This paper proposes, through a survey of models of several UAV-Structures, a generic nonlinear model for reduced scale aerial robotic vehicles (6 DOF) (Terms `light' and `reduced scale' implie that the flight range of aerial vehicles under interest is lower than 30mn.). Dynamics of an aircraft and some VTOL UAV (quadricopter, ducted fan and classical helicopter) are illustrated. This generic model focuses only on the key physical efforts acting on the dynamics in order to be sufficiently simple to design a controller. The Small Body Forces expression which can introduce a zero dynamics is then discusse