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  #51  
Old 09-20-2022, 03:50 PM
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RV7A Flyer RV7A Flyer is offline
 
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I don't have an auto-pilot, but I do have a question.... How can you trim with the AP engaged? It would be like you, the pilot, trimming while the co-pilot is trying to keep the aircraft level.
Exactly. And this is how autopilots have worked for decades (unless they have autotrim capability). The autopilot doesn't have any idea *what* is causing the aerodynamic force that is pushing it off of the setpoint (or outside the deadband). Could be a trim tab, could be the pilot or copilot pushing on the stick, could be a gust of wind, could be a change in power setting...all it "knows" is that the airplane is deviating from the setpoint, and it needs to send the signal to the servo to move the control surface to correct back to the setpoint.
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  #52  
Old 09-20-2022, 03:59 PM
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Originally Posted by gasman View Post
I don't have an auto-pilot, but I do have a question.... How can you trim with the AP engaged? It would be like you, the pilot, trimming while the co-pilot is trying to keep the aircraft level.

Not knowing what I am talking about, I might think that disabling the trim power during the time the AP is active (and vise versa) would be no brainer.
If the autopilot doesn't have an auto trim function, the usual method is get the aircraft stabilized in cruise and carefully trimmed. Then the autopilot is engaged and the servo doesn't need to fight an out-of-trim condition. This works fine until a lot of fuel has been burned or large airspeed changes occur which requires retrimming. The autopilot can be briefly disengaged to check/reset trim then re-engaged....or you can hand fly the altitude change or approach.

Large pitch excursions when the auto pilot is released are usually caused by not having the aircraft in proper trim when the autopilot is engaged. We're talking basic airmanship here.
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Last edited by Sam Buchanan : 09-20-2022 at 04:02 PM.
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  #53  
Old 09-20-2022, 05:40 PM
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Originally Posted by Sam Buchanan View Post
If the autopilot doesn't have an auto trim function, the usual method is get the aircraft stabilized in cruise and carefully trimmed. Then the autopilot is engaged and the servo doesn't need to fight an out-of-trim condition. This works fine until a lot of fuel has been burned or large airspeed changes occur which requires retrimming. The autopilot can be briefly disengaged to check/reset trim then re-engaged....or you can hand fly the altitude change or approach.

Large pitch excursions when the auto pilot is released are usually caused by not having the aircraft in proper trim when the autopilot is engaged. We're talking basic airmanship here.
I have a Dynon SkyView Touch with the Dynon autopilot, but do not have auto-trim (the separate AP panel is needed for that function).

You can keep the AP engaged through cruise, turns, climbs, and descents, and any time the AP senses that the airplane needs to be retrimmed, it prompts the pilot to retrim manually (via electric trim in my case), all while the AP stays engaged. The prompt is a visual alert followed by an aural alert 10 seconds later, e.g., "Trim Nose Down". The prompt goes away once the airplane is back in trim.
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Last edited by RV8JD : 09-20-2022 at 06:08 PM. Reason: "Manual" trim clarified.
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  #54  
Old 09-20-2022, 05:57 PM
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Originally Posted by RV8JD View Post
I have a Dynon SkyView Touch with the Dynon autopilot, but do not have auto-trim (the separate AP panel is needed for that function).

You can keep the AP engaged through cruise, turns, climbs, and descents, and when the AP senses that the airplane needs to be retrimmed, it prompts the pilot to retrim manually, all while the AP stays engaged. The prompt is a visual alert and then an aural alert 10 seconds later, e.g., "Trim Nose Down". The prompt goes away once the airplane is in trim.
I can see this working great with manual (non electric) trim. But with electric trim (operated manually) that can get activated many ways without you knowing, just looks like a failure point that can be avoided with some simple wiring changes to avoid a runaway trim with the auto pilot engaged.
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Last edited by gasman : 09-20-2022 at 11:27 PM. Reason: added bold print
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  #55  
Old 09-20-2022, 05:59 PM
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Originally Posted by gasman View Post
I can see this working great with manual trim. But with electric trim that can get activated many ways without you knowing, just looks like a failure point that can be avoided with some simple wiring changes.
I should clarify that I have electric trim. I used the phrase "manual trim" (by the pilot) to differentiate from "auto-trim" (by the system). The system has worked well for 1250 hours so far. I edited my post above.
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Last edited by RV8JD : 09-20-2022 at 07:06 PM.
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  #56  
Old 09-20-2022, 06:04 PM
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Originally Posted by gasman View Post
I can see this working great with manual trim. But with electric trim that can get activated many ways without you knowing, just looks like a failure point that can be avoided with some simple wiring changes.
Such as...? A RAC servo with no relay box and no autotrim is about as simple as a circuit could possibly get. Battery-fuse-switch-servo-ground.

There are some additional wires for talkback to an indicator or EFIS, but those are low-voltage data serial lines, not power for the servo.
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  #57  
Old 09-20-2022, 10:33 PM
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Quote:
Originally Posted by RV8JD View Post
I have a Dynon SkyView Touch with the Dynon autopilot, but do not have auto-trim (the separate AP panel is needed for that function).

You can keep the AP engaged through cruise, turns, climbs, and descents, and any time the AP senses that the airplane needs to be retrimmed, it prompts the pilot to retrim manually (via electric trim in my case), all while the AP stays engaged. The prompt is a visual alert followed by an aural alert 10 seconds later, e.g., "Trim Nose Down". The prompt goes away once the airplane is back in trim.
I get the same thing; the autopilot squawking that the trim needs to be set UP or DOWN. It's fairly tolerant of the airplane being more out of trim than you'd like if you were hand-flying. You can tell by how much you feel like you need to adjust the trim once you turn the autopilot off and take over. But the autopilot is actually not bad and only nags for trim adjustment on fairly rapid climbs or descents. One thing I've realized through all this is that I'd like to have an autopilot with auto-trim. Apparently Dynon doesn't have it, does Garmin? Or if not, who does?
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  #58  
Old 09-20-2022, 10:46 PM
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One thing I've realized through all this is that I'd like to have an autopilot with auto-trim. Apparently Dynon doesn't have it, does Garmin? Or if not, who does?
Yes, Dynon does offer auto trim. As I said in my post, you need the separate autopilot control panel to get auto trim. You can add it to your existing SkyView system.

Link --> https://dynonavionics.com/autopilot-control-panel.php

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"The Autopilot control panel is also a full featured dual-axis trim controller. It can control your electric pitch and/or roll trim motors, replacing the relay decks normally used.

With Autopilot Auto-Trim, the SV-AP-PANEL can keep the the aircraft in trim while under autopilot control. This eliminates the need for the pilot to manually actuate their trim to follow the Autopilot’s built-in trim advice. "
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Last edited by RV8JD : 09-20-2022 at 10:49 PM.
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  #59  
Old 09-20-2022, 11:34 PM
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Originally Posted by RV8JD View Post
I should clarify that I have electric trim. I used the phrase "manual trim" (by the pilot) to differentiate from "auto-trim" (by the system). The system has worked well for 1250 hours so far. I edited my post above.
I also went back and made some changes (in bold) to my post to make my concern a little clearer.
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  #60  
Old 09-21-2022, 12:44 AM
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Quote:
Originally Posted by Sam Buchanan View Post
If the autopilot doesn't have an auto trim function, the usual method is get the aircraft stabilized in cruise and carefully trimmed. Then the autopilot is engaged and the servo doesn't need to fight an out-of-trim condition. This works fine until a lot of fuel has been burned or large airspeed changes occur which requires retrimming. The autopilot can be briefly disengaged to check/reset trim then re-engaged....or you can hand fly the altitude change or approach.

Large pitch excursions when the auto pilot is released are usually caused by not having the aircraft in proper trim when the autopilot is engaged. We're talking basic airmanship here.
Then a safe way to wire the trim is to have it active only when the auto pilot is disengaged..... unless you HAVE auto trim.
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