A control approach for transitioning VTOL UAVs with continuously varying transition angle and controlled by differential thrust

This paper describes a control approach for transitioning VTOL UAVs controlled by differential thrust, allowing to fly in all flight phases spanning a continuous transition between hover and cruise flight. A quaternion based attitude controller makes use of an additional reference frame that is rotated by the transition angle with respect to the body-fixed frame. This approach allows intuitive control and applies to various vehicle configurations. After building a simulation model, a small series of tests is used to build and validate maps of the flight characteristics of the vehicle. These maps are inverted and used to control the vehicle's velocity. Test flights with a custom built VTOL UAV for transition angles up to 70°, validate the control approach.