Date of Award

Spring 2020

Document Type


Degree Name

Master of Science (MS)


Mechanical & Aerospace Engineering


Aerospace Engineering

Committee Director

Brett Newman

Committee Member

Thomas Alberts

Committee Member

Sebastian Bawab


The aim of this thesis research is to extend the previous work of Tapolcai utilizing nonlinearity index theory to quantitatively analyze nonlinearities in an aircraft model and to augment these undesirable nonlinear characteristics with feedback control. In his work Tapolcai utilized a simplified rotational three degree of freedom model to analyze spin conditions of the F-18 High Angle-of-Attack Research Vehicle model. Through the application of nonlinearity index theory, regions of severe nonlinearity were uncovered exhibiting chaotic non-periodic behavior, periodic limit cycling, and instability. If these conditions were encountered during flight, the aircraft would exhibit undesirable response characteristics thereby requiring augmented control to safely operate. In this research the F-18 model is first implemented with a complete translational and rotational six degree of freedom framework. The trim solution for a steady state spin condition is then determined subject to realizable constraints. The trim equations are then leveraged to create nonlinearity index plots to identify the regions of high nonlinearity that need to be augmented. Nonlinear Dynamic Inversion theory is then employed to design a controller for spin recovery. The effectiveness of the developed controller is confirmed with nonlinear simulations in different spin conditions that were identified from the nonlinearity index analysis.


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