Rudder counterbalance ?

[Bob Richards]

Bill,

I agree.

I had a problem 20 years ago with a sport plane that I
designed. It had very bad aileron flutter, in fact it
sheared the shaft off of the aileron servo! All this
happened in level flight.

This was a design with full-span strip ailerons with
one servo in the center of the wing. Probably the
worst case possible, considering the lack of torsional
stiffness of the typical aileron stock. I tried adding
surface area forward of the hinge line (air balance)
and that did not help at all. What I ended up with was
a very small amount of mass balance in front of the
hinge line - two inch long piece of 3/32 music wire
with a couple of wheel collars on the end. I was then
able to dive the airplane straight down full throttle
until the clunk started sucking air and the engine
quit -- no flutter.

The surface was not statically balanced, the aileron
CG was still behind the hinge line. But, the slight
addition of weight ahead of the hinge line was all
that was needed.

Bob R.

--- Bill Southwell <bnbsouthwell at avsia.com> wrote:
> 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 

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