If airspeed decreases in level flight below the speed for maximum lift/drag ratio, what happens to total drag?

If airspeed decreases in level flight below the speed for maximum lift/drag ratio, what happens to total drag?

• A. Decreases
• B. Increases due to induced drag
• C. Decreases due to parasite
• D. Stays the same

Answer: (B)

In level flight with a given weight, the wing must generate lift equal to that weight. As you slow down, you must increase the lift coefficient by raising the angle of attack. That higher lift coefficient increases the wingtip vortex strength, which raises induced drag. Parasite drag, which is tied to speed, drops as you slow, but it doesn’t drop fast enough to offset the surge in induced drag below the speed for best lift-to-drag ratio. So the total drag increases when you fly slower than the speed for maximum L/D.

In level flight with a given weight, the wing must generate lift equal to that weight. As you slow down, you must increase the lift coefficient by raising the angle of attack. That higher lift coefficient increases the wingtip vortex strength, which raises induced drag. Parasite drag, which is tied to speed, drops as you slow, but it doesn’t drop fast enough to offset the surge in induced drag below the speed for best lift-to-drag ratio. So the total drag increases when you fly slower than the speed for maximum L/D.