During the tests I made the experience that without control surfaces only with thrust vector often flight attitudes are generated without airflow, which unfortunately can only be controlled with enough yaw effect. You´re right, a delta or flying wing with elevons is perfectly manoeuvrable without yaw control. Textron can swivel all engines separately so it is possible to create extreme yaw control in FW with differential thrust. Differential panning creates Aileron in FW and yaw in hover. As a tiltrotor I have also done it with PX4 but only with individual swivel of the front 2 drives (Convergence Vtol). At the moment there is still a small problem in PX4 V1.11 which prevents the rear drive from being switched off in FW mode. Full E-flite Convergence support
With a mixer in this style it should already work with PX4 cause no engine needs to be switched off and PX4 perfectly supports differential thrust in FW. So the mentioned Textron would need 4 esc and 4 individual swivelling servos that would cover all control axes without any moving surfaces.
I previously thought of a Vtol conversion without any servos or moving parts at all.
