The notion of airplane stability and control being a balancing act between stability and control has been around as long as aeronautics. The Wright brothers’ first successful flights were born of the debate, and were successful at least in part because they spent considerable time teaching themselves how to control their otherwise unstable airplane. This thesis covers four aspects of handling for large transport aircraft: large size and the accompanying low frequency dynamics, the way in which lifting surfaces and control system elements are modelled in flight dynamics analyses, the cockpit feel characteristics and details of how pilots interact with them, and the dynamic instability associated with Pilot Induced Oscillations. The dynamics associated with large transport aircraft are reviewed from the perspective of pilot-in-the-loop handling qualities, including the effects of relaxing static stability in pursuit of performance. Areas in which current design requirements are incomplete are highlighted. Issues with modelling of dynamic elements which are between the pilot’s fingers and the airplane response are illuminated and recommendations are made. Cockpit feel characteristics are examined in detail, in particular, the nonlinear elements of friction and breakout forces. Three piloted simulation experiments are described and the results reviewed. Each was very different in nature, and all were designed to evaluate linear and nonlinear elements of the cockpit feel characteristics from the pilot’s point of view. These included understanding the pilot’s ability to precisely control the manipulator itself, the pilot’s ability to command the flight path, and neuro-muscular modelling to gain a deeper understanding of the range of characteristics pilots can adapt to and why. Based on the data collected and analyzed, conclusions are drawn and recommendations are made. Finally, a novel and unique PIO prediction criterion is developed, which is based on control-theoretic constructs. This criterion identifies unique signatures in the dynamic response of the airplane to predict the onset of instability.

We have simulated the behavior of several artificial flies, interacting visually with each other. Each fly is described by a simple tracking system (Poggio and Reichardt, 1973; Land and Collett, 1974) which summarizes behavioral experiments in which individual flies fixate a target. Our main finding is that the interaction of theses implemodules gives rise to a variety of relatively complex behaviors. In particular, we observe a swarm-like behavior of a group of many artificial flies for certain reasonable ranges of our tracking system parameters.

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The highly flexible HALE (High Altitude Long Endurance) aircraft analysis methodology is of interest because early studies indicated that HALE aircraft might have different vibration and aeroelastic characteristics from those of conventional aircraft. Recently the computer code Nonlinear Aeroelastic Trim And Stability of HALE Aircraft (NATASHA) was developed and used to the flight dynamics and aeroelastic analysis of flying wing HALE aircraft. Further analysis improvements were required to extend its capability to the ground vibration test (GVT) environment and to both GVT and aeroelastic behavior of HALE aircraft with other configurations. First, the geometrically exact fully intrinsic beam theory was extended to treat other aircraft configurations modeled as an assembly of beam elements. It includes auxiliary elevator input in the horizontal tail and fuselage aerodynamics. Second, the methodology was extended to treat the GVT environment to provide modal characteristics for model validation. A newly developed bungee formulation is coupled to the intrinsic beam formulation for the GVT modeling. After the coupling procedures, the whole formulation cannot be fully intrinsic because the geometric constraint by bungee cords makes the system statically indeterminant. Third, because many HALE aircraft are propeller driven, the methodology was extended to include an engine/nacelle/propeller system using a two-degree-of-freedom model. This step was undertaken to predict a dynamic instability called ``whirl flutter," which can be exhibited in such HALE aircrafts. For simplicity, two fundamental assumptions are made: constant approximation on the propeller aerodynamics and the use of equivalent three-bladed counterpart for two-bladed propeller system to obviate the need for Floquet theory. The validity of these assumptions is verified by investigating the periodic effect of side forces and hub moments and the periodic inertia effect. Finally, parametric studies show how the current methodology can be utilized as a unified preliminary analysis tool for the vibration and aeroelastic analysis of highly flexible HALE aircraft.

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<p>  </p> <p>In this work, a conceptual design of a new configuration for a vertical take-off and landing (VTOL) unmanned aerial vehicle (UAV) or drone, with three distinct flight modes (cruise, hover, and transition), is proposed. The drone is sized to meet mission objectives typical for a search and rescue operation and modelled in Surfaces, an aircraft modelling software, to validate its sizing and compute its stability/aerodynamic coefficients. A 3D model of the drone during the different flight modes is generated in Catia V5 and a nonlinear mathematical model of the drone in cruise mode (forward flight) is determined using Newton’s laws. A linearized model of the drone in forward flight is derived from the nonlinear model, about a trim altitude, and its flying qualities assessed. The inherent transient behavior of the drone is improved by implementing a stability augmentation system or feedback loop. Four autopilot systems are designed and tested on the linear drone model and finally implemented on the nonlinear model. The nonlinear model of the drone and autopilots are tested by simulating the flight of the drone through a set of lateral waypoints, representing victims in need of emergency assistance in a search and rescue mission. </p> <p><br></p>

As the necessity of sustainable mobility rises, the demand to reduce the environmental impact of transporting mediums increases. The SUGAR Truss-Braced Wing (TBW) aircraft is a venture of Boeing, NASA and Virginia Tech for the N+3 generation of aircraft. These high-aspect-ratio aircraft are being designed with the aim to improve the structural and aerodynamic performance by implementing advanced technologies. Aerodynamics is a major factor influencing the performance of the aircraft, affecting the fuel consumption and emissions, especially due to drag. The multidisciplinary design optimization architecture for truss-braced-wing aircraft is dedicated to generate configurations with low fuel burn, maximum weight carrying capabilities and aircraft stability for long and medium range missions. The incorporation of flight dynamics at the conceptual design stage offers enhanced aerodynamic performance and wing flexibility for the aircraft. A robust flight dynamic system would need a detailed aerodynamic analysis of the aircraft with the focus on aeroelasticity. In this thesis, various aerodynamic coefficients and stability derivatives are investigated by applying Vortex-Lattice Method using OpenVSP, an open-source platform. The variation in aerodynamic parameters with changes in configurations and flow conditions are discussed as well. OpenVSP allows for study of these results with low computational expense. This will aid in efficient aerodynamic design and lay basis for flight dynamics analysis and its inclusion in the Multidisciplinary Design Analysis and Optimization (MDAO) framework. / Master of Science / The demand for sustainable mobility and green transportation is increasing. Reduction in the environmental impact of these mediums is the prime motivation for various research studies conducted in this domain. The SUGAR Truss-Braced Wing (TBW) aircraft configuration research, led by Boeing, NASA and Virginia Tech over the last two decades, aims at developing highly fuel-efficient next-generation aircraft. These high-aspect-ratio aircraft are being researched for improving the structural and aerodynamic performance by implementing advanced technologies. Aerodynamic performance of the aircraft influences the fuel consumption and emissions produced drastically. The current design optimization framework for the TBW aircraft focuses on development of these aircraft configurations with the goal to limit fuel burn and maximize payload carrying capability. Flight dynamics analysis can be significant to improve and obtain optimal solutions from the design process. Incorporation of flight dynamics at the conceptual design stage offers enhanced aerodynamic performance and wing flexibility for the next generation aircraft. Therefore, a detailed aerodynamic analysis of the aircraft would be needed to establish a systematic flight dynamics module. This thesis presents a new approach for formulating and analysing the aerodynamic coefficients and stability derivatives by implementing Vortex-Lattice Method available in the open-source software. This will further allow for inclusion of flight dynamics study of the new configurations for long and medium range missions within the existing framework.

High aspect-ratio flying wing configurations designed for high altitude, long endurance missions are characterized by high flexibility, leading to significant static aeroelastic deformation in flight, and coupling between aeroelasticity and flight dynamics. As a result of this coupling, an integrated model of the aeroelasticity and flight dynamics has to be used to accurately model the dynamics of the flexible flying wing. Such an integrated model of the flight dynamics and the aeroelasticity developed by Patil and Hodges is reviewed in this dissertation and is used for studying the unique flight dynamics of high aspect-ratio flexible flying wings. It was found that a rigid body configuration that accounted for the static aeroelastic deformation at trim captured the predominant flight dynamic characteristics shown by the flexible flying wing. Moreover, this rigid body configuration was found to predict the onset of dynamic instability in the flight dynamics seen in the integrated model. Using the concept of the mean axis, a six degree-of-freedom reduced order model of the flight dynamics is constructed that minimizes the coupling between rigid body modes and structural dynamics while accounting for the nonlinear static aeroelastic deformation of the flying wing. Multi-step nonlinear dynamic inversion applied to this reduced order model is coupled with a nonlinear guidance law to design a flight controller for path following. The controls computed by this flight controller are used as inputs to a time-marching simulation of the integrated model of aeroelasticity and flight dynamics. Simulation results presented in this dissertation show that the controller is able to successfully follow both straight line and curved ground paths while maintaining the desired altitude. The controller is also shown to be able to handle an abrupt change in payload mass while path-following. Finally, the equations of motion of the integrated model were non-dimensionalized to identify aeroelastic parameters for optimization and design of high aspect-ratio flying wings. / Ph. D.