In swept wing aircraft, what initiates a Dutch roll?

In swept wing aircraft, a Dutch roll is primarily initiated by an asymmetrical lift due to yaw. When the aircraft yaws, meaning it turns about its vertical axis, the aerodynamic lift generated by the wings can become uneven because of their swept design. The wing that is moving forward experiences more airflow and thus can generate more lift than the wing moving backward. This differential lift can lead to a rolling motion, which, combined with the yawing motion, creates the characteristic oscillation of a Dutch roll.

This situation can tend to amplify itself; as one wing generates more lift and rises, the opposite wing will start to descend, which can further enhance the yaw motion and lead to a cycle of oscillation. Therefore, the asymmetrical lift due to yaw is crucial for understanding the dynamics behind a Dutch roll in swept wing aircraft.

The other options don’t directly cause a Dutch roll. An increase in drag affects the aircraft's speed but does not specifically lead to the yaw-induced oscillation. A sudden change in altitude is more related to vertical maneuvers and stability rather than lateral motion. A stall at the wingtip, while significant in understanding stall dynamics, does not initiate a Dutch roll in the conventional sense as it is more focused on loss of lift