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Date: Wed, 27 Nov 2013 10:51:49 -0500
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From: "Steve Colwell" <mcmess1919@yahoo.com>
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Subject:  Vibration
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Dan,

Here's what I think I know about vibration in Lancairs.  Starting with
Cirrus, they had a vibration problem with the 3 blade Hartzell aluminum
prop.  They addressed it by increasing the motor mounts to 6, with 4 of them
forward to carry the static weight bias of the engine and prop (this would
be very expensive for us).  They also went to the lighter and more expensive
composite Hartzell prop.
  
Hartzell's expert has explained the gyroscopic effect of a heavy 3 blade
prop causes anything shaking on the engine or airframe to be more
noticeable. He also said a stiff composite airframe does not damp as well as
a riveted aluminum one. That leaves us with finding every little thing that
can shake.  Balance the prop, find engine/cowl contact points and check gear
doors or wheel pants. Bob Pastusek spent some time at Greenville checking my
control surfaces, hinges and flaps for excess slop.  Motor mount isolator
stiffness could be a factor.  

Some LOBO volunteers have been compiling data looking for the answer,
apparently it could be all the above and maybe more.  The search continues.

Steve Colwell  Legacy RG 550