A STATISTICAL METHOD FOR THE EXTRACTION OF STABILITY PARAMETERS FROM FLIGHT-TEST DATA

摘要

The problem of determining from flight-test data the forces and moments acting on an aircraft is analyzed from a statistical point of view. General expressions containing unknown parameters are assumed giving the forces and moments as functions of the variables that characterize the motion of the aircraft. A new method is developed for evaluating from flight test data these and other parameters (e. g., moments of inertia) in the resulting equations of motion. This method is based on a statistical technique for estimating unknown parameters in probability density functions from samples of observed data. This statistical technique, maximum-likelihood estimation, gives the theoretically "best" estimates for unknown parameters in a wide variety of situations. Approximations are used for the responses as functions of the unknown parameters since these functions cannot usually be evaluated explicitly. The method is thereby made applicable to most aircraft-parameter-determination problems. It is applicable to both linear and nonlinear systems and may be used to determine the value of any parameter occurring linearly in the equations of motion, subject only to limitations preventing the determination of certain parameters by any method. The method can readily be coded for a digital computer, and a possible sequence of computational steps is included in this report. Testing the adequacy of the hypothesis that the assumed functions give the true forces and moments is discussed, and an error analysis is included.