Wingtip vortices cause downwash which reduces the effective angle

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Induced Drag Coefficient

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The Truth About “Induced Drag”

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Wing-Body and Vertical Tail Interference Effects on Downwash Rate of the Horizontal Tail in Subsonic Flow, Journal of Aerospace Engineering

Nature of the wake produced by wingtip vortices and its deleterious

Why wingtip vortices are detrimental to aircraft aerodynamics

WING IN GROUND EFFECT

Wingtip Vortices and Wake Turbulence - Pilot Institute

Comparison of drag coefficient (CD) on plain wing and the winglet at