ORIGINAL: willig10
Very simply stated an airfoil when passing through the air creates lift. How this occurs is the wing, if it is semi or symetrical is curved at the top and bottom and it takes longer for the wind to pass over this curved surface. As a result based on a principle called bournoulis (forgive my spelling)principle, (same as a venturi cut in half) this causes a low pressure moment on the part of the wing that is pointed up. (An airplane flying level will always have a high angle of attack either inverted or right side up. As a result the wing wants to lift towards the low pressure area to fill the void, this is called lift.
A flat bottom wing is more stable and will want to right itself due to the nature of the wing being flat on the bottom and curved on the top.
A semi or full symetrical wing is more aerobatic in nature and will tend to stay where you point it.
Di-hedral is another aspect that helps flat bottom wings be more stable and self righting, the more dihedral the more stable the airplane, on a flat bottom wing.
hope this helps
Glenn Williams
While this is true of what is happening to the fluid, the argument was made that a vacuum doesn't apply any law to lift the plane. The fluid is not made static/electromagnetic enough so it does not draw the body/foil into the vacuum. Rather the vacuum which is looking at the state of the fluid, is a state where the momentum of the air in the vacuum is not directing a force on the body equal to the force excerted on the bottom of the body experiencing the greater force of momentum or pressure. So more accurately the pressure translated in to force is greater on the bottom of the body and thus is pushing it with greater force than the pressure on the toop of the body.
This is what the engineer was arguing that looking at the fluid is looking at the fluid but not lift. Lift is the result of what happended in the fluid to create a greater force on one side of the body than the other. Why this becomes important is when you are then combining various ways of changing the momentum like where a votex meets a fence or the canard on a SU-37 changing the stall point of the flow over the wing meeting the vortex or the sweep of a wing and the use of winglets etc. etc. etc.
The reason why this was argued was that models based on looking at the state of the fluid rather than its actual force excerted on the body lead to various inaccurate models like the vacuum sucking rather than the pressure pushing.
He really simplified it by saying I lift a box... that's lift. The fluid has little to no consideration. I take a air hose and blow on the box that is lift with the fluid. The air foil is just one of many diffferent type of air hoses nozels. Lift is the resulting force pushing the body up or down.
Thus engineers seek various ways to generate this force via vortex, lifting bodies and the use of vorticies over strakes, fences, canards, area rules etc. to generate lift in ways that go beyond the convention foil.
Yes Bernoulli and the many other calculation of what is happening to the fluid all apply but lift is the exploitation of the afore to direct the force from the moment of the air on the body to create lift.