Mystery of Piccolo Pro - Vibrations

[jiri]

Hi,
I have a very strange problem. Hope that somebody can
help me. My CP heli is well balanced and it takes
off and hovers for about one minute completely without
vibrations (at cca 2100 RPM). Then suddenly and without
any reasons it starts to shake so badly that I can
hardly land!!! What's wrong?????

Thanks,
Jiri

[pgoelz]

Well, obviously something has shifted. How loose are your blade bolts?

Do you see any change in tracking when this happens?

Are you running a metal or CF mainshaft? If CF, have you checked it carefully for cracks where the hub pin goes through?

What hub are you using? If aftermarket, are you sure that the bearings are tightly attached?

[jiri]

Hi Paul,
thanks for your responce!

[ QUOTE ]
Well, obviously something has shifted. How loose are your blade bolts?

[/ QUOTE ]

My blade bolts are quite tight but they can still move
in higher RPM and find their optimal position.

[ QUOTE ]

Do you see any change in tracking when this happens?


[/ QUOTE ]

No, this is what really puzzles me. After these wild
vibrations I land, I do not adjust anything, take
off with no vibrations what so ever and after cca
one minute the same story repeats! For me it looks
like that the piccolo is tuned to vibrate in a certain
frequency but not always the frequency is reached ...

[ QUOTE ]

Are you running a metal or CF mainshaft? If CF, have you checked it carefully for cracks where the hub pin goes through?


[/ QUOTE ]

I am using a new titanium main shaft.

[ QUOTE ]

What hub are you using? If aftermarket, are you sure that the bearings are tightly attached?

[/ QUOTE ]

I checked the hub and it looks OK.

I have decided to put everything apart, rebalance
and try again. I hope the problem will be gone.
What bothers me is that I do not know why this
sudden vibrations occure ...

Thanks,
Jiri

[Erez]

It does not sound like vibration to me. I think what you are experiencing is flutter. This happened to me when I first set up my Pro. You may want to try stiffening the head with CA and baking soda. The problem is slop in the control system. I am not sure why it happens only sometimes and to some people, but I know that not all rotor heads are the same. I got one from FXAero and it was stiffer than one I got from Ikarus-USA.

If it makes a horrible sound (like wraaaa) it's flutter, not sudden vibration, although it does vibrate too when it happens. Are you using stock blades?

[jiri]

Thanks for the input. Yes, I am using stock blades.
How do you exactly make the head stiffer? What is
baking soda???

Thanks,
Jiri

[R44]

Well, 2100 RPM is a bit on the hard side, isn't it?

Dave [img]/ubbthreads/images/graemlins/cool.gif[/img]

[jeffery]

I would also say 2100 is way to high of a head speed normally it should be 1700 to 1800.

Regards, Jeff

I have to agree with Erez. what you are experiencing is flutter. I had the same problem until the did the baking soda combined with CF stiffener. upon spool up and in flight, the head on the heli is "pulled" back in level or straight. when the head unloads, imperfections in the head show up and cause the flutter. By the way, I also had a head that did the opposite. I had to try two to four times to spool up before I could fly. I was getting the flutter before taking off. [img]/ubbthreads/images/graemlins/cool.gif[/img]

[pgoelz]

If he says the tracking remains OK then it is not flutter. Flutter will be obvious as a major tracking shift.

Note that I had some minor flutter at zero pitch on my last pair of blades when I had the bolts loose. Not sure why. But when I tightened them (the way I normally run them) the flutter went away. I later discovered that the little pins in the grips that ride in the slots in the pitch arms were bent inwards just enough to contact the end of the slot at zero pitch. This created a minor increase in force required to move through zero pitch. Not sure if this was a contributing factor.

[Erez]

Paul, what do you mean by tracking shift? When I got flutter, I do not remember much as I landed right away.