Lift from Equations of Fluid Dynamics

[@pureunkim5423]

Thank you! It helped me a lot! I have a question that when we set up a conservation of momentum equation, why is the lift force defined as negative? Is this mean lift force can be generated by just a pressure difference? I thought lift force is caused by downward air flow. Thank you again

[@SidGUDayton]

The reason there is a negative sign in front of the lift is due to Newton's 3rd law. The wing exerts a force on the air by deflecting it and the air applies equivalent and opposite force on the wing which in the y-axis is lift.

[@pureunkim5423]

@@SidGUDayton Thank you! I really appreciate it!!