lördag 11 augusti 2012

Why Is MIT Fooling Its Students?

MIT presents under Theory of Flight the following description of the generation of lift of a wing:
  • The shape of a typical airfoil is asymmetrical - its surface area is greater on the top than on the bottom. 
  • As the air flows over the airfoil, it is displaced more by the top surface than the bottom. 
  • According to the continuity law, this displacement, or loss of flow area, must lead to an increase in velocity. 
  • Consider an airfoil in a pipe with flowing water. Water will flow faster in a narrow section of the pipe. 
  • The large area of the top surface of the airfoil narrows the pipe more than the bottom surface does. Thus, water will flow faster on top than on bottom. 
  • The flow velocity is increased some by the bottom airfoil surface, but considerably less than the flow on top.
  • The Bernoulli equation states that an increase in velocity leads to an decrease in pressure. Thus the higher the velocity of the flow, the lower the pressure. Air flowing over an airfoil will decrease in pressure. 
  • The pressure loss over the top surface is greater than that of the bottom surface. 
  • The result is a net pressure force in the upward (positive) direction. 
  • This pressure force is lift.
All aerodynamicists know that this is a nonsense explanation. The typical question posed by a child when confronted with this message from an adult is: How come that airplanes can fly upside down?
MIT has no answer. Is this representative of the level of education at a world leading university?

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