  Stability and satisfactory performance are critical control requirements for
Unmanned Aerial Vehicle (UAV) applications. While conventional control systems
for UAVs aim to ensure flight stability and safe operation while accomplishing
tasks, UAVs may experience various flight faults that can degrade performance
or, in severe cases, lead to instability. Unsatisfactory performance or
instability of a UAV poses risks to lives, properties, and the flying
environment. Therefore, it's essential to design a system capable of detecting
faults, pinpointing their location, assessing their severity, and using this
information to mitigate them, enabling the vehicle to continue operating
satisfactorily. Despite the importance of analysing fault performance to select
optimal fault detection and tolerance strategies, limited research has been
conducted, especially with real systems. This study examines the performance of
a 2-degree-of-freedom (2DOF) bi-rotor helicopter's control system in the
presence of various actuator faults. Results from different fault conditions
demonstrate that faults degrade the performance of conventional control systems
on UAVs and introduce vibrations into the system, particularly when faults
cause asymmetry or imbalance. However, additional experiments reveal that
effective fault diagnosis and accommodation methods can help maintain
satisfactory system performance despite the presence of faults.
