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The boat analogy previously used would only be valid for a submarine.
Wind force and water force are two separate forces. Wind shear in the air
may some application, but that is not what we are talking about. We'll
have to ask a submariner if a submarine weathervanes or er ah watervanes.
It doesn't.<br><br>
Terry Beachler<br><br>
At 07:17 10/12/2007, you wrote:<br><br>
<blockquote type=cite class=cite cite="">
<font face="Arial, Helvetica" size=2 color="#0000FF">Hi Jim.<br>
<br>
Thanks for taking the time to post your reply.
Wonder how many will agree with your clarification. Some people are
amazed with magic also.. <tic> <br>
<br>
Del<br>
</font> <br>
<font face="Arial, Helvetica" size=2 color="#0000FF">----- Original
Message ----- </font><br>
<font face="Arial, Helvetica" size=2 color="#0000FF">From: "Jim
Alberico"
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<font face="Arial, Helvetica" size=2>alberji@charter.net</a></font>
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To: "'NSRCA Mailing List'"
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Sent: Thursday, October 11, 2007 11:19 PM<br>
Subject: Re: [NSRCA-discussion] Weather Vane<br>
</font><font face="Arial, Helvetica"><br>
</font><font face="Arial, Helvetica" size=2 color="#0000FF">> Jim
Oddino said:<br>
> <br>
>>>>> ====<br>
> Wish we had a real aero guy jump in here. ...<br>
> <br>
> Best Regards, Jim<br>
> ==== >>>><br>
> <br>
> OK, Mr. Oddino, I'll take the bait.<br>
> <br>
> I qualify as a real aero guy much more than as a pattern
pilot. ;-)<br>
> <br>
> This whole thread started with the dynamics of a stall turn in a
crosswind<br>
> (I think).<br>
> <br>
> Point 1:<br>
> Initial Conditions <br>
> -- steady wind from the right (constant velocity and
direction).<br>
> -- constant aircraft velocity (or vertical rate of the cg)<br>
> <br>
> To track a vertical line, the fuse must be pointed to the
right. Under<br>
> these conditions, the thrust line counters gravity as well as the
components<br>
> of drag in the vertical and horizontal directions.<br>
> <br>
> This is similar to the familiar "crabbing" in horizontal
flight to maintain<br>
> direction. However in the vertical geometric plane, gravity
complicates<br>
> things a bit. ...enough about that.<br>
> <br>
> Note that in crosswind, rudder trim is required to maintain the
horizontal<br>
> line, as well as the vertical line. This is
important. Any "weathervane"<br>
> effect under these conditions is through control inputs. It
doesn't come<br>
> for free.<br>
> <br>
> Point 2:<br>
> Dynamics Near Stall (dynamics are always more
complicated)<br>
> -- wind still steady from right<br>
> -- aircraft is decelerating to zero, then accelerating again.<br>
> <br>
> As the vertical speed (and overall velocity) decreases, the fuse
must be<br>
> pointed more and more to the right to maintain a vertical track.
Here is<br>
> where it is very hard to generalize. So much depends on the
details of the<br>
> aircraft shape, mass properties, control inputs (including
throttle), the<br>
> wind speed, and etc. At zero speed, for example, the ONLY
force countering<br>
> the wind will be thrust. Sideslip forces certainly enter the
picture on the<br>
> final path up and the initial path down. <br>
> <br>
> Note also that the fuse must point leftward during the downward
phase to<br>
> maintain the line (hence turning into the wind requires less than
180 deg<br>
> rotation). Again, pilot provides the rudder trim to maintain
the line.<br>
> Here fuselage side force plays greater role, as thrust is
significantly<br>
> reduced. <br>
> <br>
> ...<br>
> <br>
> Regarding weathervane, the phenomenon is certainly present, but only
in<br>
> dynamic situations. <br>
> <br>
> ... But again, depends on what you mean by weathervane ... In 3D, is
a<br>
> steady angled hover in a steady wind considered weathervaning?<br>
> <br>
> I think not, but I also do not even think a weathervane
"weathervanes"<br>
> after steady state is established...<br>
> <br>
> I understand the physics fairly well...I just haven't learned to
harness it<br>
> nearly as well as just about everyone here. ;-)<br>
> <br>
> The graceful way you guys fly is amazing.<br>
> <br>
> Thanks for reading. Be sure to catch the movie version
someday.<br>
> <br>
> Best regards,<br>
> <br>
> Jim A<br>
> (ultra-newbie pattern flyer)<br>
> <br>
> <br>
> <br>
> <br>
> <br>
> <br>
> <br>
> <br>
> <br>
> <br>
> <br>
> <br>
> _______________________________________________<br>
> NSRCA-discussion mailing list<br>
>
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