Evaluation of the continued use of an aging variable stability system augmented aircraft for modern flying qualities education

The University of Tennessee Space Institute (UTSI) obtained two fly-by-wire variable stability aircraft from Princeton University in 1991. These modified Navion aircraft contain several modifications to accommodate a response-feedback type of Variable Stability System (VSS). The aircraft were used extensively while owned and operated by Princeton for research projects for the United States Navy and Federal Aviation Administration. In recent years, externally funded research opportunities have been limited and UTSI has utilized the aircraft in support of the University graduate school curriculum. The purpose of this thesis is to evaluate the continued use of these aging variable stability system augmented aircraft for a modem, flying quality curriculum. In order to determine the capabilities of the Navion Variable Stability aircraft as an in-flight simulator and teaching tool, the longitudinal equations of motion and on board Variable Stability System were modeled in the United States Naval Test Pilot School simulation laboratory using Matrix Laboratory (MATLAB) and SIMULINK modeling tools. Characteristic responses of the short period mode of motion were plotted while varying several modeled, in-flight programmable potentiometer settings. Root locus plots were then created to determine the envelope of possible responses for in-flight demonstrations. The flaps and throttle channels were modeled but were not exercised for this evaluation. Analysis of the root locus plot revealed that the Navion is capable of demonstrating a wide range of longitudinal short period characteristics, including unstable conditions. Though this was a limited study, focusing on only the longitudinal short period modes of motion, the aging Navion VSS aircraft shows excellent potential to perform as an in-flight laboratory and demonstration platform in a modem flying qualities curriculum. Additionally, research and development agencies continue to utilize variable stability aircraft for flight control system development. This aircraft possesses great potential for utilization in the professional aerospace industry and should be maintained for use in both educational and research flight activities.