Unmanned Aeial Vehicles

An unmanned aerial vehicle (UAV) is an aircraft with no onboard pilot. 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 where a human observer would be at risk, police observation of civil disturbances and scenes of crimes, and reconnaissance support in natural disasters.

There are a wide variety UAV shapes, sizes, configurations, and characteristics. For the purposes of this article, and to distinguish UAVs from missiles, a UAV is defined as being 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 might in some cases be remotely guided.

The acronym 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 US Navy to reflect the fact that these are not just aircraft, but systems including ground stations and other elements.

The earliest UAV, the Hewitt-Sperry Automatic Airplane was developed during and after World War I, and a number of advances were made with the technology rush that accompanied the Second World War; these were used both to train anti-aircraft gunners and to fly attack missions. Nevertheless, they were little more than full-sized remote controlled airplanes until the Vietnam era. Lately, with the maturing and miniaturization of applicable technologies, interest in such craft has grown within the higher echelons of the US military, as they offer the possibility of cheaper, more capable fighting machines that can be used without risk to aircrews. Initial generations have primarily been surveillance aircraft, but some have already been fitted with weaponry (such as the MQ-1 Predator, which utilizes AGM-114 Hellfire air-to-ground missiles). The military envisions that more and more roles will be performed by unmanned aircraft, initially bombing and ground attack, with air-to-air combat expected to be the last domain of the fighter pilot for now. An armed UAV is known as an Unmanned Combat Air Vehicle (UCAV). Another area of interest in the field of UAVs is to utilize the aircraft as a search and rescue instrument. Heat sensors could be put in place to help find humans trapped in mountain ranges, collapsed buildings or lost at sea.

UAVs typically fall into one of five 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)
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 2000 ft altitude, about 2 km range
Close 5000 ft altitude, up to 10 km range
NATO type 10,000 ft altitude, up to 50 km range
Tactical 18,000 ft altitude, about 160 km range
MALE (medium altitude, long endurance) up to 30,000 ft and range over 200 km
HALE (high altitude, long endurance) over 30,000 ft and indefinite range

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.[6] Northrop Grumman and General Atomics are the dominant manufacturers in this industry, on the strength of the Global Hawk and Predator/Mariner systems.[6] 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.[6] European market share represented just 4% of global revenue in 2006.[6]

Degree of autonomy

Rear view of a Predator (Reno Air Show)Some early UAVs are called drones because they are no more sophisticated than a simple radio controlled aircraft being 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:

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, 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.

Under the NATO standardization policy 4586 all NATO UAVs will have to be flown using the Tactical Control System (TCS) a system developed by the software company Raytheon.


[edit] Endurance

Border Eagle by Integrated DynamicsBecause 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 the potential for unlimited flight, a concept championed by the Helios Prototype, which unfortunately was destroyed in a 2003 crash. One of the major problems with UAVs currently is that there is no capability for in flight refuelling. Currently the US Air Force is promoting research that should end in a inflight UAV refueling capability, which should be available by 2009.