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<DIV><FONT face=Arial size=2>Jim</FONT></DIV>
<DIV><FONT face=Arial size=2>I'm waiting for the real aero guy to jump in,
LOL
</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>I think in some cases here we have nomenclature
problems and in some cases misconceptions. If the airplane did not have
directional stability we could not fly precision aerobatics. In all honesty I
have not read a lot of the comments, too busy repairing crash damage due to a
faulty receiver pack
connector.
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=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 10:45
PM</DIV>
<DIV style="FONT: 10pt arial"><B>Subject:</B> Re: [NSRCA-discussion] Weather
Vane</DIV>
<DIV><BR></DIV>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>
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