<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<HTML xmlns:o = "urn:schemas-microsoft-com:office:office"><HEAD>
<META http-equiv=Content-Type content="text/html; charset=iso-8859-1">
<META content="MSHTML 6.00.6000.16525" name=GENERATOR>
<STYLE></STYLE>
</HEAD>
<BODY bgColor=#ffffff>
<DIV><FONT face=Arial size=2>Ron</FONT></DIV>
<DIV><FONT face=Arial size=2>You are correct - an airplane does not weathervane
or weathercock - it fliies straight into the freestream unless given
rudder. BUT, as Kennie says, he hopes to be here next year to reargue the
point
!!
Nat</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=ronlock@comcast.net
href="mailto:ronlock@comcast.net">ronlock@comcast.net</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> ; <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 11:07
AM</DIV>
<DIV style="FONT: 10pt arial"><B>Subject:</B> Re: [NSRCA-discussion] Weather
Vane</DIV>
<DIV><BR></DIV>
<DIV>
<P class=MsoNormal 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>.</P>
<P class=MsoNormal style="MARGIN: 0in 0in 0pt"> </P>
<P class=MsoNormal 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></P>
<P class=MsoNormal style="MARGIN: 0in 0in 0pt"><o:p> </o:p></P>
<P class=MsoNormal 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.</P>
<P class=MsoNormal style="MARGIN: 0in 0in 0pt"><o:p> </o:p></P>
<P class=MsoNormal 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.</P>
<P class=MsoNormal style="MARGIN: 0in 0in 0pt"><o:p> </o:p></P>
<P class=MsoNormal 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.</P>
<P class=MsoNormal style="MARGIN: 0in 0in 0pt"><o:p> </o:p></P>
<P class=MsoNormal 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></P>
<P class=MsoNormal style="MARGIN: 0in 0in 0pt"><o:p> </o:p></P>
<P class=MsoNormal 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.</P>
<P class=MsoNormal style="MARGIN: 0in 0in 0pt"><o:p> </o:p></P>
<P class=MsoNormal style="MARGIN: 0in 0in 0pt">Related things to
consider-<SPAN style="mso-spacerun: yes"> </SPAN></P>
<P class=MsoNormal style="MARGIN: 0in 0in 0pt"><o:p> </o:p></P>
<P class=MsoNormal 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.</P>
<P class=MsoNormal style="MARGIN: 0in 0in 0pt"><o:p> </o:p></P>
<P class=MsoNormal 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.</P>
<P class=MsoNormal style="MARGIN: 0in 0in 0pt"><o:p> </o:p></P>
<P class=MsoNormal 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)</P>
<P class=MsoNormal style="MARGIN: 0in 0in 0pt"><SPAN
style="mso-spacerun: yes"></SPAN> </P>
<P class=MsoNormal 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</P>
<P class=MsoNormal style="MARGIN: 0in 0in 0pt"><o:p> </o:p></P>
<P class=MsoNormal 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></P>
<P class=MsoNormal style="MARGIN: 0in 0in 0pt"><SPAN
style="mso-spacerun: yes"></SPAN> </P>
<P class=MsoNormal 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></P>
<P class=MsoNormal style="MARGIN: 0in 0in 0pt"><o:p> </o:p></P>
<P class=MsoNormal style="MARGIN: 0in 0in 0pt"><o:p>Later, Ron</o:p></P>
<P class=MsoNormal style="MARGIN: 0in 0in 0pt"><o:p> </o:p></P>
<P class=MsoNormal style="MARGIN: 0in 0in 0pt"><o:p> </o:p></P>
<P class=MsoNormal style="MARGIN: 0in 0in 0pt"><o:p> </o:p></P>
<P class=MsoNormal style="MARGIN: 0in 0in 0pt"><o:p> </o:p></P>
<P class=MsoNormal style="MARGIN: 0in 0in 0pt"><o:p> </o:p></P>
<P class=MsoNormal style="MARGIN: 0in 0in 0pt"><o:p> </o:p></P>
<P class=MsoNormal 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</P></DIV>
<P>
<HR>
<P></P>_______________________________________________<BR>NSRCA-discussion
mailing
list<BR>NSRCA-discussion@lists.nsrca.org<BR>http://lists.nsrca.org/mailman/listinfo/nsrca-discussion</BLOCKQUOTE></BODY></HTML>