Sender: <marv@lancaironline.net> (Marvin Kaye)
To: lml
Date: Sun, 29 Dec 2002 23:59:37 -0500
Message-ID: <redirect-1941519@logan.com>
From: "Bill & Sue" <harrelson@erols.com>
References: <list-1941314@logan.com>
Subject: Re: [LML] Scimitar Prop
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>
> 1)   The prop is 3 in larger and weighs 20 pounds more which helps the CG
in high altitude flight so the nose is not so high.  This could account for
some of the speed advantage by virtue of less drag (?).
>

Dave,

Thanks for the info on the props. There is one little point in your post
that I'd like to bring to your attention though. There is a fundamental
error in your assumption that a more forward cg makes the airplane fly more
nose down. As intuitive as this seems, it just ain't so. As a matter of fact
the opposite is true. Here's why:

Throughout the entire cg envelope, the cg is forward of the center of
pressure (think of center of pressure as the center of lift). This is
necessary for stability. Because of this the horizontal stab is ALWAYS
pushing down. The wing must carry not only the weight of the airplane but
also the "weight" of the down force generated by the horizintal stab. Moving
the cg forward requires a LARGER down force from the horizontal stab to stay
in balance. The additional down force must be lifted by the wing along with
the weight of the airplane. Assuming a constant aircraft weight, density
altitude and airspeed, the additional lift must be produced by a HIGHER
angle of attack. (and higher total drag, known as trim drag). Therefore, the
more forward the cg, the more nose UP the airplane will fly under given
conditions, and with a corresponding INCREASE in drag.

Sorry to be so picky, must be the old flight instructor in me trying to get
out.

Bill
harrelson@erols.com
N5ZQ  LNC2  O-320  VA42   Fredericksburg, VA