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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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