Today on science friday on NPR they were discussing lift as it relates to airplanes. The speaker said that Bernoullies principle doesn't completely account for the lift that the air flow over an airplane wing generates. He said that according to Bernoullies principle a commercial jet would have to achieve 400knots to generate enough lift for takeoff. He said that this idea is a point of contention among scientists but the lift generated is as simple as air flow over the top of the wing being enough to push downward towards the earth. He cited examples such as a helicopter and the fact that fighter jets mount missles under their wings because the air flow there isn't that important. Anyone out there familiar with this "controversy"?
Hi Greg and all,
actually there is no controvery between Newtons and Bernoullies laws. The formulas which describe the behaviour of fluids are called Navier Stokes equations. One part of them are Newton laws. You may look in Wikipedia to see these equations. With some assumptions, you can simplify the Navier Stokes equations to Bernoullies law.
I guess that the speaker in the TV just wanted to explain, that you need more formulas then just Bernouilles law.
...fighter jets mount missles under their wings because the air flow there isn't that important.
It is true, that the upper surface is more sensitive than the lower surface. Hence it is better to have the spi halyard on the lower (pressure) side of the sail and not on the suction side.
This laminar flow sounds great. Why don't I promote laminar flow on my hull and stop waxing the damn thing?
In fact the boundary layer of our mast and sails is turbulent due to roughness, contamination and oscillation,
but it may be usefull to fix the separation point, i.e. have a mast with roughness at the leading edge to prevent early separation.
Cheers,
Klaus
