[NSRCA-discussion] Weather Vane

[James Oddino]

Excellent.  Not only do you understand it, but you can explain it.   
We do a lot of things instinctively after lots to trial and error.   
Everyone can benefit by understanding what it takes to do the  
maneuvers correctly under all weather conditions before they go out  
to practice.

I need one bit of clarification though.  Isn't the relative wind  
aligned with the track of the cg?

I wonder how steady the crosswind is when we climb 600 ft. in a stall  
turn?  Perhaps there is enough variation that even though the novice  
pilot never touches the rudder we see the crab?

Thank you for your patience.

Jim O


On Oct 13, 2007, at 8:00 PM, Jim Alberico wrote:

>
>
>> -----Original Message-----
>> From: James Oddino [mailto:joddino at socal.rr.com]
>> Sent: Saturday, October 13, 2007 5:29 PM
>>
>> I think we've found our expert.  Two questions:
>
> LOL.  I wish my thumbs had more expertise!!
>
>>
>> 1) Is it not considered a sideslip if the relative wind is on
>> the leeward side?
>
> <VBG>
> Maybe file "a relative wind on the windward side" with the  
> Department of
> Redundancy Department. -- maybe --
>
> I meant "windward side" in the larger sense relative to described  
> maneuver.
>
> One can cause a sideslip on either side of the vehicle, of course,  
> at any
> time.
>
> My stall turns sometimes have quite a bit of sideslip on the  
> opposite side
> when I turn way too early and the fuse has already rotated 90 deg  
> with the
> CG still going upward.  On a calm day, that is 90 deg of sideslip,  
> meaning
> the relative wind is coming straight downward onto the side.
>
>
>>
>> 2) How does a gust cause the plane to yaw when a steady wind will  
>> not?
>
> By the same reasoning exquisitely detailed by Ron Lockhart in the  
> "Weather
> Vane or Crab" thread.  The rotation (or "correction" or  
> "weathervane") due
> to directional stability can only occur whenever the airflow is not  
> aligned
> with the fuse (i.e., a sideslip).  The assumption in our example is  
> the cg
> is moving downwind at the same rate as the wind.  Therefore, no  
> sideslip,
> and no turn.
>
> Consider a steady wind of 10 mph, and our "vertical" is tracking  
> downwind at
> that rate.  Then consider a sudden increase to 15 mph.   There is a  
> delay
> time for the CG to accelerate from 10 to 15 mph. During that  
> acceleration,
> the aircraft "sees" a relative wind component at its side.   
> Initially that
> component is 5 mph.  That is when the rotation into the wind would  
> begin in
> our example.
>
> Hope this helps.
>
>
>>
>> Thanks in advance, Jim
>>
>
> You are quite welcome.
>
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