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| March 8, 2010
From Take-off to Landing, NRL First in U.S. History to Remotely Fly Pilotless Aircraft
By Daniel Parry
Unmanned Aerial Vehicles, or UAVs as they are commonly known, are ostensibly becoming a greater force in today's military arsenal of reconnaissance and weaponry. Although the concept of using, manned, aerial platforms as a device of military strategy is many centuries old, the ability to fly an unmanned, full-size, powered aircraft remotely from the ground and return it safely to its departure point has very much been a facet of the latter portion of this most recent century.
As early as World War I (1914-1918), the U.S. military began to experiment with unmanned aircraft as the need for a more safe aircraft coincided the need for a more stable aircraft. Merely 10 years after the Wright brothers first flew in 1903, aviation entrepreneur and inventor, Lawrence B. Sperry, building on the auspicious gyro-compass developed by his father, Elmer Sperry, stunned civilian and military spectators at the 1914 Airplane Safety Competition (Concours de la Securité en Aéroplane) held in France. During a low-altitude pass, Sperry and his assistant, Emil Cachin, had climbed onto the wings of the aircraft to demonstrate the enormously safe and stable operation of what became the modern day autopilot.
Several years after this perilous display, Sperry continued to work with the U.S. Army Air Service toward the development of a pilotless, gyro-stabilized aircraft capable of full, unmanned flight for the purpose of delivering explosive ordnance over enemy lines without imperiling military aviators. In 1920, the Army, also working with inventor Charles Kettering on a similar vehicle the Kettering Bug, contracted with Sperry to build a small number of his lightweight Sperry aircraft, known as Sperry Messengers, solely for this purpose. The Army named these aircraft the Messenger Aerial Torpedo (MAT), a crude precursor to the cruise missile, and began field test trials to determine the accuracy and feasibility of this novel machine.
Flying with a safety pilot on-board for observation, the drone aircraft proved capable of short distance accuracy, but failed the Army requirements for greater distance navigation and accuracy due to the inability to correct for unpredictable wind direction and velocity. Sperry devised a solution that included adding radio operated controls to the aircraft and began working with engineers at the Army's Air Service's Radio Section. With the assistance of a controlling aircraft flying close by, the Sperry MATs successfully and with considerable accuracy were able to reach their targets and return. However, the addition of a manned controlling aircraft flying within a mile of the drone proved impractical and unsatisfactory to meet the original specific design and contracted goals of the Army. With interest waning and the untimely and unrelated death of Lawrence Sperry in 1923 the decision was made a few years later to abandon the project.
Sperry's innovation and forward thinking did not fully go without recognition. The U.S. Navy, having a similar interest in work being conducted by the Army, requisitioned a modified Curtiss N-9H floatplane from the project in 1920. The N-9H aircraft, a model already in-use by the U.S. Navy, were used in the latter part of testing by the Army due to their increased stability and load carrying capabilities and were being housed at the Navy Proving Ground, Dahlgren, Va.
After considerable delay and skepticism that the pilotless aircraft would ever become a formidable military component, a board assembled by the Chief of Naval Operations, Rear Admiral Robert E. Coontz, made recommendation to the Secretary of the Navy, The Honorable Josephus Daniels, that further development of radio controlled flights conducted by the Army and Sperry could be made possible through research being developed by the Bureau of Engineering under the direction of Albert Hoyt Taylor at the Naval Aircraft Radio Laboratory at Anacostia. Taylor, best known for his later work in the development of modern day radar, had been assigned radio engineer Carlos B. (C.B.) Mirick and under the supervision of the Bureau of Ordnance were sent to Dahlgren in 1922 to begin retrofitting the acquired Curtiss aircraft for pilotless radio controlled flight.
No stranger to the concept of unmanned navigation, Carl Norden, a former partner of Elmer and Lawrence Sperry and inventor of the flywheel catapult used in the Army's experiments with Sperry's aircraft, was called upon to assist the team assembled at Dahlgren. Building on the success of the gyro-stabilizer he helped develop at Sperry Aircraft, Norden continued to improve and modify automated control systems for aircraft (Norden later developed the historically significant Norden bombsight used extensively during World War II) and after review from the Dahlgren team the Norden automatic pilot system was selected for the tests.
Mirick, experienced with the engineering challenges of aircraft radio—later developing a patented shielding design for electrical interference in aircraft—was delegated the responsibility of developing the radio control system to be mated to the Norden controls. In July 1923, now under the control of the newly created Naval Research Laboratory (NRL) in Washington, D.C., installation of the radio equipment including a Morkum teletype operating on Baudot code, a continuous wave transmitter, an amplified receiver and numerous electrical relays and other ancillary components developed at the Naval Aircraft Radio Laboratory and NRL were completed and tested.
By November 1923, 33 radio-controlled flights had been successfully flown from a ground-based command post while naval aviator Lieutenant John J. Ballentine, who's Naval career later included advancement to Vice Admiral and Commander of the Sixth Fleet, Atlantic and Mediterranean, flew on-board as an observing safety pilot. The latter flight, performed before senior officials of the Navy's Bureau of Ordnance, successfully executed 16 radio-controlled commands, actuating elevator, aileron and rudder and throttle controls during 25 minutes of radio-controlled flight. Although the flight proved mostly successful, an attempt at a fully unmanned flight was postponed for nearly a year.
With the additional down time, Mirick and scientists at the Aircraft Radio Section of the Naval Research Laboratory captured the opportunity to modify and improve electronic circuits, components and necessary radio equipment and to aid in retrofitting additional aircraft for unmanned testing and potential in-air control from an observing aircraft should interruption of radio commands from the ground deem necessary.
On September 15, 1924, following two flawless radio-controlled manned flights, the craft was beached allowing Lt. Ballentine to exit. With a bag of sand for weight distribution in his place, the single, 150-horsepower, Hispano-Suiza engine was started and the pilotless plane taxied onto the Potomac for its maiden unmanned flight.
After a successful departure, the plane was put through its paces for the duration of the 40-minute flight. Executing all but one of the 50 radio-transmitted commands, a right-turn, the plane was safely returned to Dahlgren and guided to a ceremonious landing. For the first time in U.S. history a pilotless aircraft had been flown from take-off through full flight maneuvers and returned for landing solely by ground-based radio control. Encapsulated by the shroud of secrecy covering warfare research and unbeknownst to the researchers at NRL and the Navy Bureau of Ordnance and Bureau of Engineering, the British had successfully enjoyed a similar accomplishment just 12 days earlier.
Following the success of pilotless flight, the equipment was transferred to newer Vought built seaplanes and testing resumed the following summer. With nearly 30 successful radio-controlled flights being conducted with a safety pilot onboard, an attempt to again fly fully unmanned was made December 1925. Unfortunately, radio commands sent through the Baudot device led to jerky control inputs resulting in the craft porpoising on take-off, crashing and eventually sinking. Although scientists at NRL were developing improved radio equipment and a less complex joystick type controller, interest in the program began to wane and the project eventually mothballed.
For nearly a decade, research involving pilotless aircraft at NRL remained dormant. The program was revived in the middle 1930s as the need to develop a more suitable and realistic aerial target was recognized to adequately train Navy antiaircraft gunners. With aircraft design and development assigned to the Naval Bureau of Aeronautics and Bureau of Engineering, NRL was given the responsibility to develop the radio control system to fully operate aircraft control surfaces and throttle. In 1937, the NRL system was first used in remotely operated Navy target aircraft, more formatively recognized as target drones, improving accuracy and revealing an additional need for an improved tracking and targeting system.
Unmanned Aerial Vehicles perform a wide range of missions and are used by all four branches of the military. They range from large vehicles that can carry offensive weapons to miniature systems that are light and compact enough to be carried in a soldier's backpack. The Naval Research Laboratory has been developing small UAV technologies and mission demonstrators since 1975. The modern propeller driven UAV is developed to complement current military and intelligence systems by performing missions that are too monotonous, dangerous or expensive for existing manned, and in some applications, other larger unmanned platforms.
Today, NRL continues to be at the forefront of UAV technology. November 2009, NRL researchers, through sponsorship of the Office of Naval Research and with a team from Protonex Technology Corporation, the University of Hawaii and HyperComp Engineering, demonstrated the endurance breaking Ion Tiger hydrogen fuel cell UAV. The craft shattered all previous endurance records performed by similar, propeller driven, fossil fuel and battery-powered UAVs by completing an uninterrupted 26-hour flight carrying a five-pound payload.
More information concerning UAVs and the Ion Tiger can be found on the Internet at nrl.navy.mil or by search term Unmanned Aerial Vehicles.
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