Fundamentals of Small Unmanned Aircraft Flight

132 INTRODUCTION Small unmanned aircraft systems (UASs) have become a mainstay in current military operations, providing combat troops and decision makers with vital intelligence, surveillance, and reconnaissance (ISR). A UAS, also dubbed an unmanned aerial vehicle (UAV) or drone, is a reusable aircraft that typically uses onboard sensors and processing to estimate its current kinematic state and automatically control its flight. UASs come in many different shapes and sizes and have been used in a variety of military and civilian applications including ISR, search and rescue, and atmospheric research.1, 2 The purpose of this article is to explore the fundamentals of state estimation and flight control on small (<20 lb) fixedwing UASs. Although dealing primarily with small fixedwing aircraft, much of the information discussed in this article can be applied to other sizes and types of UASs. Leveraging advances in sensor, processing, and battery technologies over the past decade, small UASs are a combination of sophisticated electronics and hobby remote-controlled (R/C) airplane components. The small UAS airframe might be specially designed or converted from a hobby R/C airplane, and it might use a battery-powered electric motor or a gas engine for powered flight. Typical small fixed-wing UASs, such as those shown in Fig. 1, can be hand-launched or launched with the assistance of a bungee or pneumatic launch device and might fly for 20–90 min at flight speeds between 10 and 50 m/s. Although capable of flying at much higher altitudes, small UASs will generally be flown between 30 and 400 m above ground level. The purpose of a UAS, of course, is to fly a payload, with the most common payload being a fixed or gimbaled video camera. Using ecause of advances in sensor, processing, and battery technologies over the past decade, unmanned aircraft systems (UASs) have become both smaller and more affordable. In particular, readily available low-weight, low-power, low-cost sensors based on microelectromechanical systems technology have facilitated the development of UAS autopilots for military and civil use, academic research, and recreation. The purpose of this article is to explore the fundamentals of state estimation and flight control for small fixed-wing UASs. The article covers the common sensors and sensor configurations used on small UASs for state estimation and, in general terms, the algorithms used to control UAS flight. Fundamentals of Small Unmanned Aircraft Flight