[NSRCA-discussion] Weather Vane

[glmiller3 at suddenlink.net]

but it doesn't YAW!

G
---- James Oddino <joddino at socal.rr.com> wrote: 
> I was thinking of dropping it from 32 feet but then decided not to  
> get hung up in numbers.  And folks would probably call an  
> accelerating wind speed a gust and throw us off track.
> 
> If you think about dropping it with the nose pointed at the ground in  
> the crosswind, you can picture the cg wanting to fall straight down.   
> However, the crosswind creates more force on the larger area behind  
> the cg than on the smaller area forward of the cg so the nose yaws  
> towards the wind.  Since the force fore and aft of the cg is in the  
> same direction (but with different magnitudes), the arrow drifts  
> downwind.
> 
> Who needs an aerodynamicist?
> 
> 
> On Oct 11, 2007, at 10:38 AM, george w. kennie wrote:
> 
> > Hey Jim,
> > I think you might need to say ,  "32 ft/sec/sec" so that the cross  
> > stays constant as the descent speed increases.
> >
> >
> >
> > ----- Original Message -----
> > From: James Oddino
> > To: NSRCA Mailing List
> > Sent: Wednesday, October 10, 2007 7:20 PM
> > Subject: Re: [NSRCA-discussion] Weather Vane
> >
> > Nat,
> >
> > If you hold an arrow (or a bomb) horizontal and drop it, what  
> > happens to it's attitude on the way down and why?  Then drop it  
> > with a crosswind of 32 ft/sec.  What happens to its attitude?
> > Seems pretty obvious to me.
> >
> > Jim
> >
> >
> > On Oct 10, 2007, at 2:21 PM, Nat Penton wrote:
> >
> >> Ron
> >> You are correct - an airplane does not weathervane or weathercock  
> >> - it fliies straight into the freestream unless given rudder. BUT,  
> >> as Kennie says, he hopes to be here next year to reargue the  
> >> point !!                                              Nat
> >> ----- Original Message -----
> >> From: ronlock at comcast.net
> >> To: NSRCA Mailing List ; NSRCA Mailing List
> >> Sent: Wednesday, October 10, 2007 11:07 AM
> >> Subject: Re: [NSRCA-discussion] Weather Vane
> >>
> >> I thought I'd throw in my 2 cents worth, but maybe it turned into  
> >> too much.  Ya been warned <G>.
> >>
> >> There is a strong, almost overwhelming, visual perception that  
> >> airplanes weathervane into the wind as seen by an observer on the  
> >> ground.
> >> If the airplane is partly connected to the ground (as in takeoff  
> >> or landing roll) it will likely weathervane into the wind.   (Like  
> >> a real weathervane on the barn).   Putting more side area behind  
> >> the CG probably increases the weathervane effect.
> >> But once airborne, an airplane no longer feels wind on side of the  
> >> airplane and does not weathervane in the sense that the  
> >> weathervane on the barn does.  Nor does the hot air balloon  
> >> mentioned in an earlier post.
> >> Just after take off, we likely see the nose is pointed some amount  
> >> into the wind.  This visual perception is true. But is it proof of  
> >> weathervaning?  It probably weathervaned into the wind during take  
> >> off roll. Once airborne the weathervane is now what we call a crab  
> >> angle into the wind.
> >> We all know stall turns are easier to do "into the wind".  Is it  
> >> because they weathervane?    On the upline to a stall turn in a  
> >> cross wind, does the pilot wind correct the airplanes track?    
> >> Most of us do, consciously or not.    If we are having any success  
> >> at all with the wind correction, the fuselage is "leaning" into  
> >> the wind a bit   It's certainly easier to get a stall turn by  
> >> continuing into the established lean, than it is to go against the  
> >> lean to the downwind direction.
> >> Pilots try to make heading adjustments to hold track, or hold  
> >> distance in lines and maneuvers.  Those adjustments (crab angles)  
> >> can appear to be a result of weathervaning, but are often pilot  
> >> inputs, consciously or not.
> >> Related things to consider-
> >> Airplanes do get "hit" in the side, top and bottom when in  
> >> turbulent wind, and wind shear situations.  We fly low, and are  
> >> often in turbulence.  There may be short, nearly random, turbulent  
> >> air effects that result in a weather vane type effect.
> >> A free flight glider does not weather vane into the wind.  The  
> >> glider may fly in circles, but it will drift downwind at the  
> >> overall average of the wind speed.   No matter how much side area  
> >> is put behind the CG, it will not find and maintain a heading into  
> >> the wind.
> >> Given flight in no wind situation, a string tied on nose of an  
> >> airplane blows exactly backwards and parallel to the fuselage.   
> >> (unless the airplane is out of rig, or has control surface  
> >> inputs).   If flown in a cross wind direction, the airplanes track  
> >> across the ground changes, but the string stays straight.   (not  
> >> counting any effect of propeller induced spiral airflow)
> >>
> >> The old full scale stories about loosing airspeed and stalling  
> >> while doing a "downwind turn" fit into this discussion to a  
> >> degree.  Does wind hit the tail of an airplane as it turns  
> >> downwind thereby reducing airspeed?   In the "old" days, pilots  
> >> often flew low and partly judged airplane speed by visual  
> >> observation of ground speed.  (similiar to our situation of  
> >> observing from the ground)   This could lead to the perception of  
> >> plenty of ground speed being plenty
> >> Sorting out the visual perception of the "obvious" weather vane  
> >> effect is tough.  Lots of things complicate the observation -  
> >> pilot inputs, turbulence, paralax, and more.
> >>
> >> IMHO, bottom line, it's not wind hitting side of airplane, no  
> >> matter how much side area is behind the CG.
> >> Later, Ron
> >> In summary, I agree that as observers on the ground, we "see"  
> >> effects that appear to be weathervaning.  But the "real" cause
> >>
> >>
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