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  #1  
Old 12-26-2019, 08:57 AM
AaronG AaronG is offline
 
Join Date: Sep 2009
Location: Hartford, CT
Posts: 107
Default G3X ESP Learning Experience

Thought I would share a recent experience with the G3X in the interest of safety. Last Saturday, I got distracted during the preflight and forgot to remove the pitot cover. Realized my error on the takeoff roll but decided to continue the takeoff and return to the airport. I know the sound and feel of the plane well enough that flying without airspeed is not a big deal.

At 500 feet the ESP system kicked in. It seems like it saw the zero airspeed, and aggressively started to push the nose down. It automatically turns on the autopilot to do this. Best I can tell it then started to trim nose down as well when I started fighting the autopilot. Fortunately it appears you can override the G3X trimming with the trim button on the stick, so I trimmed nose up, and then pulled the trim circuit breaker.

At this point, I was on downwind and still fighting the autopilot. My first thought was to turn off the master and kill all the electronics, but then I remembered the ESP turn off switch wired on the panel. Flipped the switch and all was well from there.

So my lessons learned:

- Make sure you understand the ESP system and how it works
- Know how to turn off the system, especially if you don?t have the cockpit switch
- Know how to quickly turn off the trim motor. I have a yellow cap on my circuit breaker that allowed me to quickly pull the correct breaker
- Make sure the autopilot torque is set so you can override in flight
- Fly the plane

I consider myself lucky that I have significant hours in the RV?s and had the bandwidth to fly while dealing with the issue. It all happened very quickly and near the ground. For this to happen on a first flight that near the ground, it could have quickly become dangerous.

Aaron
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  #2  
Old 12-26-2019, 09:43 AM
Walt's Avatar
Walt Walt is offline
 
Join Date: Aug 2005
Location: Dallas/Ft Worth, TX
Posts: 6,340
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Good job on keeping cool and just flying the airplane!

Interesting, according to the G3X pilots guide AP engagement should not occur below 2K ft. AGL. You can also enable ESP without the automatic AP engagement feature, or turn off ESP altogether. Curious what the G3X guys will find when they look at the data. Sounds to me like you were just fighting the servo torque of the ESP trying to "help" you, and not the AP because when you turned off ESP the fight was over (curious what is your torque set to?)

We don't fly Cirrus's so unless you're worried about becoming incapacitated during flight the ESP is a cool feature, but not necessarily great for the RV pilot who like to have fun. Personally I normally leave ESP off unless I'm just demonstrating the feature to someone.

From the Pilots Guide:

"When ESP has been engaged for more than ten seconds (cumulative; not necessarily consecutive seconds) of a 20-second interval, the autopilot can be configured to engage with the flight director in Level Mode, bringing the aircraft into level flight. An aural “Engaging Autopilot” alert is played and the flight director mode annunciation will indicate ‘LVL’ for vertical and lateral modes. Level mode as activated by ESP is limited by altitude. ESP will not be able to activate Level mode until the aircraft climbs above 2000 feet AGL. ESP will be locked out of automatically activating Level mode after the aircraft descends below 1500 feet AGL as well. Also note that Level mode as activated by ESP is different than manually selected Level mode. Manually selected Level mode is not limited by altitude at all."
NOTE: If AGL height data is unavailable (i.e., GPS altitude or terrain data is
unavailable), automatic engagement of Level mode is not supported.
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Last edited by Walt : 12-26-2019 at 10:06 AM.
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  #3  
Old 12-26-2019, 10:20 AM
g3xpert's Avatar
g3xpert g3xpert is offline
 
Join Date: Sep 2010
Location: Olathe, KS
Posts: 3,093
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Agree with Walt that we would like to review the log file to confirm what happened with this aircraft that was flown with no airspeed.

Back in V8.50 software we also made improvements in the ESP logic to prevent use in a blocked pitot scenario, so it will also be good to learn what software was being used in this aircraft.

ESP correction activities do not result in auto-trim being run like would happen when the autopilot is engaged, so it is unlikely that any pitch trim changes were occurring.

A reminder to everyone that pressing and holding the AP DISC button that everyone has on their stick activates circuitry in the GSA 28 servos that physically disables both the servo motor drive circuit and the trim motor drive circuit, so no matter what the servo processor might be trying to do, there will be absolutely no way for any control forces to be initiated by the servos.

Thanks,
Steve
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Last edited by g3xpert : 12-26-2019 at 11:07 AM.
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  #4  
Old 12-26-2019, 01:02 PM
Ed_Wischmeyer's Avatar
Ed_Wischmeyer Ed_Wischmeyer is offline
 
Join Date: May 2005
Location: Savannah, GA
Posts: 1,573
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A few random comments?

Note: ESP has been substantially improved since the following event occurred? and kudos to Garmin for the improvements. Maybe a year ago, a friend was flying steep turns with lots of back pressure, and ESP engaged. We didn?t notice this (the annunciations are now much more robust) because we were both eyes out. Then ESP activated the autopilot, and the autopilot started in full nose down trim to counter the back pressure of the steep banked turn, just like it was supposed to. The other pilot gave me back the controls with the plane trimmed full nose down, and it was? interesting. Although manageable, took a lot of force on the stick and a few seconds before my head cleared. I gave him back the controls so that I could address the problem. Actions taken were to power down the autopilot servos (below) and that allowed the electric trim to be used again.

On my plane, I have the autopilot servos on a circuit breaker toggle switch so I can disconnect the servos immediately, and that switch is on the end of a row and easy to find. This switch allows disabling unexpected trim movement from the ESP/autopilot without disabling the manually controlled electric trim. The elevator trim is on a push/pull circuit breaker, but I don?t think it likely that pulling that CB would be useful in an ESP event. You?d still have an out of trim airplane and not much you could do about it.

The way my plane is wired, and I hope I have this correct:
- Autopilot servos ON
* Autopilot enabled (not necessarily turned on, just enabled)
* ESP enabled (not necessarily turned on, but can be from the PFD)
* LVL mode enabled
* Airspeed-dependent variable elevator trim speed enabled
* All flight director functions enabled
* Flight director/autopilot control panel powered up
Autopilot servos OFF
* First four functions above disabled
* All flight director functions enabled (no change)
* Flight director/autopilot control panel powered up (no change)

Paul Dye made the excellent comment at one time that part of Phase 1 flight test should include flying the plane with trim fully deflected each way.

After thinking about all this for some time, I?ve decided that ESP is not something I want to use. If I?m on autopilot, ESP is disabled. And when I?m hand flying, I frequently am researching exercises to remediate loss of control, approaching 60? bank (or more, legally, within my airplane?s flight limitations) and 30? pitch. ESP would, of course, be inappropriate for those relatively extreme flight attitudes. Just for completeness, I should get up to speed on how ESP works, but at this point, it?s irrelevant to my flying and never used.

As for looking up details in the manual to really understand what?s going on, I?m still looking for a manual that I like. The Boeing 747 (factory) pilot?s guide and the Gulfstream Planeview II avionics manuals were widely disliked in those pilot communities, and frankly, the Garmin manuals are at that same, industry-standard level. I do not count on manuals to answer all of my questions. There?s nothing like lots of practice in VMC before you rely on anything in IMC.
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  #5  
Old 12-26-2019, 01:53 PM
DRMA DRMA is offline
 
Join Date: Jan 2016
Location: Sugar Land, TX
Posts: 497
Default AP DISC Question Regarding Trim

Quote:
Originally Posted by g3xpert View Post
A reminder to everyone that pressing and holding the AP DISC button that everyone has on their stick activates circuitry in the GSA 28 servos that physically disables both the servo motor drive circuit and the trim motor drive circuit, so no matter what the servo processor might be trying to do, there will be absolutely no way for any control forces to be initiated by the servos.

Thanks,
Steve
Steve - Can you please clarify what you mean by your statement above? When the AP DISC button is activated, does this disable the trim servo from being activated using the manual trim switch? Or are you saying that the auto trim is disabled so that the GSA 28 servo can not change the trim, but with the manual trim still functioning?

Thanks
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  #6  
Old 12-26-2019, 02:16 PM
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g3xpert g3xpert is offline
 
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Location: Olathe, KS
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Quote:
Originally Posted by DRMA View Post
Steve - Can you please clarify what you mean by your statement above? When the AP DISC button is activated, does this disable the trim servo from being activated using the manual trim switch? Or are you saying that the auto trim is disabled so that the GSA 28 servo can not change the trim, but with the manual trim still functioning?

Thanks
Hello Dave,

First, if you have your trim motor(s) connected to GSA 28 autopilot servos, here is a refresher on the 3 modes of operation.

GSA 28 Servos Powered Down (backup trim mode)
In this dirt simple backup mode a relay closes inside the GSA 28 servo and passes the trim motor wires directly through the servo. The wires connected to input pins 11,12 at the servo are directly connected to output pins 13,14.
GSA 28 Servos Powered Up, Autopilot Disengaged
This is the normal mode of operation when the autopilot is disengaged. The trim control inputs on pins 11,12 of the servo are read by the servo microprocessor, and speed scheduling is added by the servo to automatically drive the trim motor and vary the speed of the trim motor (using Pulse Width Modulation) to match the speed scheduling configuration.
GSA 28 Servos Powered Up, Autopilot Engaged
This is the normal mode of operation when the autopilot is engaged. It is very similar to the previous mode except that the servo ignores the inputs and drives the trim motor based on out-of-trim torque sensing that it does on its own.
Whenever you are operating with the servos powered, and you suspect something is wrong with either the servos or trim control, simply grasp the control stick/wheel firmly, press and hold the AP DISC button, then reach over and remove power from the AFCS (autopilot) system as time permits. This will close the trim bypass relay in the GSA 28 servo(s), and leave manual trim enabled.

Obviously if you have a trim problem with the AFCS powered off and the trim signals passing straight through the servos (backup trim mode), you will need to separately remove trim power or otherwise deal with that issue.

Thanks,
Steve
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  #7  
Old 12-26-2019, 02:32 PM
Bavafa Bavafa is offline
 
Join Date: Oct 2007
Location: Sacramento, CA
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My experience with ESP is far less than some others, one year flying with G3X so far but it has behaved as Steve has listed above. I also believe that using the manual trim while the A/P is engage will automatically disengage the A/P, perhaps the same function of DISC.

As a safety reason, I have a separate On/Off switch on my panel that powers both servo as well as the 507 controller. If any concerns with the behavior of the servos, I can quickly power off all A/P functions with the flip of a switch.
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  #8  
Old 12-28-2019, 09:39 AM
sblack sblack is offline
 
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Wow, your RV has MCAS!
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