In this paper a framework for simulation of Unmanned Aerial Vehicles (UAVs), oriented to rotary wings aerial vehicles, is presented. It allows UAV simulations for stand-alone agents or multi-agents exchanging data in cooperative scenarios. The framework, based on modularity and stratification in different specialized layers, allows an easy switching from simulated to real environments, thus reducing testing and debugging times. CAD modelling supports the framework mainly with respect to extraction of geometrical parameters and virtualization. Useful applications of the framework include pilot training, testing and validation of UAVs control strategies, especially in an educational context, and simulation of complex missions.