Every action has a reaction. It's all relative (what you measure=20 pressure or force) with respect to some other point. The sum of the=20 vertical forces must equal zero, assuming stable (no acceleration) =20 flight. Once one gets out of the local effects of the air movement, all=20 the air pressure is equal with no air movement. Draw a free body diagram=20 (a physics exercise).Therefore the forces of holding the plane up must=20 be contained within that local area since there is no air movement. The=20 air does get disrupted by the passing plane. With a plane (could be at=20 least as big as a DC-9) passing under a large plane, you can pass at=20 right angle directly under that plane by 100' with no issues, but the=20 wake turbulence (wing tip vortices) settle earthward at approximately=20 300 - 1000 feet per minute (I forget the close number). A DC-9 got into=20 that area 3 miles behind a larger aircraft, and did a un-commanded 180=20 degree roll. The ground effect is effective for the wing being closer to the ground=20 than 1/2 the wing span and yeas then the air is getting squeezed between=20 the air and the ground. This starts to define the local effects I=20 discussed above, and I'm not to try to define any further, get into the=20 mechanics of the wig tip vortices. On 1/26/2011 5:26 PM, Chris McSweeny wrote: > On Wed, Jan 26, 2011 at 9:03 PM, Ing. Marcelo Fornaso > wrote: > =20 >> Actually, planes with wings with aerodynamic profiles are pulled up by v= acuum >> (in a way to speak), more than pushing air down. >> =20 > So you're suggesting they fly without pushing any air down? > > Chris > =20 --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .