Creating a Test-Validated Finite-Element Model of the X-56A Aircraft Structure

Abstract

Small modeling errors in a finite-element model will eventually induce errors in the structural flexibility and mass, thus propagating into unpredictable errors in the unsteady aerodynamics and the control law design. One of the primary objectives of the X-56A Multi-Utility Technology Testbed aircraft is the flight demonstration of active flutter suppression and, therefore, in this study, the identification of the primary and secondary modes for the structural model tuning based on the flutter analysis of the X-56A aircraft. The ground-vibration test-validated structural dynamic finite-element model of the X-56A aircraft is created in this study. The structural dynamic finite-element model of the X-56A aircraft is improved using a model-tuning tool. In this study, two different weight configurations of the X-56A aircraft have been improved in a single optimization run. Frequency and the cross-orthogonality (mode shape) matrix were the primary focus for improvement, whereas other properties such as c.g. location, total weight, and off-diagonal terms of the mass orthogonality matrix were used as constraints. The end result was an improved structural dynamic finite-element model configuration for the X-56A aircraft. Improved frequencies and mode shapes in this study increased average flutter speeds of the X-56A aircraft by 7.6% compared to the baseline model.

Identification of Aeroelastic Models for the X-56A Longitudinal Dynamics Using Multisine Inputs and Output Error in the Frequency Domain

“…As the aircraft burns fuel, its mass properties change, which in turn change the structural vibration modes. A ground vibration test (GVT) was conducted and the FEM was tuned to this data [21]. The first four longitudinal vibration mode shapes that were observable in the flight test data discussed later are shown in Figure 2, where modal displacements are exaggerated for clarity.…”

Jig-Shape Optimization of Low-Boom Supersonic Aircraft

“…In this study, the numerical optimization procedure is performed using the O 3 tool developed at the NASA Armstrong Flight Research Center. This O 3 tool has been successfully applied to structural dynamic model tuning [14], aerodynamic model tuning [15], and multidisciplinary design optimization [16,17] challenges and solutions.…”

Aeroelastic Modeling of X-56A Stiff-Wing Configuration Flight Test Data

“…A FEM, adjusted using data from a ground vibration test (GVT), 3 provided information on the modes that was used in the estimation. Specifically, this information included values of the mode shapes at the sensor locations, frequencies, damping ratios, and generalized masses that were tabulated according to fuel weight.…”