{"id":14484,"date":"2025-06-07T16:20:16","date_gmt":"2025-06-07T10:50:16","guid":{"rendered":"https:\/\/ibexaviation.com\/pilot-training\/?p=14484"},"modified":"2026-07-26T10:30:55","modified_gmt":"2026-07-26T05:00:55","slug":"directional-gyro-indicator","status":"publish","type":"post","link":"https:\/\/ibexaviation.com\/pilot-training\/directional-gyro-indicator\/","title":{"rendered":"Directional Gyro Indicator (DGI)"},"content":{"rendered":"<p> <img decoding=\"async\" src=\"https:\/\/ibexaviation.com\/page-show\/flight-instruments\/i16-directional-gyro-indicator-1.jpg\" alt=\"\" loading=\"lazy\"\/><\/p>\n<h3>Direction measurement using Directional Gyro Indicator (DGI)<\/h3>\n<p>A DGI (Directional Gyro Indicator) is an aircraft instrument that shows the aircraft\u2019s heading using a gyroscope, independent of magnetic compass errors. It provides stable directional reference, helping pilots maintain accurate heading during turns, turbulence, and acceleration.<\/p>\n<h3>Introduction to Directional Gyro Indicator<\/h3>\n<p> <img decoding=\"async\" src=\"https:\/\/ibexaviation.com\/page-show\/flight-instruments\/i16-directional-gyro-indicator-2.jpg\" alt=\"\" loading=\"lazy\"\/><\/p>\n<ul>\n<li>DGI provides heading using a tied gyro with two degrees of freedom.<\/li>\n<li>Spin axis of the gyro is maintained in the yawing plane of the aircraft.<\/li>\n<li>Gyro motor is located in the inner gimbal, while readings are seen on the outer gimbal.<\/li>\n<li>Outer gimbal can rotate through 360&deg;.<\/li>\n<li>Rotor axis, inner gimbal, and outer gimbal are at right angles to each other.<\/li>\n<li>In an air-driven DGI, an engine-driven pump provides an air jet to spin the rotor.<\/li>\n<li>The outer gimbal turns whereas the spin axis remains at its original position.<\/li>\n<li>The readings on the outer gimbal display the heading on a lubber line.<\/li>\n<\/ul>\n<h3>Self Adjustment of DGI<\/h3>\n<p> <img decoding=\"async\" src=\"https:\/\/ibexaviation.com\/page-show\/flight-instruments\/i16-directional-gyro-indicator-3.jpg\" alt=\"\" loading=\"lazy\"\/><\/p>\n<ul>\n<li>A self-adjustment mechanism maintains the spin axis in the yawing plane.<\/li>\n<li>The self-adjustment is carried out in two distinct steps.<\/li>\n<li>Coarse adjustment takes place when a fresh air jet strikes the rotor at an angle.<\/li>\n<li>This fresh air creates an additional component of force.<\/li>\n<li>This force acts at 90&deg; to the point of application.<\/li>\n<li>As a result, the spin axis is brought back to its original position.<\/li>\n<li>Fine adjustment is done by using a wedge plate.<\/li>\n<li>The wedge plate separates the used air jet from the rotor unequally.<\/li>\n<li>This causes the rotor to return to its original position.<\/li>\n<\/ul>\n<h3>Caging Knob of DGI<\/h3>\n<p> <img decoding=\"async\" src=\"https:\/\/ibexaviation.com\/page-show\/flight-instruments\/i16-directional-gyro-indicator-4.jpg\" alt=\"\" loading=\"lazy\"\/><\/p>\n<ul>\n<li>A spring-loaded caging knob is provided to prevent topple locking mechanism.<\/li>\n<li>This spring-loaded switch can also re-erect a toppled gyro.<\/li>\n<li>The button can manually synchronize the gyro with the compass heading.<\/li>\n<\/ul>\n<h3>Limitations of an Un-caged DGI<\/h3>\n<ul>\n<li>Air-driven gyro is limited to 55&deg; pitch and roll.<\/li>\n<li>Electrically driven gyro is limited to 85&deg; pitch and roll.<\/li>\n<\/ul>\n<h3>Gimballing Error<\/h3>\n<p> <img decoding=\"async\" src=\"https:\/\/ibexaviation.com\/page-show\/flight-instruments\/i16-directional-gyro-indicator-5.jpg\" alt=\"\" loading=\"lazy\"\/><\/p>\n<ul>\n<li>Gimballing error is caused when the aircraft applies bank to turn.<\/li>\n<li>Error is caused if the outer gimbal moves to keep the spin axis steady.<\/li>\n<li>Pitching movement during bank aggravates this error.<\/li>\n<li>Maximum error is seen during bank while climbing or descending.<\/li>\n<li>In a 360&deg; turn, this error varies with direction.<\/li>\n<li>Zero error is seen in four directions which are 90&deg; apart.<\/li>\n<li>Gimballing error disappears when the aircraft levels out.<\/li>\n<\/ul>\n<h2>Calculation of Real and Apparent Drift while using Directional Gyro Indicator <\/h2>\n<h3>Real Drift due to Mechanical Imperfections<\/h3>\n<p> <img decoding=\"async\" src=\"https:\/\/ibexaviation.com\/page-show\/flight-instruments\/i16-directional-gyro-indicator-6.jpg\" alt=\"\" loading=\"lazy\"\/><\/p>\n<ul>\n<li>Real wander is caused by manufacturing imperfections or wear and tear.<\/li>\n<li>A rotor speed of 10,000 rpm has a drift rate of 1.6&deg; per hour.<\/li>\n<li>A rotor speed of 20,000 rpm has a drift rate of 1.2&deg; per hour.<\/li>\n<li>The gyro spin axis actually deviates from its orientation relative to a fixed point in space.<\/li>\n<li>Real wander is caused because of four types of manufacturing imperfections:\n<ul>\n<li>Imbalance in rotor mass.<\/li>\n<li>Imperfectly balanced gimbals.<\/li>\n<li>Uneven rotor bearing friction.<\/li>\n<li>Uneven gimbal friction.<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<h3>Apparent Drift due to Earth Rate<\/h3>\n<p> <img decoding=\"async\" src=\"https:\/\/ibexaviation.com\/page-show\/flight-instruments\/i16-directional-gyro-indicator-7.jpg\" alt=\"\" loading=\"lazy\"\/><\/p>\n<ul>\n<li>Apparent drift due to earth rate is caused by the rotation of the Earth.<\/li>\n<li>A horizontal gyro aligned to true north at a meridian appears to change direction.<\/li>\n<li>This occurs due to Earth&#8217;s rotation and meridian convergence.<\/li>\n<li>Earth rate varies with latitude because of variation in meridian convergence.<\/li>\n<\/ul>\n<h3>Apparent Drift due to Earth Rate at Equator and Poles<\/h3>\n<p> <img decoding=\"async\" src=\"https:\/\/ibexaviation.com\/page-show\/flight-instruments\/i16-directional-gyro-indicator-8.jpg\" alt=\"\" loading=\"lazy\"\/><\/p>\n<ul>\n<li>Earth rate is zero at the equator since meridian convergence is zero.<\/li>\n<li>The gyro spin axis will not deviate in its horizontal plane.<\/li>\n<li>Earth rate is maximum at the poles since meridian convergence is maximum.<\/li>\n<li>The gyro spin axis will deviate by 360&deg; in 24 hours.<\/li>\n<li>Therefore, the spin axis deviates by 15&deg; per hour.<\/li>\n<\/ul>\n<h3>Apparent Drift due to Earth Rate at Mid-Latitudes<\/h3>\n<p> <img decoding=\"async\" src=\"https:\/\/ibexaviation.com\/page-show\/flight-instruments\/i16-directional-gyro-indicator-9.jpg\" alt=\"\" loading=\"lazy\"\/><\/p>\n<ul>\n<li>Earth rate varies with latitude because of variation in meridian convergence.<\/li>\n<li>Apparent drift due to earth rate = <strong>15 \u00d7 sin(latitude)<\/strong> (&deg;\/hour).<\/li>\n<li>Gyro north is the north in the original meridian where the gyroscope was aligned.<\/li>\n<\/ul>\n<h3>Earth Rate in Southern and Northern Hemisphere<\/h3>\n<p> <img decoding=\"async\" src=\"https:\/\/ibexaviation.com\/page-show\/flight-instruments\/i16-directional-gyro-indicator-10.jpg\" alt=\"\" loading=\"lazy\"\/><\/p>\n<ul>\n<li><strong>Southern Hemisphere:<\/strong>\n<ul>\n<li>True north increases with respect to gyro north.<\/li>\n<li>Example: True north is 070 when gyro north is 360.<\/li>\n<li>Earth rate is considered <strong>positive<\/strong>.<\/li>\n<\/ul>\n<\/li>\n<li><strong>Northern Hemisphere:<\/strong>\n<ul>\n<li>True north decreases with respect to gyro north.<\/li>\n<li>Example: True north is 290 when gyro north is 360.<\/li>\n<li>Earth rate is considered <strong>negative<\/strong>.<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<h3>Latitude Nut Correction<\/h3>\n<p> <img decoding=\"async\" src=\"https:\/\/ibexaviation.com\/page-show\/flight-instruments\/i16-directional-gyro-indicator-11.jpg\" alt=\"\" loading=\"lazy\"\/><\/p>\n<ul>\n<li>The latitude nut is used to correct apparent drift due to earth rate.<\/li>\n<li>It creates real wander by varying rotor speed to correct earth rate.<\/li>\n<li>The real wander is equal and opposite to the error caused by earth rate.<\/li>\n<li>The setting is correct only at a particular latitude.<\/li>\n<li>The latitude nut moves <strong>out<\/strong> north of the equator and <strong>in<\/strong> south of the equator.<\/li>\n<\/ul>\n<h3>Latitude Nut Movement<\/h3>\n<p> <img decoding=\"async\" src=\"https:\/\/ibexaviation.com\/page-show\/flight-instruments\/i16-directional-gyro-indicator-12.jpg\" alt=\"\" loading=\"lazy\"\/><\/p>\n<ul>\n<li>The DGI is free of earth-rate drift at the corrected latitude.<\/li>\n<li>Latitude nut correction is inaccurate in the following cases:\n<ul>\n<li>Rotor speeds other than the designed speed.<\/li>\n<li>Latitudes other than the designed latitude.<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<h3>Apparent Drift due to Transport Wander<\/h3>\n<p> <img decoding=\"async\" src=\"https:\/\/ibexaviation.com\/page-show\/flight-instruments\/i16-directional-gyro-indicator-13.jpg\" alt=\"\" loading=\"lazy\"\/><\/p>\n<ul>\n<li>Apparent drift due to transport wander occurs because of aircraft movement.<\/li>\n<li>The gyro spin axis appears to shift from gyro north due to transport wander.<\/li>\n<li>Transport wander occurs during easterly or westerly movement.<\/li>\n<li>Flight along the equator has zero transport wander.<\/li>\n<li><strong>Transport Wander Formula:<\/strong><br \/>\n        Easterly component of ground speed (NM\/min) \u00d7 tan(latitude) = Drift (&deg;\/hour)\n    <\/li>\n<\/ul>\n<h3>Transport Wander in Northern and Southern Hemisphere<\/h3>\n<p> <img decoding=\"async\" src=\"https:\/\/ibexaviation.com\/page-show\/flight-instruments\/i16-directional-gyro-indicator-14.jpg\" alt=\"\" loading=\"lazy\"\/><\/p>\n<ul>\n<li><strong>Northern Hemisphere:<\/strong>\n<ul>\n<li>No effect during northerly or southerly flight.<\/li>\n<li>Easterly drift is the same as earth-rate drift (negative).<\/li>\n<li>Westerly drift is opposite to earth-rate drift (positive).<\/li>\n<\/ul>\n<\/li>\n<li><strong>Southern Hemisphere:<\/strong>\n<ul>\n<li>The above rules are reversed.<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<h3>Total Apparent Drift<\/h3>\n<p> <img decoding=\"async\" src=\"https:\/\/ibexaviation.com\/page-show\/flight-instruments\/i16-directional-gyro-indicator-15.jpg\" alt=\"\" loading=\"lazy\"\/><\/p>\n<ul>\n<li>Total apparent drift is the sum of earth rate and transport wander.<\/li>\n<li><strong>Earth Rate:<\/strong> 15 \u00d7 sin(latitude) (&deg;\/hour)<\/li>\n<li><strong>Transport Wander:<\/strong> Easterly component of ground speed (NM\/min) \u00d7 tan(latitude) (&deg;\/hour)<\/li>\n<li>Add both values if they have the same sign.<\/li>\n<li>Subtract them if they have opposite signs.<\/li>\n<\/ul>\n<h3>Direction of Drift and Topple<\/h3>\n<p> <img decoding=\"async\" src=\"https:\/\/ibexaviation.com\/page-show\/flight-instruments\/i16-directional-gyro-indicator-16.jpg\" alt=\"\" loading=\"lazy\"\/><\/p>\n<p>Refer to the drift and topple direction diagram for the Directional Gyro Indicator (DGI).<\/p>\n<h3>Total Drift Calculation of a DGI<\/h3>\n<p> <img decoding=\"async\" src=\"https:\/\/ibexaviation.com\/page-show\/flight-instruments\/i16-directional-gyro-indicator-17.jpg\" alt=\"\" loading=\"lazy\"\/><\/p>\n<p>Use the earth rate and transport wander formulas above to calculate the total drift of a Directional Gyro Indicator.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>Direction measurement using Directional Gyro Indicator (DGI) A DGI (Directional Gyro Indicator) is an aircraft instrument that shows the aircraft\u2019s heading using a gyroscope, independent of magnetic compass errors. It provides stable directional reference, helping pilots maintain accurate heading during turns, turbulence, and acceleration. Introduction to Directional Gyro Indicator DGI provides heading using a tied gyro with two degrees of freedom. Spin axis of the gyro is maintained in the yawing plane of the aircraft. Gyro motor is located in the inner gimbal, while readings are seen on the outer&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-14484","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\/14484","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=14484"}],"version-history":[{"count":1,"href":"https:\/\/ibexaviation.com\/pilot-training\/wp-json\/wp\/v2\/posts\/14484\/revisions"}],"predecessor-version":[{"id":16661,"href":"https:\/\/ibexaviation.com\/pilot-training\/wp-json\/wp\/v2\/posts\/14484\/revisions\/16661"}],"wp:attachment":[{"href":"https:\/\/ibexaviation.com\/pilot-training\/wp-json\/wp\/v2\/media?parent=14484"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/ibexaviation.com\/pilot-training\/wp-json\/wp\/v2\/categories?post=14484"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/ibexaviation.com\/pilot-training\/wp-json\/wp\/v2\/tags?post=14484"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}