The lift to drag ratio mainly determines which of the following?

The lift-to-drag ratio is a crucial aerodynamic parameter, representing the efficiency of an aircraft in producing lift compared to the drag it experiences. A higher lift-to-drag ratio indicates that an aircraft can glide further when thrust is not available, making this ratio particularly significant when considering how far an aircraft can travel horizontally while in a glide scenario without any external propulsion.

In the context of the question, the horizontal glide distance at zero wind and zero thrust is directly influenced by this lift-to-drag ratio. When an aircraft is in a gliding state, the lift provided must counteract the weight of the aircraft, while drag acts in the opposite direction. Thus, if the lift-to-drag ratio is high, the aircraft will generate more lift while experiencing less drag, enabling it to glide farther.

On the other hand, the other options relate to different performance metrics of the aircraft. Climb performance and endurance speed focus on different aspects of flight, such as the aircraft's ability to gain altitude or maximize flight time, respectively, rather than purely on the horizontal distance achievable in a glide. Thus, while they may be influenced by aerodynamic efficiency in a broader sense, they are not predominantly determined by the lift-to-drag ratio as the glide distance is.