  In order to prevent loss of control (LOC) accidents,the real-time control
performance monitoring problem is studied for multicopters. Different from the
existing work, this paper does not try to monitor the performance of the
controllers directly. In turn, the disturbances of multicopters under
off-nominal conditions are estimated to affect a proposed index to tell the
user whether the multicopter will be LOC or not. Firstly, a new degree of
controllability (DoC) will be proposed for multicopters subject to control
constrains and off-nominal conditions. Then a control performance index (CPI)
is defined based on the new DoC to reflect the control performance for
multicopters. Besides, the proposed CPI is applied to a new switching control
framework to guide the control decision of multicopter under off-nominal
conditions. Finally, simulation and experimental results show the effectiveness
of the CPI and the proposed switching control framework.
