We present a helicopter flight dynamics nonlinear model for a flybarless, articulated, pitch–lag–flap (P–L–F) main rotor (MR) with rigid blades, particularly suited for small-scale unmanned aerial vehicles (UAVs). The model incorporates the MR, tail rotor (TR), fuselage, and tails. This model is further applicable for high bandwidth control specifications and is valid for a range of flight conditions, including the vortex-ring-state (VRS) and autorotation. Additionally, the paper reviews all assumptions made in deriving the model, i.e., structural, aerodynamics, and dynamical simplifications. Simulation results show that this nonlinear model is in good agreement with an equivalent flightlab model, for both static (trim) and dynamic conditions.