- #71
K^2
Science Advisor
- 2,470
- 33
Three years later, and still nobody explained to you that neither of these cause lift?
Bernouli Equation cannot be used to derive lift, because flow at the surface is zero. It can be used as an estimate, however, by considering the layer with fastest flow.
Newton's Third cannot be used directly because there is no direct interaction. The flow that's actually deflected is not the flow that had contact with the wing.
Lift is generated by pressure differential across the wing. That pressure differential has to be found by solving the flow equations. In many situations, finding exact pressure at the surface is problematic. In that case, circulation is used. Kutta-Joukowski theorem relates circulation around a surface to the lift generated by the surface. The theorem is derived using Kutta condition, Stokes' Theorem, and momentum conservation. This is probably the most direct link to Newton's Third in the whole deal.
Bernouli Equation cannot be used to derive lift, because flow at the surface is zero. It can be used as an estimate, however, by considering the layer with fastest flow.
Newton's Third cannot be used directly because there is no direct interaction. The flow that's actually deflected is not the flow that had contact with the wing.
Lift is generated by pressure differential across the wing. That pressure differential has to be found by solving the flow equations. In many situations, finding exact pressure at the surface is problematic. In that case, circulation is used. Kutta-Joukowski theorem relates circulation around a surface to the lift generated by the surface. The theorem is derived using Kutta condition, Stokes' Theorem, and momentum conservation. This is probably the most direct link to Newton's Third in the whole deal.