Av-30c giving me headaches

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Baron_bo_loren

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Baron_von_loren
Hey guys

I have 2 av-30c units along with an avmag and avlink in my 152. After updating them to the current version and doing a new gyrocall, I’m getting drastic heading differences at take off. If I take off on a heading of 240, my ai shows around 255 and dg shows around 268. So far uavionix is trying to figure it out but was wondering if anyone where may have a guess.
 
where is the magnetometer installed?
 
I went through this a couple of years ago when I eliminated the vac system from my airplane and installed a pair AV-30C for AI and DG. The AI has been flawless. The DG, not so much. If you don't have the magnetometer, the DG will drift. A "good" one will drift about the same as a mechanical, 5-10* every 15 minutes. If it's worse than that it could be:

Vibration from engine or other sources
Installation - not true/square but at an angle
Pitch, roll and yaw trim settings (in the install menu)

One way to check the trim settings is to switch the DG to AI mode, then fly in coordinated level cruise and ensure the AI is perfectly zeroed including the slip ball at the bottom of the screen. Adjust the trim settings as necessary to get them all perfectly zeroed. Then switch that AI back to DG mode.

The DG also has an internal magnetometer that you can enable, then calibrate in flight by flying a couple of standard rate turns in each direction. But I find that this makes it drift worse - not better. Whether it improves things depends on how much EMI there is behind your panel due to radios etc. Apparently my plane (1980 172N) has enough EMI to make it worse.

If all this fails - or if you want to bypass all this troubleshooting - buy the AV-MAG external magnetometer. It is also certified. Install it out in the wing and wire it up. Then the DG will have no drift whatsoever - it will be an electronic compass instead of a gyro.
 
MRC01 said:
I went through this a couple of years ago when I eliminated the vac system from my airplane and installed a pair AV-30C for AI and DG. The AI has been flawless. The DG, not so much. If you don't have the magnetometer, the DG will drift. A "good" one will drift about the same as a mechanical, 5-10* every 15 minutes. If it's worse than that it could be:

Vibration from engine or other sources
Installation - not true/square but at an angle
Pitch, roll and yaw trim settings (in the install menu)

One way to check the trim settings is to switch the DG to AI mode, then fly in coordinated level cruise and ensure the AI is perfectly zeroed including the slip ball at the bottom of the screen. Adjust the trim settings as necessary to get them all perfectly zeroed. Then switch that AI back to DG mode.

The DG also has an internal magnetometer that you can enable, then calibrate in flight by flying a couple of standard rate turns in each direction. But I find that this makes it drift worse - not better. Whether it improves things depends on how much EMI there is behind your panel due to radios etc. Apparently my plane (1980 172N) has enough EMI to make it worse.

If all this fails - or if you want to bypass all this troubleshooting - buy the AV-MAG external magnetometer. It is also certified. Install it out in the wing and wire it up. Then the DG will have no drift whatsoever - it will be an electronic compass instead of a gyro.
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He said in his post he has an avmag
 
Good call. So the AVMag should be out in the wing away from EMI, and it is sensitive to orientation. The AV-30C install menu setting should be selected to use it, and it needs to be calibrated. The AVMAG calibration is not just the "GYRO CAL", that's a different thing.

See the latest version of the uAvionix AV-30C installation manual (a free download), pages 29, 55-67, 83-87.
 
MRC01 said:
Good call. So the AVMag should be out in the wing away from EMI, and it is sensitive to orientation. The AV-30C install menu setting should be selected to use it, and it needs to be calibrated. The AVMAG calibration is not just the "GYRO CAL", that's a different thing.

See the latest version of the uAvionix AV-30C installation manual (a free download), pages 29, 55-67, 83-87.
Click to expand...
I’m thinking I need to have someone check to make sure orientation is correct then. The mag was calibrated initially and then again by me not too long ago and it’s still causing issues. At start today I was reading 250 when my compass was 240. At climb the dg and ai were like 20 degrees off and giving me different readings. I have avmag selected on the serial 4 input on both the dg and ai currently too. It’s annoying because I know these can be amazing, they just aren’t right now.
 
I’m guessing you don’t have 2 AvMags installed and the AI and DG are sharing an input from a single AvMag? I know the wiring diagram for the AV-30s allow for a shared input, but I have mine wired for the AvMag to the DG and GPS serial out to the AI. I haven’t flown it yet, but that’s how I have it wired.

Do you have a GPS in the plane? You may have the installer disconnect the AI from the AvMag and see if there is any change. If so, then you can run a serial wire from the GPS to the AI and see what you get.

It sounds to me like there is noise on the input wire from the AvMag, or the AvMag is having problems. Disconnecting the AI would help determine that. Please correct me if I am misunderstanding, but you inferred that everything was working fine until you updated to the latest software? The AvMag may not like the new software, for whatever reason.
 
aterry1067 said:
I’m guessing you don’t have 2 AvMags installed and the AI and DG are sharing an input from a single AvMag? I know the wiring diagram for the AV-30s allow for a shared input, but I have mine wired for the AvMag to the DG and GPS serial out to the AI. I haven’t flown it yet, but that’s how I have it wired.

Do you have a GPS in the plane? You may have the installer disconnect the AI from the AvMag and see if there is any change. If so, then you can run a serial wire from the GPS to the AI and see what you get.

It sounds to me like there is noise on the input wire from the AvMag, or the AvMag is having problems. Disconnecting the AI would help determine that. Please correct me if I am misunderstanding, but you inferred that everything was working fine until you updated to the latest software? The AvMag may not like the new software, for whatever reason.
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I talked to uavionix and they said it can run the single mag just fine. I’m trying to get ahold of them now to figure out why I’m getting aggressive differences. I’m sure it had to be from the update. I’m also going to get someone to check the install location. I’m reading a lot of people install in wing tip and he did the left wing access panel which means it’s super close to the cockpit.
 
Baron_bo_loren said:
I talked to uavionix and they said it can run the single mag just fine. I’m trying to get ahold of them now to figure out why I’m getting aggressive differences. I’m sure it had to be from the update. I’m also going to get someone to check the install location. I’m reading a lot of people install in wing tip and he did the left wing access panel which means it’s super close to the cockpit.
Click to expand...


Oh yeah, I’m sorry, I should have been more clear. Yes, the single AvMag is able to provide signal to both AV-30s. What I meant was if you disconnect the AvMag from only one AV-30, that will tell you if the problem is in the AV-30 or with the AvMag. If disconnecting the AvMag changes the outcome, then it’s the AvMag. If there is no change then it’s in the AV-30. Actually after thinking about it, you should be able to simply set one AV-30 to use the internal mag and that “should” have the same effect as disconnecting it from the external AvMag.
 
aterry1067 said:
Oh yeah, I’m sorry, I should have been more clear. Yes, the single AvMag is able to provide signal to both AV-30s. What I meant was if you disconnect the AvMag from only one AV-30, that will tell you if the problem is in the AV-30 or with the AvMag. If disconnecting the AvMag changes the outcome, then it’s the AvMag. If there is no change then it’s in the AV-30. Actually after thinking about it, you should be able to simply set one AV-30 to use the internal mag and that “should” have the same effect as disconnecting it from the external AvMag.
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Oh shoot I get what you’re saying. I’ll do that on my next flight and see what happens. The drastic differences between the two occurred after I updated to the latest firmware version for some reason. I’m going to have an IA double check install to see if the other guy did it correctly too. I forgot Oshkosh is going on so it’s annoyingly impossible to get anyone on the phone with uavionix.
 
Most likely the installer did not wire the harnesses correctly to share the single AvMag input to both devices. I don't recall how, but it is shown in the instructions.
 
Ed Haywood said:
Most likely the installer did not wire the harnesses correctly to share the single AvMag input to both devices. I don't recall how, but it is shown in the instructions.
Click to expand...
Most likely. Since a single shared input should read the same on both readouts. And/or config issues in the boxes.
 
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