Mysterious Artificial Horizon AOB
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Mysterious Artificial Horizon AOB
Hi Guys (and Gals),
I have a friend who owns a Cessna 172M and we both now seem to be dumbfounded by a particular A/H mystery.
Apparently after some minutes/hours of flying, it starts to show an angle of bank to the right (to maintain / for straight and level flight).
It becomes serious when, if you were to "trust the instruments", you would find yourself slowly banking to the left.
Personally I believe it might have something to do with the air suction pipes and have changed it more than 5 times to date but to no avail.
I can understand the whole "bank & climb to the right on t/off roll" as per what we all CPL/ATPL instruments with regards to the gyroscopic precession on the rotation, but again, this is IN-FLIGHT and happens only after some time in the air.
Would anybody here have any experience with this?
Could it be that there is TOO much or TOO little suction?
Any help / insight would greatly be appreciated. Thanks so very much.
Regards,
Johan, Kuala Lumpur.
MALAYSIA
Johan Farid Khairuddin.com
I have a friend who owns a Cessna 172M and we both now seem to be dumbfounded by a particular A/H mystery.
Apparently after some minutes/hours of flying, it starts to show an angle of bank to the right (to maintain / for straight and level flight).
It becomes serious when, if you were to "trust the instruments", you would find yourself slowly banking to the left.
Personally I believe it might have something to do with the air suction pipes and have changed it more than 5 times to date but to no avail.
I can understand the whole "bank & climb to the right on t/off roll" as per what we all CPL/ATPL instruments with regards to the gyroscopic precession on the rotation, but again, this is IN-FLIGHT and happens only after some time in the air.
Would anybody here have any experience with this?
Could it be that there is TOO much or TOO little suction?
Any help / insight would greatly be appreciated. Thanks so very much.
Regards,
Johan, Kuala Lumpur.
MALAYSIA
Johan Farid Khairuddin.com
Just a guess, but I would be thinking along the lines of an air leak in the vacuum system causing the gyro to rotate at too low a speed, which perhaps only happens at certain temperatures/vibrations etc.
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Thanks bingofuel & hawker man, both are very valid points -- am sure that we are most definitely on the right track. Will be looking at this thread closely over the next day or two to see if there are any other professionals who might also have an idea of what this could be!
JFK
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Looking at your location I would also suggest disconnecting Pitot/static lines at both ends and apply low air pressure to one end and make sure your lines are not partially blocked with spiders web and other insects.
It's suprising what comes out sometimes.
I would do this first as this would also clear out any water trapped in the lines and then carry out full leak check.
Almost forgot if you have flexible hoses in the system make sure there not kinked or twisted.
It's suprising what comes out sometimes.
I would do this first as this would also clear out any water trapped in the lines and then carry out full leak check.
Almost forgot if you have flexible hoses in the system make sure there not kinked or twisted.
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Pitot and static lines for an AH snag??? That's got to be some lateral thinking! 
Could be a leak IN THE VACUUM LINE that's true. It could also be a dodgy bearing in the AH causing it to precess. Have a listen to the horizon as it's running down (you can use a long screwdriver, tip pressed against the case with the handle to your ear) and listen for any odd noises, particularly as comes to a stop.
Could be a leak IN THE VACUUM LINE that's true. It could also be a dodgy bearing in the AH causing it to precess. Have a listen to the horizon as it's running down (you can use a long screwdriver, tip pressed against the case with the handle to your ear) and listen for any odd noises, particularly as comes to a stop.
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Could be a leak IN THE VACUUM LINE that's true. It could also be a dodgy bearing in the AH causing it to precess. Have a listen to the horizon as it's running down (you can use a long screwdriver, tip pressed against the case with the handle to your ear) and listen for any odd noises, particularly as comes to a stop.
It sounds like the rotor in it is not getting up to speed, so as above is the way to go, especially as you are in Malasia with the humidity and heat, it may be a bearing in the instrument that is dragging due to a bit of corrosion on it, so it will need to be sent for repair or replaced.
If the Directional indicator is working normally and the vac pressure is normal I would tend to discount a leak as the DI is on the same system, that would also be effected by a leak.
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Dear Bingofuel, Hawker man, Mono, Nutloose,
Thank you so very much once again for giving me a lot to work on.
Yes it is now starting to make sense (somewhat to be honest!) and, I will most definitely be bringing this up to our engineering head when I can get the weather good enough to fly it VFR!
What is kinda weird though is I did bring it to the engineer (for the 5th time by the way) and miraculously every time he plays with it (or toys to fix it by taking up the tubes/changing the tubes etc), it seems to work PERFECTLY.
Its after a few hours of flying (like 10-20), it starts to act up again.
Will give this thread till the end of the weekend before closing it and compiling all your thoughts to be submitted to the engineer.
If something else comes up, please do write here. Again, I really appreciate all the help you are giving us in this. Means a lot to me! Thank you.
Regards,
Johan
Thank you so very much once again for giving me a lot to work on.
Yes it is now starting to make sense (somewhat to be honest!) and, I will most definitely be bringing this up to our engineering head when I can get the weather good enough to fly it VFR!
What is kinda weird though is I did bring it to the engineer (for the 5th time by the way) and miraculously every time he plays with it (or toys to fix it by taking up the tubes/changing the tubes etc), it seems to work PERFECTLY.
Its after a few hours of flying (like 10-20), it starts to act up again.
Will give this thread till the end of the weekend before closing it and compiling all your thoughts to be submitted to the engineer.
If something else comes up, please do write here. Again, I really appreciate all the help you are giving us in this. Means a lot to me! Thank you.
Regards,
Johan
Is there a filter on the vacuum inlet? perhaps the engineer cleans this out when you complain, and it slowly blocks again over the next few hours. Or ask him what he does when he examines the system. Is he moving a pipe which is not secured properly and then it slowly falls out of position again and maybe kinks restricting the air flow.
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To check if the gyro rotor is spinning at the correct speed start the engine and let the gyro spin up for aprox 10 minutes, stop the engine and time the time it takes the rotor to spin down any greater than 3 minutes and it is OK.
It could be a problem with the VG pressecion mechanism sticking they are weights that deflect the air to the rotor, if it is this its an overhaul.
One other thing is the suction gauge in the green?
dave
It could be a problem with the VG pressecion mechanism sticking they are weights that deflect the air to the rotor, if it is this its an overhaul.
One other thing is the suction gauge in the green?
dave
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Hi again guys,
I don't know if these pictures do any justice but here is a shot in the dark:
https://picasaweb.google.com/johan.f...81590191382578
https://picasaweb.google.com/johan.f...81604291454402
I just remember seeing him pull out a big black tube and insert it back in again. I am not sure what else he did but will most definitely ask him the next time around, when I can bring the plane up there in VMC!
Not sure why but the DC ELEC T/Coordinator just went U/S on me on my last flight last weekend as well. Could be the electrics or a CB?
Should be back in the hangar next week and will update!
Keep 'em coming if anything else pops up!
Regards, and Thanks,
Johan.
I don't know if these pictures do any justice but here is a shot in the dark:
https://picasaweb.google.com/johan.f...81590191382578
https://picasaweb.google.com/johan.f...81604291454402
I just remember seeing him pull out a big black tube and insert it back in again. I am not sure what else he did but will most definitely ask him the next time around, when I can bring the plane up there in VMC!
Not sure why but the DC ELEC T/Coordinator just went U/S on me on my last flight last weekend as well. Could be the electrics or a CB?
Should be back in the hangar next week and will update!
Keep 'em coming if anything else pops up!
Regards, and Thanks,
Johan.
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Not sure why but the DC ELEC T/Coordinator just went U/S on me on my last flight last weekend as well. Could be the electrics or a CB?
Does the little flag go out? if not then probably the brushes, unless the plug on the back has become loose...... I take it all the CB's are still in.
They can normally be overhauled, just depends on the state of the rotor the brushes run on.
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From the a/c owner:
I will check the filter in the vacuum inlet if have. good point.
pipe not secured is not the issue as it is working when starting the engine.
gyro rotates longer than 3 minutes after engine off.
End.
// Okay more to follow soon as we approach the engineer.
thanks
Andreas
I will check the filter in the vacuum inlet if have. good point.
pipe not secured is not the issue as it is working when starting the engine.
gyro rotates longer than 3 minutes after engine off.
End.
// Okay more to follow soon as we approach the engineer.
thanks
Andreas
