<HTML><BODY style="word-wrap: break-word; -khtml-nbsp-mode: space; -khtml-line-break: after-white-space; ">My thinking is expressed in black below:<DIV><BR><DIV><DIV>On Oct 10, 2007, at 5:51 PM, Ron Lockhart wrote:</DIV><BR class="Apple-interchange-newline"><BLOCKQUOTE type="cite"> <DIV><FONT face="Arial" size="2">I'm not Nat, but will throw a response anyway-</FONT></DIV> <DIV><FONT face="Arial" size="2"></FONT> </DIV> <DIV><FONT face="Arial" size="2">Assumption - the arrow is released with zero ground speed, eg from balcony of a TALL building.</FONT></DIV> <DIV><FONT face="Arial" size="2">There is zero wind.</FONT></DIV> <DIV><FONT face="Arial" size="2">As it is released it will weathervane into vertical down attitude flight. and within not too long (scientific term? <G>)</FONT></DIV> <DIV><FONT face="Arial" size="2">it will be falling perpendicular to the earth.</FONT></DIV> <DIV><SPAN class="Apple-style-span"><FONT face="Arial" size="2"></FONT> <FONT class="Apple-style-span" color="#080808">The reason it weathervaned into nose down attitude is because the cg is forward of the center of pressure. The cg tries to fall straight down but the air pressure on the tail feathers pushes the tail up.</FONT></SPAN></DIV> <DIV><FONT face="Arial" size="2">Now, change the wind from zero to some amount, say 10 knots.</FONT></DIV> <DIV><FONT face="Arial" size="2">As arrow is released it will weathervane into vertical down flight, and within not too long (scientific term? <G>) <DIV><FONT face="Arial" size="2">it will be falling with perpendicular attitude to the earth. (Arrow attitude will be perpendicular to earth, it's track will not be perpendicular to the earth) </FONT><FONT face="Arial" size="2">And, it will be drifting in downwind direction, at 10 knots.</FONT></DIV></FONT></DIV> <DIV><SPAN class="Apple-style-span"><FONT face="Arial" size="2"></FONT> <FONT class="Apple-style-span" color="#070804">Before it picks up much speed it will weathervane in yaw as well as pitch for the same reason. The cg wants to stay in the same vertical plane but the force of the crosswind on the tail creates a yaw moment. As it picks up speed, the force due to the forward speed on the tail feathers will tend to straighten it out until the force is equal on both sides of the tail. </FONT></SPAN></DIV></BLOCKQUOTE><BLOCKQUOTE type="cite"> <DIV><FONT face="Arial" size="2">In the case of dropping an arrow from zero airspeed, there is a temporary situation while arrow weathervanes to straight down attitude. It is similiar to a situation where an airplane in flight encounters a very sharp cross wind, windshear. Also a temporary situation. The airplane might weathervane into the wind for a short time, but will pretty quickly be flying on a heading only a few degree into the wind, and also drifting in downwind direction at the speed of the wind.</FONT></DIV> <DIV><FONT class="Apple-style-span" color="#000000">I agree with the last statement. If I'm landing from right to left with a strong wind at my back the plane will weathervane to its left and drift out. The amount is a function of relative speeds/vectors. If you come in too slow it can get pretty bad. </FONT></DIV></BLOCKQUOTE><BLOCKQUOTE type="cite"> <DIV><FONT face="Arial" size="2">Ron Lockhart</FONT></DIV></BLOCKQUOTE><SPAN class="Apple-tab-span" style="white-space:pre"> </SPAN></DIV><DIV>Wish we had a real aero guy jump in here. Maybe you are one and I should shut up and listen? I've been reading Einstein and he questioned everything and everyone, so I think these discussions are good no matter who has the right slant on it.</DIV><DIV><BR class="khtml-block-placeholder"></DIV><DIV>Best Regards, Jim</DIV><DIV><BR class="khtml-block-placeholder"></DIV><DIV><BR><BLOCKQUOTE type="cite"> <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 7:20 PM</DIV> <DIV style="FONT: 10pt arial"><B>Subject:</B> Re: [NSRCA-discussion] Weather Vane</DIV> <DIV><BR></DIV>Nat, <DIV><BR class="khtml-block-placeholder"></DIV> <DIV>If you hold an arrow (or a bomb) horizontal and drop it, what happens to it's attitude on the way down and why? Then drop it with a crosswind of 32 ft/sec. What happens to its attitude?</DIV> <DIV>Seems pretty obvious to me.</DIV> <DIV><BR class="khtml-block-placeholder"></DIV> <DIV>Jim</DIV> <DIV><BR class="khtml-block-placeholder"></DIV> <DIV><BR> <DIV> <DIV>On Oct 10, 2007, at 2:21 PM, Nat Penton wrote:</DIV><BR class="Apple-interchange-newline"> <BLOCKQUOTE type="cite"> <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> <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><BR class="khtml-block-placeholder"></DIV> <HR> <DIV><BR class="khtml-block-placeholder"></DIV>_______________________________________________<BR>NSRCA-discussion mailing list<BR><A href="mailto:NSRCA-discussion@lists.nsrca.org">NSRCA-discussion@lists.nsrca.org</A><BR><A href="http://lists.nsrca.org/mailman/listinfo/nsrca-discussion">http://lists.nsrca.org/mailman/listinfo/nsrca-discussion</A></BLOCKQUOTE> <DIV style="MARGIN: 0px">_______________________________________________</DIV> <DIV style="MARGIN: 0px">NSRCA-discussion mailing list</DIV> <DIV style="MARGIN: 0px"><A href="mailto:NSRCA-discussion@lists.nsrca.org">NSRCA-discussion@lists.nsrca.org</A></DIV> <DIV style="MARGIN: 0px"><A href="http://lists.nsrca.org/mailman/listinfo/nsrca-discussion">http://lists.nsrca.org/mailman/listinfo/nsrca-discussion</A></DIV></BLOCKQUOTE></DIV><BR></DIV><DIV> <BR class="khtml-block-placeholder"></DIV><HR><DIV><BR class="khtml-block-placeholder"></DIV>_______________________________________________<BR>NSRCA-discussion mailing list<BR><A href="mailto:NSRCA-discussion@lists.nsrca.org">NSRCA-discussion@lists.nsrca.org</A><BR>http://lists.nsrca.org/mailman/listinfo/nsrca-discussion</BLOCKQUOTE><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">_______________________________________________</DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">NSRCA-discussion mailing list</DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; "><A href="mailto:NSRCA-discussion@lists.nsrca.org">NSRCA-discussion@lists.nsrca.org</A></DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; "><A href="http://lists.nsrca.org/mailman/listinfo/nsrca-discussion">http://lists.nsrca.org/mailman/listinfo/nsrca-discussion</A></DIV> </BLOCKQUOTE></DIV><BR></DIV></BODY></HTML>