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<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>
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<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>
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<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>
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<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>
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<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>
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<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>
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<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>
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<P class=MsoNormal style="MARGIN: 0in 0in 0pt">Related things to consider-<SPAN style="mso-spacerun: yes"> </SPAN></P>
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<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>
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<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>
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<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>
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<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>
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<P class=MsoNormal style="MARGIN: 0in 0in 0pt"><o:p>Later, Ron</o:p></P>
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<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></body></html>