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<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'>Hi Georgie, </span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'> </span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-GB style='font-size:
10.0pt;font-family:Arial'>Would you mind giving your view on the source of roll
effect in the first place (without dihedral applied to fix it)</span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-GB style='font-size:
10.0pt;font-family:Arial'>From the theory books I read, here’s what
I understand:</span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-GB style='font-size:
10.0pt;font-family:Arial'>I think what you call datum line is the following:</span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-GB style='font-size:
10.0pt;font-family:Arial'>- 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.</span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-GB style='font-size:
10.0pt;font-family:Arial'>- If the CLA <b><span style='font-weight:bold'>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:</span></font></p>
<ul type=disc>
<li class=MsoNormal><font size=2 face=Arial><span lang=EN-GB style='font-size:
10.0pt;font-family:Arial'>Motor-side thrust.</span></font></li>
<li class=MsoNormal><font size=2 face=Arial><span lang=EN-GB style='font-size:
10.0pt;font-family:Arial'>Center of lateral area of rudder, which should
also be on this theoretical datum line</span></font></li>
</ul>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-GB style='font-size:
10.0pt;font-family:Arial'>Don’t forget. The wing isn’t flying.</span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-GB style='font-size:
10.0pt;font-family:Arial'> </span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-GB style='font-size:
10.0pt;font-family:Arial'>Clearly, I must be overlooking something serious,
such that we need to apply dihedral to fix it. Can you help?</span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-GB style='font-size:
10.0pt;font-family:Arial'> </span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-GB style='font-size:
10.0pt;font-family:Arial'>Thanks!!</span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-GB style='font-size:
10.0pt;font-family:Arial'> </span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-GB style='font-size:
10.0pt;font-family:Arial'>Patrick</span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-GB style='font-size:
10.0pt;font-family:Arial'> </span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-GB style='font-size:
10.0pt;font-family:Arial'> </span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-GB style='font-size:
10.0pt;font-family:Arial'> </span></font></p>
<p class=MsoNormal><font size=3 face="Times New Roman"><span lang=EN-GB
style='font-size:12.0pt'>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</span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-GB style='font-size:
10.0pt;font-family:Arial'> </span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-GB style='font-size:
10.0pt;font-family:Arial'> </span></font></p>
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