A smooth real-time path planning approach is proposed based on the bilevel programming(BLP) for unmanned aerial vehicles(UAVs) in complex environments,to improve the flight path smoothness which has not been achieved by most existing methods.Firstly we define the measure for the path smoothness,and then we build the model for the bi-level decision objectives,the model of obstacle avoidances and the model of performances of the UAV,and introduce a variable planning time interval.On this basis,we proceed to d...