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From: Gary Casey <glcasey@adelphia.net>
Subject: Rear fuselage stiffness

I have heard some people concern themselves with the stiffness of the  
rear fuselage of the ES and IV, specifically the joint to the tail  
section, which is in a location close to that of minimum section  
modulus.  Some have added a bulkhead to add stiffness, the idea being  
that with downward tail loads the top deflects upward, essentially  
trying to straighten out.  To accommodate this the sides deflect  
inward.  I set up an experiment to measure this effect.  I  
temporarily glued hardpoints inside the fuselage just behind the  
joint and at the height of the longitudinal joint.  I then applied a  
torque along the lateral axis of approximately 450 ft-lb and measured  
the change in width (distance between the hardpoints).  I think this  
load is something close to half of a normal load, which I estimated  
at 330 pounds of downforce at the horizontal stabilizer applied 3  
feet behind the joint.  The change in width was somewhere between . 
002 and .005, not very much.  My conclusion is that adding structure  
to reduce this deflection isn't going to buy much.  Any opinions on  
this?

Gary Casey