A. James Clark School of Engineering

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The collections in this community comprise faculty research works, as well as graduate theses and dissertations.

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    Modeling and System Identification of an Ornithopter Flight Dynamics Model
    (2012) Grauer, Jared; Hubbard, Jr., James E; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Ornithopters are robotic flight vehicles that employ flapping wings to generate lift and thrust forces in a manner that mimics avian flyers. At the small scales and Reynolds numbers currently under investigation for miniature aircraft, where viscous effects deteriorate the performance of conventional aircraft, ornithopters achieve efficient flight by exploiting unsteady aerodynamic flow fields, making them well-suited for a variety of unmanned vehicle applications. Parsimonous dynamic models of these systems are requisite to augment stability and design autopilots for autonomous operation; however, flapping flight is fundamentally different than other means of engineered flight and requires a new standard model for describing the flight dynamics. This dissertation presents an investigation into the flight mechanics of an ornithopter and develops a dynamical model suitable for autopilot design for this class of system. A 1.22 m wing span ornithopter test vehicle was used to experimentally investigate flapping wing flight. Flight data, recorded in trimmed straight and level mean flight using a custom avionics package, reported pitch rates and heave accelerations up to 5.62 rad/s and 46.1 m/s^2 in amplitude. Computer modeling of the vehicle geometry revealed a 0.03 m shift in the center of mass, up to a 53.6% change in the moments of inertia, and the generation of significant inertial forces. These findings justified a nonlinear multibody model of the vehicle dynamics, which was derived using the Boltzmann-Hamel equations. Models for the actuator dynamics, tail aerodynamics, and wing aerodynamics, difficult to obtain from first principles, were determined using system identification techniques with experimental data. A full nonlinear flight dynamics model was developed and coded in both MATLAB and FORTRAN programming languages. An optimization technique is introduced to find trim solutions, which are defined as limit cycle oscillations in the state space. Numerical linearization about straight and level mean flight resulted in both a canonical time-invariant model and a time-periodic model. The time-invariant model exhibited an unstable spiral mode, stable roll mode, stable dutch roll mode, a stable short period mode, and an unstable short period mode. Floquet analysis on the identified time-periodic model resulted in an equivalent time-invariant model having an unstable second order and two stable first order modes, in both the longitudinal and lateral dynamics.
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    DESIGN, ANALYSIS, AND TESTING OF A FLAPPING WING MINIATURE AIR VEHICLE
    (2010) Gerdes, John William; Gupta, Satyandra K; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Flapping wing miniature air vehicles (MAVs) offer several advantageous performance benefits, relative to fixed-wing and rotary-wing MAVs. The goal of this thesis is to design a flapping wing MAV that achieves improved performance by focusing on the flapping mechanism and the spar arrangement in the wings. Two variations of the flapping mechanism are designed and tested, both using compliance as a technique for improved functionality. In the design of these mechanisms, kinematics and dynamics simulation is used to evaluate how forces encountered during wing flapping affect the mechanism. Finite element analysis is used to evaluate the stress and deformation of the mechanism, such that a lightweight yet functional design can be realized. The wings are tested using experimental techniques. These techniques include high speed photography, stiffness measurement, and lift and thrust measurements. Experimentally measured force results are validated with a series of flight tests. A framework for iterative improvement of the MAV is described, that uses the results of physical testing and simulations to investigate the underlying causes of MAV performance aspects; and seeks to capture those beneficial aspects that will allow for performance improvements. Wings and flapping mechanisms designed in this thesis are used to realize a bird-inspired flapping wing miniature air vehicle. This vehicle is capable of radio controlled flights indoors and outdoors in winds up to 6.7m/s with controlled steering, ascent, and descent, as well as payload carrying abilities.