Message-ID: <000401c3fede$eb1bfa60$2402a8c0@edward>
From: "Ed Anderson" <eanderson@carolina.rr.com>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
References: <list-3050988@logan.com>
Subject: PROP Free Spinning or WindMilling???
Date: Sun, 29 Feb 2004 11:13:07 -0500
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Ok, let me see if I understand what it was I thought I hear said about
props.

Case 1:  IF the prop is free (no engine connection -crankshaft broke, etc)
to spin without any drag restriction from the engine, it will continue to
spin faster and faster due to the air flow until reaching some equilibrium
point (or comes off the aircraft).  That in effect the entire area of the
prop disk appears to the airflow as a relative solid disk to the airflow and
greatly increases drag and rate of descent. I think I understood that the
prop pitch will probably determine the rpm of such a free spinning  prop and
therefore the "solidity" of the disk to airflow. Finer pitch = more RPM =
more solid disk resistance to air flow = more drag = faster rate of descent.
Coarse pitch = less rpm = less solidary to airflow = less drag = lesser rate
of descent.  Is this more or less approximately correct??


Case 2.  On the other hand, If the prop is windmilling (ie. connected to the
engine such that it has the pumping action as a drag) then while there is
some additional drag over a completely stopped prop, its not a great deal
more. For one the rpm will undoubtedly be considerably lower than a free
spinning prop and the disk less solid.  Again depending somewhat on pitch  -
but not as much drag as case 1.

Anywhere close???

Ed


Ed Anderson
RV-6A N494BW Rotary Powered
Matthews, NC