From: "Finn Lassen finn.lassen@verizon.net" <flyrotary@lancaironline.net>
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Subject: Re: [FlyRotary] Re: dynamic balance
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
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Message-ID: <c950a872-5290-c538-ca5b-1922a679e967@verizon.net>
Date: Fri, 19 Mar 2021 18:15:57 -0400
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Thanks Steve. That really helps!

Didn't even think about the flex plate. Might try to remove that when I 
remove the PSRU to replace oil seal.

Tracy also mentioned rotor and counter weights imbalances and thinks 
that can't really compensate for those with a weight on the flywheel.
So the combustion event theory is dead.

Finn

On 3/19/2021 4:26 PM, Sboese sboese@uwyo.edu wrote:
> Finn,
>
> The FFT processing required two channels recorded simultaneously, one 
> for the position reference and one for the accelerometer.
>
> The system I used allowed sampling of each channel at 5khz with no 
> external amplification or filtering.
>
> My guess as to the prop 3x(blade) signal is that it is an interaction 
> with the ground.  The prop is 76” dia resulting in about 8” of prop 
> tip to ground clearance.
>
> Also a guess on my part is that the engine 1x vibration may be coming 
> from the flex plate shifting on the rubber dampers.  My system has 
> about 0.020” of clearance between the corners of the damper plate and 
> the flex plate rim when centered.  When attempting to balance the 
> engine, a point was reached where no further improvement was made and 
> the phase angle was not consistent between tests.  I don’t know how 
> much the splined shaft can restrict the possible shift off center of 
> the damper plate, but the intensity of the vibration was consistent 
> with the weight of the damper plate and 0.020” of eccentricity.  This 
> may also be affected by the load on the rubber dampers.
>
> Steve Boese
>


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