Cyclic gain and helicopter size

[W.W.]

Hello,

I've mounted the Spirit Pro on my Oxy 3 (300 class helicopter). What cyclic gain is recommended for this size of helicopters?

best regards

Wolfgang

[jgiannakas]

Start with 55%. I have found that all my helis require very similar head gain between 50-60%

[W.W.]

How low can I go with the cyclic gain. Even with 40% I have a wobble on the main rotor.
Helicopter is running at ~3.600 rpm headspeed (resulting in a major vibration peak of 45% for the main rotor 60Hz).

Should I lower the cyclic gain further or is there anything other, I should investigate. Maybe bad bearings, etc. ?

best regards

Wolfgang

[ZeXx86]

Normally each helicopter should fly with Cyclic Gain at least 50%. If there are oscillations, something is wrong.
Can you describe what oscillation do you see? In what axis? Is it during hovering?
If yes, then there could be a problem with:
a) too tight blades in the blade holders
b) something bent or assymetric in the main rotor

If you can see spike in the main rotor without main blades, then the problem can be there.
It could be bent main shaft. Normally vibrations are not reason for oscillations, if there is nothing bent.

Do you use flybarless blades?

[W.W.]

The helicopter is oscilating on aileron and elevator axis during hovering. Especially when decreasing pitch it is significantly better.

After changing nearly every part of the rotor system (main shaft, spindle shaft, blade holders, rotor hub, dampeners and upper main shaft bearing)
I don't believe, that something is bent.

The blades are balanced wíth a weight difference less than 0.02g and a COG difference less than 1mm. This are Zeal Energy 255 blades. They should be flybarless blades, as they are recommended by Oxy.

About to tight blades... What is to tight? They don't fall when turning or shaking the helicopter but could be moved with moderate force. On my T-Rex 250 the blades are about the same and there is no issue.

Someone mentioned the belt tension on helifreak. This is pretty hard, because the Manual says maximum deflection should be 1mm.

best regards

Wolfgang

[ZeXx86]

You can verify if axial bearings are in the correct direction. It is possible to mount them in the opposite way.

Is the unit mounted hard? If it is on a soft foam it can cause such problem too, because unit is moving there.
With our stock tapes it should be OK.

[W.W.]

It's mounted with stock tape. But I cout try to put a velcro strap around. I had to put a forex plate between boom mount and Spirit which is also fixed with a stock tape. Maybe thats to much. But I think more of a mechanical issue, because with the microbeast there was the same issue.

Axial bearings are premounted and glued by lynx/oxy, so they should be ok, and I doubt, that in every blade holder they are premounted the wrong way.

Could it help, to attach a vibration analysis? If so, I have to do one tomorrow and post it then.

best regards

Wolfgang

[Adrian]

Mainblade tracking is okay? (Spurlauf). What happens if you increase or decrease rpm by a few hundreds? I figured out that some models just don't like some specific rpm and start to oscillate. Changing rpm helped in my case. This is due to the fact that every system has it's own resonance frequency, which is pending on many factors like, weight, dampers, LiPo Pack and temperature which influences damper.

[W.W.]

Hello Adrian,

blade tracking looks ok, as far as it could be observed with the wobble. Reducing the head speed increased the wobble.

best regards

Wolfgang

[ZeXx86]

It is really looking as a bent shaft or something very bad in the rotor head.

You can send us the plot from the vibration analysis. This can tell us more.