Stability is an airfoil's tendency to return to a state of ____ after a perturbation?

The correct answer is equilibrium. In the context of aerodynamics and airfoil design, stability refers to the capability of an aircraft or airfoil to maintain its flight attitude and return to a balanced state after it experiences a disturbance, such as turbulence or a change in control inputs.

When an airfoil is stable, it will naturally seek to return to its equilibrium position after being perturbed. This means that if it tips or tilts due to external factors (like wind gusts), a stable airfoil will generate forces that correct this deviation, bringing it back to a steady flight position.

In contrast, while terms like motion, vertigo, and flight relate to the behavior of the airfoil, they do not accurately describe the specific property of returning to a balanced state after a disturbance. Motion implies any state of movement, vertigo refers to a sensation of spinning that isn't relevant in this context, and flight encompasses the general condition of flying but lacks the connotation of returning to stability after a disturbance. Therefore, equilibrium is the most precise term reflecting the airfoil’s intrinsic stability characteristics.