Aerospace Engineering Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2737
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Item SYSTEM IDENTIFICATION OF A MULTI-ROTOR VEHICLE WITH ACTIVE FEEDBACK CONTROL(2020) Cunningham, Michael A; Hubbard Jr., James E; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)As multi-rotor vehicles become integrated into the national airspace for applications such as package delivery and videography, it is important that the inner-loop control system be robust and able to meet ever-demanding performance constraints. To achieve high bandwidth control designs, it is necessary to have accurate and high bandwidth open-loop models. The material covered in this dissertation was aimed towards the flight-based identification and comprehensive understanding of the open-loop dynamics and aerodynamics of a multi-rotor vehicle despite the active feedback control system. The analytical first principles modeling and the discussion of system identification techniques informed the process for identifying the unstable multi-rotor dynamics. The inherently unstable nature of the vehicle, combined with the available measurements, necessitated a methodical approach towards identification from flight experiments. The non-negligible issue of unstable system identification was addressed by both the experiment design and the applied estimation technique. An individual propulsion system was tested on a hover stand to understand both the static and dynamic behavior of the combined propeller, motor, and electronic speed controller system. The results of the ground experiments influenced the design of the flight experiments, the postulation of the models, and the understanding of the estimated model parameters. The methodology for flight-based multi-rotor system identification involved the combined application of manual pilot inputs and automated multi-sine inputs added to the output of the controller. A series of five main flight tests were conducted for the identification of a high bandwidth open-loop linear rigid body model and two aerodynamic models of a multi-rotor vehicle. The comparison of the linear rigid body model with the two aerodynamics models emphasized the clear and substantial importance of the nonlinear rigid body coupling terms even in operations near hover. The relative improvement from the linear model to the application of the aerodynamics models to the nonlinear rigid body dynamics was considerable for the translational dynamics, yet the linear model was similarly applicable to the rotational dynamics in aggressive flight near hover.Item Aerodynamic Analysis and Simulation of a Twin-Tail Tilt-Duct Unmanned Aerial Vehicle(2010) Abdollahi, Cyrus; Humbert, James S; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The tilt-duct vertical takeoff and landing (VTOL) concept has been around since the early 1960s; however, to date the design has never passed the research and development phase. Nearly 50 years later, American Dynamics Flight Systems (ADFS) is developing the AD-150, a 2,250lb weight class unmanned aerial vehicle (UAV) configured with rotating ducts on each wingtip. Unlike its predecessor, the Doak VZ-4, the AD-150 features a V tail and wing sweep- both of which affect the aerodynamic behavior of the aircraft. Because no aircraft of this type has been built and tested, vital aerodynamic research was conducted on the bare airframe behavior (without wingtip ducts). Two weeks of static and dynamic test were performed on a 3/10th scale model at the University of Maryland's 7'x10' low speed wind tunnel to facilitate the construction of a nonlinear flight simulator. A total of 70 dynamic tests were performed to obtain damping parameter estimates using the ordinary least squares methodology. Validation, based on agreement between static and dynamic estimates of the pitch and yaw stiffness terms, showed an average percent error of 14.0% and 39.6%, respectively. These inconsistencies were attributed to: large dynamic displacements not encountered during static testing, regressor collinearity, and, while not conclusively proven, dierences in static and dynamic boundary layer development. Overall, the damping estimates were consistent and repeatable, with low scatter over a 95% confidence interval. Finally, a basic open loop simulation was executed to demonstrate the instability of the aircraft. As a result, it is recommended that future work be performed to determine trim points and linear models for controls development.Item Stability and Control Modeling of Tiltrotor Aircraft(2007-06-05) Kleinhesselink, Kristi; Celi, Roberto; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This thesis develops a simple open-source model of a tiltrotor using the basic equations of motion. The model focused on stability and control aspects of the XV-15 aircraft using simple linear analysis and, in general, did not add in correction or scaling factors to obtain a better match with flight data. Subsequent analysis performed included a trim and time history solution. A linearized state space model was also developed and analyzed using state space matrices, Bode plots, and eigenvalue analysis. The results were validated against generic tiltrotor simulation model results and compared to flight test where available. The model resulted in was able to show inherent tiltrotor characteristics, however, further model refinements are needed. Helicopter and airplane mode flight data was used for comparisons. In order to make a true assessment of how well a simple model can approximate a tiltrotor, comparison with conversion mode flight data is required.