This paper presents a formal method to design
a digital inertial control system for quad-rotor aircraft. In
particular, it formalizes how to use approximate passive models
in order to justify the initial design of passive controllers. Fundamental
limits are discussed with this approach – in particular,
how it relates to the control of systems consisting of cascades
of three or more integrators in which input actuator saturation
is present. Ultimately, two linear proportional derivative (PD)