Extraction of Aerodynamic Parameters for Aircraft at Extreme Flight Conditions

Iliff, Kenneth W. (1985) Extraction of Aerodynamic Parameters for Aircraft at Extreme Flight Conditions. Technical Report NASA TM-86730, Research Engineering, NASA Dryden Flight Research Center.

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Abstract

The maximum likelihood estimator has been used to extract stability and control derivatives from flight data for many years. Most of the literature on aircraft estimation concentrates on new developments and applications, assuming familiarity with basic concepts. This paper briefly discusses the maximum likelihood estimator and the aircraft equations of motion that the estimator uses. The current strength and limitations associated with obtaining flight-determined aerodynamic coefficients in extreme flight conditions is assessed. The importance of the careful combining of wind tunnel results (or calculations) and flight results and the thorough evaluation of the mathematical model is emphasized. The basic concepts of minimization and estimation are examined for a simple computed aircraft example, and the cost functions that are to be minimized during estimation are defined and discussed. Graphic representations of the cost functions are given to help illustrate the minimization process. Finally, the basic concepts are generalized, and estimation of stability and control derivatives from flight data is discussed.

EPrint Type:	NASA Technical Memorandum
Keywords:	Cost functions, Extreme flight conditions, Maximum likelihood, Parameter estimation, Stability and control, System identification
Subjects:	(59 - 67) Mathematical and Computer Sciences: (66) Systems Analysis Aircraft/Project: Nonaircraft-specific
ID Code:	576
Deposited On:	30 January 2006
Additional Information:	24 pages. Prepared as AGARD Paper 24, an invited paper for the AGARD Symposium on Unsteady Aerodynamics - Fundamentals and Applications to Aircraft Dynamics, Gottingen, Federal Republic of Germany, May 6–9, 1985.