Vibration when flying

[Sv.grainne]

We are test flying my Aviomania Genesis and Eric had noticed a vibration at 4200-4600 RPM. What are some suggestions on how to narrow this down? I'm thinking best to start with prop pitch, repitch a small amount and see what that does. I do not have access to a prop balancer. Others have said that some vibration at specific RPM ranges is common.

 

[Mike G]

How did you/Eric arrive at 4200-4600 rpm?
I think you have a 912, so prop imbalance would be nearer 2000 rpm and the blade passing frequency would be around 6000 rpm (assuming 3 blades) so I doubt if it's the prop.
If the 4200-4600 is engine rpm then look at carb balance especially if the vibration reduces with higher revs. If not out of balance crank (unlikely) or engine mounts.
Mike G

 

[Sv.grainne]

While in flight

 

[Sv.grainne]

Checked on ground, ran up to 4900 rpm, no vibration!

 

[Sv.grainne]

Readjusted prop, took 1deg off, ran it up on the ground, 5580rpm WOT, no vibration. Eric will fly next week and see if that changes anything.

 

[Aerofoam]

Readjusted prop, took 1deg off, ran it up on the grounds, 6580rpm WOT, no vibration. Eric will fly next week and see if that changes anything.

I've got a couple you can come balance......

 

[Sv.grainne]

Correction, 5580rpm!

 

[Tyger]

Correction, 5580rpm!

You know you can actually just edit out the original mistake, right?

 

[Sv.grainne]

Yes, but it does not edit the text in the response.

And I figured you would comment on 6580rpm on a 912UL!

 

[Tyger]

You corrected it, so nothing to comment on... but what "response" are you talking about?

 

[Sv.grainne]

I'm teasing you! 🙂