An unmanned aerial vehicle (UAV) is an unpiloted aircraft. UAVs can be remote controlled or fly autonomously based on pre-programmed flight plans or more complex dynamic automation systems. UAVs are currently used in a number of military roles, including reconnaissance and attack. They are also used in a small but growing number of civil applications such as firefighting when a human observer would be at risk, police observation of civil disturbances and crime scenes, and reconnaissance support in natural disasters. UAVs are often preferred for missions that are too "dull, dirty, or dangerous" for manned aircraft.
There is a wide variety of UAV shapes, sizes, configurations, and characteristics. For the purposes of this article and to distinguish UAVs from missiles, a UAV is defined as capable of controlled, sustained, level flight and powered by a jet or reciprocating engine. Cruise missiles are not classed as UAVs, because, like many other guided missiles, the vehicle itself is a weapon that is not reused, even though it is also unmanned and in some cases remotely guided.
The abbreviation UAV has been expanded in some cases to UAVS (unmanned-aircraft vehicle system). The Federal Aviation Administration has adopted the generic class unmanned aircraft system (UAS) originally introduced by the U.S. Navy to reflect the fact that these are not just aircraft, but systems, including ground stations and other elements.
The earliest UAV was A. M. Low's "Aerial Target" of 1916. A number of remote-controlled airplane advances followed, including the Hewitt-Sperry Automatic Airplane, during and after World War I, including the first scale RPV (Remote Piloted Vehicle), developed by the film star and model airplane enthusiast Reginald Denny in 1935. More were made in the technology rush during the Second World War; these were used both to train antiaircraft gunners and to fly attack missions. Jet engines were applied after WW2, in such types as the Teledyne Ryan Firebee I of 1951, while companies like Beechcraft also got in the game with their Model 1001 for the United States Navy in 1955. Nevertheless, they were little more than remote-controlled airplanes until the Vietnam Era.
With the maturing and miniaturization of applicable technologies as seen in the 1980s and 1990s, interest in UAVs grew within the higher echelons of the US military. UAVs were seen to offer the possibility of cheaper, more capable fighting machines that can be used without risk to aircrews. Initial generations were primarily surveillance aircraft, but some were fitted with weaponry (such as the MQ-1 Predator, which utilized AGM-114 Hellfire air-to-ground missiles). An armed UAV is known as an unmanned combat air vehicle (UCAV).
The near future will likely see unmanned aircraft employed, offensively, for bombing and ground attack. As a tool for search and rescue, UAV's can help find humans lost in the wilderness, trapped in collapsed buildings, or adrift at sea. While air-to-air combat will likely remain the last domain of the human pilot, when unmanned fighter jets do come about, they will enjoy the advantage of almost unlimited immunity to G-force effects.
In the future UAVs will be able to take full advantage of scramjet technology. Today's scramjets, while unmanned, see use only for testing purposes (e.g., NASA X-43A, NASA's Hyper-X scramjet program), but have the potential when developed for combat to out-maneuver even the most experienced pilots.
UAVs typically fall into one of six functional categories (although multi-role airframe platforms are becoming more prevalent):
They can also be categorised in terms of range/altitude and the following has been advanced as relevant at such industry events as ParcAberporth Unmanned Systems forum.
The U.S. military employs a tier system for categorizing its UAVs.
The military role of unmanned aircraft systems is growing at unprecedented rates. In 2005, tactical- and theater-level unmanned aircraft alone had flown over 100,000 flight hours in support of Operation Enduring Freedom and Operation Iraqi Freedom. Rapid advances in technology are enabling more and more capability to be placed on smaller airframes which is spurring a large increase in the number of Small Unmanned Aircraft Systems (SUAS) being deployed on the battlefield. The use of SUAS in combat is so new that no formal DoD wide reporting procedures have been established to track SUAS flight hours. As the capabilities grow for all types of UAS, nations continue to subsidize their research and development leading to further advances enabling them to perform a multitude of missions. UAS no longer only perform intelligence, surveillance, and reconnaissance missions, although this still remains their predominant type. Their roles have expanded to areas including electronic attack, strike missions, suppression and/or destruction of enemy air defense, network node or communications relay, combat search and rescue, and derivations of these themes. These UAS range in cost from a few thousand dollars to tens of millions of dollars, with aircraft ranging from less than one pound to over 40,000 pounds.
UAVs perform a wide variety of functions. The majority of these functions are some form of remote sensing; this is central to the reconnaissance role most UAVs fulfill. Less common UAV functions include interaction and transport.
UAV remote sensing functions include electromagnetic spectrum sensors, biological sensors, and chemical sensors. A UAV's electromagnetic sensors typically include visual spectrum, infrared, or near infrared cameras as well as radar systems. Other electromagnetic wave detectors such as microwave and ultraviolet spectrum sensors may also be used, but are uncommon. Biological sensors are sensors capable of detecting the airborne presence of various microorganisms and other biological factors. Chemical sensors use laser spectroscopy to analyze the concentrations of each element in the air.
UAVs can transport goods using various means based on the configuration of the UAV itself. Most payloads are stored in an internal payload bay somewhere in the airframe. For many helicopter configurations, external payloads can be tethered to the bottom of the airframe. With fixed wing UAVs, payloads can also be attached to the airframe, but aerodynamics of the aircraft with the payload must be assessed. For such situations, payloads are often enclosed in aerodynamic pods for transport.
MQ-1 Predator UAVs armed with Hellfire missiles are now used as platforms for hitting ground targets in sensitive areas. Armed Predators were first used in late 2001 from bases in Pakistan and Uzbekistan, mostly for targeted assassinations inside Afghanistan. Since then, there were several reported cases of such assassinations taking place in Pakistan, this time from Afghan based Predators. The advantage of using a drone, rather than a manned aircraft in such cases, is to avoid a diplomatic embarrassment should the aircraft be shot down and the pilots captured, since the bombings took place in countries deemed friendly and without the official permission of those countries.
A Predator, based in a neighboring Arab country, was used to kill suspected al-Qa'ida terrorists in Yemen on November 3, 2002. This marked the first use of an armed Predator as an attack aircraft outside of a theater of war such as Afghanistan.
For example, Predators, operating between 18,000-29,000 feet above sea level, performed search and rescue and damage assessment. Payloads carried were an optical sensor, (which is a daytime and infra red camera), and a synthetic aperture radar. The Predator's SAR is a sophisticated all-weather sensor capable of providing photographic-like images through clouds, rain or fog, and in daytime or nighttime conditions; all in real-time. A concept of coherent change detection in SAR images allows for exceptional search and rescue ability: photos taken before and after the storm hits are compared and a computer highlights areas of damage.
Some early UAVs are called drones because they are no more sophisticated than a simple radio-controlled aircraft controlled by a human pilot (sometimes called the operator) at all times. More sophisticated versions may have built-in control and/or guidance systems to perform low-level human pilot duties such as speed and flight-path stabilization, and simple prescripted navigation functions such as waypoint following.
From this perspective, most early UAVs are not autonomous at all. In fact, the field of air-vehicle autonomy is a recently emerging field, whose economics is largely driven by the military to develop battle-ready technology. Compared to the manufacturing of UAV flight hardware, the market for autonomy technology is fairly immature and undeveloped. Because of this, autonomy has been and may continue to be the bottleneck for future UAV developments, and the overall value and rate of expansion of the future UAV market could be largely driven by advances to be made in the field of autonomy.
Autonomy technology that is important to UAV development falls under the following categories:
Autonomy is commonly defined as the ability to make decisions without human intervention. To that end, the goal of autonomy is to teach machines to be "smart" and act more like humans. The keen observer may associate this with the development in the field of artificial intelligence made popular in the 1980s and 1990s such as expert systems, neural networks, machine learning, natural language processing, and vision. However, the mode of technological development in the field of autonomy has mostly followed a bottom-up approach, such as hierarchical control systems, and recent advances have been largely driven by the practitioners in the field of control science, not computer science. Similarly, autonomy has been and probably will continue to be considered an extension of the controls field.
To some extent, the ultimate goal in the development of autonomy technology is to replace the human pilot. It remains to be seen whether future developments of autonomy technology, the perception of the technology, and most importantly, the political climate surrounding the use of such technology, will limit the development and utility of autonomy for UAV applications. Also as a result of this, synthetic vision for piloting has not caught on in the UAV arena as it did with manned aircraft. NASA utilized synthetic vision for test pilots on the HiMAT program in the early 1980s (see photo), but the advent of more autonomous UAV autopilots, greatly reduced the need for this technology.
Interoperable UAV technologies became essential as systems proved their mettle in military operations, taking on tasks too challenging or dangerous for warfighters. NATO addressed the need for commonality through STANAG (Standardization Agreement) 4586. According to a NATO press release, the agreement began the ratification process in 1992. Its goal was to allow allied nations to easily share information obtained from unmanned aircraft through common ground control station technology. STANAG 4586 - aircraft that adhere to this protocol are equipped to translate information into standardized message formats; likewise, information received from other compliant aircraft can be transferred into vehicle-specific messaging formats for seamless interoperability. Amendments have since been made to the original agreement, based on expert feedback from the field and an industry panel known as the Custodian Support Team. Edition Two of STANAG 4586 is currently under review. There are many systems available today that are developed in accordance with STANAG 4586, including products by industry leaders such as AAI Corporation, CDL Systems, and Raytheon, all three of which are members of the Custodian Support Team for this protocol.
Because UAVs are not burdened with the physiological limitations of human pilots, they can be designed for maximized on-station times. The maximum flight duration of unmanned, aerial vehicles varies widely. Internal-combustion-engine aircraft endurance depends strongly on the percentage of fuel burned as a fraction of total weight (the Breguet endurance equation), and so is largely independent of aircraft size. Solar-electric UAVs hold potential for unlimited flight, a concept originally championed by the Aerovironment Helios Prototype, which unfortunately was destroyed in a 2003 crash. One of the major problems with UAVs is no capability for inflight refuelling. Currently the US Air Force is promoting research that should end in an inflight UAV refueling capability, which should be available by 2010.
The Defense Advanced Research Projects Agency (DARPA) is to sign a contract on building an UAV which should have an enormous endurance capability of about 5 years. The project is entitled "Vulture". The developers are certain neither on the design of the UAV nor on what fuel it should run to be able to stay in air without any maintenance for such a long period of time.
|QinetiQ Zephyr Solar Electric||82 hours 37 minutes||28-31 July 2008||QinetiQ press release|
|Boeing Condor||58 hours, 11 minutes||?||The aircraft is currently in the Hiller Aviation Museum, CA. Hiller Aviation Museum reference to the flight|
|QinetiQ Zephyr Solar Electric||54 hours||September 2007||QinetiQ press release New Scientist article|
|IAI Heron||52 hours||?||NOVA PBS TV program reference IAI reference|
|AC Propulsion Solar Electric||48 hours, 11 minutes||June 3, 2005||AC Propulsion release describing the flight|
|MQ-1 Predator||40 hours, 5 minutes||?||UAV Forum reference Federation of American Scientists reference|
|GNAT-750||40 hours||1992||Directory of US Military Rockets and Missiles reference to the flight UAV Endurance Prehistory reference|
|TAM-5||38 hours, 52 minutes||August 11, 2003||Smallest UAV to cross the Atlantic TAM Homepage|
|Aerosonde||38 hours, 48 minutes||May 3, 2006||Aerosonde release on the flight|
|I-GNAT||38 hours, landed with 10-hour reserve||?||General Atomics reference to the flight|
|RQ-4 Global Hawk||36 hours||?||Space Daily story on the flight RAND Corporation report|
|Aerosonde "Laima"||26 hours, 45 minutes||August 21, 1998||First UAV to cross the Atlantic Aerosonde Laima page|
|TIHA (Turkish MALE Unmanned Aerial Vehicle)||24 hours||Prototypes: 24 December 2004 Serial Production: To be complete by 2010||TIHA Program Turkish Aerospace Industries UAV Products|
|Vulture||Has not flown. Potential endurance 5 years||?||A DARPA project - Vulture - The Unmanned Aircraft Able to Stay in the Air for 5 Years|
UAVs have been developed and deployed by many countries around the world. For a list of models by country, see: List of unmanned aerial vehicles