  The leader-follower formation control analysis for multiple quad-rotor
systems is investigated in this paper. To achieve predefined formation in the
three-dimensional air space ($x,y$ and $z$), a novel local tracking control law
and a distributed observer are obtained. The local tracking control law starts
with finding a bounded continuous yet greater-than-zero control in $z$, based
on which following a feedback linearization controls derived for errors
associated with $x$ and $y$. The distributed observer achieves position
coordination among followers, though there are only partial followers can know
the leader's states and only neighboring communication is available. Simulation
results validate the proposed formation scheme.
