# Theory of Flight

 Updated: July 20, 2012  Funded in part by

The third description, which we are advocating here, we will call the Physical Description of lift. This description is based primarily on Newton’s laws.

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So, why has the popular explanation prevailed for so long? One answer is that the Bernoulli principle is easy to understand. There is nothing wrong with the Bernoulli principle, or with the statement that the air goes faster over the top of the wing. But, as the above discussion suggests, our understanding is not complete with this explanation. The problem is that we are missing a vital piece when we apply Bernoulli’s principle. We can calculate the pressures around the wing if we know the speed of the air over and under the wing, but how do we determine the speed?

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The preceding is an article by David Anderson, Fermi National Accelerator Laboratory, and Scott Eberhardt, formerly of the Department of Aeronautics and Astronautics, University of Washington, now at the Boeing Company.   The authors have given ALLSTAR permission to present this article on the ALLSTAR website. The authors have written an updated copy of this article and provide it for all to use.

The above is recent writing by those who took us from Bernouilli to Newton. They wrongly say there is nothing wrong with the Bernouilli approach. However, they are not clear about whether the air the plane flies through is stationary, or as in a wind tunnel. See their Figures 2, 3 and 4, which show the air having velocity before the plane arrives. Whether the “plane” or the air is stationary or moving is crucial. This is because the air approaching the wing in a wind tunnel has momentum. The situation is very different in a wind tunnel.

Ivor Catt.  19 March 2016.

There is nothing wrong with the Bernoulli principle, or with the statement that the air goes faster over the top of the wing.” – but the air is not moving! IC sept 2016