This work presents the open-loop stability analysis and an active control strategy for an airbreathing hypersonic vehicle. The 14-XB, a bidimensional flow airframe derived from the Brazilian 14-X Aerospace Hypersonic Vehicle, is adopted as study platform. In order to perform such analyses, a simulation mathematical model of the airframe longitudinal forces and moments is obtained using perfect gas equations, after considering the relevance of the real gas hypotheses for the expected Mach number range and verifying that the simpler formulation is sufficient. An all-moving horizontal tail is designed in order to enable the aircraft trimming. The horizontal tail design considered simple constraints based on static analysis, and the same gas equations as those used for the airframe study. In order to analyze the aircraft';s dynamic behavior, a Six-Degree-of-Freedom set of equations of motion considering a spherical, rotating Earth is presented in detail, and the necessary conditions to have adequate longitudinal trimming in this scenario are discussed. The open-loop stability of the 14-XB with the designed horizontal tail is assessed through eigenvalue analysis and numerical flight simulations with the horizontal tail fixed at a trim position. Having observed that the aircraft presents unstable long-term natural modes, an active control strategy is suggested in order to stabilize the vehicle and track a desired flight path angle, assuming that thrust is constant and the control surface is an all-moving horizontal tail. The suggested control structure presents pitch stability augmentation system and flight path angle compensator. Optimal gains are calculated using linear quadratic design, along with a gain-scheduling strategy based on simultaneous control design, and the resulting controller presents proper results.

This work is part of the research and development, at the Institute for Advanced Studies (IEAv), of the first Brazilian hypersonic vehicle prototype, the 14-X airplane. As this vehicle will be propelled by scramjet (supersonic combustion ramjet) engines, this work presents detailed two-dimensional CFD analyses of the airflow in the intake system of such engines based on the 14-XB scramjet geometry and the expected flight conditions. The main objective is to study the airflow in the intake of the 14-XB at nominal flight condition and also for some off-design flight conditions and geometry using numerical methods and models available in the Fluent code. Off-design values of the vehicle velocity, angle of attack and altitude as well as of the angle of the inlet compression ramp and the number of inlet compression ramps were chosen to show how these changes impact the overall intake airflow. In this study are presented results for the airflow in the entire intake system and of specific flow variables at the engine combustor entrance, as well as calculation results of some intake performance parameters. Both, wall temperature and free stream flow turbulence effects on the intake airflow have also been analyzed. Investigation of viscous flow modeling and of the effects of temperature-dependent air properties has also been performed. Inviscid flow calculations have been performed to serve as a comparison basis for the viscous flow effects and as preliminary information of the airflow. A model validation analysis of the k-kl-? and Transition SST transition models has shown that both models can calculate BL and shock wave interactions (SWBLI) quite well, although, the k-kl-? is better to calculate the separation region whereas the Transition SST is superior to predict the reattachment point. Wall temperature has shown to affect quite significantly SWBLI while viscous flow modeling has shown to have an important impact on the intake airflow with some degradation of the intake system performance.

Veículos aeroespaciais, voando a grandes velocidades, estão sob o efeito de elevadas cargas térmicas decorrentes da transformação da energia cinética do escoamento em energia térmica, causando um fenômeno conhecido como aquecimento aerodinâmico. O objetivo desta dissertação é, através de uma abordagem analítica do problema, estimar os níveis de fluxo de calor ao qual o Veículo Hipersônico Aeroespacial 14-X S estará sujeito durante o voo atmosférico. O Veículo Hipersônico Aeroespacial 14-X S faz parte de um projeto estratégico do Comando da Aeronáutica que consiste de um demonstrador da tecnologia de um estato-reator a combustão supersônica (scramjet) que está sendo desenvolvido na Divisão de Aerotermodinâmica e Hipersônica, do Instituto de Estudos Avançados (IEAv). Este trabalho apresenta uma revisão bibliográfica dos principais projetos em scramjet desenvolvidos até o momento, além das principais teorias para cálculo de fluxo de calor de veículos em voo. As cargas térmicas são obtidas através de duas modelagens distintas para o ar atmosférico, sendo a primeira como um gás perfeito e a segunda como um gás em equilíbrio termodinâmico. Depois, através do desenvolvimento de sub-rotinas computacionais desenvolvidas em linguagem MATLAB, os fluxos de calor são calculados para as diversas regiões do veículo e em diversas condições de voo simuladas, baseadas na trajetória do Veículo de Sondagem VSB 30. Os resultados foram comparados aos obtidos de projetos similares e também a uma análise preliminar na área de CFD (Computational Fluid Dynamics) apresentando uma relevante concordância.