{"id":14490,"date":"2025-06-07T16:21:44","date_gmt":"2025-06-07T10:51:44","guid":{"rendered":"https:\/\/ibexaviation.com\/pilot-training\/?p=14490"},"modified":"2026-07-26T10:32:22","modified_gmt":"2026-07-26T05:02:22","slug":"gyro-magnetic-compass","status":"publish","type":"post","link":"https:\/\/ibexaviation.com\/pilot-training\/gyro-magnetic-compass\/","title":{"rendered":"Gyro Magnetic Compass"},"content":{"rendered":"<p> <img decoding=\"async\" src=\"https:\/\/ibexaviation.com\/page-show\/flight-instruments\/i19-gyro-magnetic-compass-1.jpg\" alt=\"\" loading=\"lazy\"\/><\/p>\n<h2>Direction Measurement using Gyro Magnetic Compass<\/h2>\n<p>A gyro-magnetic compass combines the stability of a gyroscope and accuracy of compass using the Earth\u2019s magnetic field. It reduces errors caused by acceleration, turning and magnetic dip. This makes a  GMC more reliable for maintaining precise heading during flight.<\/p>\n<h3>Introduction to the Gyro Magnetic Compass<\/h3>\n<p> <img decoding=\"async\" src=\"https:\/\/ibexaviation.com\/page-show\/flight-instruments\/i19-gyro-magnetic-compass-2.jpg\" alt=\"\" loading=\"lazy\"\/><\/p>\n<ul>\n<li>A remote-indicating compass reduces many of the limitations of a direct-reading magnetic compass.<\/li>\n<li>It minimises heading errors that occur during aircraft acceleration and turns.<\/li>\n<li>It reduces magnetic deviation caused by locating the sensing element inside the cockpit.<\/li>\n<li>It allows magnetic heading information to be transmitted to other aircraft instruments.<\/li>\n<li>A gyro magnetic compass combines a directional gyro with a magnetic compass system.<\/li>\n<li>The directional gyro is continuously monitored and corrected by a magnetic detector.<\/li>\n<li>The gyro is corrected using a slow precession rate of approximately <strong>3\u00b0 per minute<\/strong>.<\/li>\n<li>The slow correction rate filters out temporary errors from the magnetic detector.<\/li>\n<\/ul>\n<h3>Construction of the Gyro Magnetic Compass<\/h3>\n<p> <img decoding=\"async\" src=\"https:\/\/ibexaviation.com\/page-show\/flight-instruments\/i19-gyro-magnetic-compass-3.jpg\" alt=\"\" loading=\"lazy\"\/><\/p>\n<ul>\n<li>The Gyro Magnetic Compass is also known as the <strong>Magnetic Heading Reference System (MHRS)<\/strong>.<\/li>\n<li>It combines the stability of a gyroscope with the directional reference of a magnetic compass.<\/li>\n<li>The system consists of a horizontal directional gyro and a magnetic flux valve detector.<\/li>\n<li>A compass dial displays heading through a precession amplifier and drive motor.<\/li>\n<li>Both manual and automatic rapid synchronisation systems are provided.<\/li>\n<li>A rapid synchronisation button quickly aligns the directional gyro with the magnetic flux valve.<\/li>\n<\/ul>\n<h3>Magnetic Flux Valve<\/h3>\n<p> <img decoding=\"async\" src=\"https:\/\/ibexaviation.com\/page-show\/flight-instruments\/i19-gyro-magnetic-compass-4.jpg\" alt=\"\" loading=\"lazy\"\/><\/p>\n<ul>\n<li>The magnetic flux valve senses the direction of magnetic north.<\/li>\n<li>A three-spoke flux valve is usually installed beneath a wing tip or inside the tail fin.<\/li>\n<li>This location minimises interference from electrical equipment.<\/li>\n<li>The flux valve is suspended pendulously using a Hooke&#8217;s joint.<\/li>\n<li>The Hooke&#8217;s joint allows the detector to remain level during aircraft pitch and roll.<\/li>\n<\/ul>\n<h2>Magnetic Flux Detector <\/h2>\n<h3>Principle of the Magnetic Flux Valve<\/h3>\n<p> <img decoding=\"async\" src=\"https:\/\/ibexaviation.com\/page-show\/flight-instruments\/i19-gyro-magnetic-compass-5.jpg\" alt=\"\" loading=\"lazy\"\/><\/p>\n<ul>\n<li>The magnetic flux valve operates on <strong>Faraday&#8217;s Law of Electromagnetic Induction<\/strong>.<\/li>\n<li>An electromotive force (EMF) is induced whenever the magnetic flux linking a conductor changes.<\/li>\n<li>The induced EMF is proportional to the rate of change of magnetic flux.<\/li>\n<li>The detector consists of a central excitation coil surrounded by three sensing spokes.<\/li>\n<li>Alternating current in the central coil creates equal magnetic fields in the surrounding spokes.<\/li>\n<li>Without an external magnetic field, the resulting output is zero.<\/li>\n<li>The Earth&#8217;s magnetic field changes the magnetic saturation of the spokes.<\/li>\n<li>This produces an output voltage proportional to the direction of magnetic north.<\/li>\n<\/ul>\n<h3>Transmission of Magnetic Heading<\/h3>\n<p> <img decoding=\"async\" src=\"https:\/\/ibexaviation.com\/page-show\/flight-instruments\/i19-gyro-magnetic-compass-6.jpg\" alt=\"\" loading=\"lazy\"\/><\/p>\n<ul>\n<li>A <strong>Selsyn (Synchro)<\/strong> system transmits heading information between transmitting and receiving units.<\/li>\n<li>The transmitter rotor rotates with the heading drive shaft.<\/li>\n<li>The rotor position represents the aircraft heading.<\/li>\n<li>The rotor induces an equivalent magnetic field in the stator windings.<\/li>\n<li>The receiving synchro develops currents that rotate its shaft to the same position.<\/li>\n<li>An error signal exists whenever the transmitter and receiver are not aligned.<\/li>\n<li>The repeater continues rotating until the error voltage becomes zero, indicating the correct heading.<\/li>\n<\/ul>\n<h3>Signal Processing to the Compass Dial<\/h3>\n<p> <img decoding=\"async\" src=\"https:\/\/ibexaviation.com\/page-show\/flight-instruments\/i19-gyro-magnetic-compass-7.jpg\" alt=\"\" loading=\"lazy\"\/><\/p>\n<ul>\n<li>The Selsyn system produces an error signal whenever the displayed heading is incorrect.<\/li>\n<li>The error signal is amplified, phase detected, and converted into direct current (DC).<\/li>\n<li>The DC output drives the precession motor that rotates the compass dial.<\/li>\n<li>The displayed heading is the directional gyro heading corrected by the magnetic flux valve.<\/li>\n<li>The compass card is read against a fixed lubber line.<\/li>\n<li>A heading bug allows the pilot to preset a desired heading.<\/li>\n<li>A warning flag indicates failure of the magnetic flux detector or associated circuitry.<\/li>\n<\/ul>\n<h3>Control Panel of the Gyro Magnetic Compass<\/h3>\n<p> <img decoding=\"async\" src=\"https:\/\/ibexaviation.com\/page-show\/flight-instruments\/i19-gyro-magnetic-compass-8.jpg\" alt=\"\" loading=\"lazy\"\/><\/p>\n<ul>\n<li>A <strong>FREE\/SLAVE<\/strong> selector chooses between gyro-only and magnetically slaved operation.<\/li>\n<li><strong>Slave Mode<\/strong> is the normal operating mode.<\/li>\n<li>In Slave Mode, the directional gyro is continuously corrected by the magnetic flux valve.<\/li>\n<li>An annunciator indicates that magnetic slaving is operating.<\/li>\n<li><strong>Free Mode<\/strong> displays gyro heading without magnetic correction.<\/li>\n<li>Free Mode is commonly used near the magnetic poles where magnetic dip is excessive.<\/li>\n<li><strong>CW<\/strong> and <strong>CCW<\/strong> controls are provided to manually synchronise the initial heading.<\/li>\n<\/ul>\n<h3>Gyro Wander<\/h3>\n<p> <img decoding=\"async\" src=\"https:\/\/ibexaviation.com\/page-show\/flight-instruments\/i19-gyro-magnetic-compass-9.jpg\" alt=\"\" loading=\"lazy\"\/><\/p>\n<ul>\n<li>Gyro wander consists of <strong>gyro drift<\/strong> and <strong>gyro topple<\/strong>.<\/li>\n<li>Drift is minimised by continuously slaving the directional gyro to the magnetic flux valve.<\/li>\n<li>Topple is corrected using mercury levelling switches and torque motors.<\/li>\n<li>These correction systems slowly precess the gyro back to the horizontal reference.<\/li>\n<li>The slow precession rate prevents unnecessary corrections caused by temporary disturbances.<\/li>\n<li>Temporary disturbances include aircraft turns and acceleration errors.<\/li>\n<li>The Selsyn (Synchro) system also distributes heading information to instruments such as the <strong>Radio Magnetic Indicator (RMI)<\/strong>, <strong>Horizontal Situation Indicator (HSI)<\/strong>, and <strong>Autopilot<\/strong>.<\/li>\n<\/ul>\n","protected":false},"excerpt":{"rendered":"<p>Direction Measurement using Gyro Magnetic Compass A gyro-magnetic compass combines the stability of a gyroscope and accuracy of compass using the Earth\u2019s magnetic field. It reduces errors caused by acceleration, turning and magnetic dip. This makes a GMC more reliable for maintaining precise heading during flight. Introduction to the Gyro Magnetic Compass A remote-indicating compass reduces many of the limitations of a direct-reading magnetic compass. It minimises heading errors that occur during aircraft acceleration and turns. It reduces magnetic deviation caused by locating the sensing element inside the cockpit. It&hellip;<\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"disable_featured_image":false,"footnotes":""},"categories":[345],"tags":[],"class_list":["post-14490","post","type-post","status-publish","format-standard","hentry","category-cpl-atpl-flight-instruments"],"_links":{"self":[{"href":"https:\/\/ibexaviation.com\/pilot-training\/wp-json\/wp\/v2\/posts\/14490","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/ibexaviation.com\/pilot-training\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/ibexaviation.com\/pilot-training\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/ibexaviation.com\/pilot-training\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/ibexaviation.com\/pilot-training\/wp-json\/wp\/v2\/comments?post=14490"}],"version-history":[{"count":1,"href":"https:\/\/ibexaviation.com\/pilot-training\/wp-json\/wp\/v2\/posts\/14490\/revisions"}],"predecessor-version":[{"id":16664,"href":"https:\/\/ibexaviation.com\/pilot-training\/wp-json\/wp\/v2\/posts\/14490\/revisions\/16664"}],"wp:attachment":[{"href":"https:\/\/ibexaviation.com\/pilot-training\/wp-json\/wp\/v2\/media?parent=14490"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/ibexaviation.com\/pilot-training\/wp-json\/wp\/v2\/categories?post=14490"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/ibexaviation.com\/pilot-training\/wp-json\/wp\/v2\/tags?post=14490"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}