Message-Id: <3.0.3.32.19990614154513.00a92b60@olsusa.com>
Date: Mon, 14 Jun 1999 15:45:13 -0400
To: lancair.list@olsusa.com
From: "Field, Peter B" <Peter.Field@MW.Boeing.com> (by way of Marvin Kaye <marvkaye@olsusa.com>)
Subject: Control Surface Balancing
Mime-Version: 1.0

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Marv:
     Another LML subscriber gave a "novel" explanation on the need for
control surface balancing in the V#18 posting.  He seems to be confusing
control surface balancing with the sensitivity effects of bobweights.  I
think you might want to post the following paragraph:

     The need for forward weight in control surfaces has nothing to do with
control system sensitivity under G load.  Control surface over balancing is
necessary to control aerodynamic flutter.  Trailing edge control surfaces
(ailerons, elevators, or rudders) can easily develop divergent (destructive)
flutter unless they are over balanced per the instructions in our manuals.
That means every control surface must be balanced "nose heavy" with all the
paint on it - ready to fly - to be safe.  It is likely that shaving
overbalance weight too closely could establish a flutter speed inside the
upper right side of the flight envelope at high speed and low "q" (high
altitudes).  Flutter can be excited aerodynamically alone or in combination
with other vibration sources such as the engine and/or propeller.  The
weighted leading edges provide damping (suppress the flutter vibration) of
the spring/mass system that the surface represents in flight.  A neutral
balance does not provide sufficient damping. 

Cheers, 
Pete


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