So much to say, so little time to say it. I’ve got cookies in the oven, work in the morning, and wifey is waiting upstairs in really sexy lingerie. Plus I prefer one topic per post so here’s a bite-size morsel of opinion.
I started watching my ASA Private Pilot Virtual Test Prep DVD collection last night and like most everywhere else, lift is explained using Bernoulli’s Principle. In short, Bernoulli states that faster flow of a liquid (or gas) results in reduced pressure. Those that apply this principle to lift say that air travels a longer path over the top of a wing, and to keep up with the flow underneath the wing it must travel faster. Faster traveling air on top of the wing equals lower pressure so the wing, and therefore the plane, is sucked up.
I never really bought this explanation. Why do the air molecules have to meet at the trailing edge of the wing though traveling different paths? This question has puzzled me for years.
Consider a 59¢ glider, the balsa wood kind. Its wings are flat; air travels the same distance on either side. I suppose air bouncing off the slightly tilted wing could explain this – the plane is light enough.
So what’s really going on? There are a number of different explanations. This page uses the Coanda effect (don’t ask) and Newton’s 3rd law. This page dismisses Newton as used in the previous link. Bernoulli has favor here, but not here (and she wrote a book about it. The phrase “plausible falsehood” comes from her page). Commune with Newton and Coanda on this page, play with an interactive airfoil here (simplified), here (advanced), and here (college level). Or just split the middle and agree with both Newton and Bernoulli.
Uh oh, hot wife is calling me…don’t want her to cool off.
Um, in summary, the math works no matter how you look at it, planes fly, so don’t worry about it too much. Gotta go now.