I found this interesting and thought that I would forward the info.  It
appears that empirical data is at odds to the theoretical.   BTW, do not
'cut down' a metal prop!

Ken Powell
-------------------------------------------------------------
Time: 07:49:06 PM PST US
From:
Subject: RV-List: constant speed prop diameters

Hi guys,

I have a couple of questions concerning constant speed prop diameters.

First, is there anyone out there running a Hartzell clipped to 68"?

I would think that the smaller diameter would allow more pitch in cruise
and
more speed.  An engineer at Hartzell says no.  He says to run the
largest
diameter possible for more speed.  He claims that the effect of the
increased parasitic drag of the fuselage goes up more with the smaller
diameter prop.  Although it doesn't seem to really hold true from the
results seen with fix pitch props.  I would think that there would be an
ideal diameter for each airplane based on parasitic drag of the fuselage
and
cruise speed.  The lower drag of a RV as compared to a Cessna I think
would
lend itself to a smaller diameter.  It is obvious that the larger
diameter
would have a big effect on climb.

Second question, has anyone tried different diameter Hartzell C/S props
on
the same airplane? (apples to apples comparison)

Thanks,

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