Test request - stall warning

[Andy]

Next time you shut down your FX-3, or other G3X Carbon Cub, would you please try the following test:

Ensure Master, IBBS, and emergency ignition are all off but all breakers are In.
Lift the stall warning vane on the left wing - Does the stall warning sound?
If stall warning sounds then pull IBBS breaker.
Lift stall warning vane - does stall warning sound?

Please report results here.

Thanks.

[Pete D]

Generally it will sound if the stall warning switch is closed within a few minutes of the master being turned off.

Power is coming from the alternator noise filter capacitor, if you pull the alternator breakers it probably won't do it.

[Andy]

Generally it will sound if the stall warning switch is closed within a few minutes of the master being turned off.

Power is coming from the alternator noise filter capacitor, if you pull the alternator breakers it probably won't do it.

The stall warning sounds if the IBBS charging breaker is in but not if it is pulled. That's a clear indication that the power source is the IBBS.

After I posted the test request I had an email exchange with TCW support. It took a while to drag the information out of them but there is an internal 50 uF capacitor connected directly between IBBS pin 5 and ground. It is this capacitor that is powering the stall warning.

Mystery solved and one more item for the FX-3 systems knowledge file.

[Pete D]

That is interesting. I have seen that behavior on older aircraft prior to the G3X panel and traced it to the alternator noise filter.

[Tsquared]

Next time you shut down your FX-3, or other G3X Carbon Cub, would you please try the following test:

Ensure Master, IBBS, and emergency ignition are all off but all breakers are In.
Lift the stall warning vane on the left wing - Does the stall warning sound?
If stall warning sounds then pull IBBS breaker.
Lift stall warning vane - does stall warning sound?

Please report results here.

Thanks.

I tried your procedure this afternoon but was unable to reproduce your results on my FX3 today. The stall horn will not sound with master,IBBS and Emer ignition off. Horn functions normally with IBBS and master on. Once IBBS/Master off horn will no longer sound.

plane is a FX3 with G3X touch. Build was completed early 2020

[Andy]

I tried your procedure this afternoon but was unable to reproduce your results on my FX3 today. The stall horn will not sound with master,IBBS and Emer ignition off. Horn functions normally with IBBS and master on. Once IBBS/Master off horn will no longer sound.

plane is a FX3 with G3X touch. Build was completed early 2020

Thanks for the report. So now the mystery is re-opened and I thought I completely understood it.