[NSRCA-discussion] Weather Vane

[Jim Alberico]

I already made a correction, and pushed send almost simultaneously as this
arrived.  I hope the revised version is palatable to all.

Certainly not trying to be controversial.  Just offering my thoughts as an
aero engineer.

Thanks.

-----Original Message-----
From: nsrca-discussion-bounces at lists.nsrca.org
[mailto:nsrca-discussion-bounces at lists.nsrca.org] On Behalf Of george w.
kennie
Sent: Friday, October 12, 2007 12:56 PM
To: NSRCA Mailing List
Subject: Re: [NSRCA-discussion] Weather Vane

By Jim's own admission he is a relatively NEW pattern flyer. Given a couple
of more years experiencing in flight aircraft reactions he may wish to
rewrite his assessment, but only time will determine that outcome.
G.




----- Original Message -----
From: "Ron Lockhart" <ronlock at comcast.net>
To: <alberji at charter.net>; "NSRCA Mailing List" 
<nsrca-discussion at lists.nsrca.org>
Sent: Friday, October 12, 2007 9:03 AM
Subject: Re: [NSRCA-discussion] Weather Vane


> Yep, I think Jim Alberico's discussion is accurate.
>
> Later, Ron Lockhart
>
> ----- Original Message ----- 
> From: "Jim Alberico" <alberji at charter.net>
> To: "'NSRCA Mailing List'" <nsrca-discussion at lists.nsrca.org>
> Sent: Thursday, October 11, 2007 11:19 PM
> Subject: Re: [NSRCA-discussion] Weather Vane
>
>
>> Jim Oddino said:
>>
>> >>>> ====
>> Wish we had a real aero guy jump in here. ...
>>
>> Best Regards, Jim
>> ==== >>>>
>>
>> OK, Mr. Oddino, I'll take the bait.
>>
>> I qualify as a real aero guy much more than as a pattern pilot.  ;-)
>>
>> This whole thread started with the dynamics of a stall turn in a 
>> crosswind
>> (I think).
>>
>> Point 1:
>> Initial Conditions
>> -- steady wind from the right (constant velocity and direction).
>> -- constant aircraft velocity (or vertical rate of the cg)
>>
>> To track a vertical line, the fuse must be pointed to the right.  Under
>> these conditions, the thrust line counters gravity as well as the
> components
>> of drag in the vertical and horizontal directions.
>>
>> This is similar to the familiar "crabbing" in horizontal flight to
> maintain
>> direction.  However in the vertical geometric plane, gravity complicates
>> things a bit. ...enough about that.
>>
>> Note that in crosswind, rudder trim is required to maintain the 
>> horizontal
>> line, as well as the vertical line.  This is important.   Any
> "weathervane"
>> effect under these conditions is through control inputs.  It doesn't come
>> for free.
>>
>> Point 2:
>> Dynamics Near Stall  (dynamics are always more complicated)
>> -- wind still steady from right
>> -- aircraft is decelerating to zero, then accelerating again.
>>
>> As the vertical speed (and overall velocity) decreases, the fuse must be
>> pointed more and more to the right to maintain a vertical track. Here is
>> where it is very hard to generalize.  So much depends on the details of
> the
>> aircraft shape, mass properties, control inputs (including throttle), the
>> wind speed, and etc.  At zero speed, for example, the ONLY force
> countering
>> the wind will be thrust.  Sideslip forces certainly enter the picture on
> the
>> final path up and the initial path down.
>>
>> Note also that the fuse must point leftward during the downward phase to
>> maintain the line (hence turning into the wind requires less than 180 deg
>> rotation).  Again, pilot provides the rudder trim to maintain the line.
>> Here fuselage side force plays greater role, as thrust is significantly
>> reduced.
>>
>> ...
>>
>> Regarding weathervane, the phenomenon is certainly present, but only in
>> dynamic situations.
>>
>> ... But again, depends on what you mean by weathervane ... In 3D, is a
>> steady angled hover in a steady wind considered weathervaning?
>>
>> I think not, but I also do not even think a weathervane  "weathervanes"
>> after steady state is established...
>>
>> I understand the physics fairly well...I just haven't learned to harness
> it
>> nearly as well as just about everyone here. ;-)
>>
>> The graceful way you guys fly is amazing.
>>
>> Thanks for reading.  Be sure to catch the movie version someday.
>>
>> Best regards,
>>
>> Jim A
>> (ultra-newbie pattern flyer)
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
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