The High-Altitude Long Endurance (HALE) aircraft is an innovative concept with great potential in telecom- munications and surveillance applications due to its ability to function as a ”pseudo-satellite” within the strato- sphere. Its unique features are accomplished in practice through numerous design requirements that ensure maximal efficiency. Regarding the airframe in particular, these lead to light wings with extremely high aspect ratios. The resulting -very flexible- structure is consequently sensitive to dynamic instabilities emerging from aeroelastic effects (i.e., flutter), which produce large-amplitude oscillations and drastically diminish the air- craft’s flight envelope. Hence, accurate prediction of flutter and the ability to mitigate it are crucial to enable reliable HALE aircraft design and operation. While numerous works have focused on this problem for a wing alone (e.g. [1]), flight dynamics is rarely taken into account. This aspect is important, as aeroelastic instabilities in this case can be of a different nature than the flutter of a cantilever beam, involving coupling between aircraft rigid-body modes and wing elastic modes [2]. In the present work, we explore passive control strategies for flexible-wing aircraft flutter based on the nonlinear effects of an added damper subsystem. To this end, an orig- inal aeroelastic model of the wing is introduced, which provides a degree of accuracy and complexity that lies at a midpoint between linear and geometrically-exact nonlinear beam models. The focus of this contribution is on damper optimization and mitigation performance evaluation.