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Unmanned aerial vehicle

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A RQ-2 Pioneer, a reconnaissance UAV of the Romanian Air Force during the Gulf and Iraq Wars.
A RQ-2 Pioneer, a reconnaissance UAV of the Romanian Air Force during the Gulf and Iraq Wars.

Although most UAVs are fixed-wing aircraft, rotorcraft designs such as this MQ-8B Fire Scout also exist.
Although most UAVs are fixed-wing aircraft, rotorcraft designs such as this MQ-8B Fire Scout also exist.

A MQ-9 Reaper, a hunter-killer surveillance UAV used by the United States Armed Forces and British Armed Forces, especially in Iraq and Afghanistan.
A MQ-9 Reaper, a hunter-killer surveillance UAV used by the United States Armed Forces and British Armed Forces, especially in Iraq and Afghanistan.

An unmanned aerial vehicle (UAV), commonly referred to as a drone is a remotely piloted aircraft. UAVs come in two varieties: some are controlled from a remote location, and others fly autonomously based on pre-programmed flight plans using more complex dynamic automation systems. Currently, UAVs perform reconnaissance as well as attack missions. While many successful drone attacks on militants have been reported, they also "often kill civilians."

UAVs are also used in a small but growing number of civil applications, such as firefighting. 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.

Front view of a MQ-1 Predator (Reno Air Show)
Front view of a MQ-1 Predator (Reno Air Show)

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, UAVs 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.

UAV classification

Luna X 2000 UAV of the German Army
Luna X 2000 UAV of the German Army

The Mexican UAV S4 Ehécatl in take-off mode
The Mexican UAV S4 Ehécatl in take-off mode

UAVs typically fall into one of six functional categories (although multi-role airframe platforms are becoming more prevalent):

  • Target and decoy - providing ground and aerial gunnery a target that simulates an enemy aircraft or missile
  • Reconnaissance - providing battlefield intelligence
  • Combat - providing attack capability for high-risk missions (see Unmanned combat air vehicle)
  • Logistics - UAVs specifically designed for cargo and logistics operation
  • Research and development - used to further develop UAV technologies to be integrated into field deployed UAV aircraft
  • Civil and Commercial UAVs - UAVs specifically designed for civil and commercial applications

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:

  • Handheld 2,000 ft (600 m) altitude, about 2 km range
  • Close 5,000 ft (1,500 m) altitude, up to 10 km range
  • NATO type 10,000 ft (3,000 m) altitude, up to 50 km range
  • Tactical 18,000 ft (5,500 m) altitude, about 160 km range
  • MALE (medium altitude, long endurance) up to 30,000 ft (9,000 m) and range over 200 km
  • HALE (high altitude, long endurance) over 30,000 ft and indefinite range
  • HYPERSONIC high-speed, supersonic (Mach 1-5) or hypersonic (Mach 5+) 50,000 ft (15,200 m) or suborbital altitude, range over 200km
  • ORBITAL low earth orbit (Mach 25+)
  • CIS Lunar Earth-Moon transfer

A computer simulation of Train Cable UAV (TCUAV)
A computer simulation of Train Cable UAV (TCUAV)

Additional category can be applied in pattern of function: fixed routes vs. dynamically variable routes:

The U.S. military employs a tier system for categorizing its UAVs.

U.S. military UAV classifications

The modern concept of U.S. military UAVs is to have the various aircraft systems work together in support of personnel on the ground. The integration scheme is described in terms of a "Tier" system, and is used by military planners to designate the various individual aircraft elements in an overall usage plan for integrated operations. The Tiers do not refer to specific models of aircraft, but rather roles for which various models and their manufacturers competed. The U.S. Air Force and the U.S. Marine Corps each has its own tier system, and the two systems are themselves not integrated.

US Air Force tiers

  • Tier N/A: Small/Micro UAV. Role filled by BATMAV (Wasp Block III). [1]
  • Tier I: Low altitude, long endurance. Role filled by the Gnat 750.
  • Tier II: Medium altitude, long endurance (MALE). Role currently filled by the MQ-1 Predator and MQ-9 Reaper.
  • Tier II+: High altitude, long endurance conventional UAV (or HALE UAV). Altitude: 60,000 to 65,000 feet (19,800 m), less than 300 knots (560 km/h) airspeed, 3,000-nautical-mile (6,000 km) radius, 24 hour time-on-station capability. Complementary to the Tier III- aircraft. Role currently filled by the RQ-4 Global Hawk.
  • Tier III-: High altitude, long endurance low-observable UAV. Same parameters as, and complementary to, the Tier II+ aircraft. The RQ-3 DarkStar was originally intended to fulfill this role before it was "terminated."

US Marine Corps tiers

  • Tier N/A: Micro UAV. Wasp III fills this role, driven largely by the desire for commonality with the USAF BATMAV. [2]
  • Tier I: Role currently filled by the Dragon Eye but all ongoing and future procurement for the Dragon Eye program is going now to the RQ-11B Raven B.
  • Tier II: Role currently filled by the ScanEagle and, to some extent, the RQ-2 Pioneer.
  • Tier III: For two decades, the role of medium range tactical UAV was filled by the Pioneer UAV. In July 2007, the Marine Corps announced its intention to retire the aging Pioneer fleet and transition to the Shadow Tactical Unmanned Aircraft System by AAI Corporation. The first Marine Shadow systems have already been delivered, and training for their respective Marine Corps units is underway.

U.S. Army tiers

Future Combat Systems (FCS) (U.S. Army) classes

  • Class I: For small units. Role to be filled by all new UAV with some similarity to Micro Air Vehicle.
  • Class II: For companies. (cancelled.) [3]
  • Class III: For battalions. (cancelled.) [4]
  • Class IV: For brigades. Role to be filled by the RQ-8A/B / MQ-8B Fire Scout.

Unmanned aircraft system

UAS, or unmanned aircraft system, is the official U.S. Department of Defense term for an unmanned aerial vehicle. Initially coined by the Navy to reflect the fact that these complex systems include ground stations and other elements besides the actual aircraft, the term was first officially used in the DoD 2005 Unmanned Aircraft System Roadmap 2005–2030. Many people have mistakenly used the term Unmanned Aerial System, or Unmanned Air Vehicle System, as these designations were in provisional use at one time or another. The official acronym 'UAS' is not widely used outside military circles, however, as the term UAV has become part of the modern lexicon.

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, in which they are organized under Task Force Liberty in Afghanistan and Task Force ODIN in Iraq. 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.

UAV functions

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.

Remote sensing

A Bell Eagle Eye, used by the US Coast Guard
A Bell Eagle Eye, used by the US Coast Guard

The RQ-7 Shadow is capable of delivering a 20-lb.
The RQ-7 Shadow is capable of delivering a 20-lb. "Quick-MEDS" canister to front-line troops.

Malazgirt VTOL Mini Unmanned System operated by Turkish Armed Forces
Malazgirt VTOL Mini Unmanned System operated by Turkish Armed Forces

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.

Scientific research

Unmanned aircraft are uniquely capable of penetrating areas which may be too dangerous for piloted craft. The National Oceanic and Atmospheric Administration (NOAA) began utilizing the Aerosonde unmanned aircraft system in 2006 as a hurricane hunter. AAI Corporation subsidiary Aerosonde Pty Ltd. of Victoria (Australia), designs and manufactures the 35-pound system, which can fly into a hurricane and communicate near-real-time data directly to the National Hurricane Center in Florida. Beyond the standard barometric pressure and temperature data typically culled from manned hurricane hunters, the Aerosonde system provides measurements far closer to the water’s surface than previously captured. Further applications for unmanned aircraft can be explored once solutions have been developed for their accommodation within national airspace, an issue currently under discussion by the Federal Aviation Administration.

Precision strikes

See also: Unmanned Combat Aerial Vehicle

Rear view of a MQ-1 Predator (Reno Air Show)
Rear view of a MQ-1 Predator (Reno Air Show)

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 an unmanned vehicle, 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.

Search and rescue

UAVs will likely play an increased role in search and rescue in the United States. This was demonstrated by the successful use of UAVs during the 2008 hurricanes that struck Louisiana and Texas.

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.

Design and development considerations

UAV design and production is a global activity, with manufacturers all across the world. The United States and Israel were initial pioneers in this technology, and U.S. manufacturers have a market share of over 60% in 2006, with U.S. market share due to increase by 5-10% through 2016. Northrop Grumman and General Atomics are the dominant manufacturers in this industry, on the strength of the Global Hawk and Predator/Mariner systems. Israeli and European manufacturers form a second tier due to lower indigenous investments, and the governments of those nations have initiatives to acquire U.S. systems due to higher levels of capability. European market share represented just 4% of global revenue in 2006.

Degree of autonomy

UAV monitoring and control at CBP
UAV monitoring and control at CBP

HiMAT Remote Cockpit Synthetic Vision Display (Photo: NASA 1984)
HiMAT Remote Cockpit Synthetic Vision Display (Photo: NASA 1984)

Early UAVs used during the Vietnam War after launch captured video that was recorded to film or tape on the aircraft. These aircraft often were launched and flew either in a straight line or in preset circles collecting video until they ran out of fuel and landed. After landing, the film was recovered for analysis. Because of the simple nature of these aircraft, they were often called drones. As new radio frequencies gained more available, UAVs were often remote controlled and the term "remotely piloted vehicle" came into vogue. Today's UAVs often combine remote control and computerized automation. 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. In news and other discussions, often the term "drone" is still mistakenly used to refer to these more sophisticated aircraft.

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:

  • Sensor fusion: Combining information from different sensors for use on board the vehicle
  • Communications: Handling communication and coordination between multiple agents in the presence of incomplete and imperfect information
  • Path planning: Determining an optimal path for vehicle to go while meeting certain objectives and mission constraints, such as obstacles or fuel requirements
  • Trajectory Generation (sometimes called Motion planning): Determining an optimal control maneuver to take to follow a given path or to go from one location to another
  • Trajectory Regulation: The specific control strategies required to constrain a vehicle within some tolerance to a trajectory
  • Task Allocation and Scheduling: Determining the optimal distribution of tasks amongst a group of agents, with time and equipment constraints
  • Cooperative Tactics: Formulating an optimal sequence and spatial distribution of activities between agents in order to maximize chance of success in any given mission scenario

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.


RQ-4 Global Hawk, a high-altitude reconnaissance UAV capable of 36 hours continuous flight time
RQ-4 Global Hawk, a high-altitude reconnaissance UAV capable of 36 hours continuous flight time

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 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.

Notable high endurance flights
UAV Flight time Date Notes
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

TAM-5 FAQ page

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

Seattle Museum of Flight

Vulture(UAV) Has not flown. Potential endurance 5 years  ? A DARPA project - Vulture - The Unmanned Aircraft Able to Stay in the Air for 5 Years

Existing UAV systems

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

Other information

See also

External links

History & Articles
Organizations and current news

Text from Wikipedia is available under the Creative Commons Attribution/Share-Alike License; additional terms may apply.

Published - July 2009

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