Longitudinal stability of Vertical-Take-Off-and-Landing (VTOL) Fixed Wing Flying Wing UAV during transitional flight

Our research concerns the vertical-take-off-and-landing (VTOL) fixed wing flying wing unmanned aerial vehicle (UAV) equipped with two primary ducted fans and a front ducted fan for producing vertical lift. The introduction of the full paper reviews some papers in the open literature and then proposes what we believe to be a promising control strategy, which sections 1 and 2 explain. Their core consists of: (1) we calculate the thrust of a three-ducted fan and aerodynamic force induced by jet/wing; (2) considering the obvious aerodynamic interference and large trimming variation during transition, we propose the transitional flight control strategy so as to prevent the UAV suffering from "transition failure cliffs"; (3) to achieve this, we preset an angle of attack, accelerate the UAV to the safety flight velocity, and finally close the primary ducted fans and the front ducted fan. Section 3 analyzes the effects of the flight velocity of the UAV, the velocity of inlet flow of ducted fans and the velocity of their outlet jet flow on the longitudinal transitional flight stability of UAV and its trimming; the results, given in Tables 3 and 4 and Fig.7, and their analysis show preliminarily that the three ducted fans can reduce the stability of short-period flight and increase the damping of phugoid flight.