An autopilot is a mechanical, electrical, or hydraulic system used to guide a vehicle without assistance from a human being. Most people understand an autopilot to refer specifically to aircraft, but self-steering gear for ships, boats, space craft and missiles is sometimes also called by this term. Self-steering gear is equipment used on ships and boats to maintain a chosen course without constant human action

The autopilot of an aircraft is sometimes referred to as "George"^[1]

Contents 1 First autopilots 2 Modern autopilots 2.1 Computer system details 3 Aviation Autopilot Categories of Landing 4 Notes 5 See also

First autopilots

In the early days of aviation, aircraft required the continuous attention of a pilot in order to fly safely. As aircraft range increased allowing flights of many hours, the constant attention led to serious fatigue. An autopilot is designed to perform some of the tasks of the pilot.

The first aircraft autopilot was developed by Sperry Corporation in 1912. Sperry Corporation (1910-1986 was a major American equipment and Electronics company whose existence spanned more than seven decades of the twentieth century Lawrence Sperry (the son of famous inventor Elmer Sperry) demonstrated it two years later in 1914, and proved the credibility of the invention by flying the aircraft with his hands away from the controls and visible to onlookers. Lawrence Burst Sperry ( December 22, 1892 – December 23, 1923 ? was an aviation pioneer Elmer Ambrose Sperry ( October 12, 1860 – June 16, 1930) was a prolific Inventor and Entrepreneur, most famous as co-inventor

The autopilot connected a gyroscopic Heading indicator and Attitude indicator to hydraulically operated elevators and rudder (ailerons were not connected as wing dihedral was counted upon to produce the necessary roll stability. A gyroscope is a device for measuring or maintaining orientation, based on the principles of Angular momentum. The heading indicator (Directional Gyro or DG) is an instrument used in an Aircraft to inform the pilot of his heading An attitude indicator (ADI also known as gyro horizon or artificial horizon, is an instrument used in an Aircraft to inform Elevators are control surfaces usually at the rear of an Aircraft, which control the aircraft's orientation by changing the pitch of the aircraft and so also A rudder is a device used to steer a Ship, Boat, Submarine, Hovercraft, or other conveyance that move through a fluid (generally air or For the band with a similar name see The Ailerons Ailerons are hinged control surfaces attached to the Trailing edge of the Wing of a Fixed-wing Dihedral is the upward angle from horizontal of the wings or tailpane of a Fixed-wing aircraft or the wing of a Bird. ) It permitted the aircraft to fly straight and level on a compass course without a pilot's attention, greatly reducing the pilot's workload.

In the early 1920s, the Standard Oil tanker J. Standard Oil was a predominant American integrated oil producing transporting refining and marketing company A Moffet became the first ship to use an autopilot.

Modern autopilots

Not all passenger aircraft flying today have an autopilot system. Older and smaller general aviation aircraft especially are still hand-flown, while small airliners with less than twenty seats may also be without an autopilot as they are used on short-duration flights with two pilots. General aviation (abbr GA) is one of two categories of Civil aviation. An airliner is a large Fixed-wing aircraft with the primary function of transporting paying passengers The fitment of autopilots to airliners with more than twenty seats is generally made mandatory by international aviation regulations. There are three levels of control in autopilots for smaller aircraft. A single-axis autopilot controls an aircraft in the roll axis only; such autopilots are also known colloquially as "wing levellers", reflecting their limitations. Flight dynamics is the science of air and space vehicle orientation and control in three dimensions A two-axis autopilot controls an aircraft in the pitch axis as well as roll, and may be little more than a "wing leveller" with limited pitch-oscillation-correcting ability; or it may receive inputs from on-board radio navigation systems to provide true automatic flight guidance once the aircraft has taken off until shortly before landing; or its capabilities may lie somewhere between these two extremes. Flight dynamics is the science of air and space vehicle orientation and control in three dimensions A three-axis autopilot adds control in the yaw axis and is not required in many small aircraft. Flight dynamics is the science of air and space vehicle orientation and control in three dimensions

Autopilots in modern complex aircraft are three-axis and generally divide a flight into taxi, take-off, ascent, level, descent, approach and landing phases. Autopilots exist that automate all of these flight phases except the taxiing. An autopilot-controlled landing on a runway and controlling the aircraft on rollout (i. e. keeping it on the centre of the runway) is known as a CAT IIIb landing or Autoland, available on many major airports' runways today, especially at airports subject to adverse weather phenomena such as fog. Fog is a cloud that is in contact with the ground Stratus clouds are usually the only clouds that touch the ground Landing, rollout and taxi control to the aircraft parking position is known as CAT IIIc. This is not used to date but may be used in the future. Some autopilots incorporate automated collision-avoidance; the most popular collision avoidance for aircraft is called Traffic Collision Avoidance System (TCAS). The Traffic alert and Collision Avoidance System (or TCAS) is an aircraft collision avoidance system designed to reduce the incidence of mid-air collisions between An autopilot is often an integral component of a Flight Management System. A flight management system or FMS is a Computerized Avionics Component found on most commercial and business Aircraft

Modern autopilots use computer software to control the aircraft. A computer is a Machine that manipulates data according to a list of instructions. The software reads the aircraft's current position, and controls a Flight Control System to guide the aircraft. In such a system, besides classic flight controls, many autopilots incorporate thrust control capabilities that can control throttles to optimize the air-speed, and move fuel to different tanks to balance the aircraft in an optimal attitude in the air. Although autopilots handle new or dangerous situations inflexibly, they generally fly an aircraft with a lower fuel-consumption than a human pilot.

The autopilot in a modern large aircraft typically reads its position and the aircraft's attitude from an inertial guidance system. An Inertial Navigation System (INS is a Navigation aid that uses a Computer and motion sensors to continuously track the position orientation and Velocity Inertial guidance systems accumulate errors over time. They will incorporate error reduction systems such as the carousel system that rotates once a minute so that any errors are dissipated in different directions and have an overall nulling effect. Error in gyroscopes is known as drift. This is due to physical properties within the system, be it mechanical or laser guided, that corrupt positional data. The disagreements between the two are resolved with digital signal processing, most often a six-dimensional Kalman filter. Digital signal processing ( DSP) is concerned with the representation of the signals by a sequence of numbers or symbols and the processing of these signals The Kalman filter is an efficient Recursive filter that estimates the state of a Dynamic system from a series of noisy measurements The six dimensions are usually roll, pitch, yaw, altitude, latitude and longitude. Altitude is the Elevation of a point or object from a known level or datum (plural data Latitude, usually denoted symbolically by the Greek letter phi ( Φ) gives the location of a place on Earth (or other planetary body north or south of the Longitude (ˈlɒndʒɪˌtjuːd or ˈlɒŋgɪˌtjuːd symbolized by the Greek character Lambda (λ is the east-west Geographic coordinate measurement Aircraft may fly routes that have a required performance factor, therefore the amount of error or actual performance factor must be monitored in order to fly those particular routes. The longer the flight the more error accumulates within the system. Radio aids such as DME, DME updates and GPS may be used to correct the aircraft position. Basic concept of GPS operation A GPS receiver calculates its position by carefully timing the signals sent by the constellation of GPS Satellites high above the Earth Inertial reference units, i. e. gyroscopes, are the basis of aircraft on-board position determining, as GPS and other radio update systems depend on a third party to supply information. IRU's are completely self-contained and use gravity and earth rotation to determine their initial position (earth rate). They then measure acceleration to calculate where they are in relation to where they were to start with. From acceleration speed can be calculated and from speed distance can be calculated. As long as the direction is known (from accelerometers) the IRU's can determine where they are (software dependent).

Computer system details

The hardware of a typical large aircraft's autopilot is a set of five 80386 CPUs, each on its own printed circuit board. A printed circuit board, or PCB, is used to mechanically support and electrically connect Electronic components using conductive pathways or traces The 80386 is an inexpensive, well-tested design that can implement a true virtual computer. New versions are being implemented that are radiation-resistant, and hardened for aerospace use. Radiation hardening is a method of designing and testing electronic components and systems to make them resistant to damage or malfunctions caused by high-energy Subatomic particles The very old computer design is intentionally favored, because it is inexpensive, and its reliability and software behavior are well-characterized.

The custom operating system provides a virtual machine for each process. An operating system (commonly abbreviated OS and O/S) is the software component of a Computer system that is responsible for the management and coordination In Computer science, a virtual machine (VM is a Software implementation of a machine (computer that executes programs like a real machine In computing a process is an instance of a Computer program that is being sequentially executed by a computer system that has the ability to run several computer This means that the autopilot software never controls the computer's electronics directly. Instead it acts on a software simulation of the electronics. Most invalid software operations on the electronics occur during gross failures. They tend to be obviously incorrect, detected and discarded. In operation, the process is stopped, and restarted from a fresh copy of the software. In testing, such extreme failures are logged by the virtualization, and the engineers use them to correct the software.

Usually, one of the processes on each computer is a low priority process that continually tests the computer.

Generally, every process of the autopilot runs more than two copies, distributed across different computers. The system then votes on the results of those processes. For triple Autoland, this is called camout, and uses median values of autopilot commands versus mechanical centre and feel mechanism positioning as a possible computation. Extreme values are discarded before they can be used to control the aircraft.

Some autopilots also use design diversity. In this safety feature, critical software processes will not only run on separate computers (possibly even using different architectures), but each computer will run software created by different engineering teams, often being programmed in different programming languages. It is generally considered unlikely that different engineering teams will make the same mistakes. As the software becomes more expensive and complex, design diversity is becoming less common because fewer engineering companies can afford it.

Aviation Autopilot Categories of Landing

Instrument-aided landings are defined in categories by the International Civil Aviation Organization. The International Civil Aviation Organization ( ICAO) an agency of the United Nations, codifies the principles and techniques of international air navigation These are dependent upon the required visibility level and the degree to which the landing can be conducted automatically without input by the pilot.

CAT I - This category permits pilots to land with a decision height of 200 ft (61 m) and a forward visibility or Runway Visual Range (RVR) of 2400 ft (730 m). An instrument approach or instrument approach procedure (IAP is a type of Air navigation that allows pilots to land an Aircraft in Simplex autopilots are sufficient.

CAT II - This category permits pilots to land with a decision height between 200 ft and 100 ft (≈ 30 m) and a RVR of 1000 ft (305 m). Autopilots have a fail passive requirement.

CAT IIIa -This category permits pilots to land with a decision height as low as 50 ft (15 m) and a RVR of 700 ft (213 m). It needs a fail-passive autopilot. There must be only a 10^-6 probability of landing outside the prescribed area.

CAT IIIb - As IIIa but with the addition of automatic roll out after touchdown incorporated with the pilot taking control some distance along the runway. This category permits pilots to land with a decision height less than 50 feet or no decision height and a forward visibility of 250 ft (76 m, compare this to aircraft size, some of which are now over 70 m long) or 300 ft (91 m) in the United States. For a landing-without-decision aid, a fail-operational autopilot is needed. For this category some form of runway guidance system is needed: at least fail-passive but it needs to be fail-operational for landing without decision height or for RVR below 375 feet (114 m).

CAT IIIc - As IIIb but without decision height or visibility minimums, also known as "zero-zero". No aircraft is approved for this category. It would necessitate a reliable way for aircraft and ground vehicles to maneuver on the ground without any visual reference.

Fail-passive autopilot: in case of failure, the aircraft stays in a controllable position and the pilot can take control of it to go around or finish landing. It is usually a dual-channel system.

Fail-operational autopilot: in case of a failure below alert height, the approach, flare and landing can still be completed automatically. It is usually a triple-channel system or dual-dual system.

↑ - Patent Storm <http://www.patentstorm.us/patents/5945943-description.html>

Notes

See also

• Gyrocompass
• Driverless car

A gyrocompass is similar to a Gyroscope. It is a Compass that finds True north by using an (electrically powered fast-spinning wheel and friction The driverless car concept embraces an emerging family of highly automated cognitive and control technologies ultimately aimed at a full "taxi-like" experience for car users

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