The prospect of aeroelastic instability, leading to large-amplitude limit cycle oscillations, is of particular concern for the highly flexible wings of solar high-altitude long-endurance (HALE) aircraft. Among the different strategies of vibration control, passive mitigation through friction dampers stands out as a promising solution in this context. While this concept has been proposed previously, related studies systematically use simple two-degrees-of-freedom airfoil models. In this paper, a more realistic structural model involving a three-dimensional nonlinear beam description of a full wing is considered. A friction damper is installed at a specific location on the wing span, and the response to aerodynamic loads is investigated numerically. Comparisons of critical speed and limit cycle amplitudes with and without the damper suggest improved vibration mitigation with respect to a linear viscous damper.