REFLECTOR:caster of NG
Al Gietzen
reflector@tvbf.org
Mon, 16 Jun 2003 21:51:47 -0700
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Subject: REFLECTOR:caster of NG
Today I started to install my new NG strut. After leveling the plane I
found the new strut was sloped 2 degrees but the in the wrong
direction. IE the bottom of the strut was further forward than the top
of the fork (bottom of the washer). Brendan confirmed this was correct
for me.
I don't believe it.
Caster must be reward for the wheel to be self centering. I think I now
see why I could not beat the shimmy problem before. I asked the fellow
who designed the current form of Cessna's NG. He said he designed 12
degrees negative for Cessna.
Various of my mechanical engineer friends confirm that with the positive
angle the weight of the aircraft will try to force the wheel out of
trail.
Wayne:
I had a long discussion (argument) with Mark Machado about 3-4 years ago
about the castor angle of the NG strut. I maintained that it needed to
be negative castor. He assured me that he had done extensive analysis,
and that with the fork geometry and gyroscopic forces on the rotating
wheel, etc, etc, that the positive angle was correct. I believe he also
said that they had (or were going to) test different angles. I've never
had much confidence in his conclusion.
If someone has evidence that we need a negative angle, it is way past
time for that issue to be made right.
Scott; does Velocity have test data on this?
Al
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<p class=3DMsoNormal style=3D'margin-left:.5in'><b><font size=3D2 =
face=3DTahoma><span
style=3D'font-size:10.0pt;font-family:Tahoma;font-weight:bold'>Subject:</=
span></font></b><font
size=3D2 face=3DTahoma><span =
style=3D'font-size:10.0pt;font-family:Tahoma'> REFLECTOR:caster
of NG</span></font></p>
<p class=3DMsoNormal style=3D'margin-left:.5in'><font size=3D3 =
face=3D"Times New Roman"><span
style=3D'font-size:12.0pt'> </span></font></p>
<div>
<p class=3DMsoNormal style=3D'margin-left:.5in'><font size=3D2 =
face=3DArial><span
style=3D'font-size:10.0pt;font-family:Arial'>Today I started to install =
my new NG
strut. After leveling the plane I found the new strut was sloped 2
degrees but the in the wrong direction. IE the bottom of the strut =
was
further forward than the top of the fork (bottom of the =
washer).
Brendan confirmed this was correct for me.</span></font></p>
</div>
<div>
<p class=3DMsoNormal style=3D'margin-left:.5in'><font size=3D3 =
face=3D"Times New Roman"><span
style=3D'font-size:12.0pt'> </span></font></p>
</div>
<div>
<p class=3DMsoNormal style=3D'margin-left:.5in'><font size=3D2 =
face=3DArial><span
style=3D'font-size:10.0pt;font-family:Arial'> I don't believe =
it.</span></font></p>
</div>
<div>
<p class=3DMsoNormal style=3D'margin-left:.5in'><font size=3D3 =
face=3D"Times New Roman"><span
style=3D'font-size:12.0pt'> </span></font></p>
</div>
<div>
<p class=3DMsoNormal style=3D'margin-left:.5in'><font size=3D2 =
face=3DArial><span
style=3D'font-size:10.0pt;font-family:Arial'>Caster must be reward for =
the wheel
to be self centering. I think I now see why I could not beat the shimmy =
problem
before. I asked the fellow who designed the current form of =
Cessna's NG. He
said he designed 12 degrees negative for Cessna.</span></font></p>
</div>
<div>
<p class=3DMsoNormal style=3D'margin-left:.5in'><font size=3D3 =
face=3D"Times New Roman"><span
style=3D'font-size:12.0pt'> </span></font></p>
</div>
<div>
<p class=3DMsoNormal style=3D'margin-left:.5in'><font size=3D2 =
face=3DArial><span
style=3D'font-size:10.0pt;font-family:Arial'>Various of my mechanical =
engineer
friends confirm that with the positive angle the weight of the aircraft =
will
try to force the wheel out of trail.</span></font></p>
</div>
<div>
<p class=3DMsoNormal style=3D'margin-left:.5in'><font size=3D3 =
face=3D"Times New Roman"><span
style=3D'font-size:12.0pt'> </span></font></p>
</div>
<div>
<p class=3DMsoNormal style=3D'margin-left:.5in'><font size=3D2 =
color=3Dblue face=3DArial><span
style=3D'font-size:10.0pt;font-family:Arial;color:blue'> </span></fo=
nt></p>
<p class=3DMsoNormal><font size=3D2 color=3Dblue face=3DVerdana><span =
style=3D'font-size:
11.0pt;font-family:Verdana;color:blue'>Wayne</span></font><font =
size=3D2
color=3Dblue face=3DVerdana><span =
style=3D'font-size:11.0pt;font-family:Verdana;
color:blue'>:</span></font></p>
<p class=3DMsoNormal><font size=3D2 color=3Dblue face=3DVerdana><span =
style=3D'font-size:
11.0pt;font-family:Verdana;color:blue'> </span></font></p>
<p class=3DMsoNormal><font size=3D2 color=3Dblue face=3DVerdana><span =
style=3D'font-size:
11.0pt;font-family:Verdana;color:blue'>I had a long discussion =
(argument) with
Mark Machado about 3-4 years ago about the castor angle of the NG strut. =
I
maintained that it needed to be negative castor. He assured me =
that he
had done extensive analysis, and that with the fork geometry and =
gyroscopic forces
on the rotating wheel, etc, etc, that the positive angle was correct. I =
believe
he also said that they had (or were going to) test different angles. =
I’ve
never had much confidence in his conclusion.</span></font></p>
<p class=3DMsoNormal><font size=3D2 color=3Dblue face=3DVerdana><span =
style=3D'font-size:
11.0pt;font-family:Verdana;color:blue'> </span></font></p>
<p class=3DMsoNormal><font size=3D2 color=3Dblue face=3DVerdana><span =
style=3D'font-size:
11.0pt;font-family:Verdana;color:blue'>If someone has evidence that we =
need a
negative angle, it is way past time for that issue to be made =
right.</span></font></p>
<p class=3DMsoNormal><font size=3D2 color=3Dblue face=3DVerdana><span =
style=3D'font-size:
11.0pt;font-family:Verdana;color:blue'> </span></font></p>
<p class=3DMsoNormal><font size=3D2 color=3Dblue face=3DVerdana><span =
style=3D'font-size:
11.0pt;font-family:Verdana;color:blue'>Scott; does Velocity have test =
data on
this?</span></font></p>
<p class=3DMsoNormal><font size=3D2 color=3Dblue face=3DVerdana><span =
style=3D'font-size:
11.0pt;font-family:Verdana;color:blue'> </span></font></p>
<p class=3DMsoNormal><font size=3D2 color=3Dblue face=3DVerdana><span =
style=3D'font-size:
11.0pt;font-family:Verdana;color:blue'>Al</span></font></p>
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