  We consider the problem of attitude tracking for small-scale aerobatic
helicopters. A small scale helicopter has two subsystems: the fuselage, modeled
as a rigid body; and the rotor, modeled as a first order system. Due to the
coupling between rotor and fuselage, the complete system does not inherit the
structure of a simple mechanical system. The coupled rotor fuselage dynamics is
first transformed to rigid body attitude tracking problem with a first order
actuator dynamics. The proposed controller is developed using geometric and
backstepping control technique. The controller is globally defined on $SO(3)$
and is shown to be locally exponentially stable. The controller is validated in
simulation and experiment for a 10 kg class small scale flybarless helicopter
by demonstrating aggressive roll attitude tracking.
