Sender: <marv@lancaironline.net> (Marvin Kaye)
To: lml
Date: Tue, 04 Jun 2002 12:36:25 -0400
Message-ID: <redirect-1281921@logan.com>
From: Epijk@aol.com
Subject: Re: [LML] Non standard metal props on Lancair 320/360
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In a message dated 6/2/2002 2:52:29 PM Pacific Daylight Time, 
ian.crowe@sympatico.ca writes:

<<<...I am aware of a limitation on the Piper Arrow with an IO-360-C1C from 
2100 to
2350 rpm.  This engine is basically similar to my engine but drives a 74"
propellor...>>>

Unlike the -A3B6D, the -C1C has NO torsional-vibration-absorbing pendulous 
counterweights on the crankshaft, hence the critical excitation range (to be 
avoided) on the tach. BUT, be aware that the 68" prop will have a 
significantly lower mass moment of inertia than the 74" prop of which you 
speak, which has the effect of reducing the torsional resonant frequency of 
the engine-prop system (hence the tach range to be avoided). Also, without 
those "counterweights", the fatigue excitation applied to the prop blades is 
greater, and the blade resonant frequencies are lower than the 74" prop. Lots 
of guessing involved if you're not using a certified engine-prop COMBINATION.
Jack Kane