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<DIV><FONT face=Arial size=2>Right on the money James !!!!!!!!!!!</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=joddino@socal.rr.com href="mailto:joddino@socal.rr.com">James
Oddino</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 1:52
PM</DIV>
<DIV style="FONT: 10pt arial"><B>Subject:</B> Re: [NSRCA-discussion] Weather
Vane</DIV>
<DIV><BR></DIV>I couldn't find the beginning of this discussion so it is
impossible to contribute a whole lot. However, airplanes do tend to
weathervane (we called it weathercock in the missile business) into a
crosswind but a plane that has static yaw stability will tend to compensate as
the relative wind strikes the vertical stabilizer and fuse area behind the
cg. At high speed the weathervaning is less (more force on the vertical
stab) than at low speed and I suspect that is why slow flying (electrics?)
planes don't look good in strong crosswinds.
<DIV><BR class=khtml-block-placeholder></DIV>
<DIV>Jim O</DIV>
<DIV><BR class=khtml-block-placeholder></DIV>
<DIV><BR>
<DIV>
<DIV>On Oct 10, 2007, at 9:07 AM, <A
href="mailto:ronlock@comcast.net">ronlock@comcast.net</A> wrote:</DIV><BR
class=Apple-interchange-newline>
<BLOCKQUOTE type="cite">
<DIV>
<DIV style="MARGIN: 0in 0in 0pt">I thought I'd throw in my 2 cents worth,
but maybe it turned into too much. Ya been warned
<G>.</DIV>
<P class=MsoNormal style="MARGIN: 0in 0in 0pt"> </P>
<DIV style="MARGIN: 0in 0in 0pt">There is a strong, almost overwhelming,
visual perception that airplanes weathervane into the wind as seen by an
observer on the ground.<SPAN style="mso-spacerun: yes"> </SPAN><SPAN
style="mso-spacerun: yes"> </SPAN></DIV>
<DIV style="MARGIN: 0in 0in 0pt"><O:P></O:P></DIV>
<DIV style="MARGIN: 0in 0in 0pt">If the airplane is partly connected to the
ground (as in takeoff or landing roll) it will likely weathervane into the
wind. <SPAN style="mso-spacerun: yes"> </SPAN>(Like a real
weathervane on the barn).<SPAN style="mso-spacerun: yes">
</SPAN>Putting more side area behind the CG probably increases the
weathervane effect.</DIV>
<DIV style="MARGIN: 0in 0in 0pt"><O:P></O:P></DIV>
<DIV style="MARGIN: 0in 0in 0pt">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.<SPAN style="mso-spacerun: yes">
</SPAN>Nor does the hot air balloon mentioned in an earlier post.</DIV>
<DIV style="MARGIN: 0in 0in 0pt"><O:P></O:P></DIV>
<DIV style="MARGIN: 0in 0in 0pt">Just after take off, we likely see the nose
is pointed some amount into the wind.<SPAN style="mso-spacerun: yes">
</SPAN>This visual perception is true. But is it proof of
weathervaning?<SPAN style="mso-spacerun: yes"> </SPAN>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.</DIV>
<DIV style="MARGIN: 0in 0in 0pt"><O:P></O:P></DIV>
<DIV style="MARGIN: 0in 0in 0pt">We all know stall turns are easier to do
"into the wind". <SPAN style="mso-spacerun: yes"> </SPAN>Is it because
they weathervane?<SPAN style="mso-spacerun: yes">
</SPAN>On the upline to a stall turn in a cross wind, does the pilot wind
correct the airplanes track?<SPAN style="mso-spacerun: yes">
</SPAN><SPAN style="mso-spacerun: yes"> </SPAN>Most of us do,
consciously or not.<SPAN style="mso-spacerun: yes"> </SPAN><SPAN
style="mso-spacerun: yes"> </SPAN>If we are having any success at
all with the wind correction, the fuselage is "leaning" into the wind a bit
<SPAN style="mso-spacerun: yes"> </SPAN>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
style="mso-spacerun: yes"> </SPAN></DIV>
<DIV style="MARGIN: 0in 0in 0pt"><O:P></O:P></DIV>
<DIV style="MARGIN: 0in 0in 0pt">Pilots try to make heading adjustments to
hold track, or hold distance in lines and maneuvers. <SPAN
style="mso-spacerun: yes"> </SPAN>Those adjustments (crab angles) can
appear to be a result of weathervaning, but are often pilot inputs,
consciously or not.</DIV>
<DIV style="MARGIN: 0in 0in 0pt"><O:P></O:P></DIV>
<DIV style="MARGIN: 0in 0in 0pt">Related things to consider-<SPAN
style="mso-spacerun: yes"> </SPAN></DIV>
<DIV style="MARGIN: 0in 0in 0pt"><O:P></O:P></DIV>
<DIV style="MARGIN: 0in 0in 0pt">Airplanes do get "hit" in the side, top and
bottom when in turbulent wind, and wind shear situations.<SPAN
style="mso-spacerun: yes"> </SPAN>We fly low, and are often in
turbulence.<SPAN style="mso-spacerun: yes"> </SPAN>There may be short,
nearly random, turbulent air effects that result in a weather vane type
effect.</DIV>
<DIV style="MARGIN: 0in 0in 0pt"><O:P></O:P></DIV>
<DIV style="MARGIN: 0in 0in 0pt">A free flight glider does not weather vane
into the wind.<SPAN style="mso-spacerun: yes"> </SPAN>The glider may
fly in circles, but it will drift downwind at the overall average of the
wind speed.<SPAN style="mso-spacerun: yes"> </SPAN><SPAN
style="mso-spacerun: yes"> </SPAN>No matter how much side area is put
behind the CG, it will not find and maintain a heading into the wind.</DIV>
<DIV style="MARGIN: 0in 0in 0pt"><O:P></O:P></DIV>
<DIV style="MARGIN: 0in 0in 0pt">Given flight in no wind situation, a string
tied on nose of an airplane blows exactly backwards and parallel to the
fuselage.<SPAN style="mso-spacerun: yes"> </SPAN>(unless the airplane
is out of rig, or has control surface inputs). <SPAN
style="mso-spacerun: yes"> </SPAN><SPAN
style="mso-spacerun: yes"> </SPAN>If flown in a cross wind direction,
the airplanes track across the ground changes, but the string stays
straight. <SPAN style="mso-spacerun: yes"> </SPAN>(not counting
any effect of propeller induced spiral airflow)</DIV>
<P class=MsoNormal style="MARGIN: 0in 0in 0pt"><SPAN
style="mso-spacerun: yes"></SPAN> </P>
<DIV style="MARGIN: 0in 0in 0pt">The old full scale stories about loosing
airspeed and stalling while doing a "downwind turn" fit into this discussion
to a degree. <SPAN style="mso-spacerun: yes"> </SPAN>Does wind hit the
tail of an airplane as it turns downwind thereby reducing airspeed?<SPAN
style="mso-spacerun: yes"> </SPAN><SPAN
style="mso-spacerun: yes"> </SPAN>In the "old" days, pilots often flew
low and partly judged airplane speed by visual observation of ground speed.
<SPAN style="mso-spacerun: yes"> </SPAN>(similiar to our situation of
observing from the ground)<SPAN style="mso-spacerun: yes">
</SPAN><SPAN style="mso-spacerun: yes"> </SPAN>This could lead to the
perception of plenty of ground speed being plenty</DIV>
<DIV style="MARGIN: 0in 0in 0pt"><O:P></O:P></DIV>
<DIV style="MARGIN: 0in 0in 0pt">Sorting out the visual perception of the
"obvious" weather vane effect is tough.<SPAN
style="mso-spacerun: yes"> </SPAN>Lots of things complicate the
observation - pilot inputs, turbulence, paralax, and more.<SPAN
style="mso-spacerun: yes"> </SPAN></DIV>
<P class=MsoNormal style="MARGIN: 0in 0in 0pt"><SPAN
style="mso-spacerun: yes"></SPAN> </P>
<DIV style="MARGIN: 0in 0in 0pt"><SPAN style="mso-spacerun: yes">IMHO,
bottom line, it's not wind hitting side of airplane, no matter how much side
area is behind the CG.</SPAN></DIV>
<DIV style="MARGIN: 0in 0in 0pt"><O:P></O:P></DIV>
<DIV style="MARGIN: 0in 0in 0pt"><O:P>Later, Ron</O:P></DIV>
<DIV style="MARGIN: 0in 0in 0pt"><O:P></O:P></DIV>
<DIV style="MARGIN: 0in 0in 0pt"><O:P></O:P></DIV>
<DIV style="MARGIN: 0in 0in 0pt"><O:P></O:P></DIV>
<DIV style="MARGIN: 0in 0in 0pt"><O:P></O:P></DIV>
<DIV style="MARGIN: 0in 0in 0pt"><O:P></O:P></DIV>
<DIV style="MARGIN: 0in 0in 0pt"><O:P></O:P></DIV>
<DIV style="MARGIN: 0in 0in 0pt">In summary, I agree that as observers on
the ground, we "see" effects that appear to be weathervaning.<SPAN
style="mso-spacerun: yes"> </SPAN>But the "real" cause</DIV></DIV>
<DIV
style="MIN-HEIGHT: 22px; MARGIN: 0px 0px 0px 56px; FONT: 18px Helvetica; COLOR: rgb(0,0,0); TEXT-INDENT: -56px"><B></B><BR></DIV>
<DIV style="MARGIN: 0px 0px 0px 56px; TEXT-INDENT: -56px"><FONT
style="FONT: 18px Helvetica; COLOR: #000000" face=Helvetica color=#000000
size=5><B>From: </B></FONT><FONT style="FONT: 18px Helvetica" face=Helvetica
size=5>"J N Hiller" <<A
href="mailto:jnhiller@earthlink.net">jnhiller@earthlink.net</A>></FONT></DIV>
<DIV style="MARGIN: 0px 0px 0px 50px; TEXT-INDENT: -50px"><FONT
style="FONT: 18px Helvetica; COLOR: #000000" face=Helvetica color=#000000
size=5><B>Date: </B></FONT><FONT style="FONT: 18px Helvetica" face=Helvetica
size=5>October 10, 2007 8:49:04 AM PDT</FONT></DIV>
<DIV style="MARGIN: 0px 0px 0px 31px; TEXT-INDENT: -31px"><FONT
style="FONT: 18px Helvetica; COLOR: #000000" face=Helvetica color=#000000
size=5><B>To: </B></FONT><FONT style="FONT: 18px Helvetica" face=Helvetica
size=5>"NSRCA Mailing List" <<A
href="mailto:nsrca-discussion@lists.nsrca.org">nsrca-discussion@lists.nsrca.org</A>></FONT></DIV>
<DIV style="MARGIN: 0px 0px 0px 76px; TEXT-INDENT: -76px"><FONT
style="FONT: 18px Helvetica; COLOR: #000000" face=Helvetica color=#000000
size=5><B>Subject: </B></FONT><FONT style="FONT: 18px Helvetica"
face=Helvetica size=5><B>Re: [NSRCA-discussion] Rudder</B></FONT></DIV>
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