Which of the following is a disadvantage of a symmetrical airfoil?

Which of the following is a disadvantage of a symmetrical airfoil?

• A. Less lift at a given angle of attack
• B. Constant center of pressure
• C. Ease of construction
• D. Lower cost

Answer: (A)

The main idea is that lift is strongly affected by camber. A symmetrical airfoil has no camber—its curvature is the same on both surfaces—so at any given angle of attack it generates less lift than a cambered airfoil. Camber adds curvature that helps air flow accelerate over the top surface, creating a higher lift coefficient for the same angle. Because of this, you’d need a larger angle of attack to achieve the same lift with a symmetric airfoil, which also brings the rotor closer to stall and reduces overall efficiency. The center of pressure for a symmetric airfoil is not fixed; it moves as the angle of attack changes, so saying the center of pressure is constant isn’t correct. And while symmetric airfoils can be easier to manufacture and cheaper, those are manufacturing considerations rather than aerodynamic disadvantages in lift production.

The main idea is that lift is strongly affected by camber. A symmetrical airfoil has no camber—its curvature is the same on both surfaces—so at any given angle of attack it generates less lift than a cambered airfoil. Camber adds curvature that helps air flow accelerate over the top surface, creating a higher lift coefficient for the same angle. Because of this, you’d need a larger angle of attack to achieve the same lift with a symmetric airfoil, which also brings the rotor closer to stall and reduces overall efficiency.

The center of pressure for a symmetric airfoil is not fixed; it moves as the angle of attack changes, so saying the center of pressure is constant isn’t correct. And while symmetric airfoils can be easier to manufacture and cheaper, those are manufacturing considerations rather than aerodynamic disadvantages in lift production.