  This study presents a real-time guidance strategy for an unmanned aerial
vehicles (UAVs) that can be used to enhance their flight endurance by utilizing
{\sl insitu} measurements of wind speeds and wind gradients. In these
strategies, periodic adjustments are made in the airspeed and/or heading angle
command, in level flights, for the UAV to minimize a projected power
requirement. In this study, UAV dynamics are described by a three-dimensional
dynamic point-mass model. A stochastic wind field model has been used to
analyze the effect of the wind in the process. Onboard closed-loop trajectory
tracking logics that follow airspeed vector commands are modeled using the
method of feedback linearization. To evaluate the benefits of these strategies
in enhancing UAV flight endurance, a reference strategy is introduced in which
the UAV would follow the optimal airspeed command in a steady level flight
under zero wind conditions. A performance measure is defined as the average
power consumption with respect to no wind case. Different scenarios have been
evaluated both over a specified time interval and over different initial
heading angles of the UAV. A relative benefit criterion is then defined as the
percentage improvement in the performance measure of a proposed strategy over
that of the reference strategy. Extensive numerical simulations are conducted
to show efficiency and applicability of the proposed algorithms. Results
demonstrate possible power savings of the proposed real-time guidance
strategies in level flights, by utilization of wind energy.

Optimization and Control