Which factor is essential for determining the best glide speed?

Determining the best glide speed is fundamentally linked to the aerodynamic characteristics of the aircraft. This speed is the point at which the aircraft achieves the maximum lift-to-drag ratio, allowing it to cover the greatest distance while descending. The aerodynamic design, including the wing shape, aspect ratio, and other performance metrics, directly influences how well the aircraft can glide.

While weight is important because it affects the overall energy state of the aircraft, the actual glide performance is primarily governed by its aerodynamic properties. Similarly, while weather conditions can affect glide performance (such as wind and turbulence), they do not define the best glide speed itself. Engine power output is not relevant to glide speed since, in a glide, the engine is not providing thrust. Thus, the aerodynamic characteristics are the primary determinant of the best glide speed.