The attitude indicator (AI), formerly known as the gyro horizon or artificial horizon, is a flight instrument that informs the pilot of the aircraft orientation relative to Earth's horizon, and gives an immediate indication of the smallest orientation change. The miniature aircraft and horizon bar mimic the relationship of the aircraft relative to the actual horizon.[1][2] It is a primary instrument for flight in instrument meteorological conditions.[3][4]
AI with pitch and roll reference lines (left) and the AI relationship to aircraft orientation (right)
Attitude is always presented to users in the unit degrees (°). However, inner workings such as sensors, data and calculations may use a mix of degrees and radians, as scientists and engineers may prefer to work with radians.
Before the advent of aviation, artificial horizons were used in celestial navigation. Proposals of such devices based on gyroscopes, or spinning tops, date back to the 1740ies.[5] Later implementations, also known as bubble horizons, were based on bubble levels and attached to a sextant.[6] In the 2010s, remnants of an artifical horizon using liquid mercury were recovered from the wreck of HMS Erebus.[7]
Use
AI interior
The essential components of the AI include a symbolic miniature aircraft mounted so that it appears to be flying relative to the horizon. An adjustment knob, to account for the pilot's line of vision, moves the aircraft up and down to align it against the horizon bar. The top half of the instrument is blue to represent the sky, while the bottom half is brown to represent the ground. The bank index at the top shows the aircraft angle of bank. Reference lines in the middle indicate the degree of pitch, up or down, relative to the horizon.[2][1]
Most Russian-built aircraft have a somewhat different design. The background display is colored as in a Western instrument, but moves up and down only to indicate pitch. A symbol representing the aircraft (which is fixed in a Western instrument) rolls left or right to indicate bank angle.[8] A proposed hybrid version of the Western and Russian systems would be more intuitive, but has never caught on.[9]
Operation
Vacuum system using a vacuum pump
Vacuum system using a venturi
The heart of the AI is a gyroscope (gyro) that spins at high speed, from either an electric motor, or through the action of a stream of air pushing on rotor vanes placed along its periphery. The stream of air is provided by a vacuum system, driven by a vacuum pump, or a venturi. Air passing through the narrowest portion of a venturi has lower air pressure through Bernoulli's Principle. The gyro is mounted in a double gimbal, which allows the aircraft to pitch and roll as the gyro stays vertically upright. A self-erecting mechanism, actuated by gravity, counteracts any precession due to bearing friction. It may take a few minutes for the erecting mechanism to bring the gyros to a vertical upright position after the aircraft engine is first powered up.[2][1][10]
Attitude indicators have mechanisms that keep the instrument level with respect to the direction of gravity.[11] The instrument may develop small errors, in pitch or bank during extended periods of acceleration, deceleration, turns, or due to the earth curving underneath the plane on long trips. To start with, they often have slightly more weight in the bottom, so that when the aircraft is resting on the ground they will hang level and therefore they will be level when started. But once they are started, that pendulous weight in the bottom will not pull them level if they are out of level, but instead its pull will cause the gyro to precess. In order to let the gyro very slowly orient itself to the direction of gravity while in operation, the typical vacuum powered gyro has small pendulums on the rotor casing that partially cover air holes. When the gyro is out of level with respect to the direction of gravity, the pendulums will swing in the direction of gravity and either uncover or cover the holes, such that air is allowed or prevented from jetting out of the holes, and thereby applying a small force to orient the gyro towards the direction of gravity. Electric powered gyros may have different mechanisms to achieve a similar effect.[12]
Older AIs were limited in the amount of pitch or roll that they would tolerate. Exceeding these limits would cause the gyro to tumble as the gyro housing contacted the gimbals, causing a precession force. Preventing this required a caging mechanism to lock the gyro if the pitch exceed 60° and the roll exceeded 100°. Modern AIs do not have this limitation and therefore do not require a caging mechanism.[2][1]
Attitude indicators are also used on crewed spacecraft and are called Flight Director Attitude Indicators (FDAI), where they indicate the craft's yaw angle (nose left or right), pitch (nose up or down), roll, and orbit relative to a fixed-space inertial reference frame from an Inertial Measurement Unit (IMU).[13] The FDAI can be configured to use known positions relative to Earth or the stars, so that the engineers, scientists and astronauts can communicate the relative position, attitude, and orbit of the craft.[14][15]
With most AHRS systems, if an aircraft's AIs have failed there will be a standby AI located in the center of the instrument panel, where other standby basic instruments such as the airspeed indicator and altimeter are also available. These mostly mechanical standby instruments may remain available even if the electronic flight instruments fail, although the standby attitude indicator may be electrically driven and will, after a short time, fail if its electrical power fails.[16]
Attitude Direction Indicator
ADI (left) with yellow V steering bars, and an AI integrated with ILS glide slope and localizer indicators (right)
The Attitude Direction Indicator (ADI), or Flight Director Indicator (FDI), is an AI integrated with a Flight Director System (FDS). The ADI incorporates a computer that receives information from the navigation system, such as the AHRS, and processes this information to provide the pilot with a 3-D flight trajectory cue to maintain a desired path. The cue takes the form of V steering bars. The aircraft is represented by a delta symbol and the pilot flies the aircraft so that the delta symbol is placed within the V steering bars.[1]: 5–23, 5–24
Soviet artificial horizon AGP-2, tilted left, and showing the aircraft nose down and banked to the left. The white "horizon" line always aligns with the wings, not with the horizon seen out of the cockpit
^Jörg F. Wagner: From Bohnenberger's Machine to Integrated Navigation Systems. 200 Years of Inertial Navigation. Photogrammetric Week 05. 2007-07-06 at the Wayback Machine
^I.C.B. Dear, Peter Kemp (ed.): The Oxford Companion to Ships an the Sea, Oxford University Press, 2016, pp. 22, 77
^2015 Artifacts, 2018 Artifacts, Wrecks of HMS Erebus and HMS Terror National Historic Site
^Learmount, David (2009-02-09), , flightglobal.com, archived from the original on October 29, 2014
^. history.nasa.gov. Archived from the original on 2015-12-24. Retrieved 2016-12-01.
^Interbartolo, Michael (January 2009). "Apollo Guidance, Navigation, and Control (GNC) Hardware Overview" (PDF). NASA Technical Reports Server. NASA. Retrieved 12 October 2018.
attitude, indicator, confused, with, altitude, aviation, artificial, horizon, redirects, here, album, artificial, horizon, album, examples, perspective, this, article, represent, worldwide, view, subject, improve, this, article, discuss, issue, talk, page, cre. Not to be confused with Altitude in aviation Artificial Horizon redirects here For the U2 album see Artificial Horizon album The examples and perspective in this article may not represent a worldwide view of the subject You may improve this article discuss the issue on the talk page or create a new article as appropriate December 2018 Learn how and when to remove this template message The attitude indicator AI formerly known as the gyro horizon or artificial horizon is a flight instrument that informs the pilot of the aircraft orientation relative to Earth s horizon and gives an immediate indication of the smallest orientation change The miniature aircraft and horizon bar mimic the relationship of the aircraft relative to the actual horizon 1 2 It is a primary instrument for flight in instrument meteorological conditions 3 4 AI with pitch and roll reference lines left and the AI relationship to aircraft orientation right Attitude is always presented to users in the unit degrees However inner workings such as sensors data and calculations may use a mix of degrees and radians as scientists and engineers may prefer to work with radians Contents 1 History 2 Use 3 Operation 4 Flight Director Attitude Indicator 5 Attitude and Heading Reference Systems 6 Attitude Direction Indicator 7 See also 8 ReferencesHistory EditBefore the advent of aviation artificial horizons were used in celestial navigation Proposals of such devices based on gyroscopes or spinning tops date back to the 1740ies 5 Later implementations also known as bubble horizons were based on bubble levels and attached to a sextant 6 In the 2010s remnants of an artifical horizon using liquid mercury were recovered from the wreck of HMS Erebus 7 Use Edit AI interior The essential components of the AI include a symbolic miniature aircraft mounted so that it appears to be flying relative to the horizon An adjustment knob to account for the pilot s line of vision moves the aircraft up and down to align it against the horizon bar The top half of the instrument is blue to represent the sky while the bottom half is brown to represent the ground The bank index at the top shows the aircraft angle of bank Reference lines in the middle indicate the degree of pitch up or down relative to the horizon 2 1 Most Russian built aircraft have a somewhat different design The background display is colored as in a Western instrument but moves up and down only to indicate pitch A symbol representing the aircraft which is fixed in a Western instrument rolls left or right to indicate bank angle 8 A proposed hybrid version of the Western and Russian systems would be more intuitive but has never caught on 9 Operation Edit Vacuum system using a vacuum pump Vacuum system using a venturi The heart of the AI is a gyroscope gyro that spins at high speed from either an electric motor or through the action of a stream of air pushing on rotor vanes placed along its periphery The stream of air is provided by a vacuum system driven by a vacuum pump or a venturi Air passing through the narrowest portion of a venturi has lower air pressure through Bernoulli s Principle The gyro is mounted in a double gimbal which allows the aircraft to pitch and roll as the gyro stays vertically upright A self erecting mechanism actuated by gravity counteracts any precession due to bearing friction It may take a few minutes for the erecting mechanism to bring the gyros to a vertical upright position after the aircraft engine is first powered up 2 1 10 Attitude indicators have mechanisms that keep the instrument level with respect to the direction of gravity 11 The instrument may develop small errors in pitch or bank during extended periods of acceleration deceleration turns or due to the earth curving underneath the plane on long trips To start with they often have slightly more weight in the bottom so that when the aircraft is resting on the ground they will hang level and therefore they will be level when started But once they are started that pendulous weight in the bottom will not pull them level if they are out of level but instead its pull will cause the gyro to precess In order to let the gyro very slowly orient itself to the direction of gravity while in operation the typical vacuum powered gyro has small pendulums on the rotor casing that partially cover air holes When the gyro is out of level with respect to the direction of gravity the pendulums will swing in the direction of gravity and either uncover or cover the holes such that air is allowed or prevented from jetting out of the holes and thereby applying a small force to orient the gyro towards the direction of gravity Electric powered gyros may have different mechanisms to achieve a similar effect 12 Older AIs were limited in the amount of pitch or roll that they would tolerate Exceeding these limits would cause the gyro to tumble as the gyro housing contacted the gimbals causing a precession force Preventing this required a caging mechanism to lock the gyro if the pitch exceed 60 and the roll exceeded 100 Modern AIs do not have this limitation and therefore do not require a caging mechanism 2 1 Flight Director Attitude Indicator Edit Apollo Flight Director Attitude Indicator left and Inertial Measurement Unit IMU right Attitude indicators are also used on crewed spacecraft and are called Flight Director Attitude Indicators FDAI where they indicate the craft s yaw angle nose left or right pitch nose up or down roll and orbit relative to a fixed space inertial reference frame from an Inertial Measurement Unit IMU 13 The FDAI can be configured to use known positions relative to Earth or the stars so that the engineers scientists and astronauts can communicate the relative position attitude and orbit of the craft 14 15 Attitude and Heading Reference Systems EditAttitude and Heading Reference Systems AHRS are able to provide three axis information based on ring laser gyroscopes that can be shared with multiple devices in the aircraft such as glass cockpit primary flight displays PFDs Rather than using a spinning gyroscope modern AHRS use solid state electronics low cost inertial sensors rate gyros and magnetometers 2 8 20 1 5 22 With most AHRS systems if an aircraft s AIs have failed there will be a standby AI located in the center of the instrument panel where other standby basic instruments such as the airspeed indicator and altimeter are also available These mostly mechanical standby instruments may remain available even if the electronic flight instruments fail although the standby attitude indicator may be electrically driven and will after a short time fail if its electrical power fails 16 Attitude Direction Indicator Edit ADI left with yellow V steering bars and an AI integrated with ILS glide slope and localizer indicators right The Attitude Direction Indicator ADI or Flight Director Indicator FDI is an AI integrated with a Flight Director System FDS The ADI incorporates a computer that receives information from the navigation system such as the AHRS and processes this information to provide the pilot with a 3 D flight trajectory cue to maintain a desired path The cue takes the form of V steering bars The aircraft is represented by a delta symbol and the pilot flies the aircraft so that the delta symbol is placed within the V steering bars 1 5 23 5 24 Soviet artificial horizon AGP 2 tilted left and showing the aircraft nose down and banked to the left The white horizon line always aligns with the wings not with the horizon seen out of the cockpitSee also EditAcronyms and abbreviations in avionics Air India Flight 855 Korean Air Cargo Flight 8509 Peripheral vision horizon display PVHD Turn and slip indicatorReferences Edit a b c d e f Instrument Flying Handbook FAA H 8083 15B PDF U S Dept of Transportation FAA 2012 p 5 17 5 19 a b c d e Pilot s Handbook of Aeronautical Knowledge FAA H 8083 25B PDF U S Dept of Transportation FAA 2016 p 8 16 8 18 8 19 Jeppesen A Boeing Company 2007 Guided Flight Discovery Private PilotJe Jeppesen pp 2 66 ISBN 978 0 88487 429 4 https www faa gov regulations policies handbooks manuals aircraft AMT Handbook Aircraft Instrument Systems page 10 56 Jorg F Wagner From Bohnenberger s Machine to Integrated Navigation Systems 200 Years of Inertial Navigation Photogrammetric Week 05 Archived 2007 07 06 at the Wayback Machine I C B Dear Peter Kemp ed The Oxford Companion to Ships an the Sea Oxford University Press 2016 pp 22 77 2015 Artifacts 2018 Artifacts Wrecks of HMS Erebus and HMS Terror National Historic Site Learmount David 2009 02 09 Which way is up for Eastern and Western artificial horizons flightglobal com archived from the original on October 29 2014 Safety expert proposes low cost loss of control fixes FlightGlobal 2011 03 04 Federal Aviation Administration FAA AMT Handbook Chapter 10 Aircraft Instrument Systems murphy alan 4 4 www faatest com Retrieved 22 March 2018 murphy alan 4 5 www faatest com Retrieved 22 March 2018 Flight Director Atitude sic Indicator www hq nasa gov Retrieved 2016 12 01 Apollo Flight Journal Apollo Operations Handbook Volume 1 history nasa gov Archived from the original on 2015 12 24 Retrieved 2016 12 01 Interbartolo Michael January 2009 Apollo Guidance Navigation and Control GNC Hardware Overview PDF NASA Technical Reports Server NASA Retrieved 12 October 2018 NTSB Safety Recommendation 2010 11 08 Retrieved from https en wikipedia org w index php title Attitude indicator amp oldid 1125534909, wikipedia, wiki, book, books, library,
