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  #1  
Old 04-12-2021, 06:53 PM
Terry Lutz Terry Lutz is offline
 
Join Date: Dec 2005
Posts: 194
Default Ground Test For Autopilot Autotrim Function

I've just completed an autopilot install on my RV-8. The panel has a G3X Touch, a GPS175, and a GMC507. The avionics tech I've worked with and myself have done the ground set up with basic settings and gains recommended by Garmin. And we've ground tested the system according to the G3X install manual. We are wondering if there is a way, on the ground, to test the autotrim functions? For example, is there a test were we can observe the trim motors moving the tabs (I'm using an aileron trim tab for roll trim)? I spoke with Garmin today, and the guy said he didn't think so, but he had heard there might be a way to do it. Any ideas out there?
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  #2  
Old 04-12-2021, 10:19 PM
wnplt wnplt is offline
 
Join Date: Feb 2013
Location: Idaho
Posts: 211
Default

TruTrak has a auto trim servo test. Maybe itís the same.
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  #3  
Old 04-13-2021, 06:39 AM
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Walt Walt is offline
 
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Location: Dallas/Ft Worth, TX
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Quote:
Originally Posted by Terry Lutz View Post
I've just completed an autopilot install on my RV-8. The panel has a G3X Touch, a GPS175, and a GMC507. The avionics tech I've worked with and myself have done the ground set up with basic settings and gains recommended by Garmin. And we've ground tested the system according to the G3X install manual. We are wondering if there is a way, on the ground, to test the autotrim functions? For example, is there a test were we can observe the trim motors moving the tabs (I'm using an aileron trim tab for roll trim)? I spoke with Garmin today, and the guy said he didn't think so, but he had heard there might be a way to do it. Any ideas out there?
Yes there is, I think it's in the trim page, could walk you thru when I'm at the hanger.
I recommend you first pull the AP CB and verify trim runs correctly.
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  #4  
Old 04-13-2021, 07:33 AM
lr172 lr172 is offline
 
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Location: Schaumburg, IL
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They give you a button in config mode that has the AP actuate trim in different directions to confirm that the orientation matches your wiring. There is also a setting to reverse the orientation if it doesn't match.
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  #5  
Old 04-14-2021, 07:06 AM
Terry Lutz Terry Lutz is offline
 
Join Date: Dec 2005
Posts: 194
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Thanks for the responses. Walt, I'll try to call on Thursday afternoon, if you will be in the shop. We did verify that trim moves in the proper direction when on the autopilot, but wondered if there is another test where we can observe autotrimming on ground before going to flight.
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  #6  
Old 04-14-2021, 08:04 AM
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g3xpert g3xpert is offline
 
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Location: Olathe, KS
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Default Auto-Trim Function

Quote:
Originally Posted by Terry Lutz View Post
Thanks for the responses. Walt, I'll try to call on Thursday afternoon, if you will be in the shop. We did verify that trim moves in the proper direction when on the autopilot, but wondered if there is another test where we can observe autotrimming on ground before going to flight.
Auto-Trim is inhibited on the ground, to prevent the GSA 28 from altering your pre-takeoff trim setting. Section 35.4.10 of the G3X Touch Installation Manual provides detailed instructions to assure the autopilot (including trim control) has been installed and configured correctly. If you have confirmed each step of that section in order, your system should be safe to fly, however taking the precautions outlined in Appendix A of the same manual is still highly advised.

Appendix A provides an outline for initial Autopilot engagement, and tuning. There are important pieces of guidance contained in this section relating to the first flight, including the disabling of Trim motor controls, to prevent the engagement of auto-trim during the first flight all together. We want to ensure proper autopilot mode operation and performance before ever getting to auto-trim performance.

Please let us know if you have any other questions, we are happy to help. It is always best to keep an SD card in the display, flight data logs can be especially helpful in analyzing autopilot performance and identifying any room for improvement.

Thanks,

Justin
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  #7  
Old 04-14-2021, 07:03 PM
Terry Lutz Terry Lutz is offline
 
Join Date: Dec 2005
Posts: 194
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Thanks for the reply Justin. We did the initial setup on the ground with the auto trim disabled, as directed on page A-1. However, it doesn't say to enable the auto trim later on for the ground tests. I found the guidance for the tests inflight with the auto trim disabled, but it was in Ch 34 and not Appendix A. I have some basic idea of how to test the auto trim, which I can do after all the other tests. Do you have any guidance on testing auto trim inflight? The doesn't appear to be any guidance in Appendix A. The airplane is just returning to flight after winter maintenance, so I have other tests to do as well. After a leak check on ground tomorrow, I should be ready to fly when weather is suitable.
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