Difficulty dynamically balancing RV-12iS

[DavidHarris]

My daughter and I recently finished building N912EH, a RV12-iS, and had an first flight with no abnormal behavior.

We took the plane to the FBO to dynamically balance. They found it was at 0.2 (unsure of units) without any weights attached. They said that is good enough, but ideally could be improved to 0.1 or 0.15 with weights.

They found that adding weights caused the balance to change erratically, and were unable to improve the balance. When they removed all weights, the balance was back at 0.2.
They hypothesized that something might be loose (such as an engine mount), but could not say whether there is a safety of flight issue.

Can anybody on this forum comment on whether this may be pointing to a potential safety issue, and whether the balance of 0.2 is adequate?

Thank you,

David Harris

 

[G JWTP]

As a guide.

John.

 

[seagull]

At .2 ips it is not unsafe, the average plane that comes to me is .25. - .50 ips and the owners think they are smooth. If the operator of the balancer is experienced with balancing they can balance it below .06. If your engine is new and you are not done tweaking the prop pitch I wouldn’t waste money on balancing unless it is extremely out of balance, yours isn’t. Put 30+ hours on the plane and engine then get it balanced.

 

[N8DAV8R]

Follow Seagull's advice. Don't panic about .2 ips for now. Put some time on the airplane.

While you're out flying, ask around with people you come across that also have homebuilts. Network a little, it's easy once you're out there in an airplane that you built. Good chance you come across someone with access to a balancing setup that is willing to help and put some time into getting it right, or loan it to you so you can tinker with it yourself and figure things out.

 

[Walt]

I have found some of the Rotax/prop combo's to be "challenging" to balance. It usually helps to slow down a little, like 2000 prop RPM.
You should be able to improve from .2 but I wouldn't fret too much, getting it under .1 IPS would be better.

 

[rvbuilder2002]

I fully agree with all of the replies posted so far but will add that after balancing quite a few RV 12s, I have never not been able to get it well below .1 ips.
Often times in the .02 - .04 range.

So I think the problem may be the capabilities of the person that was doing the balancing.

I totally agree that you should wait to try again until you are sure that you are no longer going to make any propeller pitch adjustments. And I will add to that that much difference in pitch between the blades can have a strong influence on how smooth of a balance you can get.
Just using the gauge pin that comes with the propeller, to set the blade pitch is not a reliable method. You need to be measuring the actual picture of each blade and try and get them to read within .1° of each other.

 

[DavidHarris]

Thank you for all this expert advice. We will continue to fly as is and perhaps revisit later.

 

[rcarsey]

In the meantime, you could check the the pitch of each blade again.. I think the spec was +/- 0.1 degrees of each other.