500 Intermittent vibration

[Robair]

In hover and normal straight and level flight my 550E is vibration free but as soon as I apply a slight left or right bank at a somewhat faster forward speed, the machine develops a high speed vibration that I notice in the skid gear vibrating rapidly.

I have checked the tail rotor and main rotor shaft for straightness (Perfect) Blade tracking is spot on. Balanced both Main and tail rotor blades to microscopic accuracy.

The vibration is also somewhat intermittent as I don't always notice it.

What am I missing here?

Thanks in advance.

 

[Tony]

Sounds like your cyclic gain is just a touch too high. Try lowering it about 5% and see if it goes away.

 

[Robair]

Thanks Tony,
I will give that a go and see what happens.
Rob

- - - Updated - - -

Tony,
Sorry for this really dumb question.
I am using a JRXG8 transmitter and a 3GX Gyro.
Search as much as I have, I cannot find a setting for the cyclic gain. Not on the Tx or on the PC based software.
I am guessing that I am missing something that is staring me in teh face.
Rob

 

[Tony]

It's one of the pots on the top of the gyro its self. Look in the program when you change it. I suggest a setting of 105 in the program, but may have to go down as far as 95 to get it to hold steady.

 

[Robair]

Tony,
Now I feel like a proper burk.
I found it but here is the question.
On the TX the Aileron expo is set at 10% and on the PC software the "Cyclic pitch expo setting" is at 2.
The info popup on the software indicates that if TX expo setting is used, the software setting can or should be 0.
So, do I set the software to 0 and reduce the expo on the TX from 10% to 5% or do I reduce the setting on the software from 2 to 1?
Sorry about this runaround.

 

[Tony]

Hey, it's not a problem. This is what we are here for.

If you are using expo in the Tx, set the gyro software to 0 and raise your Tx up to about 20. It will soften it up in the beginning stick movements. I usually suggest a setting of 30% expo and 70% dual rate for beginner pilots, but each person has to get a feel for it and set it to what they feel is comfortable.

 

[Robair]

Thanks Tony,
Now I can say with more conviction that I will give that a try and let you know how it works out.
Rob

 

[Tony]

I'll be looking forward to it.

 

[Robair]

Hi Tony,

Sorry this took so long but I believe I have finally tracked down the vibration issue.

I played around with the Expo and both forward and lateral cyclic gains but nothing seemed to make any difference.

No matter what I did, the machine was still displaying an intermittent low speed vibration in certain stages of flight. Especially high speed straight and level and high speed shallow bank angles. The slow speed vibration made me think that it must be a main rotor imbalance of some sort as opposed to a high speed vibration which would have led me to think it was a tail rotor imbalance.

I believe this thinking was correct, so I replaced the mail rotor blades after a rebalance, BUT this time I rebalanced around the CofG of each blade as well as the blade bolt holes - as opposed to balancing around the center of the 2 blade disc, ie. the center of the main rotor system.

Bingo! that seems to have been the problem.

Balancing the 2 blades on the main rotor bolt axis and just adjusting the weight of the lighter blade anywhere along the blade is just not good enough. However, adjusting the weight of the lighter blade at the CofG of that blade seems to do the trick. I should really have known this but so we continue learning.

Thanks for your assistance anyway. It was most helpful.
Regards
Rob

 

[Tony]

I'm glad you found out your issue and it was something most commonly overlooked. Now all we need is video of it in the air