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Does G3X alert when its ADAHRS and the G5 ADAHRS disagree?

iamtheari

Well Known Member
My planned panel is a G3X installation with a single GSU 25 ADAHRS and a G5 as a backup flight instrument. My understanding is that the G5 will provide ADAHRS data to the G3X system in the event the GSU 25 fails. What about the situation when the GSU 25 and G5 provide conflicting information? How does the G3X resolve that situation? How safe is this setup without a second GSU 25 to cross-check against the primary GSU 25 and the G5?
 
My planned panel is a G3X installation with a single GSU 25 ADAHRS and a G5 as a backup flight instrument. My understanding is that the G5 will provide ADAHRS data to the G3X system in the event the GSU 25 fails. What about the situation when the GSU 25 and G5 provide conflicting information? How does the G3X resolve that situation? How safe is this setup without a second GSU 25 to cross-check against the primary GSU 25 and the G5?

Hello Ari,

In a G3X Touch system with dual GSU 25 ADAHRS (with/without a G5), there is indeed miscompare monitoring which will result in an attitude miscompare annunciation should significant differences in pitch/roll/heading occur between the 2 ADAHRS units. The displays do not attempt to decide which attitude source is better, but the pilot may make this decision and choose which GSU 25 is displayed on any PFD. The default for a multi display G3X Touch system is to display ADAHRS #1 on the pilot side and ADAHRS #2 on the copilot side, but each pilot may over-ride this selection.

In a G3X Touch system with single GSU 25 (with/without a G5) there is no miscompare monitoring. When a G5 is present, it is the pilot's job to compare the attitude data on the G5 and adjacent PFD and decide which to use. In extreme cases, the single GSU 25 can be powered off and the PFD will then revert to using the G5 provided attitude data.

The system doesn't have to "resolve" anything. It is the pilot's responsibility to choose which of the available attitude sources are to be used on any display.

Thanks,
Steve
 
In extreme cases, the single GSU 25 can be powered off and the PFD will then revert to using the G5 provided attitude data.

I am intending to use a G5 as a backup ADHRS with my non-touch G3X installation. Is there any other way to use the G5's ADHRS, in the event the GSU 25 becomes unreliable or fails outright? If not, how does one turn off the GSU 25? Do I need a separate switch for this?

This is somewhat surprising, as I was told that the G3X could use the g5 as a backup ADAHRS.
Larry
 
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I have also wanting to test the redundancy of the G5 to the GSU25 to see if the system automatically get attitude info from G5 and/or how long it takes to realize one is dead to provide the info. In my last attempt, I couldn't power off the GSU25 since it has a redundant power so pulling the CB didn't do it.
 
Our system has a couple times done the following

Attitude indication on the G3X screens starts to drift showing a bank when straight and level. The G5 remains accurate.

I will get an AHRS REVERT message. Shortly followed by AHRS ALIGN, then everything is back to normal.

So, it's doing something automatically. G3Xpert? can you expand on what the system is doing here?


I haven't gone through troubleshooting that yet as we're throwing a new engine on soon and need to run the vibration tests again anyway.
 
I am intending to use a G5 as a backup ADHRS with my non-touch G3X installation. Is there any other way to use the G5's ADHRS, in the event the GSU 25 becomes unreliable or fails outright? If not, how does one turn off the GSU 25? Do I need a separate switch for this?

This is somewhat surprising, as I was told that the G3X could use the g5 as a backup ADAHRS.
Larry

Hello Larry,

No one said that the PFD would not automatically revert to using the G5 ADAHRS data should the GSU 25 fail. It will and does.

We just pointed out that if the pilot didn't like what was shown on the PFD from the primary ADAHRS, and wanted to force the reversion to using G5 data on the PFD, the GSU 25 could be turned off.

Whether or not you have switches or breakers on your panel to turn on/off devices is up to you.

Thanks,
Steve
 
Personally, whenever I do a panel upgrade that will be IFR equipped, it is getting dual GSU25's with a G5.
This way the G3X will warn you if the GSU25's don't agree, and with a quick glance, you can tell which unit is not behaving.
 
My system (dual G3X Touch, single GSU25 ADAHRS, G5) periodically exhibits the exact symptoms described above by Matt - PFD horizon gradually tips, AHRS Revert (with CAS alert) and then realign while G5 remains stable. Interestingly, the autopilot remains engaged throughout with no adverse affect.
 
Our system has a couple times done the following

Attitude indication on the G3X screens starts to drift showing a bank when straight and level. The G5 remains accurate.

I will get an AHRS REVERT message. Shortly followed by AHRS ALIGN, then everything is back to normal.

So, it's doing something automatically. G3Xpert? can you expand on what the system is doing here?


I haven't gone through troubleshooting that yet as we're throwing a new engine on soon and need to run the vibration tests again anyway.

Hello Matt (and Keith),

What you describe should never happen, so it is likely that installation improvements are needed.

We are currently working with a turboprop aircraft owner with very similar problems. When we review the data logs we see that the GSU 25 units are experiencing significant vibration in all flight phases - even taxi. Despite our strong recommendation to not mount the GSU 25 units to the back of displays, that is exactly where they are mounted in this aircraft.

Please contact us directly and we would happy to help troubleshoot.

Thanks,
Steve
 
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Hello Matt (and Keith),

What you describe should never happen, so it is likely that installation improvements are needed.

Please contact us directly and we would happy to help troubleshoot.

Thanks,
Steve

Thanks, Steve. I've emailed in the past about it, but haven't dug into the issue yet as there have been other things took precedence. With the new engine, we're finally planning to take it IFR, so we will have to get it sorted soon. It's just rare that it even happens. I'm thinking the right idea might be to add a second GSU25 even after we sort this out.
 
Hello Larry,

No one said that the PFD would not automatically revert to using the G5 ADAHRS data should the GSU 25 fail. It will and does.

We just pointed out that if the pilot didn't like what was shown on the PFD from the primary ADAHRS, and wanted to force the reversion to using G5 data on the PFD, the GSU 25 could be turned off.

Whether or not you have switches or breakers on your panel to turn on/off devices is up to you.

Thanks,
Steve

Thanks for the info. Feel better now. I think I will add an on/off switch to allow the reversion if I like the G5 data over the G3X.

Larry
 
Thanks for the info. Feel better now. I think I will add an on/off switch to allow the reversion if I like the G5 data over the G3X.

Larry

Hello Larry,

Sounds good. It is never a bad thing to have more switches. I use switches and fuse blocks, and I can quickly load-shed or isolate anything in the panel including both ADAHRS and both displays. Comes in real handy in the hangar when updating software or databases too.

Many people overlook providing a power switch or breaker for their datalink(s). I am not worried about nefarious activities, but there is lots of traffic and weather data being fed into our system, and I want a way to easily shut down the GDL 52R if necessary should that data stream contain information that the system is having difficulty processing. We put lots of protection mechanisms in the software, but we sometimes get blind-sided by something new that was unanticipated. There is currently a certified primary flight display on the market that was made unstable by recently added new FIS-B datalink information.

Thanks,
Steve
 
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Please contact us directly and we would happy to help troubleshoot.

Thanks,
Steve

Thanks, Steve. I agree that this is going to require some digging and will contact G3XPERT. I have already completed a very thorough wiring and connection integrity check. Right now the plane is out of service, so it may not be immediate.
 
My system (dual G3X Touch, single GSU25 ADAHRS, G5) periodically exhibits the exact symptoms described above by Matt - PFD horizon gradually tips, AHRS Revert (with CAS alert) and then realign while G5 remains stable. Interestingly, the autopilot remains engaged throughout with no adverse affect.

I have the same problem periodically, especially during turbulence. Any solution from Garmin? Is it perhaps a design flaw for the gsu25? I have a g3x touch plus a g5.
 
Any solution from Garmin? Is it perhaps a design flaw for the gsu25? I have a g3x touch plus a g5.

Any solution from Garmin?
Did you ask Garmin? [email protected] 1-866-854-8433

Is it perhaps a design flaw for the gsu25?
There are many of us out here flying around with similar equipment that do not have this issue. Likely an isolated case where the issue presents itself. Garmin could use your logs to help find the root cause. I highly suggest contacting them.
 
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Any solution from Garmin?
Did you ask Garmin? [email protected] 1-866-854-8433

Yes, I asked G3Xpert via email on 14 December 2018 and I've been suggested to run a vibration test as per G3X manual, which turned out ok. I think an adhars should have a zero "intermittent fault" rate and a very low "permanent fault" rate since it is a critical (ie life depending) piece of avionics. I owned an Avidyne Entegra and a Garmin G1000 and never had a fake horizon by more than 5 degrees bank (with the G3X we are talking 15 degrees of fake bank, periodically but rarely enough to be tempted to trust the system for IFR).

Also, I tried to force my G3X to revert to G5 adahrs in flight by pulling the GSU25 breaker and the autopilot keeps working but only in NAV and not in HDG mode. This corresponds to the fact that the magnetometer indication in the G3X disappears (red cross) as soon as I pull the GSU25 breaker. Do I need to purchase a second magnetometer for the G5 in order for the G5 to be a complete backup in case I pull the GSU25 breaker (as indicated by G3Xpert in this thread as the standard procedure to use the G5 as the backup Adhars for the G3X)?
 
Yes, I asked G3Xpert via email on 14 December 2018 and I've been suggested to run a vibration test as per G3X manual, which turned out ok. I think an adhars should have a zero "intermittent fault" rate and a very low "permanent fault" rate since it is a critical (ie life depending) piece of avionics. I owned an Avidyne Entegra and a Garmin G1000 and never had a fake horizon by more than 5 degrees bank (with the G3X we are talking 15 degrees of fake bank, periodically but rarely enough to be tempted to trust the system for IFR).

Also, I tried to force my G3X to revert to G5 adahrs in flight by pulling the GSU25 breaker and the autopilot keeps working but only in NAV and not in HDG mode. This corresponds to the fact that the magnetometer indication in the G3X disappears (red cross) as soon as I pull the GSU25 breaker. Do I need to purchase a second magnetometer for the G5 in order for the G5 to be a complete backup in case I pull the GSU25 breaker (as indicated by G3Xpert in this thread as the standard procedure to use the G5 as the backup Adhars for the G3X)?

I suspect changing to an GMU11 would allow the G5 to use heading data, as well as the gsu25. Also, do you really need it in an emergency/failure? The G3X AP with G5 AHRS should happily fly a track. Assuming you're navigating somewhere, track is more valuable anyways and I am sure ATC would give you track vectors, instead of heading, if you explain the equip failure. They are really assigning tracks anyways and then convert them to headings based upon the wind correction they have observed to be working.

Larry
 
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I suspect changing to an GMU11 would allow the G5 to use heading data, as well as the gsu25.
Larry

What do you mean by "changing to a GMU11"? I currently have a GMU22: do you mean to ADD a GMU11 dedicated to the G5, or REPLACE the GMU22 with a GMU11? When I was in the building phase 1y ago I explicitly asked this point to G3xpert, with regard to using the G5 as Adahrs backup and they answered by email :
<<The G3X will be able to share GMU 22 information to the G5 over the CAN Bus. There is no need to change to a GMU 11.>>

Can somebody (Garmin?) please clarify if one needs to install a second magnetometer dedicated to the G5 for the G5 to be used as an ADHARS backup for the GSU25 (including HDG info)?


yesterday I did this experiment:

g3x before pulling the GSU25 breaker:

https://lh3.googleusercontent.com/c...1pUtKEXSUPttPWx1AY5mhe8yPqEFReo4=w944-h708-no

pulled breaker (the one with "adahrs" written above):

https://lh3.googleusercontent.com/H...UaaCmDqhx2krh0sh7cP8eRWrIWHzuR58=w944-h708-no

g3x 10 seconds after pulling the GSU25 breaker:

https://lh3.googleusercontent.com/I...0dL-OA08oGywnsgZcxszX3cWTjzpth_8=w944-h708-no



Why do I lose the GMU22 signal (and also the transponder signal)? Also why do I lose the 3d perspective? As said above, the autopilot works ok after pulling the breaker, but only in NAV or Roll mode (I do not have a Track mode since I have a GMC307).
 
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Hello Ari,

In a G3X Touch system with dual GSU 25 ADAHRS (with/without a G5), there is indeed miscompare monitoring which will result in an attitude miscompare annunciation should significant differences in pitch/roll/heading occur between the 2 ADAHRS units. The displays do not attempt to decide which attitude source is better, but the pilot may make this decision and choose which GSU 25 is displayed on any PFD. The default for a multi display G3X Touch system is to display ADAHRS #1 on the pilot side and ADAHRS #2 on the copilot side, but each pilot may over-ride this selection.

In a G3X Touch system with single GSU 25 (with/without a G5) there is no miscompare monitoring. When a G5 is present, it is the pilot's job to compare the attitude data on the G5 and adjacent PFD and decide which to use. In extreme cases, the single GSU 25 can be powered off and the PFD will then revert to using the G5 provided attitude data.

The system doesn't have to "resolve" anything. It is the pilot's responsibility to choose which of the available attitude sources are to be used on any display.

Thanks,
Steve

Hmmn- this seems to be correcting another misconception that I did not know I had! I thought I’d read that the G5 would default to ADAHRS data from the GSU25 when provided on the can bus! Not true? I went to a lot of trouble centering my GSU25 right on the roll axis , but I guess the G5, located way off to the left of the 10” G3X Touch, will not benefit from this.:rolleyes:- Otis
 
Thanks for the info. Feel better now. I think I will add an on/off switch to allow the reversion if I like the G5 data over the G3X.

Larry

Why not just power thegsu25 from a discrete pullable breaker- should not happen often enough to warrant a switch.
 
What do you mean by "changing to a GMU11"? I currently have a GMU22: do you mean to ADD a GMU11 dedicated to the G5, or REPLACE the GMU22 with a GMU11? When I was in the building phase 1y ago I explicitly asked this point to G3xpert, with regard to using the G5 as Adahrs backup and they answered by email :
<<The G3X will be able to share GMU 22 information to the G5 over the CAN Bus. There is no need to change to a GMU 11.>>

Can somebody (Garmin?) please clarify if one needs to install a second magnetometer dedicated to the G5 for the G5 to be used as an ADHARS backup for the GSU25 (including HDG info)?


yesterday I did this experiment:

g3x before pulling the GSU25 breaker:

https://lh3.googleusercontent.com/c...1pUtKEXSUPttPWx1AY5mhe8yPqEFReo4=w944-h708-no

pulled breaker (the one with "adahrs" written above):

https://lh3.googleusercontent.com/H...UaaCmDqhx2krh0sh7cP8eRWrIWHzuR58=w944-h708-no

g3x 10 seconds after pulling the GSU25 breaker:

https://lh3.googleusercontent.com/I...0dL-OA08oGywnsgZcxszX3cWTjzpth_8=w944-h708-no



Why do I lose the GMU22 signal (and also the transponder signal)? Also why do I lose the 3d perspective? As said above, the autopilot works ok after pulling the breaker, but only in NAV or Roll mode (I do not have a Track mode since I have a GMC307).

Check out page 13 of rev K of the pilots guide.

The GMU22 and the Xponder connect to the GSU25 via RS232/RS-485. Pull the plug on the GSU25 and you lose the GSU25, GMU22, and the xponder. The GMU11 uses CAN Bus and would remain available to all if the GSU25 was offline.
 
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What do you mean by "changing to a GMU11"? I currently have a GMU22: do you mean to ADD a GMU11 dedicated to the G5, or REPLACE the GMU22 with a GMU11? When I was in the building phase 1y ago I explicitly asked this point to G3xpert, with regard to using the G5 as .

GMU 22 goes to AHRS and then data passed to CAN bus. G5 can grab the heading data off the CAN bus. However, if you power down the AHRS, the heading goes with it because the AHRS is it's bridge to the can bus. The GMU11 talks on the can bus directly, so G5 can get it with AHRS off line. If the G3X recognizes AHRS problems and grabs the G5 data, I suspect your gmu22 heading data will still be presented, but don't know for sure.

You don't need both. The G3X can get head data from either.

Larry
 
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I went to a lot of trouble centering my GSU25 right on the roll axis , but I guess the G5, located way off to the left of the 10” G3X Touch, will not benefit from this.:rolleyes:- Otis

You'll have to explain this one for me. An experiment to prove a counter theory to yours. Take a 2x4 and drill a hole in the middle and bolt to wall. Then set it at 5* from level. Take various measurements with a level across the 2x4 and let me know what variation you find at different points on the 2x4.

Larry
 
You'll have to explain this one for me. An experiment to prove a counter theory to yours. Take a 2x4 and drill a hole in the middle and bolt to wall. Then set it at 5* from level. Take various measurements with a level across the 2x4 and let me know what variation you find at different points on the 2x4.

Larry

I installed my GSU25 way off the center-line, following the same reasoning, but if from a static point of view you are right, I start to think that from a dynamic point of view the off-center mount would experience upward and downward accelerations while the plane is just banking. However this should not be a strong effect since I understand Garmin does not require center-line mount. More generally, can I ask where do people normally mount the GSU25 on an RV6/7/9? I put mine under the pilot seat, bolted to the bottom skin.
 
I installed my GSU25 way off the center-line, following the same reasoning, but if from a static point of view you are right, I start to think that from a dynamic point of view the off-center mount would experience upward and downward accelerations while the plane is just banking. However this should not be a strong effect since I understand Garmin does not require center-line mount. More generally, can I ask where do people normally mount the GSU25 on an RV6/7/9? I put mine under the pilot seat, bolted to the bottom skin.

My GSU73 is mounted behind the PFD between the panel and the sub panel. My GSU25 is mounted behind the MFD (on the copilots side) on the aft side of the subpanel. Centerline mounting is not required on these small airplanes.
 
If the G3X recognizes AHRS problems and grabs the G5 data, I suspect your gmu22 heading data will still be presented, but don't know for sure.

that's the main question, that is actually answered a few lines above by G3xpert: no automatic switch from G3x to G5 in case of miscompare: pilot must pull the GSU25 breaker. So the GMU22 is NEVER going to work in case of use of the G5 as Adahrs backup (despite what G3xpert wrote me a few months ago, but I had already purchased the GMU22 anyway, so no bad feelings :). I wonder if I can ADD a GMU11 to the G5 (I think it can screw to its back) while keeping all the rest unchanged (ie GMU22 feeding the GSU25 in normal conditions).
 
I installed my GSU25 way off the center-line, following the same reasoning, but if from a static point of view you are right, I start to think that from a dynamic point of view the off-center mount would experience upward and downward accelerations while the plane is just banking. However this should not be a strong effect since I understand Garmin does not require center-line mount. More generally, can I ask where do people normally mount the GSU25 on an RV6/7/9? I put mine under the pilot seat, bolted to the bottom skin.

True acceleration may be different, but all points on the axis get to the same degree of rotation at the same time. Just look at your propeller. Engine spinning at 2500 RPM. You have to assume the entire length of the blade is arriving at the same radial point at the same time / speed, otherwise it would be bending. The root and the tip get to the same place at the same time, relative to degrees of radial movement, during rotation. The tip just had to travel a further distance to get there. But that is not relevant when all we are measuring is the number or degree it has rotated across it's radial plane. The tip is moving faster than the root in a true speed sense, but it is not rotating on it's radial axis any faster than the root.

Larry
 
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You'll have to explain this one for me. An experiment to prove a counter theory to yours. Take a 2x4 and drill a hole in the middle and bolt to wall. Then set it at 5* from level. Take various measurements with a level across the 2x4 and let me know what variation you find at different points on the 2x4.

Larry

If the GMU25 is far off the center of the roll axis, it is describing an arc instead of pure rotation in roll, inducing a complicated and erroneous input of vertical and lateral accellerations when the only real displacement aboutthe 3-DC.G. is rotation about the roll axis. There may be compensating internal math to back that out, but That poor CPU is going to work hard to keep up with the situation! Mine is dead center span-wise and about 2.5? below the crankshaft axis. That second number is just a guess, of course, but probably not too far off. Finding the true vertical CG is tricky.- Otis
 
If the GMU25 is far off the center of the roll axis, it is describing an arc instead of pure rotation in roll, inducing a complicated and erroneous input of vertical and lateral accellerations when the only real displacement aboutthe 3-DC.G. is rotation about the roll axis. There may be compensating internal math to back that out, but That poor CPU is going to work hard to keep up with the situation! Mine is dead center span-wise and about 2.5” below the crankshaft axis. That second number is just a guess, of course, but probably not too far off. Finding the true vertical CG is tricky.- Otis

The AHRS will have three discrete sensors for each axis. Not sure how the roll axis could describe and arc, as an arc implies two axis'. The roll sensor will simply read degrees from level.

Does your wing form an arc when you are banked relative to your fuselage? The entire length of the wing is tilted at the same number of degrees from level as the tip of the wing is. Maybe I didn't take enough physics, but I am not understanding your issue here. Leaving dihedral out of this simple example.

A graphical representation would be an arc. However, that is "representation" and not related to a sensor that only capture movement across once axis.

Take my 2x4 example. How does the presence or absence of an arc impact the level's reading? It is either 5* from level or it is not. It is that binary.

Larry
 
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If you have a GMU 22, and you want to ensure that you have heading data if you lose the GSU 25, you can simply add a GMU 11 to your system. The G3X and G5 share a CAN bus, so once you install the GMU 11 on the CAN bus, it could be used by either the G5 or the GSU 25.

Regarding placement of an AHRS unit, the ideal location is in the center of rotation for all 3 axis. However, that is not practical or required for good performance in a small aircraft. When you are not on the center of rotation, in a dynamic maneuver you will add some error to the reading. For instance, if the AHRS were mounted out in the left wing, rolling left would be seen as a left bank but also as a vertical acceleration downward as the wing drops. In a small aircraft the affects are pretty small. The following note in the installation manual is written for this very purpose:

The GSU 25 should be mounted within 13 feet (4.0 meters) longitudinally and 6.5 feet (2.0 meters) laterally of the aircraft CG (center of gravity). In cases where the longitudinal distance from the CG is planned to be greater than 6.5 feet (2.0 meters), it is preferable to mount the GSU 25 forward of the aircraft CG if possible, to enable better acceleration outputs for autopilot use.

Thanks,
Levi Self

Team X Project Manager
 
The AHRS will have three discrete sensors for each axis. Not sure how the roll axis could describe and arc, as an arc implies two axis'. The roll sensor will simply read degrees from level.

Does your wing form an arc when you are banked relative to your fuselage? The entire length of the wing is tilted at the same number of degrees from level as the tip of the wing is. Maybe I didn't take enough physics, but I am not understanding your issue here. Leaving dihedral out of this simple example.

A graphical representation would be an arc. However, that is "representation" and not related to a sensor that only capture movement across once axis.

Take my 2x4 example. How does the presence or absence of an arc impact the level's reading? It is either 5* from level or it is not. It is that binary.

Larry

Larry, During maneuvers, the aircraft rotates about its 3-D CG. Imagine the extreme of installing the GMU25 in a wingtip. During an abrupt roll, it would register the roll, a non-existent sharp climb, and a significant non-existent lateral acceleration. If you can agree that the wingtip would be a really bad place to put the GMU25, it follows that any other location apart from the roll axis is also bad, albiet less and less so as you approach the roll axis. This points pretty convincingly to the roll axis as the best of all possible locations. The same argument applies to both of the other axis, but to a lesser degree because of the much gentler nature of rotation about those axis during maneuvers.-Otis
 
Larry, During maneuvers, the aircraft rotates about its 3-D CG. Imagine the extreme of installing the GMU25 in a wingtip. During an abrupt roll, it would register the roll, a non-existent sharp climb, and a significant non-existent lateral acceleration. If you can agree that the wingtip would be a really bad place to put the GMU25, it follows that any other location apart from the roll axis is also bad, albiet less and less so as you approach the roll axis. This points pretty convincingly to the roll axis as the best of all possible locations. The same argument applies to both of the other axis, but to a lesser degree because of the much gentler nature of rotation about those axis during maneuvers.-Otis

Why would a wing drop be read as a climb. The fact that the wingtip fell relative to gravity has no bearing on the pitch axis. It may mess with the units measurement of lateral G forces, but no bearing on pitch or roll indication. The AHRS would only show a climb if it' relative pitch angle increased and a wing drop in a roll won't do that. As long as the pitch axis is unchanged, a wing drop would not show a climb unless the aircrafts pitch axis also changed along with it's roll axis.

I don't mean to argue and will stop here. I think you and I have different ideas as to what is being measured inside of an AHRS and neither of us has the background to settle that argument.

Larry
 
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If you have a GMU 22, and you want to ensure that you have heading data if you lose the GSU 25, you can simply add a GMU 11 to your system. The G3X and G5 share a CAN bus, so once you install the GMU 11 on the CAN bus, it could be used by either the G5 or the GSU 25.

Regarding placement of an AHRS unit, the ideal location is in the center of rotation for all 3 axis. However, that is not practical or required for good performance in a small aircraft. When you are not on the center of rotation, in a dynamic maneuver you will add some error to the reading. For instance, if the AHRS were mounted out in the left wing, rolling left would be seen as a left bank but also as a vertical acceleration downward as the wing drops. In a small aircraft the affects are pretty small. The following note in the installation manual is written for this very purpose:

The GSU 25 should be mounted within 13 feet (4.0 meters) longitudinally and 6.5 feet (2.0 meters) laterally of the aircraft CG (center of gravity). In cases where the longitudinal distance from the CG is planned to be greater than 6.5 feet (2.0 meters), it is preferable to mount the GSU 25 forward of the aircraft CG if possible, to enable better acceleration outputs for autopilot use.

Thanks,
Levi Self

Team X Project Manager

Levi- I missed this response prior to posting just below. Glad to hear confirmation that the center of rotation is the ideal, but surprised by the generous off-center allowances. And my bad, GSU25 not GMU25. I guess the fact that it cross-references pitot , static, and AOA with accelleration data makes this possible. I?m still going for the center!

Your team?s active participation in this forum is very much appreciated by all!- Otis
 
If you have a GMU 22, and you want to ensure that you have heading data if you lose the GSU 25, you can simply add a GMU 11 to your system. The G3X and G5 share a CAN bus, so once you install the GMU 11 on the CAN bus, it could be used by either the G5 or the GSU 25.

Regarding placement of an AHRS unit, the ideal location is in the center of rotation for all 3 axis. However, that is not practical or required for good performance in a small aircraft. When you are not on the center of rotation, in a dynamic maneuver you will add some error to the reading. For instance, if the AHRS were mounted out in the left wing, rolling left would be seen as a left bank but also as a vertical acceleration downward as the wing drops. In a small aircraft the affects are pretty small. The following note in the installation manual is written for this very purpose:

The GSU 25 should be mounted within 13 feet (4.0 meters) longitudinally and 6.5 feet (2.0 meters) laterally of the aircraft CG (center of gravity). In cases where the longitudinal distance from the CG is planned to be greater than 6.5 feet (2.0 meters), it is preferable to mount the GSU 25 forward of the aircraft CG if possible, to enable better acceleration outputs for autopilot use.

Thanks,
Levi Self

Team X Project Manager


Thanks, do you think that the 3d vision will come back once I have installed the GMU11, when I pull the GSU25 breaker?
 
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Thanks, do you think that the 3d vision will come back once I have installed the GMU11, when I pull the GSU25 breaker?

If the G3X Touch has reverted to using the G5 ADAHRS data because the GSU 25 is powered down/failed and you have a GMU 11, the G3X Touch Display will show the G5 Attitude and Air Data with Synthetic Vision.

Thanks,
Levi Self

Team X Project Manager
 
Larry and Otis,

You would both be correct IF your assumptions of what is happening inside of the little black box (GSU 25) were correct.

There are 3 axis gyros and accelerometers inside the GSU 25 which are used in complex algorithms written by some of the smartest engineers (not me :p) to output an attitude solution as well as the turn rate indicator and slip skid indicator.

Because acceleration data is used by the system, an erroneous acceleration due to GSU placement would have a negative affect on performance of these indications. As stated in an earlier post, the G3X Install manual covers what locations are acceptable. If you follow this guidance, you will not have an issue.

Another simple way to think about this is to take the example of the slip skid indicator, which is a measure of lateral acceleration. If the GSU was in a wingtip and you did an aileron roll, you would measure lateral acceleration, but you could still be perfectly coordinated.

Thanks,
Levi Self

Team X Project Manager
 
Larry and Otis,

You would both be correct IF your assumptions of what is happening inside of the little black box (GSU 25) were correct.

There are 3 axis gyros and accelerometers inside the GSU 25 which are used in complex algorithms written by some of the smartest engineers (not me :p) to output an attitude solution as well as the turn rate indicator and slip skid indicator.

Because acceleration data is used by the system, an erroneous acceleration due to GSU placement would have a negative affect on performance of these indications. As stated in an earlier post, the G3X Install manual covers what locations are acceptable. If you follow this guidance, you will not have an issue.

Another simple way to think about this is to take the example of the slip skid indicator, which is a measure of lateral acceleration. If the GSU was in a wingtip and you did an aileron roll, you would measure lateral acceleration, but you could still be perfectly coordinated.

Thanks,
Levi Self

Team X Project Manager

Thanks for clarifying and helping us better understand what is happening inside the black box.

Larry
 
Larry and Otis,

You would both be correct IF your assumptions of what is happening inside of the little black box (GSU 25) were correct.

There are 3 axis gyros and accelerometers inside the GSU 25 which are used in complex algorithms written by some of the smartest engineers (not me :p) to output an attitude solution as well as the turn rate indicator and slip skid indicator.

Because acceleration data is used by the system, an erroneous acceleration due to GSU placement would have a negative affect on performance of these indications. As stated in an earlier post, the G3X Install manual covers what locations are acceptable. If you follow this guidance, you will not have an issue.

Another simple way to think about this is to take the example of the slip skid indicator, which is a measure of lateral acceleration. If the GSU was in a wingtip and you did an aileron roll, you would measure lateral acceleration, but you could still be perfectly coordinated.

Thanks,
Levi Self

Team X Project Manager

Yes, ditto to Larry?s comment, it is refreshing to have a company insider make the effort to take some of the mystery out of a very complex system. -Otis
 
If the G3X Touch has reverted to using the G5 ADAHRS data because the GSU 25 is powered down/failed and you have a GMU 11, the G3X Touch Display will show the G5 Attitude and Air Data with Synthetic Vision.

Thanks,
Levi Self

Team X Project Manager

As per my posted pictures, when I pull the GSU25 breaker, I also lose the transponder. I understand if I install the GMU11 I will no longer lose HDG nor 3d vision: is there something I can do to keep the transponder as well when I revert to G5 as adahrs backup by pulling the GSU25 breaker (which, I understand, is the only way to use the G5 as adahrs backup)? I have a remote GTX23ES. thanks
 
As per my posted pictures, when I pull the GSU25 breaker, I also lose the transponder. I understand if I install the GMU11 I will no longer lose HDG nor 3d vision: is there something I can do to keep the transponder as well when I revert to G5 as adahrs backup by pulling the GSU25 breaker (which, I understand, is the only way to use the G5 as adahrs backup)? I have a remote GTX23ES. thanks

When the GSU 25 is powered off, you lose control of the transponder and the transponder will lose air data. However, the transponder will continue transmitting. If you are talking to ATC you will likely get a call from ATC that they have lost your altitude, as this information is provided to the GTX from the GSU.

The above information is true for both the GTX 23ES and the GTX 35R and 45R.

Thanks,
Levi Self

Team X Project Manager
 
I tested my setup today by powering off the GSU25 and I lost transponder, OAT and TAS, no other abnormal behavior was noted.

Here is the following messages I got.
AHRS REVERT
ADC REVERT
AHRS FAIL
ADC FAIL
AOA FAIL

When I powered the GSU 25 back on, everything came back to normal.

I have a GMU 11 installed.
 
I tested my setup today by powering off the GSU25 and I lost transponder, OAT and TAS, no other abnormal behavior was noted.

Did the transponder stop transmitting or just lose it's altitude and it's display on the G3X? Guessing you may not know.

Larry
 
Did the transponder stop transmitting or just lose it's altitude and it's display on the G3X? Guessing you may not know.

Larry
Hi Larry,
I do not know, I had a red X cross the transponder, OAT and TAS. Based on that, I am guessing it was not working. Attitude was working as normal and correspond to the G5. Auto pilot was also functional as normal, thought I did not try any approaches.
 
Did the transponder stop transmitting or just lose it's altitude and it's display on the G3X? Guessing you may not know.

Larry

The experts touched on this a post or two back.

When the GSU 25 is powered off, you lose control of the transponder and the transponder will lose air data. However, the transponder will continue transmitting. If you are talking to ATC you will likely get a call from ATC that they have lost your altitude, as this information is provided to the GTX from the GSU.

The above information is true for both the GTX 23ES and the GTX 35R and 45R.

Thanks,
Levi Self

Team X Project Manager
 
After reading my post, I thought I should add one more clarification about transponder operation. :D

The GTX will remain in the current state if it loses communication with the G3X. If the transponder is in air and transmitting, it will continue to do so. However, if the transponder is in standby, it will not start transmitting when you lose communication. The G3X gives you the red X since the state of the GTX is unknown to the G3X and we are very careful to never show misleading information.

One other point which was not specifically mentioned below is that you do lose AOA if you have no GSU 25 with AOA functioning. This is indicated by the AOA FAIL message.

Thanks,
Levi Self
 
After reading my post, I thought I should add one more clarification about transponder operation. :D

The GTX will remain in the current state if it loses communication with the G3X. If the transponder is in air and transmitting, it will continue to do so. However, if the transponder is in standby, it will not start transmitting when you lose communication. The G3X gives you the red X since the state of the GTX is unknown to the G3X and we are very careful to never show misleading information.

One other point which was not specifically mentioned below is that you do lose AOA if you have no GSU 25 with AOA functioning. This is indicated by the AOA FAIL message.

Thanks,
Levi Self

Thanks for the clarification.
 
2 out 3 issue

It seems to be dual ADAHRS and if they are not the same the G5 breaks the tie. Easy enough I guess as the G3X warns you something is not right and then we look to the G5 to agree with one of them while we take the other off line. I think that's what I read. (I am a Dynon user but building a 14 and in the next few weeks need to decide on avionics, probably Garmon this time) Dual G3X touch and a 750. Rather than go through the decision to decide which ADAHRS is correct, can 3 ADAHRS be used and the G3X decides which 2 to use. Since they are on canbus seems possible but not sure. Any help from a Garmin expert.
 
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