Spirithawk is a sponsored research project performed at VCU, in collaboration with UVA and sponsored by the Army. The most significant output of this research was a unique VTOL, tri-motor aircraft capable of being 3D-printed and assembled with zero hardware (snap-together construction). With UVA providing aircraft design and manufacturing expertise, VCU, with myself as the senior grad student on the program, agreed to modify its flight control system to fully support this complex aircraft.

Early iteration of the test aircraft. Later versions would have custom front motors that mount flush and don’t protrude beyond the body, and an all-around more powerful propulsion system.

Noting that the rear motor is on a two-axis gimbal, flight control is implemented as a tri-copter multirotor system, delta wing fixed-wing system, and a VTOL system overlaying the two and managing transitions between them.

The hovering-to-forward flight transition proved challenging and required a combination of software solutions and hardware changes. The power system simply isn’t strong enough to both support the aircraft while hovering, and concurrently significantly tilting the rear motor to generate forward thrust. Test flights were executed to determine the critical tilt angle where motor headroom was exhausted, the stall speed of the fixed-wing aircraft, and the amount of forward velocity able to be generated at various tilt and power combinations.

Ultimately, the project was successful, as seen in the video below. The final hover-to-forward transition utilizes the improved power system and flight controller programming to schedule the motor tilt against airspeed, and utilize the fixed-wing control surfaces in addition to the multi-rotor control scheme.

Successful test flight with a vertical takeoff, automatic transitions, and forward flight