GSU 25 Wing vs Cowl

[garick]

Since I am building my own wiring harness, would it make sense to use the left wing location for the GSU 25 vice the tray as mentioned in G3X video (Also discussed in the valuable Dave E posts)? I’m not sure if there are any advantages either way.

[Andy]

Since I am building my own wiring harness, would it make sense to use the left wing location for the GSU 25 vice the tray as mentioned in G3X video (Also discussed in the valuable Dave E posts)? I’m not sure if there are any advantages either way.

CubCrafters continued to use the wing location for factory assist/built aircraft even after they found the avionics tray location gave satisfactory performance. They changed the wing installation from rigid mounting to mounting on vibration isolators. Builders of other aircraft have found that GSU mounting direct to the GDU is also satisfactory but that is likely influenced by panel stiffness.

The avionics tray has limited space. If you decide to fit an IFR GPS you need room for the GAD 29. This may infuence where you fit the GSU.

If you haven't purchased the GSU 25 yet then be sure to buy the GSU 25C Mod 1 version. Garmin developed this mod after investigating reports of hazardously misleading pitch attitude that had been reported in some GSU 25C installations.

[garick]

Thanks Andy for the reply. That is great information. I did find this bullet within the Garmin installation instruction book:

“The wing is not an ideal location to install the GSU 25. Installing a GSU 25 in the wing may exceed the lateral CG boundary for the unit, exposes the unit to potential wing flex (of which any amount is a problem), and may expose the unit to unacceptable levels of acoustic noise resulting from precipitation impacting the leading edge of the wing. These are potential sources of error in the determination of attitude and should be avoided.”

I am positive these have not been issues for CC but will go with the mounting location from the Mitch video.

Garick

[Andy]

“The wing is not an ideal location to install the GSU 25. Installing a GSU 25 in the wing may exceed the lateral CG boundary for the unit, exposes the unit to potential wing flex (of which any amount is a problem), and may expose the unit to unacceptable levels of acoustic noise resulting from precipitation impacting the leading edge of the wing. These are potential sources of error in the determination of attitude and should be avoided.”

You should not be positive CC has not experienced these issues! Most of that paragraph you quoted is the result of Garmin's investigation of multiple misleading pitch attitude events that I experienced during my FX-3 phase 1 flight test. The investigtion resulted in Garmin and CubCrafters safety alert bulletins and the change from hard mounting of the wing GSU to soft mounting.

According to Garmin only one other aircraft type has experienced these hazardously misleading pitch attitude events with the GSU 25C. They are very hard to repeat but I decided I would not fly my FX-3 at night or in IMC without a redundant attitude source. I fitted a G5 soon after I got my FX-3 home. It was about 6 months later that Garmin was able to reproduce the problem, the alert were issued, and the vibration isolation mounts were introduced.

Ref:

https://support.garmin.com/en-US/?fa...O83csyCLAkL029
https://cubcrafters.com/c/wp-content...ert-Rev-NC.pdf

[garick]

You should not be positive CC has not experienced these issues! Most of that paragraph you quoted is the result of Garmin's investigation of multiple misleading pitch attitude events that I experienced during my FX-3 phase 1 flight test. The investigtion resulted in Garmin and CubCrafters safety alert bulletins and the change from hard mounting of the wing GSU to soft mounting.

According to Garmin only one other aircraft type has experienced these hazardously misleading pitch attitude events with the GSU 25C. They are very hard to repeat but I decided I would not fly my FX-3 at night or in IMC without a redundant attitude source. I fitted a G5 soon after I got my FX-3 home. It was about 6 months later that Garmin was able to reproduce the problem, the alert were issued, and the vibration isolation mounts were introduced.

Ref:

https://support.garmin.com/en-US/?fa...O83csyCLAkL029
https://cubcrafters.com/c/wp-content...ert-Rev-NC.pdf

That certainly settles it for me. Thanks for sharing.