What structural feature is commonly used for vortex generators on aircraft?

The correct choice highlights small, angled fins as a common structural feature used for vortex generators on aircraft. Vortex generators are small aerodynamic surfaces that are attached to the wings and other control surfaces of an aircraft to enhance airflow and reduce drag, particularly at high angles of attack or low speeds.

These small fins are strategically positioned to create controlled vortices in the airflow, which helps to keep the boundary layer attached to the wing, minimizing flow separation. This is particularly beneficial during takeoff and landing phases of flight when angle-of-attack is increased, as it enhances lift and improves overall aerodynamic performance.

While flat plates, curved wings, and large retractable flaps serve important aerodynamic functions, they do not specifically provide the focused and efficient airflow manipulation that vortex generators are designed to achieve. Flat plates may not effectively generate the necessary vortices, curved wings may enhance lift but do not specifically address boundary layer behavior in the same way, and large flaps are primarily used for increased lift during low-speed operations rather than as vortex-generating devices.