Originally Posted by
RetiredF4
In our post stall discussion there are no formulas available to compute lift from drag, because there is no constant behaviour anymore outside the wind tunnel.
indeed there is no way to calculate Lift from drag as Lift is not a function of drag.
What we have are merely datapoints from experiments on given airfoils.
That is everything we have. That said I hope I wasn't unclear when referring to drag acting as lift. That does not mean a mixing of Cl and Cd. They are orthogonal to each other. The trick is the coordinate system. When the aircraft has a high AoA there is an angle between both Cl an Cd and the Airframe itself as Cl and Cd are measured along the stream of air, i.e.the flight path. Wwhereas the moment and its related arm act on the airframe which is angled against these forces.
Lets assume the plane is falling at 90°. In that case it would only be the drag component of the Tail that would lead to ND forces. The Cl compnent would work orthoginally to the flight path, i.e. forward, which would be Nulll in that case.
I hope it gets clearer now what I want to explain.