Nonlinear Dynamical Modeling of a High Altitude Long Endurance Unmanned Aerial Vehicle Ilhan Tuzcu 1 Department of Mechanical Engineering California State University Sacramento, CA 95819 Pier Marzocca 2 Department of Mechanical and Aeronautical Engineering Clarkson University, CAMP 234 Potsdam, NY 13699-5725 Kahtan Awni 3 Global Hawk Program Northrop Grumman Edwards, CA Abstract This paper aims to address dynamics of High-Altitude-Long-Endurance (HALE) Unmanned Aerial Vehicles (UAVs). A comprehensive formulation is first derived that accounts for both rigid-body and elastic degrees of freedom, as well as nonlinear structural effects. The resulting equations are used to design a open-loop control that will steer the aircraft to follow a desired maneuver. Aircraft stability on the flight path is addressed by linearizing the equations by means of a perturbation approach and solving the corresponding eigenvalue problem. Numerical results are given for an aircraft in steady level flight. The model developed is also compared to the other available aircraft models. I. Introduction High-Altitude-Long-Endurance (HALE) Unmanned Aerial Vehicles (UAVs) are becoming widely used. These UAVs are expected to maintain flights at stratospheric atmosphere with altitudes varying from 17 to 25 km and to stay aloft for a long duration of time. Possible areas of their use vary from surveillance to telecommunications. There have been several designs of solar-powered HALE UAVs in the past years. Worth to mention are the NASA’s Pathfinder, Pathfinder Plus, and Helios, whose wing spans range from 30.2 m to 75.3 m, 1,2 , and also the recent effort by Boeing to develop a fuel cell powered HALE-UAV. There are also a number of European Union projects directed toward developing effective, safe, and reliable HALE-UAVs. Among them, it is worth to mention the Politecnico di Torino projects: HELIPLAT, a project to design a solar-powered HALE for telecommunication and earth observation applications; a stratospheric platforms HELINET project, an Heliplat Network concept for traffic monitoring, environmental surveillance and broadband services; the project CAPECON; 3 and UAVNET, a Civilian UAV thematic network. More recently, a blended wing body (BWB) solar aircraft with multi payload and operation capabilities (SHAMPO) was developed by the same research group. 4,5 Due to their performance requirements, the HALE UAVs usually need to be lightweight and capable of carrying a considerable amount of nonstructural weight. For low drag, they usually need to have high aspect ratio. Moreover, safety margins for unmanned aircraft are not as high as those for manned aircraft. All these clearly imply that most of the HALE UAVs are highly flexible with very low structural frequencies, perhaps in the order of frequencies involved in flight dynamics. Hence, the frequency separation between the elastic and rigid body dynamics of the aircraft no longer exists implying that a unified approach accounting for both rigid body and elastic motions must be used. Also, for control design, it is important to use an accurate aircraft model 1 Assistant Professor, AIAA Senior Member, Corresponding Author 2 Associate Professor, AIAA Senior Member 3 Flight Test Engineer 1 50th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference <br>17th 4 - 7 May 2009, Palm Springs, California AIAA 2009-2404 Copyright © 2009 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.