Eric E. Fox

Date of Award

12-1990

Document Type

Thesis

Degree Name

Master of Science in Aeronautical Engineering

Department

Department of Aeronautics and Astronautics

First Advisor

J. Planeaux, Captain, USAF

Abstract

Bifurcation analysis was used to investigate the nonlinear behavior of a simple powered lifting hypersonic vehicle in circular orbit about a spherical nonrotating Earth with gradients in atmospheric density and pressure and an inverse square law for gravity. Vehicle motion is constrained to a vertical plane so only longitudinal dynamics were modeled. Bifurcation analysis was conducted using the AUTO software package. A simple five-state model with three different thrust laws was derived to describe an unaugmented vehicle whose geometric and aerodynamic characteristics follow those of the literature. A parameter representing a body flap deflection was used to conduct one set of bifurcation sweeps for each thrust law. A second set of bifurcation sweeps for each thrust law was obtained using a parameter representing a throttle which scaled the thrust. Secondary parameters representing simple feedback gains were subsequently added. Results were surprising for a simple system with basically linear aerodynamics . Periodic branches arising from the loss of pitch stability or associated with a resonance altitude are routinely found with significant amplitude, and periods on the order of an elliptical orbit's period for a given geocentric radius. Rotational states generally had sub-oscillations of greater frequency.

AFIT Designator

AFIT-GAE-ENY-90D-07

DTIC Accession Number

ADA230826

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