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.%针对由两个主涵道风扇和一个前涵道风扇组成垂直升力部件的垂直起降固定翼飞翼布局无人机,估算出风扇推力和喷流/机翼的诱导气动力,考虑到过渡飞行过程的气动干扰明显和配平控制量变化较大的影响,并且为了防止无人机进入失效陡壁,提出一种预置飞行迎角加速到安全速度后,先关闭主涵道再关闭前涵道风扇的过渡飞行控制策略,分析了无人机平飞速度、涵道风扇入口来流、出口喷流对配平和过渡飞行纵向稳定性的影响,得到了涵道风扇的作用减小了过渡飞行的短周期稳定性、增加了长周期的阻尼的结论.
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