What is observed with induced drag when an aircraft slows down below the optimum airspeed?

When an aircraft slows down below the optimum airspeed, induced drag increases. Induced drag, which is a byproduct of lift, is primarily related to the angle of attack and the amount of lift an aircraft generates. At lower speeds, the aircraft requires a higher angle of attack to maintain lift. This increased angle of attack leads to greater induced drag because the aerodynamic forces acting on the aircraft become less efficient.

As the aircraft moves slower, it is often operating at or near its critical angle of attack, where the lift generated becomes less effective, and drag naturally rises as a consequence. Therefore, when the aircraft is not at its optimum airspeed, which is designed to minimize drag for a given lift requirement, induced drag becomes more prominent, resulting in an overall increase.