What's new
Van's Air Force

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

GMC 307 w/ G3X AND G5

lr172

Well Known Member
I intend to have a G3X with a G5 backup. I would like the ability to fly coupled approaches with the G5, if an emergency dictates the need. The 307 communicates with the 370 via RS-232. I imagine that the G5 would get / send the AP data via relay through the CAN bus, but need a plan for complete failure and power down of the 370.

Do I just run the RS-232 feed through a switch to allow it to be connected to either the 370 or G5? Clearly the 307 needs data in order to fly approaches or even track a heading.

Wondering how others have approached this. Maybe I just skip the coupled approaches. Its not really critical, but would be nice to have assuming a combined 370 failure plus mental exhaustion situation. However, it seems I couldn't even track a heading without the RS-232 connection.

Larry
 
Last edited:
I intend to have a G3X with a G5 backup. I would like the ability to fly coupled approaches with the G5, if an emergency dictates the need. The 307 communicates with the 370 via RS-232. I imagine that the G5 would get / send the AP data via relay through the CAN bus, but need a plan for complete failure and power down of the 370.

Do I just run the RS-232 feed through a switch to allow it to be connected to either the 370 or G5? Clearly the 307 needs data in order to fly approaches or even track a heading.

Wondering how others have approached this. Maybe I just skip the coupled approaches. Its not really critical, but would be nice to have assuming a combined 370 failure plus mental exhaustion situation. However, it seems I couldn't even track a heading without the RS-232 connection.

Larry

Hello Larry,

As shown in the G3X Installation manual, the GMC 307 has dual RS-232 ports and connects both to the GDU 37X/4XX and to the GSA 28 roll servo.

When the GDU displays are down, the roll servo still gets the button/knob information from the GMC 307 and passes it to the G5 over the CAN network.

We do that test all the time where we make the big displays go dark, and fly the instrument approach with the remaining G5, GMC 307, GAD 29, and GTN.

Keep in mind that the GMC 307 is NOT the brains of the autopilot, just a relatively simple autopilot control panel. The real brains of the autopilot are in the GDUs and G5.

Thanks,
Steve
 
Last edited:
Hello Larry,

As shown in the G3X Installation manual, the GMC 307 has dual RS-232 ports and connects both to the GDU 37X/4XX and to the GSA 28 roll servo.

When the GDU displays are down, the roll servo still gets the button/knob information from the GMC 307 and passes it to the G5 over the CAN network.

We do that test all the time where we make the big displays go dark, and fly the instrument approach with the remaining G5, GMC 307, GAD 29, and GTN.

Keep in mind that the GMC 307 is NOT the brains of the autopilot, just a relatively simple autopilot control panel. The real brains of the autopilot are in the GDUs and G5.

Thanks,
Steve

Thanks Steve. I couldn't see how the G5 communicated with the 307, as the 307 has no CAN port. I just realized that the 307 can communicate on the CAN by passing the data through the servo to get to the CAN.

So, is the bulk of AP control information flowing between the 370 and the servo via the CAN bus? That makes more sense. I was initially thinking that it flowed from the 370 to the 307 and then to the servo, but the CAN bus makes more sense.

Larry
 
Last edited:
Thanks Steve. I couldn't see how the G5 communicated with the 307, as the 307 has no CAN port. I just realized that the 307 can communicate on the CAN by passing the data through the servo to get to the CAN.

So, is the bulk of AP control information flowing between the 370 and the servo via the CAN bus? That makes more sense. I was initially thinking that it flowed from the 370 to the 307 and then to the servo, but the CAN bus makes more sense.

Larry

Hello Larry,

Yes, you are correct. The CAN bus provides the servos with high speed ADAHRS data from 1 to 3 GSU 25 ADAHRS sources, and a backup G5 instrument. Additionally, it provides flight director data from either a GDU (normal mode) or the G5 backup instrument when needed.

The GMC 307 is just a smart button/knob control panel.

Thanks,
Steve
 
Back
Top