The axis does not necessarily identify the component causing the vibration. I believe that the y axis vibrations are usually measured the highest because the heli is the least stable in that direction. The y axis is the short direction of the skids whereas the x axis is the long direction of the skids.

The key to help determine the cause of vibrations is to determine the rpm of the offending component. The rpm can be determined by hovering the mouse pointer over the peak on the graph or you can multiply the frequency by 60 to determine rpm. A peak at headspeed rpm would indicate something amiss in the main drive or head and a peak at tail rotor rpm would indicate a problem there. A higher rpm at motor speed would indicate a motor vibration.

Yes I know, im very used to spectrum analyses with the vbar but I just wanted to understand the directions and what advantages it gives to be able to measure 3 axis in stead of 1.

Just saying its more easy to locate a problem is not an explanation. To use it we need info, practical examples...

According to Tomas they aren't correct but according to what you say and what I can find (very good guide Google skookum vibration for dummies) it was right. If not I hope someone can explain it in dept. Its a pitty to have this functions in the fbl unit but no explanation.

_________________
[b]-TT E700 V2-Spirit Pro-mks950-980-Kontronik Kosmik 160 HV -Pyro 700 rewound by PD / Voodoo 600 -PD-MX700-470kv--BLS255hv-VBAR 5.3+- Gaui X3+ Spirit Pro

My guess is that all three axes are shown because depending on the layout, design, and configuration of helis and the orientation of the fbl unit on the heli, showing all three axes eliminates the possibility of the most sensitive axis on any heli is not inadvertently ignored, and a high vibration is not recorded.

Yes could be that you see problems quicker because by fusing everything in one some things aren't visible?

_________________
[b]-TT E700 V2-Spirit Pro-mks950-980-Kontronik Kosmik 160 HV -Pyro 700 rewound by PD / Voodoo 600 -PD-MX700-470kv--BLS255hv-VBAR 5.3+- Gaui X3+ Spirit Pro

I'm a little confused too. The manual states:

It is possible to measure vibrations in three separate axes:
Y – aileron axis
Z – rudder axis
X – elevator axis

Most resources that I've seen on helicopters identify the axes based on a rotation about each axis. This is from OpenTx for example:

Aileron (roll)
Elevator (pitch)
Rudder (yaw)

So if you move the rudder, the heli yaws to the left or right, or rotates about the vertical axis of the heli, which is Z. If you move the aileron, the heli rolls left or right, or rotates about the long axis (nose-tail), which according to the Spirit manual is Y. If you move the elevator, the heli pitches up or down, or rotates about the short axis (left-right), which must be X.

Most pictures that I've seen of heli coordinate systems, however, define aileron as X and elevator as Y. So my questions are:

1. Do the X and Y axes in the Spirit manual correspond to pitch and roll, respectively?
2. Is the vibration analyzer in the unit reporting vibration along the axis (translational), or vibration around that axis (rotational)?

A picture showing the coordinate system might be worth a thousand posts!

The axis that shows the highest vibration (elevator, aileron, or rudder) does not necessarily indicate that the elevator, aileron, or rudder is causing the vibration. The axes are used to indicate the directions that the sensor in the fbl is measuring the vibration, but the directions are not critical to determining the cause of the vibration.

The critical criterion for vibration analysis is the frequency/rpm of the vibration, which help to identify the components that are causing the vibration by their rotational speed.

Absolutely no disagreement that the freq/rpm provides the primary information. However, knowing whether the vib is linear/rotational and what axis its associated with would also help in the diagnosis.

Put differently, if freq/rpm was the only thing that mattered, then Spirit would only output some type of average quantity.

Sent from my phone using Tapatalk

And you could very well be right in post 13, but right now it's just a speculation. Just looking for a clarification since I can't piece it together myself.

Sent from my phone using Tapatalk

The reason that I am not particularly concerned about the vibration axes is that to me, the vibration direction mostly does not tell me much. I say this because a typical heli has rectangular shaped skids. When the vibrations are measured with the heli on its skids on carpet or grass, the heli is less stable and less damped in the y direction because of the narrow direction of the skids, versus the x direction which is the long direction. Therefore, the measured vibration will be higher in the y direction most of the time, regardless of the source.

I say measured vibration because the heli is resting on its skids and the skid layout, distribution of mass of the heli, structural properties of the heli, and the surface material that the skids are resting on (and probably other factors) will affect or dampen the vibrations unequally in the various directions and will affect the measured vibrations in each axis. The measured vibrations may be different if the heli is not supported or restrained by its skids.

Of course this is just my theory, but this is why I don't worry about the axes of vibration and just pay attention to the frequency (the Spirit manual and Tomas also says to use frequency/rpm to determine source of vibration).

I understand, but I would still very much appreciate answers to my two questions in post 15.

Sent from my phone using Tapatalk