What is the main difference between parasitic drag and profile drag as speed increases?

The main difference between parasitic drag and profile drag as speed increases lies in their relationship with airflow over the aircraft and how it impacts drag.

Parasitic drag is a composite drag that includes all drag forces acting on an aircraft that are not related to lift. This type of drag increases with the square of the speed due to the higher kinetic energy of the airflow around the aircraft. It encompasses factors such as form drag and skin friction drag.

Profile drag, on the other hand, specifically refers to drag due to the shape of the aircraft and how the body interacts with the air. At lower speeds, profile drag is significant because the airflow has more time to adhere to the surface of the aircraft, resulting in higher resistance.

As speed increases, profile drag becomes less significant until a critical point, at which parasitic drag predominates because of its squared relationship with speed. This means that initially, profile drag plays a more substantial role, but as speed continues to rise, parasitic drag begins to dominate the total drag forces acting on the aircraft.

By understanding this dynamic, we can see why the choice that states "Profile drag starts out significant, but parasitic drag becomes more significant" accurately captures the relationship between these two types of drag as speed varies.