Erik Hofman wrote:
Try this for a start:
An airflow over the wing is causing the downwash at the end of the airfoil. The airflow below the wing is now kind of captured between the airfoil and the layer(s) of air underneath itself.
In this situation it can go in just two directions, up or down, The majority of the flow will go down, bu a tiny fraction of the molecules has to go up. If the number of molecules that go up is high enough it will lift the airfoil up with it.
This is really what DaVinci already had discovered back in 1530-something.
This is really getting into a blog than anything else, but here is what I've come up with in a few moments:
The air over the airfoil is having a constant battle between cohesive forces (the force that makes a material stick to itself) and adhesive forces (the force that makes two materials of a different kind stick together). The adhesive forces make the air and the airfoil (metal) stick together, the cohesive forces tries to pull the air into a straight line.
As long as the adhesive forces are larger than the cohesive forces the *result* will be a faster airflow over the airfoil (because of pressure loss) and a downwash will be generated right after the airfoil.
The moment the cohesive forces are larger than the adhesive forces the result will be an unsteady detached airflow (e.g. stall).
Now, back to the explanation above, a pulling force really doesn't exist. A pushing force however does, and is caused by a difference in pressure difference at the two sides of an object.
Erik
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