From: "Marvin Kaye" <marv@lancaironline.net>
Subject: Re: [LML] More on Lift and flow around wings
To: lml
Date: Sat, 10 Feb 2007 10:18:46 -0500
Message-ID: <web-1828511@logan.com>
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Posted for "rtitsworth" <rtitsworth@mindspring.com>:

  Yes, I understand, and it is perhaps fair to call it arcane math to get a
  "proper" reference frame.  But the "wind tunnel view" tends to hide the fact
  that the air is actually being "moved/pushed/drug" in the same directions as
  the wing (in real life) - not the opposite direction.
  
Furthermore, the air on top is not actually moving faster (per say) -
  certainly not as is depicted by the wind tunnel reference frame.  The air on
  top is shown in a wind tunnel as moving faster, because it's speed relative
  to the wing is faster.  In reality, the air on the top is relatively
  stationary (fore-aft) versus it's original resting position.  Rather, it is
  the air bottom that is actually being moved faster (pushed, accelerated) by
  the wing and it's surrounding pressure gradient, thus that air is being
  accelerated fwd - (thus a slower relative speed in the wind tunnel).
  
  As it is accelerated fwd a higher pressure gradient is built in-front of and
  below the wing.  This causes the updraft out in front of the wing.  This
  sets up the actual flow of the air which is thereafter mostly vertical (up
  and down).  This up-down motion almost appears as secondary in the wind
  tunnel view since the "flow" there is primarily "seen" as horizontal.  The
  arcane math (resting air reference frame) leads to calculation/awareness of
  the actual acceleration of the air "packets" which is initially horizontal
  in-front and below the wing and then becomes much more vertical in nature
  above, which is commonly miss-understood from the wind tunnel view.
  
  The movement of the actual air packets (relative their resting reference
  frame) is fwd, then up, then back, then down.  This essentially is a circle.
  This circle flow is essentially a lateral (spanwise horizontal) vortex which
  moves with the wing, and which is centered just in-front of and above it
  (along/above the leading edge).  The low pressure "in this vortex" (think of
  a sideways tornado) is what allows the relatively higher pressure air  below
  (or "inside" for you purists) to impart a vertical force on the wing (ie.
  Lift).
  
  As AOA and/or airspeed is increased this spanwise horizontal votex becomes
  more energized - i.e. more lift.  When the AOA gets too large the votex is
  spoiled and the lift effect is reduced/gone (i.e stalled)
  
  Good discussion ;-)
  
  Rick