Identification of an Unsteady Aerodynamic Stall Model from Flight Test Data.

An unsteady aerodynamic model for high lift including flow separation and stall is presented. The model provides four parameters and two time constants, which can be identified from suitable flight test data in order t o describe specific stall characteristics. Using this model, lift, drag, and pitching moment are a function of an internal state, namely the position of the flow separation point on the wing surface. This position is formulated as a function of the angle of attack, the angle of attack rate, and the time (first order differential equation). The identifiability of the model parameters and the plausibility of the model structure is discussed using flight test data of C-160 and VFW-614 ATTAS aircraft. Validation plots demonstrate the model accuracy and it can be seen clearly that there are considerable unsteady effects a t high angles of attack caused by flow separation, which cannot be described properly using conventional flight mechanic models.