Vibration Problems? It's the tail.

[Skookum]

For anybody out there that has vibration affecting their SK720's accelerometers:

A while back I did a survey of every vibration log we've ever been sent. The results were:

10% Motor (nitro or electric)
10% Misc (often bearings or gears)
80% Tail.

The cause seems to be that the makers of blades now ship their main blades balanced both statically and dynamically, but they don't bother for tail blades.

The answer is simple: Statically *and* dynamically balance the tail. "Dynamic" balance sounds scary, but in practice it just means the tail blades should have their lengthwise C of M at the same point. Only after that is done, should the tail unit as a whole be statically balanced (with a prop balancer or similar).

For cases where your electric's motor is the source, we haven't yet figured out how to balance them. However, much of the time it's a warning sign of impending failure: A magnet has come unglued inside the motor and is sliding around.

- Art

[gitbse]

I'll second that from experience. Also, check your tail shaft bearings regularly. That is the #1 cause of wear problems on my ENV. The bearings are seated straight into carbon fiber, so they slowly wear the holes a little and cause the tail to act like it has a bent shaft. A little CA in the flange of the bearings cures it right up. The same thing can happen in metal tail hubs though. Once the bearings get some good wear, they will have lateral play and will cause the same problem.

[Larry227]

Yep all my vibe problems on my two helis have always been tail related. Most of the time if the bearings aren't the problem I can solve them with a small piece of tape on one blade.

[tomd27858]

Originally Posted by Larry227

Yep all my vibe problems on my two helis have always been tail related. Most of the time if the bearings aren't the problem I can solve them with a small piece of tape on one blade.

I'll chime in and second that on my Align birds. If there are vibration issues, the tail is suspected first.

[RiazP]

Its always been the tail...

I fly many trex 450 machines of various power and build, not like LMH but almost

the tail is always the issue. i now resort to buying tail grips in pairs so that i can combine the two good grips or have the choice of two hubs, but once the tail is happy all is good!

Wish i had not read this article as i will now have to balance all my tail blades

[jcflyer]

Originally Posted by RiazP

Its always been the tail...

I fly many trex 450 machines of various power and build, not like LMH but almost

the tail is always the issue. i now resort to buying tail grips in pairs so that i can combine the two good grips or have the choice of two hubs, but once the tail is happy all is good!

Wish i had not read this article as i will now have to balance all my tail blades

Or you can buy some that come balanced from the factory...

[spikestabber]

Agreed,

Every single time my 450 had vibration problems, it was ALWAYS THE TAIL.

The tail when unbalanced seems to be the "optimal" vibration frequency to throw off the accelerometers...

[snaaakeey]

Its amazing how many times I have hear people say they dont bother balancing the tail or even the mains. Every set of 600/700 blades I have ever owned have needed a good inch or more of tape on the C of G. I guess nitro birds are vibie enough but electrics once properly balanced with lowest possible vibes are and eerie quiet and look like they are running on a flight sim.

Thats the 1st time I have heard a recomendation for dynamic balancing on the tail though. Is this done in the same way as the mains are eg tape at the root till c of g is the same as the other blade then add tape on the c of g untill both blades balance on a prop balancer?

[gitbse]

On 450s I used to balance the blades, and then take the whole head off and dynamically balance the whole assembly on the desk. the way I did that was to spin up to straighten the blades, then take the head off and put the main shaft through 2 spare bearing blocks that were fixed to the edge of my desk. Then it's just like balancing a prop.

Not as easy with a 700, but with the fbl heads now it's not worth the time. balancing weight and cg on the blades is enough.


However taking the tail hub off and doing that would work perfectly.

[jcflyer]

Originally Posted by snaaakeey

Its amazing how many times I have hear people say they dont bother balancing the tail or even the mains. Every set of 600/700 blades I have ever owned have needed a good inch or more of tape on the C of G. I guess nitro birds are vibie enough but electrics once properly balanced with lowest possible vibes are and eerie quiet and look like they are running on a flight sim.

Thats the 1st time I have heard a recomendation for dynamic balancing on the tail though. Is this done in the same way as the mains are eg tape at the root till c of g is the same as the other blade then add tape on the c of g untill both blades balance on a prop balancer?

I don't know what type blades you have tried but, the Radix blades come balanced from the factory, maybe you can try those and see the results...

[snaaakeey]

Originally Posted by jcflyer

I don't know what type blades you have tried but, the Radix blades come balanced from the factory, maybe you can try those and see the results...

I have one set of these and they too have 1/2 an inch of tape on one blade. Maybe I'm just unlucky but I suspect tolerances aren't as fine as they would have us believe .

Sent from my GT-P3110 using Tapatalk HD

[RiazP]

Originally Posted by jcflyer

I don't know what type blades you have tried but, the Radix blades come balanced from the factory, maybe you can try those and see the results...

Only use Radix or Edge on the 450 tails and radix and rail on the .90. was also of the opinion that those brands were more immune to non matched pairs so usually just bang them on.

that's why i will have to check, to make the OCD go away

[mkovalcson]

Originally Posted by RiazP

Only use Radix or Edge on the 450 tails and radix and rail on the .90. was also of the opinion that those brands were more immune to non matched pairs so usually just bang them on.

that's why i will have to check, to make the OCD go away

I've noticed that my Radix blades run noticably better tolerances than my Edge blades, especially for main blades. This was measuring mains between 425-710mm blades.

Most of my tail blades seem to be accurate to .01-.02 grams.
I have to admit that I really haven't been testing them for matching CG's though...

OK, one more step from now on