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2 Answers

Errors of Gyroscope in INS : transport wander, apparent drift , coriolis effect

Asked by: 8885 views Aircraft Systems

can any one please explain me following errors of gyroscopes used in inertial navigation systems of aircraft :
a) what is transport wander , how actually it happens ?
b) what is apparent drift in gyroscope ?
c) what is coriolis effect and how it causes errors in gyroscopes ?

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2 Answers

  1. Brian on Mar 21, 2011

    Hi gkr,
    I would suggest visiting forums.jetcareers.com or http://www.airlinepilotforums.com and ask them your question. Many of us here do not use INS systems in our everday flying. The airline crowds that visit those two forums are more likely to be familiar with this systems. 
    Good luck.

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  2. Paul Tocknell on Mar 23, 2011

    First off, I’m going to quote my source for finding the answers to your questions.  The book is Global Navigation for Pilots by Remer and McLean published by ASA.  This book is great for those wanting to learn about international procedures.  I’m actually reading it now getting ready for my first international procedures class which takes place next month.  It has an entire chapter discussing basic navigation instruments (chapter 4) and inertial naviation systems (chapter 11).  The answers to your questions can be found in those chapters.  My trick here will be digesting an entire chapter of excellent material into 2-3 sentences for your answers and trying my best not to copy his material word for word.


    1) Transport Rate / Wander.


    Some background info is needed here but here is the gist of it.  We all know that if you fly from point A to point B your flight line won’t be straight, it will curve.  The path becomes an arc because well, the earth is a sphere.  Gyros in the INS think that the airplane is rotating / turning (you can’t have a curved path without rotation). The INS computer corrects for this perceived rotational force by entering a correction. Transport Wander (Remer / McLean use the term Transport Rate) is this perceived rate of rotation.  The IRS figures out this rate and the subtracts that value from the measurements.  If you want to know how it figures out this rate…well, read the book.


    2) Apparent Drift.

    Ok, I’m still trying to get my head around this one but here’s what I’ve learned.  A gyro’s best attribute is ridigity in space which also is the source of this error.  The gyro remains stationary while you fly even though the earth spins beneath it.  This is the source of “Drift”.  Remer makes an example of a fictional airplane on the north pole headed south (stationary).  Over a 24 hour time frame, the aircraft will have passed every line of longitude and every hour, the DG will have shown a 15° turn even though the airplane is still headed due south (this is because of the earth’s spin). At 30° north, this drift is about 7.5° an hour and at 60° north, about 13° an hour.  

    3) Corolis effect on gyroscopes.

    I don’t have a good answer yet (because the book didn’t directly discuss this) and maybe I’m confusing the answer above (apparent drift) with Corolis effect but they seem to share a similar cause; that being the earth rotates / spins beneath the airplane but I might have to get back to you on this one…..sorry.



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