Thanks for your excellent point! I believe that you are correct. The Bernoulli principle is only a piece of the explanation of how a wing produces lift. The Newtonian explanation that you describe is also a big part of it. Lift certainly does vary with the angle of attack of the wing, increasing as the angle of attack increases, up to the critical angle of attack and the resulting stall. As you mention, this is what makes inverted flight and “flat” wings, or even sails possible.

You make a great point, however I am not convinced that the angle of attack piece of the equation is more important than Bernouilli. The relative importance of Newton vs. Bernoulli seems to be a matter of intense debate, even among physicists and aeronautical engineers. If you have never Googled “newton bernoulli lift” I recommend that you try it, especially if this interests you (I find it quite fascinating!) Try reading this site: http://hyperphysics.phy-astr.gsu.edu/hbase/fluids/airfoil.html, or this forum for an example of heated debate: http://www.pprune.org/tech-log/355523-why-do-aircraft-fy-flat-plate-lift-vs-bernoulli.html. Here is a very extensive article on lift and airfoils: http://www.av8n.com/how/htm/airfoils.html#sec-bernoulli. I believe both theories play a part in lift-producing airfoils. I’ll leave the proportion-determining to those who know more than I!

PS. I am so glad you brought this up, I wondered if anyone would. I intentionally kept my post very, very simple and that bothered me. But I feared glazing the eyes of those readers who are less enthusiastic about about aviation and science than I am (which would probably be most of them). Thanks again for the great comment!

One thought though, I don’t believe your explanation of how a wing provides lift is correct. The Bernoulli principle does contribute to lift but it isn’t the most important affect. Indeed, if Bernoulli was all that matters then it would be impossible for a plane to fly upside down. Most planes can fly upside down (as long as the airframe can handle an upside down wing load, but that has nothing to do with lift). Even big planes like a 707 have been flown upside down. In addition, planes with equal upper and lower chords have been flown (the Wright Flyer had equal wing chords as do paper airplanes).

Most of the lift provided by the wing is due to the deflection of air downards by the wing. Air forced down means the wing is forced up. As long as the leading edge of the wing is above the trailing edge the air flow is forced downwards, regardless of the top and bottom chord lengths of the wing. In your airflow over airfoil drawing the leading edge is above the trailing edge. That tilt (pitch) is providing more lift than the Bernoulli affect.

With a enough information on the flight envelope of a particular aircraft the relative contribution of wing pitch and the Bernoulli affect can be estimated. What is the level flight pitch when the plane is right-side up versus upside down? If Bernoulli isn’t contributing then the pitch is the same. If Bernoulli contributes then the pitches are different and the difference in pitch is related to twice the Bernoulli affect.

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Anyway, this toy is like an upside down hair dryer and it blows lightweight balls into the air and sometimes they fly away, sometimes they drop into a little chute and go back down into the air stream. I never even thought to use it for teaching, but I will now!

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