The lift-to-drag ratio at an angle of attack of 2 degrees is approximately the same as the lift-to-drag ratio at which angle?

The lift-to-drag ratio at an angle of attack of 2 degrees is approximately the same as the lift-to-drag ratio at which angle?

• A. 5°
• B. 20°
• C. 16.5°
• D. 1°

Answer: (C)

Lift-to-drag ratio measures how efficiently the wing can glide: lift grows with angle of attack while drag rises, and their balance changes as you sweep through angles. It reaches a peak at a moderate angle, then drag climbs rapidly as you approach stall, so the ratio falls off. Because of that shape, you can have roughly the same L/D at a small angle like 2 degrees and at a much higher angle where drag is large but lift is still present. At 16.5 degrees you’re well into the high-drag region near stall, so the L/D can be similar to what you get at 2 degrees. The other angles wouldn’t match as well: about 5 degrees is typically near the best L/D, so the ratio there would be higher than at 2 degrees; 20 degrees is usually well past stall with very poor L/D; 1 degree is very close to 2 degrees and would be similar but not the commonly cited near-stall comparison.

Lift-to-drag ratio measures how efficiently the wing can glide: lift grows with angle of attack while drag rises, and their balance changes as you sweep through angles. It reaches a peak at a moderate angle, then drag climbs rapidly as you approach stall, so the ratio falls off. Because of that shape, you can have roughly the same L/D at a small angle like 2 degrees and at a much higher angle where drag is large but lift is still present. At 16.5 degrees you’re well into the high-drag region near stall, so the L/D can be similar to what you get at 2 degrees.

The other angles wouldn’t match as well: about 5 degrees is typically near the best L/D, so the ratio there would be higher than at 2 degrees; 20 degrees is usually well past stall with very poor L/D; 1 degree is very close to 2 degrees and would be similar but not the commonly cited near-stall comparison.