[NSRCA-discussion] Weather Vane

[Jim Alberico]

> -----Original Message-----
> From: James Oddino [mailto:joddino at socal.rr.com] 
> Sent: Sunday, October 14, 2007 1:21 PM
> To: alberji at charter.net; NSRCA Mailing List
> Subject: Re: [NSRCA-discussion] Weather Vane
> 
> 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.
> 

And I can benefit from learning to fly pattern from the experts.  I got a
few sloppy sequences in today to reinforce that.  Getting better, but a long
way to go. No crosswind today.  Aligned with runway, but highly variable.
Luckily, I have access to a couple of FAI-level mentors, and some others at
varying skill levels.  Ruined another prop with another Navy-style landing
on the last flight of the day.

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

Not sure what you mean by aligned, but I'll take a stab at it.
In our hypothetical case, the cg is moving upward and steadily downwind.  We
also specified that the fuse is pointed to the sky, perpendicular to the
ground.  Before the gust, the only relative wind is straight on to the fuse,
nose-to-tail (no sideslip).  That *component* does not go away.  At the
beginning of the gust, a sideslip *component* is added exactly perpendicular
to the fuse, but NOT perpendicular to the CG path (recall the path is tilted
downwind). 

> 
> 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?
> 

I don't know the answer, but generally one can expect a positive gradient
(increasing wind speed) from ground to altitude.  Hard for me to say if that
factors in, but it possibly could.  If it matches your experience, then
maybe you have hit upon an explanation.  Good thought.

> Thank you for your patience.
> 

No problem.  Sorry I had to take a break from email activity to go out and
fly.  ;-) Thank everyone else for the patience to put up with the long
"Weather Vane" thread.

I've learned a lot about how to think about stall turns when I'm actually
*flying* them!

Best,

Jim A


> 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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