Rudder counterbalance ?

[Bill Southwell]

If a counter balance is a "trick" Then full scale aerodynamic/structure
engineers have been doing a poor job for years! I would say it is a cure not
a patch or trick. If you need to stiffen your structure and or control
system you will most likely add weight to the aft end of the airplane. If
you "spend" the same weight to add mass ahead of the hinge line and the same
effort aft of the hinge line to remove weight you make flutter impossible
regardless of your stiff control system or lack of it. Dick Hanson proved
this long ago. He also showed less stress on servos and a lighter plane
overall. If an ounce or two on a under weight pattern ship cost the airframe
and gear with in it, it is a rather false economy.  If you eliminate the
possibility of divergence via surface balance you will not have flutter
occur. If you have a component fail in a stiff  ( but unbalanced) system and
the surface gets "loose" then you have the flutter get you.if its balanced
it can't.  Of course none of us have any thing fail on us do we :>) 

 

Regards

Bill 

 

  _____  

From: discussion-request at nsrca.org [mailto:discussion-request at nsrca.org] On
Behalf Of Gray E Fowler
Sent: Thursday, April 28, 2005 10:09 AM
To: discussion at nsrca.org
Subject: RE: Rudder counterbalance ?

 


"Why not mass balance for flutter elimination. When most full scale aircraft
get painted they have to check balance of the surface ( ie Piper
Cherokee's). 

Bill " 


Because most spend hundreds of dollars removing ounces of weight. 

Flutter is natural frequency-speed driven. If you have flutter it is usually
an indication of a serious stiffness problem, either in the set up or the
structure itself. Instead of counter balances and otehr tricks, just
increase the stiffness. That will be the biggest bang for the weight buck.



Gray Fowler
Principal Chemical Engineer
Composites Engineering

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