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A prototype nonlinear energy sink, whose design is based upon parameters determined to effectively suppress transonic aeroelastic instabilities of a wind-tunnel wing model (denoted as generic transport wing) via passive targeted energy transfer, is introduced. The lightweight nonlinear energy sink is mounted within a low-profile winglet, which is attached to the tip of the generic transport wing. In addition, safety features and measurement hardware have been built in to the prototype to facilitate a future transonic wind-tunnel experiment. The effects of the nonlinear energy sink on the structural dynamics of the model wing are demonstrated in ground vibration tests, both experimental and computational. Results show that the nonlinear energy sink causes a significant increase in the dissipation rate of energy in the second bending mode of the generic transport wing, even for small wing-tip oscillations. This is a strong indication that the prototype nonlinear energy sink will be effective in wind-tunnel tests because the frequency of the second bending mode is within the range of experimental and computational flutter frequencies of the generic transport wing. Furthermore, accompanying computational analysis is used to show that moderate friction damping in the nonlinear energy sink is unlikely to have a significant effect on the qualitative interaction between the nonlinear energy sink and the generic transport wing. Nomenclature c = nonlinear energy sink viscous damping coefficient E = energy in reduced-order system E j = energy of jth mode E 2;max = maximum energy in the second mode during a response E nes ,Ê nes = nonlinear energy sink energy in the complete and reduced-order systems F ext t = external force vector f nes , F nes = nonlinear energy sink coupling forces and vector of coupling forceŝ f nes = conservative nonlinear energy sink coupling force in reduced system I y r = component of winglet mass moment of inertia applied at the rth wing-tip node k i = nonlinear energy sink polynomial stiffness coefficients k lin , k nl = experimental linear nonlinear stiffness coefficients of nonlinear energy sink l = distance between wing-tip finite-element nodes M r = component of winglet mass applied at the rth wingtip node m = nonlinear energy sink mass M, C, K = mass, damping, and stiffness matrices of wing P = wing-tip location at which the nonlinear energy sink is coupled t = time t max = time at which energy is maximum u = nonlinear energy sink displacement relative to wing tip (y − w) w = wing-tip heave at P x = vector of finite-element wing displacements y = nonlinear energy sink displacement α = exponent of experimental nonlinear stiffness term β = mode-shape rescaling parameter E = normalized second mode energy η j , η = jth modal displacement and modal displacement vector μN = friction force ξ = physical displacement at P due to mode 2 τ = t − t max ϕ j , Φ = jth mass-orthonormalized mode-shape vector and mode-shape matrix ω j = jth modal frequency, rad∕s ζ j = jth modal damping ratio Subscript p = hea...