Ahhh OK you applied my trick 
https://discuss.ardupilot.org/t/beaglebone-blue-based-flying-wing-do-i-have-whats-needed/20717/12
Yes power is not applied by default … sorry I overlooked that
And yes , you can copy that in /etc/rc.local
/bin/echo 1 > /sys/class/gpio/gpio80/value