Abstract
This study evaluates the VTOL behaviour of a 4.18 m-span, 15.5 kg flying-wing UAV and proposes a simplified propulsion-layout redesign. Three flights of the original tri-rotor configuration were analysed using attitude, motor and servo PWM, altitude, and vibration data. Roll and pitch tracking errors averaged 0.54° and 0.80°, whereas yaw error averaged 1.36° and showed persistent bounded oscillations. Static equilibrium showed that the rear rotor had to provide 40.7% of hover thrust, compared with 29.7% for each lateral rotor. A four-rotor fixed vertical layout was therefore designed around the established center of gravity, while the original rear motor was retained horizontally for cruise. The new thrust centroid is only 0.81 mm from the center of gravity and the nominal hover load is approximately 38.01 N per rotor. The redesign is expected to provide more symmetric loading and simpler VTOL control.