Introduction to UAV Systems. Mohammad H. Sadraey

comprised of two chapters, 1 and 2.

      Chapter 1 presents a brief history of UAVs. It then identifies and describes the functions of the major elements (subsystems) that may be present in a generic UAS. Finally, it provides a short history of a major UAV development program that failed to produce a fielded UAS, despite significant success in many of the individual subsystems, and teaches useful lessons about the importance of understanding the inter‐relationship and interactions of the subsystems of the UAS and the implications of system performance requirements at a total‐systems level. This story is told here to emphasize the importance of the word “system” in the terms “UAV System” and “UAS.”

      Chapter 2 contains a survey of UAS that have been or presently are in use and discusses various schemes that are used to classify UAV systems according to their size, endurance, and/or mission. The information in this chapter is subject to becoming dated because the technology of many of the subsystems of a UAS is evolving rapidly as they become more and more part of the mainstream after many years of being on the fringes of the aeronautical engineering world. Nonetheless, some feeling for the wide variety of UAS concepts and types is needed to put the later discussion of design and system integration issues into context. Currently about 100 countries are employing military drones.

1 History and Overview

      1.1 Overview

      The first portion of the chapter reviews the history of UAV systems from the earliest and crudest “flying objects” through the events of the last decade, which has been a momentous period for UAV systems.

      The second portion of the chapter describes the subsystems that comprise a complete UAV system configuration to provide a framework for the subsequent treatment of the various individual technologies that contribute to a complete UAS. The air vehicle itself is a complicated system including structures, aerodynamic elements (wings and control surfaces), propulsion systems, and control systems. The complete system includes, in addition, sensors and other payloads, communication packages, and launch and recovery subsystems.

      Finally, a cautionary tale is presented to illustrate why it is important to consider the UAV system as a whole rather than to concentrate only on individual components and subsystems. This is the story of a UAS that was developed between about 1975 and 1985 and that may be the most ambitious attempt at completeness, from a system standpoint, that has so far been undertaken in the UAS community.

      It included every key UAS element in a totally self‐contained form, all designed from scratch to work together as a portable system that required no local infrastructure beyond a relatively small open field in which a catapult launcher and a net recovery system could be located. This system, called the Aquila remotely piloted vehicle (RPV) system, was developed and tested over a period of about a decade at a cost that approached a billion dollars. It eventually could meet most of its operational requirements.

      The Aquila UAS turned out to be very expensive and required a large convoy of 5‐ton trucks for transportation. Most importantly, it did not fully meet some unrealistic expectations that had been built up over the decade during which it was being developed. It was never put in production or fielded. Nonetheless, it remains the only UAS of which the authors are aware that attempted to be complete unto itself and it is worth understanding what that ambition implied and how it drove costs and complexity in a way that eventually led the system to be abandoned in favor of less complete, self‐sufficient, and capable UAV systems that cost less and required less ground support equipment.

1.2 History

      1.2.1 Early History

      Throughout their history, UAV systems have tended to be driven by military applications, as is true of many areas of technology, with civilian applications tending to follow once the development and testing had been accomplished in the military arena.

      One could say that the first UAV was a stone thrown by a caveman in prehistoric times or perhaps a Chinese rocket launched in the thirteenth century. These “vehicles” had little or no control and essentially followed a ballistic trajectory. If we restrict ourselves to vehicles that generate aerodynamic lift and/or have a modicum of control, the kite would probably fit the definition of the first UAV.

      In 1883, an Englishman named Douglas Archibald attached an anemometer to the line of a kite and measured wind velocity at altitudes up to 1,200 ft. Mr. Archibald attached cameras to kites in 1887, providing one of the world’s first reconnaissance UAVs. William Eddy took hundreds of photographs from kites during the Spanish–American war, which may have been one of the first uses of UAVs in combat.

      It was not until World War I, however, that UAVs became recognized systems. Charles Kettering (of General Motors fame) developed a biplane UAV for the Army Signal Corps. It took about 3 years to develop and was called the Kettering Aerial Torpedo, but is better known as the “Kettering Bug” or just plain “Bug.” The Bug could fly nearly 40 mi at 55 mi/h and carry 180 lb of high explosives. The air vehicle was guided to the target by pre‐set controls and had detachable wings that were released when over the target, allowing the fuselage to plunge to the ground as a bomb. Also, in 1917, Lawrence Sperry developed a UAV, similar to Kettering’s, for the Navy, called the Sperry‐Curtis Aerial Torpedo. It made several successful flights out of Sperry’s Long Island airfield, but was not used in the war.

      We often hear of the UAV pioneers who developed the early aircraft, but other pioneers were instrumental in inventing or developing important parts of the system. One was Archibald Montgomery Low, who developed data links. Professor Low, born in England in 1888, was known as the “Father of Radio Guidance Systems.” He developed the first data link and solved interference problems caused by the UAV engine. His first UAVs crashed, but on September 3, 1924, he made the world’s first successful radio‐controlled flight. He was a prolific writer and inventor and died in 1956.

      In 1933, the British flew three refurbished Fairey Queen biplanes by remote control from a ship. Two crashed, but the third flew successfully, making Great Britain the first country to fully appreciate the value of UAVs, especially after they decided to use one as a target and couldn’t shoot it down.

      In 1937 another Englishman, Reginald Leigh Denny, and two Americans, Walter Righter and Kenneth Case, developed a series of UAVs called RP‐1, RP‐2, RP‐3, and RP‐4. They formed a company in 1939 called the Radioplane Company, which later became part of the Northrop‐Ventura Division. Radioplane built thousands of target drones during World War II. (One of their early assemblers was Norma Jean Daugherty, later known as Marilyn Monroe.) Of course, the Germans used lethal UAVs (V‐1’s and V‐2’s) during the later years of the war, but it was not until the Vietnam War era that UAVs were successfully used for reconnaissance.

      1.2.2 The Vietnam War

      The first real use of UAVs by the United States in a combat reconnaissance role began during the Vietnam War. UAVs, such as the AQM‐34 Firebee developed by Teledyne Ryan, were used for a wide range of missions, such as intelligence gathering, decoys, and leaflet dropping.

During the Vietnam War era, UAVs were used extensively in combat, but for reconnaissance missions only. The air vehicles were usually air launched from C‐130’s and recovered by parachute. The air vehicles were what might be called deep penetrators and were developed from existing target drones.

      The impetus to operations in Southeast Asia came from activities during the Cuban Missile Crisis when UAVs were developed for reconnaissance but not used because the crisis ended before they became available. One of the first contracts was between Ryan and the Air Force, known as 147A, for vehicles based on the Ryan Firebee target drone (stretched versions). This was in 1962 and they were called Fireflys. Although the Fireflys were not operational during the Cuban crisis, they set the stage for Vietnam.