As airspeed decreases below the maximum lift-to-drag ratio, what happens to total drag?

As airspeed decreases below the maximum lift-to-drag ratio, total drag increases primarily due to elevated induced drag. At lower airspeeds, the aircraft must generate more lift to maintain level flight. Lift increases the total induced drag, which is a component of the overall drag experienced by the aircraft.

The relationship between lift and induced drag is critical; as an aircraft produces more lift, the induced drag increases significantly, especially at lower speeds where the effect is more pronounced. This phenomenon is encapsulated in the theory of aerodynamics where induced drag is inversely related to airspeed: as the airspeed decreases and lift is maintained or increased, the induced drag rises, leading to an overall increase in total drag.

Parasite drag, on the other hand, pertains to the non-lifting aspects of drag and does not significantly change in response to airspeed in the same way that induced drag does in this context. The maximum lift-to-drag ratio specifically occurs at an optimal airspeed; falling below this speed shifts the balance, resulting in a deteriorating efficiency due to the increased induced drag.