  This paper introduces the powerline unmanned surfer (PLUS) concept to extend
the limited endurance of fixed wing unmanned aerial vehicles (UAVs) via
in-flight energy harvesting from overhead electrical distribution power lines,
and develops the flight dynamics and control framework to support
centimeter-scale longitudinal powerline frequency tracking. The dynamics
framework models the UAV's shape adaptive structure, aerodynamic forces, and
control inputs, and applies the coupled flight mechanics framework to low
clearance tracking of powerline contours. This study develops a "trajectory to
shape-adaptive UAV" controller design approach for longitudinal powerline
tracking through local spatial frequency matching. The frequency-matching
approach dynamically regulates the aircraft modes' frequency to the powerline
catenary spatial frequency using a generalized parameter linearization
approach. Performance is assessed on an example UAV implementing camber and
thickness morphing by quantifying clearance distance from neighborhood to high
voltage powerline environments and across span and chord combinations. This
approach achieves alternating periods of low-clearance tracking and antiphase
oscillation, with 34% of the powerline having tracking error less than 1m.
Airfoil thickness increase has a stronger effect over Phugoid mode wavelength
than thickness decrease. Wingspan, chord, and powerline parameter sensitivities
are quantified, providing a foundation for near-field long-distance powerline
tracking and energy harvesting.
