{"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":"2025-06-09T19:21:59","modified_gmt":"2025-06-09T13:51:59","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":"\n<h2>Directional Gyro Indicator<\/h2>\n\n\n\n<h3>Introduction to Directional Gyro Indicator<\/h3>\n\n\n\n<ul><li>DGI provides heading using a tied gyro with two degrees of freedom<\/li><li>Spin axis of gyro is maintained in the yawing plane of the aircraft<\/li><li>Gyro motor is located in the inner gimbal and readings seen on outer gimbal<\/li><li>Outer gimbal can rotate through 360 deg<\/li><li>Rotor axis, inner and outer gimbals are at right angles to each other<\/li><li>In an air driven DGI, engine driven pump provides air jet to spin the rotor<\/li><li>The outer gimbal turns whereas spin axis remains at its original position<\/li><li>The readings on outer gimbal displays heading on a lubber line<\/li><\/ul>\n\n\n\n<h3>Self Adjustment of DGI<\/h3>\n\n\n\n<ul><li>A self adjustment mechanism maintains the spin axis in the yawing plane<\/li><li>The self adjustment is carried out in two distinct steps<\/li><li>Coarse adjustment takes place when fresh air jet strikes the rotor at an angle<\/li><li>This fresh air creates an additional component of force<\/li><li>This force acts at 90 deg to the point of application<\/li><li>As a result, the spin axis is brought back to its original position<\/li><li>Fine adjustment is done by using a wedge plate<\/li><li>Wedge plate separates the used air jet from rotor unequally<\/li><li>This causes the rotor to return to its original position<\/li><\/ul>\n\n\n\n<h3>Caging Knob of DGI<\/h3>\n\n\n\n<ul><li>Spring loaded caging knob is provided to prevent topple locking mechanism<\/li><li>This spring-loaded switch can also re erect a toppled gyro<\/li><li>The button can manually synchronise the gyro with compass heading<\/li><li>Limitations of an un-caged DGI with the type of power source<\/li><li>Air driven gyro is limited to 55 deg pitch and roll<\/li><li>Electrically driven gyro is limited to 85 deg roll and pitch<\/li><\/ul>\n\n\n\n<h3>Gimballing Error<\/h3>\n\n\n\n<ul><li>Gimballing error is caused when aircrafts applies bank to turn<\/li><li>Error is caused if the outer gimbal moves to keep the spin axis steady<\/li><li>Pitching movement during bank aggravates this error<\/li><li>Maximum error is seen in bank during climb or descent<\/li><li>In a 360-degree turn, this error varies with direction<\/li><li>Zero error is seen in 4 directions which are 90 degrees displaced<\/li><li>Gimballing error disappears when aircraft levels out<\/li><\/ul>\n\n\n\n<h3>Real Drift due to Wander<\/h3>\n\n\n\n<ul><li>Real wander is caused due to manufacturing imperfections or wear and tear<\/li><li>Rotor speed of 10 000 rpm has a drift rate of 1.6\u00c2\u00b0 per hour<\/li><li>Rotor speed of 20 000 rpm has a drift rate of 1.2\u00c2\u00b0 per hour<\/li><li>The gyro spin axis actually deviates from its orientation to fixed point in space<\/li><li>Real wander is caused because of four types of manufacturing imperfections<\/li><li>Imbalance in rotor mass<\/li><li>Imperfectly balanced gimbals<\/li><li>Uneven rotor bearing friction<\/li><li>Uneven gimbal friction<\/li><\/ul>\n\n\n\n<h3>Apparent Drift due to Earth Rate<\/h3>\n\n\n\n<ul><li>Apparent drift due to earth rate is caused due to rotation of earth<\/li><li>Horizontal gyro aligned to true north at a meridian appears to change direction<\/li><li>Due to rotation of earth and meridian convergence<\/li><li>Earth rate varies with latitude due to variation in meridian convergence<\/li><\/ul>\n\n\n\n<h3>Apparent Drift due to Earth Rate at Equator and Poles<\/h3>\n\n\n\n<ul><li>Earth rate is zero at equator since meridian convergence is zero<\/li><li>Gyro spin axis will not deviate in its horizontal plane<\/li><li>Earth rate is maximum at the poles since meridians convergence is maximum<\/li><li>Gyro spin axis will deviate by 360 degrees in 24 hours<\/li><li>So, the spin axis will deviate by 15 degrees per hour<\/li><\/ul>\n\n\n\n<h3>Apparent Drift due to Earth Rate at Mid-latitudes<\/h3>\n\n\n\n<ul><li>Earth rate varies with latitude due to variation in meridian convergence<\/li><li>Apparent drift due earth rate = 15 x sin latitude in degrees per hour<\/li><li>Gyro north is the north in the original meridian where gyroscope was aligned<\/li><\/ul>\n\n\n\n<h3>Earth Rate in Southern and Northern Hemisphere<\/h3>\n\n\n\n<ul><li>In southern hemisphere, true north increases with respect to gyro north<\/li><li>True north is 070 when gyro north is 360<\/li><li>True north is more than gyro north hence earth rate is termed positive<\/li><li>In northern hemisphere, true north decreases with respect to gyro north<\/li><li>True north is 290 when gyro north is 360<\/li><li>True north is less than gyro north hence earth rate is termed negative<\/li><\/ul>\n\n\n\n<h3>Latitude Nut Correction<\/h3>\n\n\n\n<ul><li>Latitude nut is used to correct apparent drift due to earth rate<\/li><li>Creates real wander by varying rotor speed to correct earth rate<\/li><li>Real wander is equal and opposite to the error caused due to earth rate<\/li><li>The setting is correct only at a particular latitude<\/li><li>Latitude nut moves out north of equator and moved in south of equator<\/li><\/ul>\n\n\n\n<h3>Latitude Nut Movement<\/h3>\n\n\n\n<ul><li>Latitude nut moves out north of equator and moved in south of equator<\/li><li>DGI is free of drift due to earth rate at the corrected latitude<\/li><li>Latitude nut correction is inaccurate in two cases<\/li><li>Rotor speeds other than the designed speed<\/li><li>Latitudes other than designed latitude<\/li><\/ul>\n\n\n\n<h3>Apparent Drift Due Transport Wander<\/h3>\n\n\n\n<ul><li>Apparent drift due to transport wander occurs due to movement of aircraft<\/li><li>Spin axis of gyro appears to shift from its gyro north due to transport wander<\/li><li>Transport wander occurs during in easterly or westerly movement<\/li><li>Flight along the equator has zero apparent drift due to transport wander<\/li><li>Transport wander =<\/li><li>Easterly component of ground speed per minute x tan lat in deg per hour<\/li><\/ul>\n\n\n\n<h3>Transport Wander in Northern and Southern Hemisphere<\/h3>\n\n\n\n<ul><li>In northern hemisphere:<\/li><li>Transport wander will not affect flights in a northerly or southerly direction<\/li><li>Drift in easterly movement of aircraft will be same as due to earth rate<\/li><li>Hence, drift is designated negative like earth rate<\/li><li>Drift in westerly movement of aircraft will be opposite to that of earth rate<\/li><li>Hence, drift is designated positive which is opposite to earth rate<\/li><li>In the southern hemisphere the rules are reversed<\/li><\/ul>\n\n\n\n<h3>Total Apparent Drift<\/h3>\n\n\n\n<ul><li>Total apparent drift due to earth rate and transport wander can be calculated<\/li><li>Apparent drift due earth rate =<\/li><li>15 x sine latitude in degrees per hour<\/li><li>Apparent drift due to transport wander =<\/li><li>Easterly component of ground speed per minute x tan latitude<\/li><li>Expressed in degrees per hour<\/li><li>Earth rate and transport wander are added if they have same sign<\/li><li>Earth rate and transport wander are subtracted if they have opposite signs<\/li><\/ul>\n\n\n\n<h2>Share this Page<\/h2>\n","protected":false},"excerpt":{"rendered":"<p>Directional Gyro Indicator Introduction to Directional Gyro Indicator DGI provides heading using a tied gyro with two degrees of freedom Spin axis of gyro is maintained in the yawing plane of the aircraft Gyro motor is located in the inner gimbal and readings seen on outer gimbal Outer gimbal can rotate through 360 deg Rotor axis, inner and outer gimbals are at right angles to each other In an air driven DGI, engine driven pump provides air jet to spin the rotor The outer gimbal turns whereas spin axis remains&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},"categories":[345],"tags":[],"_links":{"self":[{"href":"https:\/\/ibexaviation.com\/pilot-training\/wp-json\/wp\/v2\/posts\/14484"}],"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":0,"href":"https:\/\/ibexaviation.com\/pilot-training\/wp-json\/wp\/v2\/posts\/14484\/revisions"}],"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}]}}