried Tom's tape suggestion. I put the tail hub assembly on a prop balancer and was amazed how far off it was. After 4 inches of scotch tape its alot smoother.

Thanks for the suggestion Tom.

[skytrekin]

I have had good luck with the Edge tail blades as well.

With the servo link off of at the servo you should be able to move the tail pitch easily. Like buttery easily. I have found when its all very smooth you can run higher gains in your gyro. Also keeping the slop to a minimum helps.

[gwright]

As stated above, can't have equal spacing on bearing on torque tube,.. you always want dissimilar lengths of torq tube between supports or it sets up a sine wave and you get a buzz/shake/etc. It's not hugely critical where the bearing(s) are, just that you don't have equal lengths of torque tube on either side