<br><font size=2 face="sans-serif">It is all about the natural frequency of both the aero surface and the structure. Those who have seen tail failures in the Impact talk about the rudder flutter, but it could be induced totally by the fuselage. If the fuse is flex twisting, then how is the servo supposed to hold the rudder in position? It cannot and the rudder flutters and the results are known. Our planes are low speed and our aero surfaces are really light weight and relatively stiff, creating a high natural frequency for the control surface. Opposite that is a fuselage, with a distance of about 40 inches from the wing to the tail, with all the fiber at 0/90 degrees creating a much lower natural frequency. This is where the problem starts, and the first indication of this is when a former in the tail fixes a problem.</font>
<br><font size=2 face="sans-serif">Relating full scale stuff to our planes may make for interesting conversation, but what we do the best and what they do the best are not neccesarily the same thing. I never implied that the full scale guys do a poor job, but I would venture to state that a full scale aerodynamic/stucture engineers first attempt at designing a pattern plane would in essence "suck".</font>
<br><font size=2 face="sans-serif">Spend your weight budget on a stiffer airframe. Not only will your aero surfaces NOT flutter, but you plane will fly better.<br>
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Gray Fowler<br>
Principal Chemical Engineer<br>
Composites Engineering</font>
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<td><font size=1 face="sans-serif"><b>"Bill Southwell" <bnbsouthwell@avsia.com></b></font>
<br><font size=1 face="sans-serif">Sent by: discussion-request@nsrca.org</font>
<p><font size=1 face="sans-serif">04/28/2005 11:41 AM</font>
<br><font size=1 face="sans-serif">Please respond to discussion</font>
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<br><font size=1 face="sans-serif"> Subject: RE: Rudder counterbalance ?</font></table>
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<br><font size=2 color=#000080 face="Arial">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 :>) </font>
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<br><font size=2 color=#000080 face="Arial">Regards</font>
<br><font size=2 color=#000080 face="Arial">Bill </font>
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<br><font size=2 face="Tahoma"><b>From:</b> discussion-request@nsrca.org [mailto:discussion-request@nsrca.org] <b>On Behalf Of </b>Gray E Fowler<b><br>
Sent:</b> Thursday, April 28, 2005 10:09 AM<b><br>
To:</b> discussion@nsrca.org<b><br>
Subject:</b> RE: Rudder counterbalance ?</font>
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"Why not mass balance for flutter elimination. When most full scale aircraft<br>
get painted they have to check balance of the surface ( ie Piper<br>
Cherokee's). <br>
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Bill "</font><font size=3 face="Times New Roman"> <br>
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Because most spend hundreds of dollars removing ounces of weight.</font><font size=3 face="Times New Roman"> <br>
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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.<br>
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Gray Fowler<br>
Principal Chemical Engineer<br>
Composites Engineering</font>
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