This is incorrect. A wing can impart momentum to air even in the absence of viscosity. However, the optimal wing shape is different. For an example of a wing

This is incorrect. A wing can impart momentum to air even in the absence of viscosity. However, the optimal wing shape is different. For an example of a wing that moves air "down" without viscosity, look at turbomolecular vacuum pumps: http://www.physics.rutgers.edu/ugrad/387/388s06/UHV_LEED/UHV_Pumps.pdf http://www.physics.rutgers.edu/ugrad/387/388s06/UHV_LEED/UHV...