Which statement best defines the best-glide speed in a glider?

Which statement best defines the best-glide speed in a glider?

• A. The airspeed that minimizes sink rate
• B. The airspeed that produces the lowest air drag at cruise
• C. The airspeed that gives the best climb rate
• D. The airspeed that yields the longest gliding distance for given altitude

Answer: (D)

The best-glide speed is the airspeed at which the airplane achieves the maximum lift-to-drag ratio (L/D). At this speed the glide angle is the smallest, so you convert the most altitude into forward distance. In other words, you can travel the farthest horizontally from a given altitude when flying at the speed where L/D is highest. This isn’t the minimum-sink speed, which minimizes vertical descent rate but doesn’t maximize distance. It isn’t simply the lowest-drag speed at cruise, because the overall efficiency for gliding depends on the balance between lift and drag, not just drag alone. And it isn’t about climb rate, since gliders glide downward unless aided by a vertical air current.

The best-glide speed is the airspeed at which the airplane achieves the maximum lift-to-drag ratio (L/D). At this speed the glide angle is the smallest, so you convert the most altitude into forward distance. In other words, you can travel the farthest horizontally from a given altitude when flying at the speed where L/D is highest.

This isn’t the minimum-sink speed, which minimizes vertical descent rate but doesn’t maximize distance. It isn’t simply the lowest-drag speed at cruise, because the overall efficiency for gliding depends on the balance between lift and drag, not just drag alone. And it isn’t about climb rate, since gliders glide downward unless aided by a vertical air current.