We tried using an APM 2.5 as a flight data recorder in a Cessna 208B. It was built into a 3D printed box with own power supply and recording done on a mobile phone.
There is one problem though: When the aircraft is in a steady bank the APM HUD indicates horizontal attitude as the resultant g-load is downwards relative to the APM. The difference between APM indicated attitude and aircraft artificial horizon is shown below. (Aircraft AH indicates about 30deg LH bank in top right corner)
UPDATE: THE PROBLEM SEEMS TO BE THAT ARDUCOPTER CODE WAS LOADED AND IT WAS FLOWN AS DISARMED, INSTEAD OF USING ARDUPLANE - THANKS DEVELOPERS!
@Gisela & Joe: That is one of the reasons for this blog. I usually use arducopter code, but we loaded Arduplane on the APM (Some version current in November 2013). I'm not familiar with Arduplane, but am surprised to see this fundamental error and was wondering if someone else had noticed it?
@Pieter: yes, there is a GPS in the box and a battery that can be charged through USB.
Do you have a GPS connected to the APM?
Does this mean that the APM will show zero bank angle when a fixed wing UAV is circling a point of interest?
I do not believe the developers would make such a fundamental oversite.