Now for some questions _ _ _ (that can be ohjects of discussions)ġ- Both airfoils obviously have a graph of their lift coefficient that is expected to be pretty well linear up to about 3 or 4 degrees of their maximum. Upward and downward to be interpreted as when the airplane is sitting normally on the ground on its landing gear or is in normal cruising flight.Īll above can be discussed in a friendly manner with anyone having a different understanding. We call this force "lift" and labelled positive if upward or negative if downward. The results are that a mass of air (atmosphere) is deflected (accelerated) and produce a reaction which is convenient to interpret as a force (vector) acting at 90 degrees to the flight trajectory. While this is true as I see it, I prefer to consider the results of these pressure differentials. I do not endorse the theory that lift is due to increased pressure under the wing and a vacuum that really is not a vacuum but rather a decreased pressure on the wings top surfaces. I do not intend to go into mathematics and consequently the Reynold's number is not taken into account. It takes more than one to have a discussion. I believe that the angle of attack range from 2 to 4 degrees is typical and applicable to any airfoil. The three (3) degrees illustrated in the pictures would, I believe, be close to the typical angle of attack of an aiplane flying at cruise speed or somewhat lower than cruise.
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