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Re: a couple of points on flight



At 07:36 1/16/99 -0600, you wrote:
[Bill]
... If we look at the entire pattern of air surrounding the
airfoil out to a fair distance, it appears that the momentum change in the
air is first upwards in the upstream section, then downwards at the
airfoil, then upwards again in the downstream section, for a net change of
zero.
**********************************
[Jack]
It's a quantitative question that depends upon the "angle of attack"
of the airfoil. If the angle is sufficient to give lift, then the downstream
deflection is greater than the upstream deflection, giving a net lift. This
is apparently illustrated in the Anderson-Eberhart paper.
Regards,
Jack

What Jack said....with the proviso, the angle of attack for
effective lift can include the angle zero for asymmetric sections.
Following along with the earlier discussion I received the uncomfortable
image of a moving footprint of air in the shape of the moving wing
finally pressing upon the ground.
I am more comfortable with an image of molecules of the downwards
air parcel sharing their largesse with others, in the manner of a
marble running down a (Dalton's??) pinboard.
Brian
brian whatcott <inet@intellisys.net>
Altus OK