UAV drag additions and how to simulation/approximate them
 

I am simulating a fixed wing UAV with a clean geometry (with no servo horns, antennas and prop effects). I understand that the drag that is obtained from the said simulation might be for an ideal case. I want to however estimate how much extra drag addition will occur if the prop wash, servo horns, antennas (GPS and telemetry), manufacturing defects will add so that I can try to co-relate the simulation results to the thrust values obtained from real world flight tests.