What is unmanned aerial vehicle (UAV) ?

An unmanned aerial vehicle (UAV), commonly known as a drone, is an aircraft without a human pilot aboard. UAVs are a component of an unmanned aircraft system (UAS); which include a UAV, a ground-based controller, and a system of communications between the two. The flight of UAVs may operate with various degrees of autonomy: either under remote control by a human operator or autonomously by onboard computers.

Compared to manned aircraft, UAVs were originally used for missions too "dull, dirty or dangerous"  for humans. While they originated mostly in military applications, their use is rapidly expanding to commercial, scientific, recreational, agricultural, and other applications, such as policing, peacekeeping,  and surveillance, product deliveries, aerial photography, agriculture, smuggling,  and drone racing. Civilian UAVs now vastly outnumber military UAVs, with estimates of over a million sold by 2015, so they can be seen as an early commercial application of Autonomous Things, to be followed by the autonomous car and home robots.

Terminology

Multiple terms are used for unmanned aerial vehicles, which generally refer to the same concept.

The term drone, more widely used by the public, was coined in reference to the resemblance of the sound, of navigation and loud-and-regular motor of old military unmanned aircraft, to the male bee. The term has encountered strong opposition from aviation professionals and government regulators.

The term unmanned aircraft system (UAS) was adopted by the United States Department of Defense (DoD) and the United States Federal Aviation Administration in 2005 according to their Unmanned Aircraft System Roadmap 2005–2030.  The International Civil Aviation Organization (ICAO) and the British Civil Aviation Authority adopted this term, also used in the European Union's Single-European-Sky (SES) Air-Traffic-Management (ATM) Research (SESAR Joint Undertaking) roadmap for 2020.  This term emphasizes the importance of elements other than the aircraft. It includes elements such as ground control stations, data links and other support equipment. A similar term is an unmanned-aircraft vehicle system (UAVS) remotely piloted aerial vehicle (RPAV), remotely piloted aircraft system (RPAS).  Many similar terms are in use.

A UAV is defined as a "powered, aerial vehicle that does not carry a human operator, uses aerodynamic forces to provide vehicle lift, can fly autonomously or be piloted remotely, can be expendable or recoverable, and can carry a lethal or nonlethal payload".  Therefore, missiles are not considered UAVs because the vehicle itself is a weapon that is not reused, though it is also unmanned and in some cases remotely guided.

The relation of UAVs to remote controlled model aircraft is unclear.[citation needed] UAVs may or may not include model aircraft. Some jurisdictions base their definition on size or weight, however, the US Federal Aviation Administration defines any unmanned flying craft as a UAV regardless of size. For recreational uses, a drone (as apposed to a UAV) is a model aircraft that has first person video, autonomous capabilities or both.

Classification

Although most UAVs are fixed-wing aircraft, rotorcraft designs (i.e., RUAVs) such as this MQ-8B Fire Scout are also used.

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 aerial vehicle)
Logistics – delivering cargo
Research and development – improve UAV technologies
Civil and commercial UAVs – agriculture, aerial photography, data collection

The U.S. Military UAV tier system is used by military planners to designate the various individual aircraft elements in an overall usage plan.

Vehicles can be categorised in terms of range/altitude. The following has been advanced[by whom?] as relevant at industry events such as ParcAberporth Unmanned Systems forum:
Hand-held 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
High-Altitude Long Endurance (high altitude, long endurance – HALE) over 30,000 ft (9,100 m) 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 200 km
Orbital low earth orbit (Mach 25+)
CIS Lunar Earth-Moon transfer
Computer Assisted Carrier Guidance System (CACGS) for UAVs

Other categories include:

Hobbyist UAVs – which can be further divided into
Ready-to-fly (RTF)/Commercial-off-the-shelf (COTS)
Bind-and-fly (BNF) – that require minimum knowledge to fly the platform
Almost-ready-to-fly (ARF)/Do-it-yourself (DIY) – that require significant knowledge to get in the air.
Midsize military and commercial UAVs
Large military-specific UAVs
Stealth combat UAVs

Classifications according to aircraft weight are quite simpler:

Micro air vehicle (MAV) – the smallest UAVs that can weight less than 1g.
Miniature UAV (also called SUAS) – approximately less than 25 kg.
Heavier UAVs.

UAV components

Manned and unmanned aircraft of the same type generally have recognizably similar physical components. The main exceptions are the cockpit and environmental control system or life support systems. Some UAVs carry payloads (such as a camera) that weigh considerably less than an adult human, and as a result can be considerably smaller. Though they carry heavy payloads, weaponized military UAVs are lighter than their manned counterparts with comparable armaments.

Small civilian UAVs have no life-critical systems, and can thus be built out of lighter but less sturdy materials and shapes, and can use less robustly tested electronic control systems. For small UAVs, the quadcopter design has become popular, though this layout is rarely used for manned aircraft. Miniaturization means that less-powerful propulsion technologies can be used that are not feasible for manned aircraft, such as small electric motors and batteries.

Control systems for UAVs are often different than manned craft. For remote human control, a camera and video link almost always replace the cockpit windows; radio-transmitted digital commands replace physical cockpit controls. Autopilot software is used on both manned and unmanned aircraft, with varying feature sets.

Body

The primary difference for planes is the absence of the cockpit area and its windows. Tailless quadcopters are a common form factor for rotary wing UAVs while tailed mono- and bi-copters are common for manned platforms.

Power supply and platform
Small UAVs mostly use lithium-polymer batteries (Li-Po), while larger vehicles rely on conventional airplane engines.

Battery elimination circuitry (BEC) is used to centralize power distribution and often harbors a microcontroller unit (MCU). Costlier switching BECs diminish heating on the platform.

Computing

UAV computing capability followed the advances of computing technology, beginning with analog controls and evolving into microcontrollers, then system-on-a-chip (SOC) and single-board computers (SBC).

System hardware for small UAVs is often called the Flight Controller (FC), Flight Controller Board (FCB) or Autopilot.

Sensors
Position and movement sensors give information about the aircraft state. Exteroceptive sensors deal with external information like distance measurements, while exproprioceptive ones correlate internal and external states.

Non-cooperative sensors are able to detect targets autonomously so they are used for separation assurance and collision avoidance.

Degrees of freedom (DOF) refer to both the amount and quality of sensors on-board: 6 DOF implies 3-axis gyroscopes and accelerometers (a typical inertial measurement unit – IMU), 9 DOF refers to an IMU plus a compass, 10 DOF adds a barometer and 11 DOF usually adds a GPS receiver.

Actuators

UAV actuators include digital electronic speed controllers (which control the RPM of the motors) linked to motors/engines and propellers, servomotors (for planes and helicopters mostly), weapons, payload actuators, LEDs and speakers.

Software

UAV software called the flight stack or autopilot. UAVs are real-time systems that require rapid response to changing sensor data. Examples include Raspberry Pis, Beagleboards, etc. shielded with NavIO, PXFMini, etc. or designed from scratch such as Nuttx, preemptive-RT Linux, Xenomai, Orocos-Robot Operating System or DDS-ROS 2.0.