The best lift/drag ratio occurs when which drag components are equal?

The best lift/drag ratio occurs when which drag components are equal?

• A. Parasite drag equals induced drag
• B. Parasite drag is minimized
• C. Induced drag is zero
• D. Lift equals weight

Answer: (A)

The best glide (maximum lift-to-drag ratio) occurs at the speed where parasite drag equals induced drag. In a glide, lift must balance weight, so the required lift is fixed. Induced drag arises from producing that lift and increases as you generate more lift (lower speed, higher angle of attack). Parasite drag comes from the airframe and skin friction and increases with speed. By adjusting speed, you trade off these two drag components. When they are equal, the total drag D = Di + Dp is minimized for the given lift, which makes the lift/drag ratio the highest. If parasite drag is minimized without regard to the balance, or if induced drag isn’t present (zero), you don’t achieve the smallest possible total drag for the needed lift.

The best glide (maximum lift-to-drag ratio) occurs at the speed where parasite drag equals induced drag. In a glide, lift must balance weight, so the required lift is fixed. Induced drag arises from producing that lift and increases as you generate more lift (lower speed, higher angle of attack). Parasite drag comes from the airframe and skin friction and increases with speed. By adjusting speed, you trade off these two drag components. When they are equal, the total drag D = Di + Dp is minimized for the given lift, which makes the lift/drag ratio the highest. If parasite drag is minimized without regard to the balance, or if induced drag isn’t present (zero), you don’t achieve the smallest possible total drag for the needed lift.