What relationship exists between airspeed and thrust required in level flight?

In level flight, the relationship between airspeed and thrust required is influenced primarily by aerodynamic drag. As an aircraft increases its airspeed, the drag experienced by the aircraft also increases. This is due to the fact that drag is typically a nonlinear function of velocity – specifically, it increases with the square of the airspeed.

In steady, level flight, the thrust produced by the engines must counteract this drag to maintain altitude. Therefore, as airspeed increases and, correspondingly, drag increases, the thrust required to maintain level flight also increases. This relationship indicates that maintaining flight at higher speeds necessitates greater thrust to overcome the additional drag forces acting on the aircraft.

It's important to recognize that factors like aircraft weight also play a significant role in flight performance, but when specifically considering the impact of airspeed on thrust requirements in level flight, the dominant effect is the increase in drag. Thus, as airspeed goes up, the thrust required to maintain level flight also rises, leading to the conclusion that the correct answer reflects this significant aerodynamic principle.