Although it is hard to discuss such subjects over a forum due to subtleties of the subject, I will throw in my 2 cents in response to keep the subject from getting too butchered.
For symmetric airfoils (on which this thread started) the only sentence that is correct is the first one. The presence of curvature of the airfoil does not produce a large increase in lift. Like I said before (and I will keep saying it), for flat plates at moderate angles-of-attack (< ~11 deg) the lift curve slope is nearly the same as for most conventional, thin
symmetric airfoils (yes, like the one on your airplane). Therefore, at angles < 11 deg, thin symmetric airfoils produce about the same lift as a flat plate. This is not intuitive, and grasping for the easiest answers will lead you quickly to a wrong understanding of what's going on.
For thin symmetric airfoils (typically used on modern aviation), the curvature itself has little to do with the act of accelerating the air; a flat plate will accelerate the air just as well. The additonal curvature produces a very small acceleration compared to the presence of the airfoil itself. The curvature has to do with reducing drag, controlling separation characteristics (chordwise pressure distribution), controlling pitching moments, wave (compressibility) drag, and general lift and drag behavior of the airfoil at different angles and speeds. There's nothing in the physics that suggests that flat plates can't accelerate the air as quickly as symmetric airfoiled surfaces.
The airfoil does a really good job of producing
circulation, which is the fundamental basis for lift.Circulation is a measure of rotation of the airflow around the airfoil. The Kutta condition (that the flow must leave tangentially at the trailing edge) determines the amount of circulation for a particular airfoil. Lift is directly proportion to circulation, that is: Lift = circulation*density*airspeed*wingspan
You produce more circulation, then you get more lift. Period.
Any object (anything) will produce circulation in presence of a velocity and density field. Airfoils are good at producing large amounts of circulation (in the vertical direction) for minimum drag.
By the way, since you;re probably wondering where I came from, I've got a BS degree in Mechanical and Aeronautical Engineering, and Masters Degree in aeroautical engineering. I have been working in aerodynamics for 8 years straight out of school; for NASA (Glenn and Ames Research Centers), and Military defense contractors. I deal with this stuff every day.
| Quote: Originally Posted by wings19 | | | | |
| Lift is created when the air over the top of and airfoil is traveling faster than that over the bottom reducing the pressure on the top(bernoulli). Therefore, an airfoil would make more lift at the same AOA as a flat plate because the air has to travel a greater distance over the top of that surface than the bottom making a much lower pressure compared to a flat plate where the air wouldn't travel as far. When the air has to travel further it speeds up. I forget why it speeds up but I know it does because I was taught why in my ground schools but can't remember why  | |
| | |