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<DIV><FONT face=Arial size=2>This discussion has reared it's head in several
forums. I'm still of the opinion that when your nose points in the
direction of the crosswind, the proper term wouldn't be "weathervane" it
would actually be "wind induced yaw".</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>Of course, there are many more knowledgable people
on the list than I.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>Ken</FONT></DIV>
<BLOCKQUOTE
style="PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #000000 2px solid; MARGIN-RIGHT: 0px">
<DIV style="FONT: 10pt arial">----- Original Message ----- </DIV>
<DIV
style="BACKGROUND: #e4e4e4; FONT: 10pt arial; font-color: black"><B>From:</B>
<A title=ed_alt@hotmail.com href="mailto:ed_alt@hotmail.com">Ed Alt</A> </DIV>
<DIV style="FONT: 10pt arial"><B>To:</B> <A
title=nsrca-discussion@lists.nsrca.org
href="mailto:nsrca-discussion@lists.nsrca.org">'NSRCA Mailing List'</A> </DIV>
<DIV style="FONT: 10pt arial"><B>Sent:</B> Wednesday, October 10, 2007 11:36
AM</DIV>
<DIV style="FONT: 10pt arial"><B>Subject:</B> Re: [NSRCA-discussion] Weather
Vane</DIV>
<DIV><BR></DIV>
<DIV class=Section1>
<P class=MsoNormal><FONT face=Arial color=navy size=2><SPAN
style="FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: Arial">Hi
Ron:</SPAN></FONT></P>
<P class=MsoNormal><FONT face=Arial color=navy size=2><SPAN
style="FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: Arial">I wonder if the
weathervane effect is there because of the greater distribution of side area
aft of the CG? I’m not sure of that, just an idea.</SPAN></FONT></P>
<P class=MsoNormal><FONT face=Arial color=navy size=2><SPAN
style="FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: Arial"></SPAN></FONT> </P>
<P class=MsoNormal><FONT face=Arial color=navy size=2><SPAN
style="FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: Arial">Ed</SPAN></FONT></P>
<P class=MsoNormal><FONT face=Arial color=navy size=2><SPAN
style="FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: Arial"></SPAN></FONT> </P>
<P class=MsoNormal style="MARGIN-LEFT: 0.5in"><FONT face=Tahoma size=2><SPAN
style="FONT-SIZE: 10pt; FONT-FAMILY: Tahoma">-----Original
Message-----<BR><B><SPAN style="FONT-WEIGHT: bold">From:</SPAN></B> <A
href="mailto:nsrca-discussion-bounces@lists.nsrca.org">nsrca-discussion-bounces@lists.nsrca.org</A>
[mailto:nsrca-discussion-bounces@lists.nsrca.org] <B><SPAN
style="FONT-WEIGHT: bold">On Behalf Of </SPAN></B><A
href="mailto:ronlock@comcast.net">ronlock@comcast.net</A><BR><B><SPAN
style="FONT-WEIGHT: bold">Sent:</SPAN></B> Wednesday, October 10, 2007 11:08
AM<BR><B><SPAN style="FONT-WEIGHT: bold">To:</SPAN></B> NSRCA Mailing List;
NSRCA Mailing List<BR><B><SPAN style="FONT-WEIGHT: bold">Subject:</SPAN></B>
Re: [NSRCA-discussion] Weather Vane</SPAN></FONT></P>
<P class=MsoNormal style="MARGIN-LEFT: 0.5in"><FONT face="Times New Roman"
size=3><SPAN style="FONT-SIZE: 12pt"></SPAN></FONT> </P>
<DIV>
<P class=MsoNormal style="MARGIN-LEFT: 0.5in"><FONT face="Times New Roman"
size=3><SPAN style="FONT-SIZE: 12pt">I thought I'd throw in my 2 cents worth,
but maybe it turned into too much. Ya been warned
<G>.</SPAN></FONT></P>
<P class=MsoNormal style="MARGIN-LEFT: 0.5in"><FONT face="Times New Roman"
size=3><SPAN style="FONT-SIZE: 12pt"></SPAN></FONT> </P>
<P class=MsoNormal style="MARGIN-LEFT: 0.5in"><FONT face="Times New Roman"
size=3><SPAN style="FONT-SIZE: 12pt">There is a strong, almost overwhelming,
visual perception that airplanes weathervane into the wind as seen by an
observer on the ground. </SPAN></FONT></P>
<P class=MsoNormal style="MARGIN-LEFT: 0.5in"><FONT face="Times New Roman"
size=3><SPAN style="FONT-SIZE: 12pt"></SPAN></FONT> </P>
<P class=MsoNormal style="MARGIN-LEFT: 0.5in"><FONT face="Times New Roman"
size=3><SPAN style="FONT-SIZE: 12pt">If the airplane is partly connected to
the ground (as in takeoff or landing roll) it will likely weathervane into the
wind. (Like a real weathervane on the barn). Putting
more side area behind the CG probably increases the weathervane
effect.</SPAN></FONT></P>
<P class=MsoNormal style="MARGIN-LEFT: 0.5in"><FONT face="Times New Roman"
size=3><SPAN style="FONT-SIZE: 12pt"></SPAN></FONT> </P>
<P class=MsoNormal style="MARGIN-LEFT: 0.5in"><FONT face="Times New Roman"
size=3><SPAN style="FONT-SIZE: 12pt">But once airborne, an airplane no longer
feels wind on side of the airplane and does not weathervane in the sense that
the weathervane on the barn does. Nor does the hot air balloon mentioned
in an earlier post.</SPAN></FONT></P>
<P class=MsoNormal style="MARGIN-LEFT: 0.5in"><FONT face="Times New Roman"
size=3><SPAN style="FONT-SIZE: 12pt"></SPAN></FONT> </P>
<P class=MsoNormal style="MARGIN-LEFT: 0.5in"><FONT face="Times New Roman"
size=3><SPAN style="FONT-SIZE: 12pt">Just after take off, we likely see the
nose is pointed some amount into the wind. This visual perception is
true. But is it proof of weathervaning? It probably weathervaned into
the wind during take off roll. Once airborne the weathervane is now what we
call a crab angle into the wind.</SPAN></FONT></P>
<P class=MsoNormal style="MARGIN-LEFT: 0.5in"><FONT face="Times New Roman"
size=3><SPAN style="FONT-SIZE: 12pt"></SPAN></FONT> </P>
<P class=MsoNormal style="MARGIN-LEFT: 0.5in"><FONT face="Times New Roman"
size=3><SPAN style="FONT-SIZE: 12pt">We all know stall turns are easier to do
"into the wind". Is it because they weathervane? On
the upline to a stall turn in a cross wind, does the pilot wind correct the
airplanes track? Most of us do, consciously or
not. If we are having any success at all with the wind
correction, the fuselage is "leaning" into the wind a bit It's
certainly easier to get a stall turn by continuing into the established lean,
than it is to go against the lean to the downwind direction.
</SPAN></FONT></P>
<P class=MsoNormal style="MARGIN-LEFT: 0.5in"><FONT face="Times New Roman"
size=3><SPAN style="FONT-SIZE: 12pt"></SPAN></FONT> </P>
<P class=MsoNormal style="MARGIN-LEFT: 0.5in"><FONT face="Times New Roman"
size=3><SPAN style="FONT-SIZE: 12pt">Pilots try to make heading adjustments to
hold track, or hold distance in lines and maneuvers. Those adjustments
(crab angles) can appear to be a result of weathervaning, but are often pilot
inputs, consciously or not.</SPAN></FONT></P>
<P class=MsoNormal style="MARGIN-LEFT: 0.5in"><FONT face="Times New Roman"
size=3><SPAN style="FONT-SIZE: 12pt"></SPAN></FONT> </P>
<P class=MsoNormal style="MARGIN-LEFT: 0.5in"><FONT face="Times New Roman"
size=3><SPAN style="FONT-SIZE: 12pt">Related things to consider-
</SPAN></FONT></P>
<P class=MsoNormal style="MARGIN-LEFT: 0.5in"><FONT face="Times New Roman"
size=3><SPAN style="FONT-SIZE: 12pt"></SPAN></FONT> </P>
<P class=MsoNormal style="MARGIN-LEFT: 0.5in"><FONT face="Times New Roman"
size=3><SPAN style="FONT-SIZE: 12pt">Airplanes do get "hit" in the side, top
and bottom when in turbulent wind, and wind shear situations. We fly
low, and are often in turbulence. There may be short, nearly random,
turbulent air effects that result in a weather vane type
effect.</SPAN></FONT></P>
<P class=MsoNormal style="MARGIN-LEFT: 0.5in"><FONT face="Times New Roman"
size=3><SPAN style="FONT-SIZE: 12pt"></SPAN></FONT> </P>
<P class=MsoNormal style="MARGIN-LEFT: 0.5in"><FONT face="Times New Roman"
size=3><SPAN style="FONT-SIZE: 12pt">A free flight glider does not weather
vane into the wind. The glider may fly in circles, but it will drift
downwind at the overall average of the wind speed. No matter how
much side area is put behind the CG, it will not find and maintain a heading
into the wind.</SPAN></FONT></P>
<P class=MsoNormal style="MARGIN-LEFT: 0.5in"><FONT face="Times New Roman"
size=3><SPAN style="FONT-SIZE: 12pt"></SPAN></FONT> </P>
<P class=MsoNormal style="MARGIN-LEFT: 0.5in"><FONT face="Times New Roman"
size=3><SPAN style="FONT-SIZE: 12pt">Given flight in no wind situation, a
string tied on nose of an airplane blows exactly backwards and parallel to the
fuselage. (unless the airplane is out of rig, or has control surface
inputs). If flown in a cross wind direction, the airplanes track
across the ground changes, but the string stays straight. (not
counting any effect of propeller induced spiral airflow)</SPAN></FONT></P>
<P class=MsoNormal style="MARGIN-LEFT: 0.5in"><FONT face="Times New Roman"
size=3><SPAN style="FONT-SIZE: 12pt"></SPAN></FONT> </P>
<P class=MsoNormal style="MARGIN-LEFT: 0.5in"><FONT face="Times New Roman"
size=3><SPAN style="FONT-SIZE: 12pt">The old full scale stories about loosing
airspeed and stalling while doing a "downwind turn" fit into this discussion
to a degree. Does wind hit the tail of an airplane as it turns downwind
thereby reducing airspeed? In the "old" days, pilots often flew
low and partly judged airplane speed by visual observation of ground
speed. (similiar to our situation of observing from the
ground) This could lead to the perception of plenty of ground
speed being plenty</SPAN></FONT></P>
<P class=MsoNormal style="MARGIN-LEFT: 0.5in"><FONT face="Times New Roman"
size=3><SPAN style="FONT-SIZE: 12pt"></SPAN></FONT> </P>
<P class=MsoNormal style="MARGIN-LEFT: 0.5in"><FONT face="Times New Roman"
size=3><SPAN style="FONT-SIZE: 12pt">Sorting out the visual perception of the
"obvious" weather vane effect is tough. Lots of things complicate the
observation - pilot inputs, turbulence, paralax, and more.
</SPAN></FONT></P>
<P class=MsoNormal style="MARGIN-LEFT: 0.5in"><FONT face="Times New Roman"
size=3><SPAN style="FONT-SIZE: 12pt"></SPAN></FONT> </P>
<P class=MsoNormal style="MARGIN-LEFT: 0.5in"><FONT face="Times New Roman"
size=3><SPAN style="FONT-SIZE: 12pt">IMHO, bottom line, it's not wind hitting
side of airplane, no matter how much side area is behind the
CG.</SPAN></FONT></P>
<P class=MsoNormal style="MARGIN-LEFT: 0.5in"><FONT face="Times New Roman"
size=3><SPAN style="FONT-SIZE: 12pt"></SPAN></FONT> </P>
<P class=MsoNormal style="MARGIN-LEFT: 0.5in"><FONT face="Times New Roman"
size=3><SPAN style="FONT-SIZE: 12pt">Later, Ron</SPAN></FONT></P>
<P class=MsoNormal style="MARGIN-LEFT: 0.5in"><FONT face="Times New Roman"
size=3><SPAN style="FONT-SIZE: 12pt"></SPAN></FONT> </P>
<P class=MsoNormal style="MARGIN-LEFT: 0.5in"><FONT face="Times New Roman"
size=3><SPAN style="FONT-SIZE: 12pt"></SPAN></FONT> </P>
<P class=MsoNormal style="MARGIN-LEFT: 0.5in"><FONT face="Times New Roman"
size=3><SPAN style="FONT-SIZE: 12pt"></SPAN></FONT> </P>
<P class=MsoNormal style="MARGIN-LEFT: 0.5in"><FONT face="Times New Roman"
size=3><SPAN style="FONT-SIZE: 12pt"></SPAN></FONT> </P>
<P class=MsoNormal style="MARGIN-LEFT: 0.5in"><FONT face="Times New Roman"
size=3><SPAN style="FONT-SIZE: 12pt"></SPAN></FONT> </P>
<P class=MsoNormal style="MARGIN-LEFT: 0.5in"><FONT face="Times New Roman"
size=3><SPAN style="FONT-SIZE: 12pt"></SPAN></FONT> </P>
<P class=MsoNormal style="MARGIN-LEFT: 0.5in"><FONT face="Times New Roman"
size=3><SPAN style="FONT-SIZE: 12pt">In summary, I agree that as observers on
the ground, we "see" effects that appear to be weathervaning. But the
"real" cause</SPAN></FONT></P></DIV></DIV>
<P>
<HR>
<P></P>_______________________________________________<BR>NSRCA-discussion
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