1GLOBAL NONLINEAR PARAMETRIC MODELING WITH APPLICATION TO F-16 AERODYNAMICS

A global nonlinear parametric modeling technique is described and demonstrated. The technique uses multivariate orthogonal modeling functions generated from the data to determine nonlinear model structure, then expands each retained modeling function into an ordinary multivariate polynomial. The final model form is a finite multivariate power series expansion for the dependent variable in terms of the independent variables. Partial derivatives of the identified models can be used to assemble globally valid linear parameter varying models. The technique is demonstrated by identifying global nonlinear parametric models for nondimensional aerodynamic force and moment coefficients from a subsonic wind tunnel database for the F-16 fighter aircraft. Results show less than 10 % difference between wind tunnel aerodynamic data and the nonlinear parameterized model for a simulated doublet maneuver at moderate angle of attack. Analysis indicated that the global nonlinear parametric models adequately captured the multivariate nonlinear aerodynamic functional dependence. NOMENCLATURE c wing reference chord, ft b wing span, ft Cx, Cy, Cz aerodynamic force coefficients Cl, Cm, Cn aerodynamic moment coefficients p,q, r body axis angular rates, rad/sec PSE predicted squared error V airspeed, ft/sec a angle of attack, rad b sideslip angle, rad δe, δa, δr elevator, aileron, rudder deflections, rad xcg longitudinal c.g. position xcgref reference longitudinal c.g. position = 0.35 1