Which flight condition provides maximum glide distance for a given weight and density?

• A. Maximum lift/drag ratio
• B. Minimum airspeed
• C. Maximum speed
• D. Maximum range

Answer: (A)

Max glide distance is achieved when the lift-to-drag ratio is at its maximum. In a glide, lift must balance weight, and the distance you travel forward for each unit of altitude you lose (the glide ratio) is essentially L/D. The higher this ratio, the less drag you incur for the lift you need, so you cover more ground before you descend. The maximum L/D occurs at a specific angle of attack where induced drag (from lift at low speeds) and parasite drag (from the airframe at higher speeds) are balanced. If you fly too slowly, induced drag dominates and the glide distance shortens; if you fly too fast, parasite drag dominates and the glide distance also shortens. So the condition that yields the best glide distance is the one with maximum lift-to-drag ratio.