In recent years, applications for drones have multiplied, from surveillance, exploration, rescue and transport applications. UAVs are more and more autonomous, therefore real-time trajectory planning is necessary and can be achieved with potential fields. A quick study is proposed to better scale attractive and repulsive forces which has always been problematic when dealing with artificial potential fields. The purpose of this article is to develop a new dynamical fractional potential attractive and repulsive field usable in a dynamical 3D environment by taking into account the obstacle dynamics (position and speed) and theirs dangerousness. This makes it possible to avoid the obstacle in a more robust way, both from a safety point of view and from a trajectory optimization point of view. The potential fields are based on the relative position and speed of the drone in relation to the target for the attractive potential field or to the obstacle for the repulsive one.