The Effect of Systematic Error in Forced Oscillation Testing

Abstract

One of the fundamental problems in flight dynamics is the formulation of aerodynamic forces and moments acting on an aircraft in arbitrary motion. Classically, conventional stability derivatives are used for the representation of aerodynamic loads in the aircraft equations of motion. However, for modern aircraft with highly nonlinear and unsteady aerodynamic characteristics undergoing maneuvers at high angle of attack and/or angular rates the conventional stability derivative model is no longer valid. Attempts to formulate aerodynamic model equations with unsteady terms are based on several different wind tunnel techniques: for example, captive, wind tunnel single degree-of-freedom, and wind tunnel free-flying techniques. One of the most common techniques is forced oscillation testing. However, the forced oscillation testing method does not address the systematic and systematic correlation errors from the test apparatus that cause inconsistencies in the measured oscillatory stability derivatives. The primary objective of this study is to identify the possible sources and magnitude of systematic error in representative dynamic test apparatuses. Sensitivities of the longitudinal stability derivatives to systematic errors are computed, using a high fidelity simulation of a forced oscillation test rig, and assessed using both Design of Experiments and Monte Carlo methods. Nomenclature

Nonlinear Unsteady Aerodynamic Modeling Using Wind-Tunnel and Computational Data

“…A number of techniques have been developed to improve modeling of nonlinear unsteady conditions and to take advantage of the integration of CFD, SID, and DOE technologies. In [65] the sensitivities of systematic errors on stability derivatives using a high fidelity simulation of a forced-oscillation test was done using both DOE and Monte Carlo methods. In [21] modeling of a complex aircraft with 23 factors required DOE to allow an efficient and statistically rigorous experiment to be designed.…”