Browsing by Author "Van Zyl, Izaak"

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    Extremum-seeking control for constrained optimal formation flight of commercial airliners
    (Stellenbosch : Stellenbosch University, 2018-03) Van Zyl, Izaak; Engelbrecht, J. A. A.; Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.
    ENGLISH ABSTRACT: Formation flight of commercial airliners has become a topic of interest due to the possibility of significant fuel savings. With air traffic rapidly increasing, the aeronautical industry recognizes the necessity to improve fuel efficiency of long distance ights. Previous studies have shown that extended formation flight of existing commercial aircraft is plausible, but have not dedicated much attention to fully utilising the wingtip generated wakes. This study presents the design, implementation, and verification of a perturbation-based extremum-seeking controller that enables follower aircraft to locate and maintain optimal formation separations in a practical formation flight scenario. Typically, the trailing vortices of the leader aircraft are displaced due to atmospheric disturbances, such as static winds and turbulence, and models of the vortex positions are not exact. Due to the dangers related to flight deep in the leader's wake, a novel constrained objective function is proposed that prevents the extremum-seeking controller from guiding the follower aircraft too close to the vortex core. In this constrained objective function, the extremum is represented by a constrained extremum contour instead of a single point. A novel extremum-seeking state machine is proposed that controls the different modes of operation that the follower aircraft transitions through as it approaches the constrained extremum. The states and the state transition boundaries are defined as functions of the objective function, which allow them to follow the displaced trailing vortex, instead of remaining static relative to the leader aircraft. This also enables the extremum-seeking control to not only track a static trailing vortex, but also a constrained extremum for a dynamic trailing vortex. It is also shown that by approaching the constrained extremum at a constant approach rate, rather than the classical proportional approach rate, the effects of the non-linear wake on the seeking performance may be mitigated. The extremum-seeking controller was verified in simulation on a formation flight model of two Boeing 747 aircraft in right echelon formation. The formation is subjected to realistic atmospheric disturbances and sensor noise. The simulation results show that the extremumseeking controller is able to successfully guide the follower to the constrained extremum, even in the presence of varying static wind and light turbulence, and that thrust reductions of up to 23% may be achieved.