The autopilot market for small and research UAVs offers several products, but most of them,
although widely configurable or even open-source, do not constitute a practical and safe development system
for custom guidance, navigation and control systems. The ICARO project aims at providing the small UAV
community with a valid autopilot alternative. The ICARO autopilot exploits rapid control system prototyping
techniques and immersive manned simulation with the possibility of testing the autopilot using the Hardware-
In-the-Loop (HIL) approach. This paper describes the hardware-in-the-loop and man-in-the-loop simulator for
the ICARO II platform together with the synchronization protocol we developed to keep simulator and
autopilot synchronized. Experimental evidence of the effectiveness of the synchronization protocol is given
