You can't have a fixed wing and copter in the same FC. You could have two FC's if you could find a way to switch from one to the other.
Or there are ways to set it up so that you don't have to change the flight mode. Take off vertically, pitch over and fly horizontally, all in rate mode. Hover yaw becomes flight roll.
so for these vehicle with only less than 3 motors, under what configuration should we set it as? aero or heli? if it is heli, is it tricopter or quad?
I think a VTOL tilt-rotor vehicle configuration for a fixed wing with 2 motors is possible using Librepilot if using Elevons (not ailerons + rudder).
Should start/hovers like a quad/tricopter and can transition in to fixed wing flight flight and back again.
The configuration would need be Custom (not Multirotor, Fixedwing or Heli), I think.
The Yaw is not used on an Elevon Fixedwing so in Hover mode the yaw is free to control the vertical tilt of the motors (moving in opposite directions to create the yaw motion control).
Ch1 and Ch2: 2 motors, one at each wingtip of the fixed wing
Ch3 and Ch4: 2 servos to control the vertical tilt of the motors
Ch5 and Ch6: 2 servors to control the two Elevons
In total 6 output from the flight controller (Revo board etc only have 6 outputs).
Provided you get the center of gravity aligned over center of lift it
should be able to hover with two motors.
The assigning and mixing channels for pitch, yaw, roll is done by the FC and not in the radio transmitter, maybe something like this...
The flight mode switch can have 3 modes to put the vertical servos tilting 1. vertical (hover) 2. 45% (half forward) and 3. 90% (full fixed wing mode).
I have not tried this but I think it could work