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22 February 2019 03:14

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### Question

Subject: Erection errors
Question: Hey,

I'm student pilot and studying now 'instruments'.
I understand the basics of the gyroscoop but thats it. In the attitude indicator
in an aircraft, based on a Vertical Tied Earth Gyro, there is my problem.

When an aircraft performs a coordinated turn, the pendulous vanes will try to
line up with the 'apparent vertical' aircrafts bottem. So we get an error.
But then rises the problem...

After 90° turn (of the aircraft) the error will show us a nose up attitude and a bank underreading.
After 180° turn the bank angle will be correct but we will have a maximum pitch up error.
After 270° turn the pitch error has reduced and bank overreads.

Can anyone explain this to me?

Thanks,
Steven
Date: 26 August 2005
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Answer: Jim Warchol - 06/09/2005 18:23:54
This is called "gimbal lock". When the gyro platform is rotated 90 degrees two of the axis will be aligned thereby losing a reference.

For example, an airplane uses three references, pitch (angle up/down), yaw (angle left/right on a vertical axis) and roll (angle left/right on the horizontal axis). If an airplane heads straight up or down (change of pitch), one other reference (the yaw) is cancelled, one loses a dimension of rotation, because there is always a value for one angle of rotation that yields infinite values of the other two angles (in this case, the yaw).

Also in a three gyro platform each gyro's gimbal can only phsyically rotate 90 degrees. So the sensor cannot read anything above that angle.

Hope this helps.

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Answer: sung-hyuk koh - 21/12/2009 19:03:03

The explanation is based on the precession and the pendulousity of the erection mechnism of the instrument.
The above link would answer your question and could you please tell me where you saw the explanation? "After 90 degree turn the error will show us a nose up attitude...etc"

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Answer: sung-hyuk koh - 21/12/2009 19:11:00

The explanation is based on the precession and the pendulousity of the erection mechnism of the instrument.
The above link would answer your question and could you please tell me where you saw the explanation? "After 90 degree turn the error will show us a nose up attitude...etc"

Most texts I read has a different explanation of the turtning error you mentioned above.

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Answer: sung-hyuk koh - 21/12/2009 19:11:47