Which speed indicates maximum surplus thrust?

Maximum surplus thrust occurs at the speed where the aircraft can gain the most additional thrust beyond what is required to maintain level flight. This is directly related to the aircraft's ability to climb effectively. The maximum angle of climb speed is crucial because it ensures that the aircraft can achieve the steepest ascent in the shortest horizontal distance, maximizing the available surplus thrust.

At this speed, the aircraft not only has enough thrust to overcome drag but also has enough excess thrust to begin climbing efficiently. This scenario provides the ideal balance of speed and power that enables the aircraft to gain altitude most effectively. In contrast, other speeds, such as minimum drag speed or takeoff speed, do not necessarily correlate with this maximum surplus thrust condition. Minimum drag speed refers to the point where drag is lowest, while takeoff speed is determined by the need for sufficient lift to become airborne, neither of which are specifically tied to maximum climb performance in terms of surplus thrust.