Kutta–Joukowski theorem

For steady two-dimensional inviscid flow of density $\rho$, far-field velocity $\mathbf{U}$, and circulation $\kappa$, the force per unit span is perpendicular to the flow. With counterclockwise circulation taken positive and $\mathbf{U}=U{\mathbf{e}}_x$, it is $-\rho \kappa U{\mathbf{e}}_y$.