REFLECTOR: 65VT/ angle-of-attack system

[Douglas Holub]

So, would you say that the airspeed indicator is just as useful as an AOA indicator for establishing maximum glide or maximum rate of climb?  Or would Vx and Vy vary more with CG and weight than an AOA indicator would?
  ----- Original Message ----- 
  From: Jim Sower 
  To: Velocity Aircraft Owners and Builders list 
  Sent: Monday, October 04, 2004 8:54 PM
  Subject: Re: REFLECTOR: 65VT/ angle-of-attack system


  Al,
  <...The relative AOA of the two airfoils is fixed. ...>
  Actually, they're not.  AoA / incidence are respectively the angle(s) between the chord of the airfoil and the airstream / fuselage centerline respectively.  The airfoil chord line is the line between the "stagnation point" on the nose of the airfoil to the tip of the trailing edge.  Wing flap or canard elevator deflection increase the camber of the airfoil and increase both the incidence angle and the AoA.  An AoA indicator measures airflow relative to a fixed line (the fuselage centerline?) and assumes fixed incidence angle (which is not the case with a canard unless you never deflect the elevator).

  <...could be useful for determining canard stall at one configuration; full elevator deflection ...>
  Actually, the canard stall does not always occur at full elevator deflection either.  

  With aft CG, relatively little elevator deflection rotates the fuselage considerably, and the the canard will stall at an AoA that consists of the largish fuselage AoA plus the relatively small increase in incidence caused by relatively small elevator deflection.

  With forward CG, it takes much more (full?) elevator deflection to rotate the fuselage less, for the canard to stall.  Here, the fuselage AoA is much smaller, but the canard incidence increase is much larger with full elevator deflection.  

  The canard stalls in both instances, but the "AoA" that the transducer sees is a good bit lower at forward CG than at aft CG.

  You may recall from your Cessna days that the airplane had to be pretty cocked up to stall clean, and much less so to stall with the flaps down.  The AoA of the airfoil was not that much different clean or dirty, but the incidence of the chord line increased radically when you lowered the flaps.  By the same token, cruising at, say 70 kts the airplane had relatively level attitude, but drop the flaps and maintain 70 kts straight and level and you were looking at the trees.  The AoA of the airfoil didn't change radically, but the angle between the wing chord line and the fuselage did.

  So for a canard, AoA is a little like teats on a bull .... Jim S.


  Al Gietzen wrote:

Angle of Attack is a very useful tool for conventional plan form 
airplanes.  It is of little value for canard type aircraft since the 
wing you're trying to observe is the canard, and the incidence and 
aerodynamic properties (like stall AoA) are constantly changing (with 
elevator deflection). 

It just doesn't tell you anything particularly useful ... Jim S.

Good point, Jim.  However, I do think that it could be useful for
determining canard stall at one configuration; full elevator deflection.
Using the pressure port system, I'd expect installation on the main wing
will work fine; you just need to calibrate it the canard stall point.  The
relative AOA of the two airfoils is fixed.

Al

_______________________________________________
To change your email address, visit http://www.tvbf.org/mailman/listinfo/reflector

Visit the gallery!  www.tvbf.org/gallery
user:pw = tvbf:jamaicangoose
Check new archives: www.tvbf.org/pipermail
Check old archives: http://www.tvbf.org/archives/velocity/maillist.html


  



------------------------------------------------------------------------------


  _______________________________________________
  To change your email address, visit http://www.tvbf.org/mailman/listinfo/reflector

  Visit the gallery!  www.tvbf.org/gallery
  user:pw = tvbf:jamaicangoose
  Check new archives: www.tvbf.org/pipermail
  Check old archives: http://www.tvbf.org/archives/velocity/maillist.html
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://www.tvbf.org/mailman/private/reflector/attachments/20041005/167ed338/attachment.htm