the confirmation i think is that we are supporting the same aircraft weight at one G thus lift is unchanged.
Joe,
I think you are thinking of landing, and I am thinking of climbing...
This was in your link... at the bottom I highlighted some of it...
How VGs Work
With the installation well underway, I asked Bob Desroche and Jay Falatko if they could explain to me the theory behind how vortex generators reduce stall speeds and Vmc. What ensued was a cram course in Aerodynamics 101 which I found illuminating and fascinating.
VGs are
boundary layer control devices, so it isn't surprising that to understand how they work you first need to know something about the boundary layer. I'd certainly heard the term before, but never really understood its significance. Bob and Jay were glad to fill me in, and here's what I learned.
When an airplane is in flight, we usually think in terms of air passing over the top of the wing at the airspeed of the aircraft. But it turns out that the viscosity of the air and the friction of the wing surface cause the air molecules in contact with the wing to adhere to its surface and therefore have zero velocity. Air molecules slightly farther away from the wing surface will be slowed due to friction with the zero-velocity molecules but won't be completely stopped. As we move still farther away from the wing surface, the air molecules will be slowed less and less, until at some distance from the surface a point is reached where the air molecules are not slowed at all.
The layer of air from the surface of the wing to the point where there is no measurable slowing of the air is known as the boundary layer.  Boundary layer changes from laminar to turbulent flow as it moves aft along the wing. |
 Laminar vs turbulent. |
Near the leading edge of the wing, the boundary layer is very thin, and the air molecules in it move smoothly and parallel to the wing surface. This is known as
laminar flow. But as the airflow progresses aft from the leading edge, the boundary layer becomes progressively thicker and more unstable, and transitions to
turbulent flow in which intermixing of faster and slower air molecules starts to take place. (Another easily-seen example of laminar and turbulent flow can be seen by watching the smoke rise from a lighted cigarette in a draft-free room.)
It turns out that laminar flow is a good-news/bad-news situation. The good news is that laminar flow provides greatly reduced drag compared to turbulent flow. The bad news is that laminar flow permits the boundary layer to separate easily from the wing surface at high angles of attack. That's why so-called "laminar flow airfoils" (which are designed to move the transition to turbulent flow further aft) tend to provide low drag at cruise but nasty stall characteristics.
Turbulent flow in the boundary layer produces more drag, but is much more resistant to separation (and therefore to stalling). However, even in areas of turbulent flow, there tends to be a thin sub-layer of laminar flow in the immediate vicinity of the wing surface which becomes increasingly slow-moving and stagnant toward the trailing edge of the wing. It is this "aerodynamically dead" sub-layer that allows airflow to separate and the wing to stall.
 By energizing the boundary layer, VGs allow the airfoil to operate
at higher angles-of-attack without airflow separation.
(Copyright Micro AeroDynamics) |
If we could find a way to energize this sublayer, flow separation would be supressed and the onset of stall delayed. This is precisely what vortex generators do. Each VG creates a pencil-thin tornado-like cone of swirling air that stimulates and organizes the turbulent flow of the boundary layer on the aft portion of the wing. The swirl of the vortices pull fast-moving air down through the boundary layer into close proximity to the wing surface, energizing the previously-dead air there.
The result is a wing that can fly at significantly higher angles of attack before the onset of boundary layer separation, and can therefore achieve a significantly higher maximum lift coefficient.When mounted on the wings, VGs reduce stall speed and increase climb capability. When mounted on the vertical tail, they increase rudder effectiveness and lower Vmc.
