  This paper presents an approach for deploying and maintaining a fleet of
homogeneous fixed-wing unmanned aerial vehicles (UAVs) for all-time coverage of
an area. Two approaches for loiter circle packing have been presented: square
and hexagon packing, and the benefits of hexagon packing for minimizing the
number of deployed UAVs have been shown. Based on the number of UAVs available
and the desired loitering altitude, the proposed algorithm solves an
optimization problem to calculate the centres of the loitering circles and the
loitering radius for that altitude. The algorithm also incorporates fault
recovery capacity in case of simultaneous multiple UAV failures. These failures
could form clusters of survivor (active) UAVs over the area with no overall
survivor information. The algorithm deploys a super-agent with a larger
communication capacity at a higher altitude to recover from the failure. The
super-agent collects the information of survivors, and updates the homogeneous
radius and the locations of the loitering circles at the same altitude to
restore the full coverage. The individual survivor UAVs are then informed and
transit to the new loitering circles using Dubin's paths. The relationship with
the extent of recoverable loss fractions of the deployed UAVs have been
analysed for varying the initial loiter radii. Simulation results have been
presented to demonstrate the applicability of the approach and compare the two
presented packing approaches.
