Introduction to Unmanned Aircraft
An over-simplistic view of an unmanned aircraft is that it is an aircraft with its aircrew removed and replaced by a computer system and a radio-link. In reality, it is more complex than that, and the aircraft must be properly designed, from the beginning, without aircrew and their accommodation, etc. The aircraft is merely part, albeit an important part, of a total system. The whole system benefits from its being designed, from the start, as a complete system which, briefly comprises:
a) a control station (CS) which houses the system operators, the interfaces between the operators and the rest of the system;
b) the aircraft carrying the payload which may be of many types;
c) the system of communication between the CS which transmits control inputs to the aircraft and returns payload and other data from the aircraft to the CS (this is usually achieved by radio transmission);
d) support equipment which may include maintenance and transport items.
Some Applications of UAS.
Before looking into UAS in more detail, it is appropriate to list some of the uses to which they are, or maybe, put. They are very many, the most obvious being the following:
- Aerial photography – Film, video, still, etc.
- Agriculture – Crop monitoring and spraying; herd monitoring and driving.
- Coastguard Search and rescue, coastline and sea-lane monitoring.
- Conservation – Pollution and land monitoring.
- Customs and Excise – Surveillance for illegal imports.
- Electricity companies – Powerline inspection.
- Fire Services and Forestry – Fire detection, incident control.
- Fisheries – Fisheries protection.
- Gas and oil supply companies – Land survey and pipeline security.
- Information services – News information and pictures, feature pictures, e.g. wildlife.
- Lifeboat Institutions – Incident investigation, guidance, and control.
- Local Authorities – Survey, disaster control
- Meteorological services – Sampling and analysis of atmosphere for forecasting, etc.
- Traffic agencies – Monitoring and control of road traffic
- Oil companies – Pipeline security
- Ordnance Survey – Aerial photography for mapping
- Police Authorities – Search for missing persons, security and incident surveillance
- Rivers Authorities – Water course and level monitoring, flood and pollution control
- Survey organizations – Geographical, geological and archaeological survey
- Water Boards – Reservoir and pipeline monitoring
Shadowing enemy fleets
Decoying missiles by the emission of artificial signatures
Relaying radio signals
Protection of ports from offshore attack
Placement and monitoring of sonar buoys and possibly other forms of anti-submarine warfare
Surveillance of enemy activity
Monitoring of nuclear, biological or chemical (NBC) contamination
Target designation and monitoring
Location and destruction of landmines
- Air Force:
Long-range, high-altitude surveillance
Radar system jamming and destruction
Airfield base security
Airfield damage assessment
Elimination of unexploded bombs
What are UAS?
An unmanned aircraft system is just that – a system. It must always be considered as such. The system comprises a number of sub-systems which include the aircraft (often referred to as a UAV or unmanned air vehicle), its payloads, the control station(s) (and, often, other remote stations), aircraft launch and recovery sub-systems where applicable, support sub-systems, communication sub-systems, transport sub-systems, etc.
It must also be considered as part of a local or global air transport/aviation environment with its rules, regulations, and disciplines. UAS usually have the same elements as systems based upon manned aircraft, but with the airborne element, i.e. the aircraft being designed from its conception to be operated without an aircrew aboard. The aircrew (as a sub-system), with its interfaces with the aircraft controls and its habitation is replaced by an electronic intelligence and control subsystem. The other elements, i.e. launch, landing, recovery, communication, support, etc. have their equivalents in both manned and unmanned systems.
Unmanned aircraft must not be confused with model aircraft or with ‘drones’, as is often done by the media. A radio-controlled model aircraft is used only for sport and must remain within sight of the operator. The operator is usually limited to instructing the aircraft to climb or descend and to turn to the left or to the right.
A drone aircraft will be required to fly out of sight of the operator but has zero intelligence, merely being launched into a pre-programmed mission on a pre-programmed course and a return to base. It does not communicate and the results of the mission, e.g. photographs, are usually not obtained from it until it is recovered at the base. A UAV, on the other hand, will have some greater or lesser degree of ‘automatic intelligence’. It will be able to communicate with its controller and to return payload data such as electro-optic or thermal TV images, together with its primary state information – position, airspeed, heading and altitude. It will also transmit information as to its condition, which is often referred to as ‘housekeeping data’, covering aspects such as the amount of fuel it has, temperatures of components, e.g. engines
If a fault occurs in any of the sub-systems or components, the UAV may be designed automatically to take corrective action and/or alert its operator to the event. In the event, for example, that the radio communication between the operator and the UAV is broken, then the UAV may be programmed to search for the radio beam and re-establish contact or to switch to a different radio frequency band if the radio-link is duplexed.
A more ‘intelligent’ UAV may have further programmes which enable it to respond in an ‘if that happens, do this’ manner. For some systems, attempts are being made to implement onboard decision-making capability using artificial intelligence in order to provide it with the autonomy of operation, as distinct from automatic decision making.
The definition of UAS also excludes missiles (ballistic or homing).
The development and operation of UAS have rapidly expanded as a technology in the last 30 years and, as with many new technologies, the terminology used has changed frequently during that period. The initials RPV (remotely piloted vehicle) were originally used for unmanned aircraft, but with the appearance of systems deploying land-based or underwater vehicles, other acronyms or initials have been adopted to clarify the reference to airborne vehicle systems. These have, in the past, included UMA (unmanned air vehicle), but the initials UAV (unmanned aerial vehicle) are now generally used to denote the aircraft element of the UAS. However, UAV is sometimes interpreted as ‘uninhabited air vehicle’ in order to reflect the situation that the overall system is ‘manned’ in so far as it is not overall exclusively autonomous, but is commanded by a human somewhere in the chain. ‘Uninhabited air vehicle’ is also
seen to be more politically correct! More recently the term UAS (unmanned aircraft system) has been introduced. All of the terms: air vehicle; UAV; UAV systems and UAS will be seen in this volume, as appropriate, since these were the terms in use during its preparation.
Categories of Systems Based upon Air Vehicle Types.
Although all UAV systems have many elements other than the air vehicle, they are usually categorized by the capability or size of the air vehicle that is required to carry out the mission. However, it is possible that one system may employ more than one type of air vehicle to cover different types of mission, and that may pose a problem in its designation. However, these definitions are constantly being changed as technology advances allow a smaller system to take on the roles of the one above. The boundaries,
therefore, are often blurred so that the following definitions can only be approximate and subject to change.
The terms currently in use cover a range of systems, from the HALE with an aircraft of 35 m or greater wingspan, down to the NAV which may be of only 40 mm span.
They are as follows:
- HALE – High altitude long endurance. Over 15 000 m altitude and 24+ hr endurance. They carry out extremely long-range (trans-global) reconnaissance and surveillance and increasingly are being armed. They are usually operated by Air Forces from
- MALE – Medium altitude long endurance. 5000–15000 m altitude and 24 hr endurance. Their roles are similar to the HALE systems but generally operate at somewhat shorter ranges, but still in excess of 500 km. and from fixed bases.
- TUAV – Medium Range or Tactical UAV with a range of order between 100 and 300 km. These air vehicles are smaller and operated within simpler systems than are HALE or MALE and are operated also by land and naval forces.
- Close-Range UAV used by mobile army battle groups, for another military/naval operations, and for diverse civilian purposes. They usually operate at ranges of up to about 100 km and have probably the most prolific of uses in both fields, including roles as diverse as reconnaissance, target designation, NBC monitoring, airfield security, ship-to-shore surveillance, power-line inspection, crop-spraying, and traffic monitoring, etc.
- MUAV or Mini UAV – relates to UAV of below a certain mass (yet to be defined) probably below 20 kg, but not as small as the MAV, capable of being hand-launched and operating at ranges of up to about 30 km. These are, again, used by mobile battle groups and particularly for diverse civilian purposes.
- Micro UAV or MAV. The MAV was originally defined as a UAV having a wing-span no greater than 150 mm. This has now been somewhat relaxed but the MAV is principally required for operations in urban environments, particularly within buildings. It is required to fly slowly, and preferably to hover and to ‘perch’ – i.e. to be able to stop and to sit on a wall or post. To meet this challenge, research is being conducted into some less conventional configurations such as flapping wing aircraft. MAV are generally expected to be launched by hand and therefore winged versions have very low wing loadings which must make them very vulnerable to atmospheric turbulence. All types are likely to have problems in precipitation.
- NAV – Nano Air Vehicles. These are proposed to be of the size of sycamore seeds and used in swarms for purposes such as radar confusion or conceivably, if camera, propulsion and control sub-systems can be made small enough, for ultra-short range surveillance.
Some of these categories – possibly up to the TUAV in size – can be fulfilled using rotary wing aircraft, and are often referred to by the term remotely piloted helicopter (RPH) – see below.
- RPH, remotely piloted helicopter or VTUAV, vertical take-off UAV. If an air vehicle is
capable of vertical take-off it will usually be capable also of a vertical landing, and what can be sometimes of even greater operational importance, hover flight during a mission. Rotary wing aircraft are also less susceptible to air turbulence compared with fixed-wing aircraft of low wing-loading.
- UCAV and UCAR. Development is also proceeding towards specialist armed fixed-wing UAV which may launch weapons or even take part in air-to-air combat. These are given the initials UCAV for the unmanned combat air vehicle. Armed rotorcraft are also in development and these are known as UCAR for Unmanned Combat Rotorcraft.
However, HALE and MALE UAV and TUAV are increasingly being adapted to carry air-to-ground weapons in order to reduce the reaction time for a strike onto a target discovered by their reconnaissance. Therefore these might also be considered as combat UAV when so equipped. Other terms which may sometimes be seen, but are less commonly used today, were related to the radius of action in operation of the various classes. They are:
- Long-range UAV – replaced by HALE and MALE
- Medium-range UAV – replaced by TUAV
- Close-range UAV – often referred to as MUAV or midi-UAV.
Why Unmanned Aircraft?
Unmanned aircraft will only exist if they offer an advantage compared with manned aircraft. An aircraft system is designed from the outset to perform a particular role or roles. The designer must ˆ decide the type of aircraft most suited to perform the role(s) and, in particular, whether the role(s) may be better achieved with a manned or unmanned solution. In other words, it is impossible to conclude that UAVs always have an advantage or disadvantage compared with manned aircraft systems. It depends
vitally on what the task is. An old military adage (which also applies to civilian use) links the use of UAVs to roles which are dull, dirty or dangerous (DDD). There is much truth in that but it does not go far enough. To DDD add covert, diplomatic, research and environmentally critical roles. In addition, the economics of operation is often to the advantage of the UAV.
Military and civilian applications such as extended surveillance can be a dulling experience for aircrew, with many hours spent on a watch without relief, and can lead to a loss of concentration and therefore loss of mission effectiveness. The UAV, with high-resolution color video, low light level TV, thermal imaging cameras or radar scanning, can be more effective as well as cheaper to operate in such roles. The ground-based operators can be readily relieved in a shift-work pattern.
Again, applicable to both civilian and military applications, monitoring the environment for nuclear or chemical contamination puts aircrew unnecessarily at risk. Subsequent detoxification of the aircraft is easier in the case of the UAV. Crop-spraying with toxic chemicals is another dirty role which now is conducted very successfully by UAV.
For military roles, where the reconnaissance of heavily defended areas is necessary, the attrition rate of a manned aircraft is likely to exceed that of a UAV. Due to its smaller size and greater stealth, the UAV is more difficult for an enemy air defense system to detect and more difficult to strike with anti-aircraft fire or missiles. Also, in such operations, the concentration of aircrew upon the task may be compromised by the threat of attack. Loss of the asset is damaging, but equally damaging is the loss of trained aircrew and the political ramifications of capture and subsequent propaganda, as seen in the recent conflicts in the Gulf. The UAV operators are under no personal threat and can concentrate specifically, and therefore more effectively, on the task in hand. The UAV, therefore, offers a greater probability of mission success without the risk of loss of aircrew resource. Power-line inspection and forest fire control are examples of applications in the civilian field for which experience sadly has shown that manned aircraft crew can be in significant danger. UAV can carry out such tasks more readily and without risk to personnel.
Operating in extreme weather conditions is often necessary for both military and civilian fields. Operators will be reluctant to risk personnel and the operation, though necessary, may not be carried out. Such reluctance is less likely to apply with a UAV.
In both military and civilian policing operations, there are roles where it is imperative not to alert the ‘enemy’ (other armed forces or criminals) to the fact that they have been detected. Again, the lower detectable signatures of the UAV (see Chapter 7) make this type of role more readily achievable. Also in this category is the covert surveillance which arguably infringes the airspace of foreign countries in uneasy peacetime. It could be postulated that in examples such as the Gary Powers/U2 aircraft affair of 1960, loss of an aircraft over alien territory could generate less diplomatic embarrassment if no aircrew are involved.
UAVs are being used in research and development work in the aeronautical field. For test purposes, the use of UAV as small-scale replicas of projected civil or military designs of manned aircraft enables airborne testing to be carried out, under realistic conditions, more cheaply and with less hazard. Testing subsequent modifications can also be effected more cheaply and more quickly than for a larger manned aircraft, and without any need for changes to aircrew accommodation or operation. Novel configurations may be used to advantage for the UAV. These configurations may not be suitable
for containing an aircrew.
Environmentally Critical Roles.
This aspect relates predominantly to civilian roles. A UAV will usually cause less environmental disturbance or pollution than a manned aircraft pursuing the same task. It will usually be smaller, of lower mass. Typical of these are the regular inspection of power-lines where local inhabitants may object to the noise produced and where farm animals may suffer disturbance both from the noise and from sighting the low-flying aircraft.
*Learn more about UAVs on the book written by Reg Austin – Unmanned Air Systems, UAV Design, Development, and Deployment.