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Revista Brasileira de Ensino de Física
On-line version ISSN 1806-9126
WELTNER, Klaus; INGELMAN-SUNDBERG, Martin; ESPERIDIAO, Antonio Sergio and MIRANDA, Paulo. Complementation of fluid dynamics and aerodynamic lift. Rev. Bras. Ensino Fís. [online]. 2001, vol.23, n.4, pp. 429-443. ISSN 1806-9126. http://dx.doi.org/10.1590/S0102-47442001000400009.
The conventional explanation of aerodynamic lift based on Bernoulli's law has important mistakes, which are pointed out. Lift is be explained here in a coherent way using Newton's laws. We show that the higher streaming velocity at the upper side of an aerofoil is the consequence but not the cause of the lower pressure. The cause of lift is the downward acceleration of air by the aerofoil. For a detailed analysis we regard the normal acceleration of air in case of curved streamlines that results in pressure gradients perpendicular to the streamlines. The analysis of curvature of streamlines in the vicinity of obstacles shows the generation of pressure distribution on the surface. Other misleading and erroneous aplications of Bernoulli's law are also analyzed and corrected. We present classroom experiments to demonstrate convincingly the downward movement of air caused by an aerofoil and the generation of pressure by the deflection of air stream.