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-   -   Surprise Pitch Trim Excursion (https://vansairforce.net/community/showthread.php?t=144436)

czechsix 11-30-2016 08:22 AM

G3X autopilot has these protection features built in
 
If you install the G3X autopilot and wire the trim system per the installation manual, the autopilot will disconnect immediately if you touch the trim switch (just like certified autopilot systems). G3X also allows you to configure trim speed vs airspeed (so it runs slower at higher airspeeds) and you can configure a trim run time limit as an additional safety feature.

istrumit 11-30-2016 08:41 AM

Yes. I am aware of the long standing and much discussed solutions proposed. Both the trim protection and the co-pilot disconnect switch.

I looked at three different -10s when selecting this one, and two of them had copilot disconnect.

This one didn't, but man was it absolutely loaded with everything else I could have wanted.

I have not been at all concerned about it. My wife and I have been flying together for 22 years and she knows what to do and what not to do.

But, by son has only been in the front seat three times...my fault for not thoroughly briefing him.

Besides that lesson, the other lesson is that the RV-10 can indeed withstand an auto-pilot disconnect with full pitch up trim. It really didn't seem to stress the plane, but it did the stress the passengers.

bkthomps 11-30-2016 09:21 AM

Shouldn't trim disconnect the auto pilot? it does on my G3X setup, then again, my servos are commanding trim

istrumit 11-30-2016 12:34 PM

I have a G900X with a TruTrak Sorcerer.

The Sorcerer does not have an auto-trim function, at least its not set up on this plane if it does.

The Sorcerer provides on-screen feedback directing you to trim neutral in one direction or the other while the AP is engaged.

vlittle 11-30-2016 04:40 PM

It would make sense to mount the copilot/pax trim switches (and PTTs) on the panel (side by side) or bulkhead (tandem). It's very easy for a pax to accidentally active the trim switch in a stick.

In the G3X system, this disconnects the autopilot, which is annoying.

I developed an autotrim system for SkyView systems that allows trim inputs without autopilot disconnect. I think it should always be the pilot's decision on when the autopilot disconnects and that automatic disconnects can lead to unexpected behavior, even with audio alerts. [Note, there was a bug in the old Garmin 296 that could cause DigiTrak autopilots to silently switch from ground track to heading mode, leading you off course without alerts!]

My autotrim controller also includes a trim fault system that detects and corrects stuck switches or conflicting copilot switch input without 3-second time-outs on the trim input. If you ever have done a touch and go in a Harmon Rocket, you'll quickly see that you need several seconds of trim down or the climb rate will be very uncomfortable/dangerous. To have a trim controller shut off by making a wrong assumption is IMHO wrong. Again, I don't like the aircraft making assumptions/decisions for the pilot. Much better to detect and alert on fault rather than autonomously take action.

In the same vein, auto-flap systems that retract flaps when above Vfe are making decisions best left to the pilot. During a forced landing, I just may want to put my flaps out at >Vne if my life depended on it.

These are just opinions FWIW.

czechsix 11-30-2016 06:24 PM

Quote:

Originally Posted by vlittle (Post 1130813)
It would make sense to mount the copilot/pax trim switches (and PTTs) on the panel (side by side) or bulkhead (tandem). It's very easy for a pax to accidentally active the trim switch in a stick.

In the G3X system, this disconnects the autopilot, which is annoying.

If you don't want autopilot disconnects due to inadvertent trim activation by the passenger you can locate the trim switch where it's less likely to be bumped (as you suggested) or add a switch that de-activates the passenger switch functions when not needed. The latter is pretty easy to do since most of the functions typically located on the stick are activated via a path to ground, so if you simply open the ground path you've accomplished the objective.

Quote:

Originally Posted by vlittle (Post 1130813)
I developed an autotrim system for SkyView systems that allows trim inputs without autopilot disconnect.

Autotrim by definition means the autopilot is automatically trimming the aircraft. No autopilot will disconnect itself when it is commanding the trim to run.

Quote:

Originally Posted by vlittle (Post 1130813)
I think it should always be the pilot's decision on when the autopilot disconnects and that automatic disconnects can lead to unexpected behavior

The whole point of disconnecting as soon as an external trim input is detected is to avoid the unexpected behavior experienced by the original poster in this thread.


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