• The class of high altitude long endurance (HALE) aircraft often have very slender wings with minimal structure. This leads to large trim deections and coupling between the vehicle ight dynamics and wing vibrations. When this coupled behavior becomes unstable, it is referred to as body-freedom utter (BFF). BFF behavior is dependent on the inertial and constitutive properties of the wing as well as the fuselage. This relationship is explored for a typical ying wing aircraft representative of the Horten IV ying wing using an efficient yet rigorous analysis that relies on geometrically-exact, fully intrinsic beam equations and a finite-state induced ow model, implemented in the computer code NATASHA (Non-linear Aeroelastic Trim and Stability of HALE Aircraft). The wing inertial and stiffness properties were calculated using a realistic representative section using the powerful section analysis tool VABS. Trade studies on the BFF behavior were performed by varying the fuselage properties and the internal wing structure and examining the effects on the utter speed, utter frequency, and utter mode shape. © 2012 AIAA.