Thread: Discussion A non-aerodynamic proof that a lifting wing pushes down on the earth View Single Post
 Nov 17, 2012, 12:49 PM Grad student in aeronautics United States, GA, Atlanta Joined Oct 2010 525 Posts Crossplot, Thank you for giving something tangible to talk about in this discussion. I read the whole article and found many problems with it. They gave the well known equation for centripetal force but fail to offer any way of calculating the lift from it. There is no way to show that they are right or wrong because they do not provide any useful equations. To lead into this discussion they say "The air flow near the aerofoil follows the geometrical shape of the upper surface generating a pressure gradient and acceleration, both perpendicular to the streamlines and directed to the centre of the flow trajectory." The acceration is most certainly not entirely perpendicular to the streamlines. The flow near the surface accelerates rapidly past the leading edge and then. Yes some acceleration will be perpindicular to the surface, but consider the face that the change in the length of the vectors they show in the Fig. 4 indicates the velocity change parallel to the surface. They also discuss viscosity: "This variation of viscosity induces a decrease of air velocity inside the boundary layer from its outer frontier to the aerofoil surface." This is completely wrong. For a Newtonian fluid (like air and water), viscosity only changes with temperature. This only becomes important for very high speed flows. The velocity is lower inside the boundary layer because of the no slip condition at the surface. Their conclusion: "In summary, lift occurs when flow is shifted downwards." This is the first time they use the word "shift", thereby making this statement very ambiguous. In actuality, lift is created by sending more streamlines above the body than below. -David