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Patrick,
<BR>Don't want to shake you up too badly here, but books on theory I ain't
got! I only know what happens when I design my own airplanes.
<BR>There are so many variables that enter into the equation that it can
make your head spin.I have found that some of the strongest contributors
<BR>to the roll scenario are dihedral and the center of pressure of the
rudder. I know that if you have a ship that has proverse couple you can
correct
<BR>the problem, or at least affect it in a very substantial way, by making
the rudder taller and if that doesn't fix it, stick a balance tab on the
front of
<BR>the rudder ahead of the hinge line overhanging the top of the fin,
and if you go too far you'll end up with adverse couple.However, I have
found that the inverse of this
<BR>procedure, i.e., adding area to the bottom of the rudder is less effective
than the stuff you do at the top of the rudder and my guess is that it's
harder
<BR>to get the same leverage because the bottom is closer to the datum
line. So, knowing what effect the rudder produces, while it is helpful
knowledge
<BR>is still skinning the cat with a rubber spatula. The proper aerodynamic
fix is to saw the wing in half and add the correct amount of dihedral to
each
<BR>panel and if you tell me how far below the datum line the center of
the wing is, I'll tell you how much dihedral you need to add (however,
this figure
<BR>could be affected be the current shape of the rudder and may end up
being erroneous). Of course, as I mentioned before, the Edge 540 has already
<BR>dealt with all these areas of frustration and flies appropriately.
It's getting close to auction time.I think you may have some desirable
equipment.
<BR>Good Luck,
<BR>Georgie
<P>PPandelaers wrote:
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<DIV class="MsoNormal"><SPAN style='font-size:10.0pt;
font-family:Arial'><FONT FACE="Arial"><FONT SIZE=-1>Hi
Georgie, </FONT></FONT></SPAN></DIV>
<P class="MsoNormal"><SPAN style='font-size:10.0pt;
font-family:Arial'><FONT FACE="Arial"><FONT SIZE=-1> </FONT></FONT></SPAN>
<P class="MsoNormal"><SPAN lang=EN-GB style='font-size:
10.0pt;font-family:Arial'><FONT FACE="Arial"><FONT SIZE=-1>Would
you mind giving your view on the source of roll effect in the first place
(without dihedral applied to fix it)</FONT></FONT></SPAN>
<P class="MsoNormal"><SPAN lang=EN-GB style='font-size:
10.0pt;font-family:Arial'><FONT FACE="Arial"><FONT SIZE=-1>From
the theory books I read, here’s what I understand:</FONT></FONT></SPAN>
<P class="MsoNormal"><SPAN lang=EN-GB style='font-size:
10.0pt;font-family:Arial'><FONT FACE="Arial"><FONT SIZE=-1>I
think what you call datum line is the following:</FONT></FONT></SPAN>
<P class="MsoNormal"><SPAN lang=EN-GB style='font-size:
10.0pt;font-family:Arial'><FONT FACE="Arial"><FONT SIZE=-1>-
if on the fuselage. the center of lateral area (CLA) and the vertical CG
are connected, you get the line which should be the wind-direction during
flight as the plane faces it. This is in fact the theoretical datum line,
in most construction drawings this line will be shifted up, but parallel
with what I describe. So during the design of a plane, you assume a desired
flight attitude of the fuselage, in this attidude youmake sure the CLA
is on the height of the vertical CG.</FONT></FONT></SPAN>
<P class="MsoNormal"><SPAN lang=EN-GB style='font-size:
10.0pt;font-family:Arial'><FONT FACE="Arial"><FONT SIZE=-1>-
If the CLA <SPAN style='font-weight:bold'><B>is</SPAN></B> on this
theoretical datum line during knife edge ( and I tend to set wing incidence,
hence fuselage attidude, to fly knife edge as neutral as possible),
assuming no dihedral, than the only possible contributors to roll are:</FONT></FONT></SPAN>
<UL type=disc>
<LI class="MsoNormal">
<SPAN lang=EN-GB style='font-size:
10.0pt;font-family:Arial'><FONT FACE="Arial"><FONT SIZE=-1>Motor-side
thrust.</FONT></FONT></SPAN></LI>
<LI class="MsoNormal">
<SPAN lang=EN-GB style='font-size:
10.0pt;font-family:Arial'><FONT FACE="Arial"><FONT SIZE=-1>Center
of lateral area of rudder, which should also be on this theoretical datum
line</FONT></FONT></SPAN></LI>
</UL>
<DIV class="MsoNormal"><SPAN lang=EN-GB style='font-size:
10.0pt;font-family:Arial'><FONT FACE="Arial"><FONT SIZE=-1>Don’t
forget. The wing isn’t flying.</FONT></FONT></SPAN></DIV>
<P class="MsoNormal"><SPAN lang=EN-GB style='font-size:
10.0pt;font-family:Arial'><FONT FACE="Arial"><FONT SIZE=-1> </FONT></FONT></SPAN>
<P class="MsoNormal"><SPAN lang=EN-GB style='font-size:
10.0pt;font-family:Arial'><FONT FACE="Arial"><FONT SIZE=-1>Clearly,
I must be overlooking something serious, such that we need to apply dihedral
to fix it. Can you help?</FONT></FONT></SPAN>
<P class="MsoNormal"><SPAN lang=EN-GB style='font-size:
10.0pt;font-family:Arial'><FONT FACE="Arial"><FONT SIZE=-1> </FONT></FONT></SPAN>
<P class="MsoNormal"><SPAN lang=EN-GB style='font-size:
10.0pt;font-family:Arial'><FONT FACE="Arial"><FONT SIZE=-1>Thanks!!</FONT></FONT></SPAN>
<P class="MsoNormal"><SPAN lang=EN-GB style='font-size:
10.0pt;font-family:Arial'><FONT FACE="Arial"><FONT SIZE=-1> </FONT></FONT></SPAN>
<P class="MsoNormal"><SPAN lang=EN-GB style='font-size:
10.0pt;font-family:Arial'><FONT FACE="Arial"><FONT SIZE=-1>Patrick</FONT></FONT></SPAN>
<P class="MsoNormal"><SPAN lang=EN-GB style='font-size:
10.0pt;font-family:Arial'><FONT FACE="Arial"><FONT SIZE=-1> </FONT></FONT></SPAN>
<P class="MsoNormal"><SPAN lang=EN-GB style='font-size:
10.0pt;font-family:Arial'><FONT FACE="Arial"><FONT SIZE=-1> </FONT></FONT></SPAN>
<P class="MsoNormal"><SPAN lang=EN-GB style='font-size:
10.0pt;font-family:Arial'><FONT FACE="Arial"><FONT SIZE=-1> </FONT></FONT></SPAN>
<P class="MsoNormal"><SPAN lang=EN-GB
style='font-size:12.0pt'><FONT FACE="Times New Roman"><FONT SIZE=+0>What
you're experiencing is known as "adverse roll couple"! You can prove this
just by flying right side up and applying full rudder deflection in either
direction and you will see that the airplane will roll in the opposite
direction to whatever rudder you are applying.The cause of the phenomenon
is that the wing is located too far below the Datum line without sufficient
dihedral to compensate for the offset</FONT></FONT></SPAN>
<P class="MsoNormal"><SPAN lang=EN-GB style='font-size:
10.0pt;font-family:Arial'><FONT FACE="Arial"><FONT SIZE=-1> </FONT></FONT></SPAN>
<P class="MsoNormal"><SPAN lang=EN-GB style='font-size:
10.0pt;font-family:Arial'><FONT FACE="Arial"><FONT SIZE=-1> </FONT></FONT></SPAN></DIV>
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