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  #11  
Old 03-15-2021, 10:56 AM
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Dugaru Dugaru is offline
 
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Default That explains it...

I don't have a G3X!

Quote:
Originally Posted by Walt View Post
Can be found in the G3X install manual.
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  #12  
Old 03-15-2021, 10:57 AM
lr172 lr172 is online now
 
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Quote:
Originally Posted by Walt View Post
Can be found in the G3X install manual.
Yes, It is in one of the appendices.
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  #13  
Old 03-15-2021, 10:59 AM
lr172 lr172 is online now
 
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Quote:
Originally Posted by Dugaru View Post
I don't have a G3X!
It might still work. They have you adjust gain unti getting a certain amount of oscillations before stabilizing and then back off a certain amount. That approach should work with most PID logic that I believe all AP's use, though I suspect some variability in the approach and the back off amount is not likely to be portable to other systems. That is likely unique to the Garmin code base.

Larry
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  #14  
Old 03-15-2021, 12:18 PM
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Dugaru Dugaru is offline
 
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Default I think I'm on the right track

I've got the Garmin autopilot running off of a G5 and a GMC 307, so presumably it's the same procedure. I just don't have the manual for the G3X.

Many thanks!

Quote:
Originally Posted by lr172 View Post
It might still work. They have you adjust gain unti getting a certain amount of oscillations before stabilizing and then back off a certain amount. That approach should work with most PID logic that I believe all AP's use, though I suspect some variability in the approach and the back off amount is not likely to be portable to other systems. That is likely unique to the Garmin code base.

Larry
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  #15  
Old 03-15-2021, 01:44 PM
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g3xpert g3xpert is offline
 
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Default AP Porpoise

Quote:
Originally Posted by Dugaru View Post
I've got the Garmin autopilot running off of a G5 and a GMC 307, so presumably it's the same procedure. I just don't have the manual for the G3X.

Many thanks!
The G3X Installation Manual can be downloaded here, Appendix A contains the autopilot tuning outline.

Does your autopilot porpoise occur in ALT mode only?

You will want to first verify that PIT mode is working as it should, per the outline in Appendix A. If it is, you can move on to optimizing ALT hold mode. ALT mode is controlled by the Vertical Speed Gain. Instructions for tuning the Vertical Speed Gain are also included in Appendix A, but it is very important that you ensure PIT mode is working correctly before getting to it. The Vertical Speed gain relies on the standard pitch gain (what you change to optimize PIT mode) being correctly tuned for the airframe.

Please feel free to email us at G3Xpert@Garmin.com if you would like.

Thanks,

Justin
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  #16  
Old 03-15-2021, 04:06 PM
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Dugaru Dugaru is offline
 
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Default porpoising

Good question! I'll download the instructions and give it a whirl, in that order. Many thanks for the info.

Quote:
Originally Posted by g3xpert View Post
The G3X Installation Manual can be downloaded here, Appendix A contains the autopilot tuning outline.

Does your autopilot porpoise occur in ALT mode only?

You will want to first verify that PIT mode is working as it should, per the outline in Appendix A. If it is, you can move on to optimizing ALT hold mode. ALT mode is controlled by the Vertical Speed Gain. Instructions for tuning the Vertical Speed Gain are also included in Appendix A, but it is very important that you ensure PIT mode is working correctly before getting to it. The Vertical Speed gain relies on the standard pitch gain (what you change to optimize PIT mode) being correctly tuned for the airframe.

Please feel free to email us at G3Xpert@Garmin.com if you would like.

Thanks,

Justin
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  #17  
Old 07-11-2021, 03:00 PM
ljbuller ljbuller is offline
 
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Default porpoise after rain

Quote:
Originally Posted by DanBaier View Post
If the tweaks don't work, you might have a problem with the static source - there can be a reservoir effect with too many gadgets hooked up and then the altitude hold does a lot of hunting and can't keep up. If that turns out to be the case, you'll want to consider a dedicated static line for the autopilot.
I realize this thread is relating to the Garmin, but bear with me here. My RV7A with dynon skyview ap (ver 16 firmware) and ray allen trim. The pitch, pitch trim and everything works great, EXCEPT. If its raining when I take off, it will develop a pitch porpoise. I have safe air static ports, one on each side, normal location with the tubes from each angling up so water should not be able to collect. I am using the Dynon non heated pitot tube. Dan, you mentioned the reservoir effect. If it did not work normally, I would accept that. The static line does go all the way forward to my D6 standby (which is rock solid)

Is there any possibility that the holes in the static port could be enlarged a bit?

Its almost like a drop of water gets in the static port and the autopilot senses that, however when I get back on the ground, the ports are clear and I can suck air from one side to the other.

I have tried slipping the aircraft trying to put a cross flow to clear it with no help.

I have also tweaked the pitch settings to no avail. remember it works great when the take of is dry. some of the older cessnas had a bulb near the static port. seems like that would be a problem as well, but of course most of those airplanes did not have an auto pilot.
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  #18  
Old 07-12-2021, 10:23 AM
lr172 lr172 is online now
 
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Default

Quote:
Originally Posted by ljbuller View Post
I realize this thread is relating to the Garmin, but bear with me here. My RV7A with dynon skyview ap (ver 16 firmware) and ray allen trim. The pitch, pitch trim and everything works great, EXCEPT. If its raining when I take off, it will develop a pitch porpoise. I have safe air static ports, one on each side, normal location with the tubes from each angling up so water should not be able to collect. I am using the Dynon non heated pitot tube. Dan, you mentioned the reservoir effect. If it did not work normally, I would accept that. The static line does go all the way forward to my D6 standby (which is rock solid)

Is there any possibility that the holes in the static port could be enlarged a bit?

Its almost like a drop of water gets in the static port and the autopilot senses that, however when I get back on the ground, the ports are clear and I can suck air from one side to the other.

I have tried slipping the aircraft trying to put a cross flow to clear it with no help.

I have also tweaked the pitch settings to no avail. remember it works great when the take of is dry. some of the older cessnas had a bulb near the static port. seems like that would be a problem as well, but of course most of those airplanes did not have an auto pilot.
If it only happens when raining before T/O, I would assume that water is messing with something and the static ports are the most logical. I would look closer at the port setup to be sure you are not collecting water there. Might consider a tee, with a small stub going downward to let water move away.

Angling up is not the recommended approach. A 90* fitting is recommended. If the angle is too slight, the water can possibly collect.
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Last edited by lr172 : 07-12-2021 at 10:25 AM.
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