Aerodynamic lift

Thanks for a very cogent article on aerodynamic lift. Among many articles on this subject, mine is http://arxiv.org/abs/nlin/0507032 on ArXiV. (In order to see the animation, download the entire .zip file and compile the .tex with pdflatex.) I humbly submit that Bernoulli’s equation is not applicable because the conditions for its applicability are not met on or around an airfoil. Your description of the cause of the Coanda effect and its accompanying pressure decrease on a surface curving away from the flow seems to me to be very clear. The pressure profile around a wing is shown in John D. Anderson’s “Introduction to Flight” and was measured independently also by Tilman Buntz for Marco Colombini for their research at the University of Genoa (see http://www.av8n.com/irro/ ). The greatest pressure difference is near the leading edge just downstream from the stagnation line. The upwash resulting from the interaction of the air molecules with the bottom surface of the wing adds to the flow here.

Over the surface of the wing, the pressure field is the result of the impacts of the air molecules and nothing else. Circulation, upwash, drag, lift… all are the result of the interaction of the air molecules with each other and with the surface of the wing. Newton’s third law predicts this exactly but we have no computers to keep track of so many collisions (of the order of 10^23). In order to be able to even begin to handle the problem, the fluid approximation is made. This approximation is good for a good part of the flow but it becomes invalid in the vicinity of the surface, i.e. the boundary layer. As soon as there is significant particle-particle interaction, the fluid approximation runs into trouble.

Charlie Crummer (charlie.crummer@gmail.com)

Is this the article you are commenting on? How do Airplaines Fly, really?

ccrummer: welcome to the Straight Dope Message Boards, we’re glad to have you here. Read around, we think you’ll find things to attract you.

When starting a thread, it’s helpful to others to provide a link to the column or staff report you’re commenting on. Saves lots of search time, and stops people from repeating what’s already in the article. I’m hoping that Khadaji got the right link? And you’ll know for next time.