Planning physically realistic and easily controllable motions of flying robots requires considering dynamics. This paper presents a local trajectory planner, based on a simplified dynamic model of quadrotors, which fits the requirements to be integrated into a global motion planning approach. It relies on a closed-form solution to compute curves in the kinodynamic state space that tend to minimize the flying time. These curves have suitable continuity properties and guarantee respect of physical limits of the system (i.e. bounds for the time-derivatives of the pose coordinates). The paper explains how this local planner can be used within different motion planning approaches that enable the treatment of difficult problems in constrained environments.