What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

RV12iS with G3X Auto trim wrong way around

RV10inOz

RV10inOz

Well Known Member
Just been test flying the Flight Youth Engineering RV12iS and the auto trim trims up despite being given a perfectly trimmed aeroplane. Eventually you disconnect and it pulls up as you would expect.

I have looked at all the obvious settings. The trim manually is perfect.

It also displays the PTRIM warning in red which is not mentioned in the G3X manual anywhere, but is in the GFC500 manual (this has a 507). The fault says "Pitch Trim Fail – Manual Electric Pitch Trim is inoperative." but I can assure everyone Manual Trim is 100% operative.

I am keen to know what settings are in other 12iS with Garmin AP. Or just point me at the blatantly obvious that I may have missed.

Any hints would be appreciated.
 
Last edited:
G3X Autotrim

Have you installed all the proper G3X Preset files available in the Van's Aircraft Downloads area (see photo) and configured the system using the Pre-Sets Read-Me File? See this link.

The G3X installation manual has all the details on the autopilot autotrim starting is section 35.1.13. Here is the link.

You also MUST install G3X updated software version 9.14 or higher, there was a problem with runaway trim in previous versions! Here is the link.
.
 

Attachments

  • G3X Downloads.JPG
    G3X Downloads.JPG
    101 KB · Views: 49
  • G3x AP Trim.JPG
    G3x AP Trim.JPG
    94.9 KB · Views: 52
Tony, thanks for the rapid reply. Yes we downloaded the files from the website three weeks ago.

I will double check tomorrow that it all installed correctly.
 
The "PTRIM" message indicates that someone has enabled the pitch trim servo LRU. In the RV-12 you have a DC trim motor, not a GSA 28 pitch trim servo (such as might be found in a Cessna) so you need to disable this on the LRU configuration page.

As for the trim movement direction issue, this is very common and easily addressed by using the trim direction configuration setting. Be sure to follow the entire autopilot post-installation checkout procedure, which is detailed in the G3X installation manual.
 
Matt, thank you. That sounds entirely likely.

I will check that too.

Trim direction otherwise is correct.
 
Last edited:
Trim Direction

RV10inOz said:
Matt, thank you. That sounds entirely likely.

I will check that too.

Trim direction otherwise is correct.
Click to expand...

You have a single output from the GSA 28 to the DC trim motor. The trim switches are an input to the GSA 28. When manually trimming, your switch commands simply pass through the GSA 28 to the DC trim motor. Separately, when the autopilot is engaged, it generates the trim commands for auto-trim independent of any kind of pilot input. The direction in which the display commands trim movement is configurable, this is how you can end up with manual trim moving one direction, and auto trim moving the other. As long as you complete the on-ground set up during your installation (mentioned by mburch), your trim will be moving in the correct direction for both manual and auto trim.

The PTRIM indication means you have configured a GSA 28 as a trim motor. In configuration mode, select LRU, and disable Pitch Trim Servo.

Thanks,

Justin
 
mburch said:
The "PTRIM" message indicates that someone has enabled the pitch trim servo LRU. In the RV-12 you have a DC trim motor, not a GSA 28 pitch trim servo (such as might be found in a Cessna) so you need to disable this on the LRU configuration page.
Click to expand...

I'm a little confused by this. My RV-12is has 2 GSA-28s, which is a DC motor equipped smart autopilot servo.
 
FlyingDiver said:
The elevator trim is different than the autopilot servos.
Click to expand...

Yes, just so. In the Garmin parlance, a "servo" refers to a GSA 28. A two-axis autopilot will have two GSA 28 servo LRUs.

Garmin also supports using an additional GSA 28 servo, equipped with a cable capstan, to control the pitch or roll trim in an aircraft with cable-driven trim. This capability is not applicable to any RV, so you should always leave the "pitch trim servo" LRU configuration item on its default Disabled setting.

The primary confusion arises from the fact that the device sold by the Ray Allen company for the pitch trim application in RVs and similar aircraft is commonly referred to as a "servo", even though in reality it really isn't one; look up the dictionary definition of the word to see why. Garmin refers to this type of device as a "DC trim motor" which is more correct and serves to differentiate Garmin GSA 28 autopilot servo LRUs from Ray Allen style trim motors.

A GSA 28 servo installed to control the pitch (or roll) axis of an autopilot can optionally drive one of these trim motors to affect pitch (or roll) trim. This is the typical RV application.

Bottom line for an RV with electric trim: leave "pitch trim servo" disabled, and set "trim motor control" to Enabled only in conjunction with the installation manual's guidance, including the on-ground checkout procedure which is important to understand and follow for safe operation.
 
Last edited:
Justin, just an FYI, even if the on ground check out works perfectly, airborne the wrong direction occurs. So as you suggest the LRU selection should solve the PTRIM flag and the error in the system operation.

It is a pity that the G3X manual (install & pilot) do not appear to have one reference to PTRIM. Or none that my search function could detect. And yes, they are the latest versions. ;)

Thanks everyone, I am sure the problem is identified.
 
You must log in or register to reply here.
Back
Top