Blade 130X Tail Vibration Fix
by J. Salt
While spooling up, a good number of people are reporting 130X tail vibration issues. As I
mentioned in my 130X review, I have experienced this as well on my 130X. To be honest,
I never really thought it was an issue since it was so short lived and by the time the rotors
were up to flight speed, it was gone (mine phased in at about 17% throttle and was gone
by 25% throttle).
I also had over a hundred flights on my 130X before doing anything about it and it was
working fine the entire time. Plus the fact most of my helis will have one or two tail
resonances during spool up (not nearly as strong as the 130's mind you) pretty much
made me insensitive to the problem. I guess that was Horizon's stance as well from the
feedback I was getting.
Anyways, it wasn't until I was contacted by a few people with vibration questions and
also heard hobby shops were having a fair number of 130X returns due to excessive
130X tail vibrations that I started to take this problem a little more seriously and started
playing around with possible fixes. I honestly didn't have time for this, but I was getting
rather annoyed by all this negativity over such a great little micro heli. Yes, at the end of
the day this is still a low cost, micro size heli, so really how much should we expect? As
it turns out, more than I thought...
Identifying The 130X Tail Vibration
Before getting into the fix, I thought I should go over the vibration characteristics, how to
identify them, and what damage they can actually do.
The 130X's visible tail vibration is transitional in nature; by that I mean it's not there all
the time (or at least it's not visible all the time). The visual vibration we actually see is a
resonance vibration that builds in amplitude at a very specific tail RPM/frequency.
Essentially what happens is at a certain tail RPM, the tail vibration frequency matches the
natural frequency of the tail boom along it's length wise axis and at that point, the tail
boom will resonate/oscillate along its torsonal axis. If you look at the 130X's tail case
block end on while it's resonating, you will see the entire tail case and tail shaft
oscillating up and down in a twisting blur/buzz along the torsonal axis of the boom when
the resonance peaks.
So why does it do this? From my experience and others, it's a simple tail rotor blade
imbalance issue. Basically the vibration is there all the time, but only at that specific
frequency does it set up the harmonic resonance in the tail boom, and then it's hard to miss or ignore. I have read some reports this is caused by tail shaft hubs that are not
aligned correctly on the shaft, but I have yet to see it first hand. Still, it's something to
check for first since the best balancing job will be meaningless if the hub is not sitting at
a right angle to the shaft.
I have also heard people saying the stock tail bearings are garbage, but again, is that
factual evidence from actual bearing failures, or is the excessive resonance if allowed to
occur for extended periods taking out the tail bearings prematurely? Like I mentioned, I
had over a hundred flights on my 130X with not much bearing play increase at all
because I quickly ran through the resonance every time I spooled up. That said, even if
you run through that harmonic resonance quickly, the underlying tail blade imbalance
and short lived resonance each time you spool up will certainly cause premature bearing
failure over time.
There are better bearings available - no question there, but even higher end bearings will
fail faster if the blade imbalance is not corrected first. In fact, when I replaced the tail
shaft bearings with better ones before balancing the tail blades, the resonance got even
worse (higher in amplitude) due to the fact the little bit of slop that had developed in the
stock bearings was absorbing some of the vibration energy so it couldn't build in
amplitude as strongly as it could with the new bearings that had next to no slop.
130X Tail Vibration Fix
As I said in the 130X review, the fix is so simple and easy... The other great thing is that
the resonating tail boom is actually the best tool we have for determining when the tail
blades are in dynamic balance. If the tail boom never resonated after all, chances are we
would never know the tail blades were not in dynamic balance. Who knows, perhaps it
was engineered that way so we all could balance our tail blades correctly? Okay, not
likely but I like to look at the glass half full and see this as a benefit to be used to our
To dynamically balance the 130X tail blades,
just pick one blade and put a small piece of
electrical tape on it. About 4mm X 10mm
seems to be a good size to start with about mid way lengthwise on the tail blade. Mid
way seems to work best because it's roughly at the lengthwise center of gravity of the blade
and won't upset the lead/lead characteristics of
the tail blades that much. Speaking of lead/lag - DON'T over tighten the tail blade grip screws.
The blades have to remain fairly loose in the
grips (loose enough they hang down under
gravities influence) so they can lead and lag
properly. If they are too tight, you will introduce
lead/lag oscillations as well to the tail or
prolong and increase the amplitude of the
resonance through a broader RPM range.
Now spool up your 130X into that resonance
sweet spot and see what happens, did it get
worse or better? If it got worse or made little
impact, move the tape to the other blade and try
again. It should have gotten better now if this
was in fact a blade balance issue.
Once I find which blade the tape helps to reduce the vibration, I will mark it somehow so
I know which blade gets the tape from here on in. I just used a silver permanent marker to
illustrate this with an "X", you can certainly be more subtle in blade identification.
Now it's fine tuning time. Perhaps that 4mm X 10mm tape totally eliminated the vibration
if you are really lucky and hang out with magical leprechauns; but in the real world, you
are going to have to play around with the size a bit to get the dynamic balance perfect.
Just experiment with different sizes of tape until you get it as good as possible. You
should be able to reduce it to the point you will only see a slight vibration in the bottom
half of the tail fin, but no more torsional oscillations should be evident on the tail case
block or tail rotor shaft.
Once you have the size of tape you need, you
might want to record that somewhere so if the
tape goes flying off the blade, you know what
size to make its replacement.
It also greatly helps after you determine what
size, to place the tape over the leading edge of
the blade so it's less likely to come off. I used
red tape here to help see it better in the photo,
but black or clear tape can be used if you wish
to have a more "invisible" balance job.
My second Blade 130X didn't have much tail vibration at all and was in pretty good
balance out of the box, but there was just the shortest lived resonance that I wanted to see
if I could eliminate. This makes it much harder to find which blade is lighter and heavier
since they are both so close in balance. If your 130X has very little vibration, but it's still
enough to visually cause the tail shaft to "blur" for a brief moment, use a smaller piece of tape to start with. If you start out with a larger 4mm X 10mm piece, the vibration will get
worse no matter what blade you put it on since you are throwing the balance out so much
regarless of what blade you pick first.
As you can see, the 130X tail in the background
needed a much smaller piece (about 4mm x
4mm) to dynamically balance the tail. A piece
this small won't stick well! I had to use a larger
piece of clear Scotch Tape (which is lighter than
electrical tape) so I could wrap it over the
leading edge. Again I only used the red tape for
visual purposes in the photos - if you have very
little vibration to start with, you are likely better
off using clear Scotch tape from the get go...
The other (better) option which I tried next (due
to the very small amount of mass needed to balance this blade set), is to remove a little
blade material on the opposite (heavy blade). A little sand paper work on the end tip of the blade and keep testing until the resonance is gone. This actually worked very well
(sanding off a small amount of the heavy blade tip) and I was amazed at how little
material actually had to be removed to balance this blade set. In short, don't get carried
away, only a little bit at a time (one or two passes) and again, this only seems to work if
the imbalance is very slight so you don't upset the lead/lag angles that much. The only
issue afterwards was I started experiencing a little bit of gyro induced tail wag at higher
head RPM's so I had to go into the special gyro gain setting program in the 5-in-1 unit
(that I mention on the review page) to lower the tail gain until the wag was gone. This
"gain adjustment" is also likely going to be required if aftermarket tail blades are used so
it's very handy that Blade gave us a gain adjustment program on this bird to fine tune and
eliminate any tail wag caused by tail blade modification or non stock replacements.
Adding A Dampening Mass
After you get the blade balance as good as possible, if you are really fussy and wish to
absorb any slight remaining resonance, you can add a simple dampening mass.
Here I have just placed a small cube of Zeal
tape (an almost Jell-O like gyro mounting tape
with excellent vibration absorption qualities) on
the tail fin in line with the axis of the tail boom.
This small dampening mass totally eliminated
any remaining tail vibration to the point even
the bottom tip of the tail fin won't vibrate as the tail RPM passes through the resonance frequency.
Basically it's better than any collective pitch heli I currently fly right now in the tail
resonance department. Yes, it's ugly as hell and a little excessive, but I just wanted to
mention it and throw the idea out there. No doubt there are better and more attractive
ways to add a dampening device to the 130X's tail; so all you budding mechanical
engineers, go to town on that one if you wish.
The stock tail shaft bearings should last a fairly long time if you fix most of the vibration
early on. That said, if and when you notice your tail shaft bearings (or any other bearings
on your 130X for that matter) are starting to develop a fair amount of lateral runout and
play, there is a very nice little 130X bearing upgrade kit from Boca Bearings for only $30
bucks. Definitely better bearings over the stock ones and I've been very happy with them
on my 130X and will definitely be ordering a another set for my second 130X when the
Boca also has the 1.5mm x 4.0 mm x 2.0 flanged tail shaft bearings separate if you just
wanted to get the tail shaft bearings individually for $9 bucks each (the whole kit as you
can see is a much better value).
Lastly, if you want the best quality bearings you can put in the tail, Boca has a full
stainless steel flanged SMF681X-ZZ 1.5 x 4 x 2 bearing. A little more money than the
chrome steel ones, but they should last a little longer.
Hope something in here helps cure your 130X tail vibrations should you have them...
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*This article is posted here by permission of the author (J. Salt). It is not permitted to be copied without specific permission.