AI Dip

Mooney Fan

Mooney Fan

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Sep 17, 2017
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Mooney Fan
Just got my plane back from annual.

Pulled the AI and had it overhauled and the problem is still there. She has a dip to the left. Suction is fine.

We are starting to think static line?

Appreciate comments sans (Should of gone G5 crowd lol)

Pic below is in straight level flight.



IMG_7997.jpg
 
I'm no A&P, but I'm pretty sure the static line has nothing to do with the AI. The static line serves the vertical speed indicator, altimeter, and as a reference to the airspeed indicator. Assuming it is mounted correctly, I'd double check the vacuum (or pressure, as a very few airplanes use an air pump to create the pressure differential to spin the gyros).
 
Shoulda had a V8. but seriously ours in the 182 had a dip and it was annoying. We sent it out to get overhauled and ended up having to replace it.
 
Quite possible that the gyro isn’t spinning like it should be, which could be the result of a leak within the vacuum pressure line or bearings starting to go bad. It is NOT a static line issue, that much I can say for certain.
 
I didn't mention the bearings, since it was just overhauled. However, junk getting into the bearings from the vacuum system can cause precession, which causes the lean.
 
Ryanb said:
Quite possible that the gyro isn’t spinning like it should be, which could be the result of a leak within the vacuum pressure line or bearings starting to go bad. It is NOT a static line issue, that much I can say for certain.
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It was just Overhauled and certified. Same result
 
does it function normal with just a constant wing low indication in flight? is the aircraft flying straight and level when it indicates wing low? are the mounting holes slotted? was the unit leveled when installed and was the aircraft level?
 
This could be really stupid, so apologies in advance, but just thinking out loud... are you sure your control surfaces are trimmed properly and that you are in coordinated flight? It's possible to be in a straight and level flight path with the airplane itself not straight and level. What does your turn and slip indicator show? Do you have access to an AHRS-based readout from a Stratus/Stratux or similar to check it against?
 
Does your Mooney have a tilted panel? Is it the correct instrument for it? I don't have knowledge as to what would happen if you put a normal AI into a tilted panel or vice versa, I would think errors would be more extreme, but it's worth checking.

Are there any other errors? If you do a prolonged turn and roll out what does the AI show?
 
unsafervguy said:
does it function normal with just a constant wing low indication in flight? is the aircraft flying straight and level when it indicates wing low? are the mounting holes slotted? was the unit leveled when installed and was the aircraft level?
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Level straight flight. They tried rotating in slots no joy. Don’t know about whether it was level. Same indication on the ground.
 
Maybe the self erecting vanes are off, so it's still erecting, but just slightly to the left. The gyro seems to think "level" is slightly off
 
dmspilot said:
Does your Mooney have a tilted panel? Is it the correct instrument for it? I don't have knowledge as to what would happen if you put a normal AI into a tilted panel or vice versa, I would think errors would be more extreme, but it's worth checking.

Are there any other errors? If you do a prolonged turn and roll out what does the AI show?
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Not a Mooney. It’s a Cherokee 140. I used to bump around in. 70 Ranger.
MuseChaser said:
This could be really stupid, so apologies in advance, but just thinking out loud... are you sure your control surfaces are trimmed properly and that you are in coordinated flight? It's possible to be in a straight and level flight path with the airplane itself not straight and level. What does your turn and slip indicator show? Do you have access to an AHRS-based readout from a Stratus/Stratux or similar to check it against?
Click to expand...
Aircraft was rigged last year with no change in AI. Needle and ball centered
 
dmspilot said:
Does your Mooney have a tilted panel? Is it the correct instrument for it? I don't have knowledge as to what would happen if you put a normal AI into a tilted panel or vice versa, I would think errors would be more extreme, but it's worth checking.

Are there any other errors? If you do a prolonged turn and roll out what does the AI show?
Click to expand...
During steep 360 turns it’s spot on.
 
My guess would be it's the vanes I referenced above. If the gyro seems to work fine, but is just slightly off when it should be "level" that tells me one of the vanes may be off.. or there's a piece of crud or something that's lodged in the exhaust port

I don't see why static or vacuum "pressure" would make it turn in one direction in particular

Granted, I'm just an idiot at a computer so take this with a few sacks of salt, and the $0.00 you paid for it.

upload_2020-5-24_15-7-10.png
 
Mooney Fan said:
Appreciate comments
Click to expand...
Not enough info yet. Was the AI working before your annual? Were the vacuum system filter(s) changed during the annual? Was any t/shooting performed before AI remove/OH/install? Define "suction is fine" numerically.
 
Bell206 said:
Not enough info yet. Was the AI working before your annual? Were the vacuum system filter(s) changed during the annual? Was any t/shooting performed before AI remove/OH/install? Define "suction is fine" numerically.
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I mentioned earlier the AI has had the same issue for a while. I see no reference filter for vac were changed but if required I’m confident it would have been. Suction smudge over 5. No troubleshooting otherwise.
 
If it's not the static line, then it's got to be the muffler bearings.
 
Air and vacuum lines not reversed? That can mess with the levelling vanes.
An old vacuum central filter can shed debris that fouls it up too.
And no, the static system has nothing to do with it.
 
Bell206 said:
Must have missed that part. I only read: "Just got my plane back from annual. Pulled the AI..." Regardless, for merely a timeline, this problem was there before the annual?

That's good. Is it a steady 5?
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Haven’t noticed any variances.
 
Pull it and send it back to have it checked. It might have been fine when it left the overhaul facility...shipping is hard on gyros..

If it is under warranty, do not wait too long.

Dumb question: is your panel level ? A couple bad shock mounts can allow your panel to dip.

Good luck !
 
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Mooney Fan said:
Yes, it’s had the issue before annual.
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Well, that can negate the usual suspects after an annual. Is there any other instrument connected to the vacuum system? Was there any work performed prior to you noticing the AI droop? What aircraft?
 
MauleSkinner said:
and specifically what visual cues are you using?
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Actually it’s a turn coordinator. Flying 3’ off the wing of Cherokees, Saratoga’s and Grumman’s. They all can’t be flying crooked and in formation the AI dips like the pic. Weird.
 
Mooney Fan said:
Actually it’s a turn coordinator. Flying 3’ off the wing of Cherokees, Saratoga’s and Grumman’s. They all can’t be flying crooked and in formation the AI dips like the pic. Weird.
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So specifically placarded something to the effect of “no bank information”.

If you’re looking for help troubleshooting on the internet, you’re going to have to be much more specific than “I’m using visual references that I think are right, but really don’t know.”
 
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