A Method to Predict Deep Stall

The high angle of attack pitching moment behavior of a conventional airplane depends on the behavior of the wing-fuselage and on that of the horizontal tail. The massive flow separation at high angles of attack can affect the flow over the horizontal tail. With this the effectiveness of the tail for stability and control purposes can reverse or vanish all together. Currently no detailed methods exist for predicting deep stall during preliminary design. This can lead to under sizing or incorrectly positioning the horizontal tail. Often wind tunnel testing is used to discover the problems and to come up with a satisfactory solution. This paper describes the initial investigation into the deep stall problem and how to predict it. A method is developed to estimate whether the horizontal tail will be affected. Methods will be described and compared to wind tunnel data.