Re: How Important Is Cross-section Shape Of Wing?

Date:         04 Apr 2001 16:41:27 
From: (Gord Beaman)
Organization: ISLAND TEL
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>BBarksdl <> wrote:
>> In the April issue of Discover magazine, Robert Kunzig challanges the textbook
>> explanation of the principles of flight.
>Personally I found the article less explicit (and more confusing) than
>this. It seemed to suggest that the mass of an aircraft must be supported
>by displacing an equal mass of air downward (at least, if the aircraft is
>gliding without engine power). But the article did acknowledge that a
>classic airfoil section does result in lower density air above the wing;
>and therefore I conclude from this that it's another way of saying that
>air mass has been displaced downward.

Sure...the 'path' over the top of the wing is longer than the
path under it so the pressure has to be lower on the top
inflight. So as the AOA increases the pressure 'under' the wing
increases while the pressure on top decreases therefore the wing
wants to move up. As you say, this pressure differential is
basically the result of displacing air mass downward but it's the
pressure differential that provided lift.

>The article was more explicit in renouncing the idea that lower density
>air pulls the aircraft upward. Fair enough; a vacuum, or partial vacuum,
>doesn't pull anything anywhere unless there is a higher density pushing on
>the opposite side.
Of course...people say "A window burst and a passenger was sucked
out of the a/c". The pax was 'pushed' out of the a/c by the
higher air pressure inside. To prove that just imagine an
unpressurized fuselage when a window falls out, not too many pax
will be 'sucked' out then I'll wager.