  In trajectory planning and control design for unmanned air vehicles, highly
simplified models are typically used to represent the vehicle dynamics and the
operating environment. The goal of this work is to perform real-time, but
realistic flight simulations and trajectory planning for quad-copters in low
altitude (<500m) atmospheric conditions. The aerodynamic model for rotor
performance is adapted from blade element momentum theory and validated against
experimental data. Large-eddy simulations of the atmospheric boundary layer are
used to accurately represent the operating environment of unmanned air
vehicles. A reduced-order version of the atmospheric boundary layer data as
well as the popular Dryden model are used to assess the impact of accuracy of
the wind field model on the predicted vehicle performance and trajectory. The
wind model, aerodynamics and control modules are integrated into a
six-degree-of-freedom flight simulation environment with a fully nonlinear
flight controller. Simulations are performed for two representative flight
paths, namely, straight and circular paths. Results for different wind models
are compared and the impact of simplifying assumptions in representing rotor
aerodynamics is discussed. The simulation framework and codes are open-sourced
for use by the community.
