Re:How Airplanes Fly: A Physical Description of Lift (1999)
by pif on Thursday December 10, 2015 @04:15AM
(#10709698)
Just one more bit: "Air has viscosity". Without naming viscosity, the explication doesn't hold. If the air didn't have any viscosity, like it is natural to imagine, planes could not fly.
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Re:How Airplanes Fly: A Physical Description of Lift (1999)
by FiatLuxDave on Thursday December 10, 2015 @09:03AM
(#10710604)
This is incorrect. A wing can impart momentum to air even in the absence of viscosity. However, the optimal wing shape is different. For an example of a wing that moves air "down" without viscosity, look at turbomolecular vacuum pumps:
http://www.physics.rutgers.edu/ugrad/387/388s06/UHV_LEED/UHV...
Re:How Airplanes Fly: A Physical Description of Lift (1999)
by zby on Thursday December 10, 2015 @05:33AM
(#10709930)
Not really - if a wing moves through fluid without viscosity it still has to move the particles down.
Re:How Airplanes Fly: A Physical Description of Lift (1999)
by onion2k on Thursday December 10, 2015 @07:36AM
(#10710312)
The impulse required to move particles of a fluid with zero viscosity would be zero, so the equal and opposite force that we call lift would also be zero. Consequently you couldn't fly if air had no viscosity.
Re:How Airplanes Fly: A Physical Description of Lift (1999)
by dhimes on Thursday December 10, 2015 @08:16AM
(#10710431)
If the particles have mass then the impulse wouldn't be zero.
Re:How Airplanes Fly: A Physical Description of Lift (1999)
by meagain20000 on Thursday December 10, 2015 @09:06AM
(#10710620)
Is there such a thing as non-viscous fluid?
Re:How Airplanes Fly: A Physical Description of Lift (1999)
by mcguire on Thursday December 10, 2015 @10:12AM
(#10710945)
Yes, one example is superfluid helium.
https://en.wikipedia.org/wiki/Superfluid_helium-4
Viscosity is weird.