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There are two types of vibration in piston engines,
torsional and lateral. Torsional vibration is from the power stroke of the
pistons as the combustion gasses burn and lateral vibration is from a net
imbalance in the rotating masses. The balance checking equipment described so
far is only checking the lateral vibration . . . and then only in one plane, at
the front of the engine. To check dynamic balance, the rotating mass needs to be
checked in two parallel planes, one at the front of the crank shaft and the
other at the rear of the crank shaft. This allows for checking "wobble" of the
engine. The front could be out of balance at one angle and the rear could be out
of balance at another angle. This is checked on car wheels by automatic machines
that determine weights to be applied both inside and outside of the
rims.
The silicon filled harmonic balancer does help
with engine vibration but only the torsional vibration. If the silicon suspended
weight is allowed to move laterally then some lateral vibration can be
compensated automatically.
Wolfgang
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Wolfgang,
The harmonic damper you refer to (12 pounds, bolts to Lyc flywheel)
contains a steel ring in viscous silicone. Its purpose is to dampen
negative torque pulses and to provide for more flywheel momentum. It
is especially effective for light wooden props (rpm increase of
approximately 100) but also serves it purpose with CS props even
though the result appears to be un-measurable.
Review the torsional effects of a 4 cylinder engine
here:
It contributes nothing to dynamic prop balance :-(
Grayhawk
In a message dated 8/12/2010 3:45:09 P.M. Central Daylight Time,
Wolfgang@MiCom.net writes:
Or put a silicon filled balance ring at the
prop hub :-)
Wolfgang
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Vibration sensor is placed on engine to
measure how engine is moving in space.
Prop imbalance will make
engine move in bigger circle.
So mayny Millivolts are genrated
per vibration severity.
Relative location of heavy spot is
signaled by photo cell, or strobe light flash as heavy spot
passes and polarity changes. Up-down =
plus-minus.
The prop's static weigh slugs can be adjusted
or large area washers can be bolted to spinner bulkhead to
counterbalance the heavy spot.
How much depends weigh
depends on how much imbalance there was to begin
with.
Common to have 10-30 grams of weight for a momento of
100-200 inch pounds.
Kent Felkins
Tulsa
Oklahoma
----- Original Message ----- From: "Greenbacks,
UnLtd." <N4ZQ@comcast.net>
To:
<lml@lancaironline.net>
Sent: Thursday, August 12, 2010
7:20 AM
Subject: [LML] Re: Prop Balance
Could one of you describe the process of
dynamically balancing a
typical prop?
My old brain cannot
visualize how weights are attached.
Angier
Ames
N4ZQ
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