KleinHeerenbrink, Marco Christoffer Johansson, L. Hedenström, Anders Spreading of vorticity and increased span efficiency from Multi-cored vortices support function of slotted wing tips of birds in gliding and flapping flight Explanation of the relation between spreading of vorticity and induced drag reduction and a short clarification on the high span efficiency observed in quantitative data on gliding flight. animal flight;slotted wing tips;separated outer primary feathers;flight efficiency;jackdaw Corvus monedula;wind tunnel 2017-05-08
    https://rs.figshare.com/articles/journal_contribution/Spreading_of_vorticity_and_increased_span_efficiency_from_Multi-cored_vortices_support_function_of_slotted_wing_tips_of_birds_in_gliding_and_flapping_flight/4982672
10.6084/m9.figshare.4982672.v1