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Backwash Causes Lift?
Hi,
Student pilot here, self-teaching using the Jeppensen Private Pilot Kit after taking ground school. I read in the book that combustion "creates" energy, which is technically not true, but I decided to ignore it since the pictures are sooo pretty. Now, in Chapter 3, section about airfoils, it actually says: "In addition to the lowered pressure, a downward-backward flow of air also is generated from the top surface of the wing. The reaction to this downwash results in an upward force on the wing which demnstrates Newtons' third law of motion. This action/reaction principle also is apparent as the airstream strikes the lwoer surface of the wing when inclinded at a small angle (the angle of attack) to its direction of motion. The air is forced downward and therefore causes an upward reaction resulting in positive lift." IMHO, the latter part of this paragraph is correct, but the former part is wrong. Obviously, any air above the wing can only result in a force downward on top of the wing. The only force causing the plane to want to move upward comes from beneath the wing. The effect of any air above the wing is to cause rarefication above the wing, resulting in lower pressure, thereby giving the 14.7lbs/in^2 (plus) to do its work. That "reaction" coming from downward movement of air seems just plain silly to me. I am also inclined to take issue with the explanations of Bernouilli's Principle which I see often in the literature, but that's a different subject. [Note, I don't doubt Bernouilli's Principle, I just think there is more to it than the way it is being described in context of flying.] -Le Chaud Lapin- |
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