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Old 7th Aug 2006, 17:24
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bookworm
 
Join Date: Aug 2000
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While I agree with your sentiment, I disagree with the detail of your analysis of a couple of the questions:

Q 240, H912 CFI
An aircraft wing is designed to produce lift resulting from:
A) negative air pressure below the wing's surface and positive air pressure above the wing's surface;
B) positive air pressure below the wing's surface and negative air pressure above the wing's surface;
C) a larger center of pressure above the wing's surface and a lower center of pressure below the wing's surface.
FAA Answer (according to Gleim) = B
Correct answer = C. Newtonian (Impact) Lift theory is the only case in which a net positive air pressure (i.e. greater than atmospheric) can exist below a flat plate wing. An aircraft wing (aerofoil) develops negative air pressure above AND below the wing.
Positive pressure coefficients often exist, and dominate, below lifting aerofoils, including flat plates. While a positive average pressure coefficient on the lower surface is not strictly necessary for lift, answer B represents the design goal. Answer C is meaningless. As you correctly point out, the center of pressure is a point. It is nonsensical to describe it as "larger".

Q 96, H912 CFI
Which statement relates to Bernoulli's principle?
A) For every action there is an equal and opposite reaction;
B) An additional upward force is generated as the lower surface of the wing deflects air downward;
C) Air traveling faster over the curved upper surface of an airfoil causes lower pressure on the top surface.
FAA Answer (according to Gleim) = C
Correct answer = There is no correct answer to this question since lift over an aerofoil is not a function of curvature.
The question doesn't assert that the curvature is the cause of the lower pressure, but rather that the air velocity is. Answer C, while misleading, is strictly speaking correct, and is certainly the statement most closely related to the Bernoulli principle.
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