Abstract— Most unmanned aerial robots use a Global Navigation Satellite System (GNSS), such as GPS, GLONASS, and Galileo, for their navigation. However, from time to time the GNSS fails to function due to geographical restrictions and deliberated jamming. This paper proposes an Unscented Kalman Filter-based GPS/IMU integration method in order to accurately estimate the position and velocity of an unmanned miniature helicopter even when the GNSS malfunctions completely. Different from previous GPS/IMU integration methods that cannot propagate noisy inertial measurements to the position and velocity estimations on the rapid vibratory Vertical Take-Off and Landing (VTOL) platforms during the GNSS outage, this method novelly prioritises the propagations of the states in the Unscented Kalman Filter (UKF) algorithm and leverages the time-varying GNSS dilution of precision in line with the adjustments of the measurement noise covariances. Moreover, this method models the stochastic process ...