Reply-To: <glcasey@gte.net>
Reply-To: lancair.list@olsusa.com
From: "Gary Casey" <glcasey@gte.net>
To: <lancair.list@olsusa.com>
Subject: dynamic balancing
Date: Sun, 18 Nov 2001 05:39:07 -0800
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>>After balance we
ended up with a 20+ rpm increase in static max rpm and in flight I feel I
got at least 20 rpm more.  And a 40% reduction in vibration which I can
feel as less noise and more quiet-smoother in flight .<<

I think dynamic balancing is a necessary step, but...
1.  I don't see where it will add power.  The internal friction of the
engine doesn't really change as the hydrodynamic losses in the bearings are
99% independent of the load on them.  Other than that there is the damping
losses in the engine mount rubber, which is pretty insignificant.  20 rpm
equates to about 3 to 5% more power.  I don't see how this could be.  A lot
of racers run at higher rpm, increasing the effect of out-of-balance
conditions.  It also seems like they have more money.
2.  Assuming the "damper" was accurately balanced by itself, yes, it won't
affect the overall balance of the engine.  I assume you are using one
because you have a wooden prop on a 4-cylinder engine.  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.
3.  40% reduction in perceived vibration and noise?  Absolutely, assuming
something was out of balance to start with.  That can happen in a number of
ways, mostly from imperfect alignment of the prop and crank.  A very small
runout, within the spec of each component separately, can cause a relatively
large imbalance.  If the required weights are in line with the blades
(2-blade prop) one thing I would try first is to rotate the prop 180 and see
if it goes down before adding the weight.
4.  A good balance will make a lot of things last longer - gyros, radios,
etc., but doesn't have much of anything to do with the engine itself lasting
longer.  The reduced stresses are miniscule compared to the combustion and
inertia forces within the engine.

Just my 2 cents worth.

Gary Casey
ES project

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