PX4 as "data logger" for glider flights

For a personal project, I need to analyse complexe powered-glider flights (roll/yaw/pitch, throttle, altitude, GPS points …) to use it as a template to build automatize flights with PX4.
I’ve got a friend very good at flying RC powered-gliders, he’s got strong skills and I want to reproduce his flights automatically with PX4.
To be honest, like many RC fans, he doesn’t want to unmanned his glider, his skills are based on his ability to produce wonderful flights, and he’s doing that for years !
My idea is to build a very lite and small box with a complete hardware and software under PX4 “flight controller board + barometer + GPS + lipo”, and put this box in my friend’s glider. The weight is really important to not make perturbations to the flights.
My problem today is that it has to be a “black” box for him (he’s a RC fan, not a UAV one …), he’ll only have to turn a switch to “on”, make his flight, turn the switch to “off” and send me the box, so I’ll be able to make this analysis. There’ll not have ANY actions from the flight controller on the glider, it’ll be only use as a “datalogger”, I’ll not be with him so no remote telemetry at all, no check from myself, no one will “arm” the system.
How do you think I can build this “black” box to make it working easily ? Any idea if someone did it before ?
Thanks for your help

Set the FC param SDLOG_MODE to “2: from boot until shutdown”,and it will record log into SD card once power on.