Flashing ArduPlane or iNav firmware to flight controllers using BetaFlight

Some quadcopter flight controllers can be used on fixed wing aircraft using iNav (which supports more targets, and is based on BetaFlight) and ArduPilot/ArduPlane. 

Before buying, MAKE SURE the FC is supported.  For example, I purchased two F722 boards... which is not the same as F7 v2, which has more memory.  Poof there goes $64.

ARDUPILOT
Go to ardupilot.org
Downloads > Firmware
Select plane (not copter or anytnign else)
Choose latest stable release eg stable-4.0.5
Choose your flight controller
download the ardupilot_with_bl.hex file

iNav is similar.  Note, although iNav supposedly can flash firmware, on versions newer than 2.0 flashing doesn't work on MacOs.  So I was back to BetaFlight.

PROCEDURE
hold down boot button on the board as you plug it into USB on your computer
start Betaflight
select DFU as the port if not selected
go to the firmware flasher tab
load firmware [local]
select arduplane with bl or the inav firmware .hex file
make sure no reboot sequence is selected (otherwise BF will show it is erasing, finish, and get stuck at the flashing step)

Now flash and hopefully you get PROGRAMMING: SUCCESSFUL

If not, try with full chip erase disabled.  If flashing gets stuck, close Betaflight and re-open it and try again.

You can always re-load the BF firmware this way too.