Bill - >There are no forces on the surface of a wing EXCEPT >those of air pressure. > >If you disagree... then you need to explain in detail >what these non-air-pressure forces are. > >But I already know the answer. It's simple: Pressure >differentials explain 100% of the lifting force, while >flow-deflection (the acceleration of fluid masses) also >explains 100% of the lifting force. These are simply >two independant ways of attacking the problem.
Yeah, that's what I was trying to say, more or less, while answering that notion that the air travels further & faster over the top, etc. *causing* the differential. I don't agree with that version. >But the incoming air will fill the vacuum chamber, with >the wave travelling at roughly the speed of sound! >In human time scale, as soon as you open the valve >and generate an air jet, significant air pressure >appears on the OTHER side of the wing. You can't >just claim that the pressure there is insignificant, >instead you have to measure it, millisecond by millisecond. The pump is large compared to the small jar volume, and once that dense air in the jet disperses, which it does very quickly, density and pressure get pretty low pretty fast before much of it swirls around underneath the foil. To see it and its scale is convincing. Seeing my writing about it isn't. >If you can show that air can PULL on a curved wing >(i.e. create an absolute negative pressure,) >that's something very interesting. Yup. It's been shown too, but not by me. Google should bring it up with words like van der Waals, airfoil, boundary layer, etc. Why else would a flow stick against a surface and follow it down around a curve like that? I never finished construction on it, but I started a rig where the airfoil sat on a membrane with good vacuum under the membrane in a separate chamnber from the air above the foil. Air jet would hit the top of the foil as before, but the whole bottom side would be against the membrane. Pump would keep the air above at as low a pressure as possible while the jet shot across the foil surface. I figure the foil would still rise into the airflow, pulling up on the membrane with the certain-to-be-lower pressure below it. Maybe simpler to use a split chamber with water instead of air? - Rick
