INS Gimbal Lock
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INS Gimbal Lock
Hi all.
I'm studying the INS system mostly for the joy in understanding old and obsolete aircraft systems and instruments. I've found a question that perhaps someone could help me with.
I understand that the platform has 3 rate integrating gyros. According to a picture that I have of a platform, two of the gyros have their output axis oriented tha same way (but with the gyro spin axes at 90 degree angles to each other). I was wondering why there would be 2 gyros providing the same output? Then I thought it might be to cover if one of the gyros experience gimbal lock. Can this happen?
Providing that the rate integrating gyros are free to precess about their respective gimbal axes, I figure that there must be some point when the input axis and the rotor axis of a gyro coincide. In my small world of understanding this would create gimbal lock and must surely cause a fault in the system if not corrected. As you might understand my base of knowledge isn't that wide when it comes to this so if it's a stupid question, it's because I don't know what I don't know. Can someone please explain this to me?
/LnS
I'm studying the INS system mostly for the joy in understanding old and obsolete aircraft systems and instruments. I've found a question that perhaps someone could help me with.
I understand that the platform has 3 rate integrating gyros. According to a picture that I have of a platform, two of the gyros have their output axis oriented tha same way (but with the gyro spin axes at 90 degree angles to each other). I was wondering why there would be 2 gyros providing the same output? Then I thought it might be to cover if one of the gyros experience gimbal lock. Can this happen?
Providing that the rate integrating gyros are free to precess about their respective gimbal axes, I figure that there must be some point when the input axis and the rotor axis of a gyro coincide. In my small world of understanding this would create gimbal lock and must surely cause a fault in the system if not corrected. As you might understand my base of knowledge isn't that wide when it comes to this so if it's a stupid question, it's because I don't know what I don't know. Can someone please explain this to me?
/LnS
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The answer is a "fail" light to most of us. "Gimbel Lock" is something by word I mistakenly thought of as a failed Gimbel, wiki gave me some interesting insight and thx for the post. I believe that even the "old Delco" carousels were more advanced to prevent this failure. That being said, I am afraid there are few still alive who understand the answer to your question practicaly or with practial experience..
Miss the old INU's, a hard rerack or drop check to knock the carbon build up off the gimbels used to keep them running.
Miss the old INU's, a hard rerack or drop check to knock the carbon build up off the gimbels used to keep them running.
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More spellings of gimbal than there were answers!! How about gymbal???
Cheeky monkey grounded. I've worked on INS systems (admittedly years ago) and I'm not yet 50!
Low n' Slow - you need to study your gyro theory a little more as you've almost answered your question. Rate gyros are NOT free to precess about their axis, they're restrained such that their angular output corresponds to an angular RATE of change.
In an INS (lets exclude the Delco carosel as it had a rotating platform to help eliminate long term errors, although the principle is the same) the outputs of these rate gyros are used to operate motors on the platform gimbals (NOT the gyro) which maintained the alignment of the platform irrespective of the attitude of the a/c. This meant that to all intents and purposes the gyros didn't move because as soon as the gyro produced an output, the correction was sent to the respective platform gimbal motor which corrected the platform and nulled the gyro.
The 3 gyros each have their axis and gimbal position, such that they sense movement in a particular plane. 2 spinning horizontally (i.e. a vertical spin axis) but with gimbals positioned to sense pitch and roll and the 3rd spinning vertically (horizontal spin axis) to sense directional changes.
What you could get however, was PLATFORM gimbal lock. Usually the chances of this were reduced by adding a 4th driven gimbal which maintained angular separation of the inner gimbals.
Hope this helps a little.
Cheeky monkey grounded. I've worked on INS systems (admittedly years ago) and I'm not yet 50!
Low n' Slow - you need to study your gyro theory a little more as you've almost answered your question. Rate gyros are NOT free to precess about their axis, they're restrained such that their angular output corresponds to an angular RATE of change.
In an INS (lets exclude the Delco carosel as it had a rotating platform to help eliminate long term errors, although the principle is the same) the outputs of these rate gyros are used to operate motors on the platform gimbals (NOT the gyro) which maintained the alignment of the platform irrespective of the attitude of the a/c. This meant that to all intents and purposes the gyros didn't move because as soon as the gyro produced an output, the correction was sent to the respective platform gimbal motor which corrected the platform and nulled the gyro.
The 3 gyros each have their axis and gimbal position, such that they sense movement in a particular plane. 2 spinning horizontally (i.e. a vertical spin axis) but with gimbals positioned to sense pitch and roll and the 3rd spinning vertically (horizontal spin axis) to sense directional changes.
What you could get however, was PLATFORM gimbal lock. Usually the chances of this were reduced by adding a 4th driven gimbal which maintained angular separation of the inner gimbals.
Hope this helps a little.
Stilton the Gemini spacecraft had 4 gyros and had little worry of gimbal lock (an entire order of probability less worry anyway).
Apollo only had 3 gyros and could indeed run into gimbal lock situations, the most problematic of which was on Apollo 11. Several astronauts had been vocal about the decision to drop the 4th gyro on Apollo and after the problem on Apollo 11 Micheal Collins quipped "How about sending me a 4th gyro for Christmas"
Apollo only had 3 gyros and could indeed run into gimbal lock situations, the most problematic of which was on Apollo 11. Several astronauts had been vocal about the decision to drop the 4th gyro on Apollo and after the problem on Apollo 11 Micheal Collins quipped "How about sending me a 4th gyro for Christmas"
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Unless i'm mistaken Mercury had a 4 gyro system whereas Apollo was only 3 gyro. Hence they can't have experienced lock and recovered (although by all accounts 13 came very close!).
