Experimental Identification of Linear and Nonlinear Dynamic Characteristics of a Foam Aircraft Model for Morphing Applications

Abstract

The genesis of so-called morphing aircraft has been mandated by the need for an expanded flight envelope to fulfill a variety of flight objectives. In order to address the need for expanded flight envelopes, researchers must consider the possibility of dynamic instability due to morphing associated with complex aero-structural interactions during design, development, and flight. The linear and nonlinear dynamic response characteristics of a model aircraft structure are examined in this paper. To identify the linear modal characteristics, impact testing was conducted and the nominal frequency response functions were extracted. Nonlinear characteristics are identified using time-frequency, restoring force, and higher-order frequency response analysis of swept sine response data. The scale-model aircraft with reconfigurable pre-stressed components exhibits strong nonlinearity in the 20-40 Hz frequency range. A cubic stiffness nonlinearity is identified in one portion of the aircraft. In the 40-60 Hz frequency range, stiffness nonlinearities dominate and damping characteristics are primarily linear in nature. Effective characterization of the nonlinearity is a prerequisite for efficient reduced-order models that accurately predict dynamic instability.