Critical Think | IRS Align Mode - Carefully Measuring Earth's Rotation (Mirror) @CriticalThink | Uploaded October 2018 | Updated October 2024, 7 hours ago.
Mirrored with permission, an excellent video from 53C52
The original video here: youtu.be/tUwHc_wUykk
This video is for those that say "no evidence of earth rotation", and for those that ask "how can you measure earth rotation?", and for those that don't know the difference between an Inertial Navigation System and a MEMS equipped cellphone or drone.
Also for those that know the earth is a globe so that they can gloat over this wonderful demonstration.
Explanation from the video:
For several decades, long-range aircraft have used Inertial Navigation Systems/Inertial Reference Systems as sources for position information and as the primary sources for orientation information (pitch/bank/yaw/heading).
This video demonstrates the alignment process of a Honeywell IRS as it carefully measures the slow rotation of the earth to determine the aircraft's latitude and direction to the geographic north pole.
Key points to note are:
1. The IRS consistently determines the correct direction to geographic north, even when it is initialized to an incorrect location.
2. The IRS can be initialized at a grossly incorrect longitude because it is unable to use the rotation of the earth to determine longitude, and therefore is unable to complete a reasonableness check of the initial longitude being supplied to the device.
3. The IRS uses Earth rotation to calculate an accurate latitude which it will use to cross-check the initial position that is supplied during the align mode for reasonableness. This calculation of latitude using direct measurement of Earth's rotation makes it impossible to operate the IRS in navigation mode if the initial position sent to the IRS contains a grossly incorrect latitude.
Early Inertial Navigation Systems use 3 precision mechanical gyros. The gyros are mounted so that each spins on an axis that is 90 degrees to the other two along with 3 linear accelerometers mounted in a similar fashion.
Those components are mounted on a platform that is free to rotate on gimbals within the case. In order to use an INS, it first needs to go through an alignment process. During alignment, the aircraft needs to be stationary so that the gyros are subjected to movement caused only by the very slow rotation of the earth. This rotation is sensed as gyroscopic precession which is then used to drive servo motors to rotate the platform to align it in the direction of geographic north and parallel to local level.
The video linked below is an example of an INS coarse alignment. This rapid alignment is sufficient for the instrument to output attitude information, but the full alignment process to get the instrument ready for position tracking takes several minutes.
youtu.be/w4yaNn4Xmfg
Today's Inertial Reference Systems are an improvement on that old design and use ring laser gryos in place of the mechanic gyros. RLGs are not really gyros in the traditional sense of the word because they do not consist of a spinning mass, and do not exhibit the gyroscopic properties of precession and rigidity in space. They are, however, very good at measuring very small rates of rotation.
IRS does not use a floating platform as was used with the old mechanical gyros. The accelerometer and RLG orientations with respect to the airplane are fixed. This is why this type of unit is referred to a "strap-down" inertial. Like the older INS, IRS also needs to complete an initialization process called alignment, but in the IRS there is no physical alignment of a platform taking place.
Mirrored with permission, an excellent video from 53C52
The original video here: youtu.be/tUwHc_wUykk
This video is for those that say "no evidence of earth rotation", and for those that ask "how can you measure earth rotation?", and for those that don't know the difference between an Inertial Navigation System and a MEMS equipped cellphone or drone.
Also for those that know the earth is a globe so that they can gloat over this wonderful demonstration.
Explanation from the video:
For several decades, long-range aircraft have used Inertial Navigation Systems/Inertial Reference Systems as sources for position information and as the primary sources for orientation information (pitch/bank/yaw/heading).
This video demonstrates the alignment process of a Honeywell IRS as it carefully measures the slow rotation of the earth to determine the aircraft's latitude and direction to the geographic north pole.
Key points to note are:
1. The IRS consistently determines the correct direction to geographic north, even when it is initialized to an incorrect location.
2. The IRS can be initialized at a grossly incorrect longitude because it is unable to use the rotation of the earth to determine longitude, and therefore is unable to complete a reasonableness check of the initial longitude being supplied to the device.
3. The IRS uses Earth rotation to calculate an accurate latitude which it will use to cross-check the initial position that is supplied during the align mode for reasonableness. This calculation of latitude using direct measurement of Earth's rotation makes it impossible to operate the IRS in navigation mode if the initial position sent to the IRS contains a grossly incorrect latitude.
Early Inertial Navigation Systems use 3 precision mechanical gyros. The gyros are mounted so that each spins on an axis that is 90 degrees to the other two along with 3 linear accelerometers mounted in a similar fashion.
Those components are mounted on a platform that is free to rotate on gimbals within the case. In order to use an INS, it first needs to go through an alignment process. During alignment, the aircraft needs to be stationary so that the gyros are subjected to movement caused only by the very slow rotation of the earth. This rotation is sensed as gyroscopic precession which is then used to drive servo motors to rotate the platform to align it in the direction of geographic north and parallel to local level.
The video linked below is an example of an INS coarse alignment. This rapid alignment is sufficient for the instrument to output attitude information, but the full alignment process to get the instrument ready for position tracking takes several minutes.
youtu.be/w4yaNn4Xmfg
Today's Inertial Reference Systems are an improvement on that old design and use ring laser gryos in place of the mechanic gyros. RLGs are not really gyros in the traditional sense of the word because they do not consist of a spinning mass, and do not exhibit the gyroscopic properties of precession and rigidity in space. They are, however, very good at measuring very small rates of rotation.
IRS does not use a floating platform as was used with the old mechanical gyros. The accelerometer and RLG orientations with respect to the airplane are fixed. This is why this type of unit is referred to a "strap-down" inertial. Like the older INS, IRS also needs to complete an initialization process called alignment, but in the IRS there is no physical alignment of a platform taking place.
