From: Epijk@aol.com
Message-ID: <161.42f029c.292b2791@aol.com>
Date: Mon, 19 Nov 2001 22:27:13 EST
Subject: Re: dynamic balancing
To: lancair.list@olsusa.com
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Reply-To: lancair.list@olsusa.com

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glcasey@gte.net writes:

<< The purpose of the Damper - correctly called a "tuned absorber" is to 
dampen torsional vibrations in the crankshaft, not the linear vibrations you 
were trying to get rid of. >>

Gary:
 
In most cases, you are entirely correct, that is, the thing on the end of the 
crankshaft that everyone likes to call a "damper" is actually a tuned 
absorber. The most common form is the 
hub-with-elastomeric-spring-with-outer-vibrating-ring, the mass and spring 
rate of which are is tuned to absorb a particular frequency. 

The loose "counterweights" attached to the crankshaft of most LycoNentals by 
sized pins in hardened bushings are pendulous absorbers which absorb specific 
orders of torsional oscillation (as opposed to a specific frequency). 

However, if the "damper" the guy was originally talking about is the "Mark 
Landoll" device, that thing actually IS a damper (a knockoff of the 
"Fluidampr" automotive product) consisting of a ring-mass suspended in a 
silicone oil, encapsulated in the rotating hub. It adds a small amount of 
damping (energy dissipation) to the system, but also adds some mass moment of 
inertia (sadly missing with a lightweight prop) which helps to bring the 
engine-prop system torsional resonant frequency back down toward where it was 
initially intended to be.

If you are interested, these subjects are treated in some detail at the 
following links:

http://www.epi-eng.com/VibrationBasics.htm

http://www.epi-eng.com/TorsVibSum.htm

http://www.epi-eng.com/PistonExcit.htm

http://www.epi-eng.com/TorsAbsrbrs.htm

Jack Kane
EPI, Inc.

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