I've just submitted a pull-request adding support for tailsitter aircraft to APM:Plane. This allows for a wide range of tailsitters, but also allows for flying 3D capable fixed wing aircraft as a quadplane, using the ability to hang on the prop for hover.
The above video shows APM:Plane 3.8.0beta3 flying a Precision Aerobatics AddictionX
in RealFlight 7.5, using the KnifeEdge FlightAxis toolkit to allow control by ArduPilot. It demonstrates flying both in hover and fixed wing flight, along with transitions between fixed wing and VTOL modes.
This is still considered very experimental, but I hope it will provide some fun for people with 3D aircraft who want to push ArduPilot a bit further.
As I own a real AddictionX I am going to install a Pixhawk on it and try flying it with the real aircraft. I'll make another post once I've done that.
I'd also like to note that this is not the first time someone has added prop hanging ability to ArduPilot. In 2013 Brian Marchini did it as part of his masters thesis
. That work was never merged and was based on a very old version of ArduPilot (even then). Hopefully this new attempt will be merged soon.