[NSRCA-discussion] Weather Vane

[Del K. Rykert]

Hi Jim..
     Back when I entered competition, I used to freeze on the dumb thumb (left) and not do anything. I can't recall a time it didn't flop like a wounded duck..  Don't recall if the nose/tail angle changed any..  Admits to having sometimers. 
 
    Del
 
----- Original Message ----- 
From: "James Oddino" <joddino at socal.rr.com>
To: <alberji at charter.net>; "NSRCA Mailing List" <nsrca-discussion at lists.nsrca.org>
Sent: Friday, October 12, 2007 8:14 PM
Subject: Re: [NSRCA-discussion] Weather Vane


> Hi Jim A,
> 
> Thanks for your input.  Now you are going to have to answer all our  
> questions.  Welcome to the club.
> 
> Your description of the vertical portion of a stall turn sounds good  
> to me .  I never did find the beginning of the thread and only jumped  
> in because it sounded like some folks didn't believe that air  
> vehicles weathervane in flight.
> 
> My experience is with antitank missiles that are launched at  
> relatively low velocity from a tube pointed roughly at the target.   
> The low velocity is a result of a short launch motor burn time,  
> completed within the tube so the gunner doesn't get a blast in the  
> face.  A flight motor ignites when the missile is a safe distance in  
> front of the gunner.
> 
> If we launch this missile with locked controls, we'd expect it to yaw  
> slightly into any crosswind (and drift downwind off the line of  
> sight) as it exits the tube.  Sound right?
> 
> Back to the vertical portion of the stall turn with a pattern plane,  
> only this time with locked rudder.  We all agree it will drift off  
> the track as it slows to a stop.  The question is, will it yaw into  
> the wind on its own as it slows to a stop?  If it does, this is my  
> definition of weathervaning.
> 
> I'm recovering from an emergency appendectomy so I'm depending on all  
> you other guys to go try a cross wind stall turn with no rudder  
> command tomorrow and report on your results.
> 
> Best Regards, Jim O
> 
> 
> On Oct 11, 2007, at 8:19 PM, Jim Alberico wrote:
> 
>> 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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> 
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