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A positively cambered aerofoil will generate...
  • A
    Zero drag at approximately -4º alpha.
  • B
    Zero lift at zero alpha.
  • C
    Positive lift at zero alpha.
  • D
    Positive lift at approximately -4º alpha.

Refer to figures.
Camber is the asymmetry between two acting surfaces on an airfoil. For a helicopter, these are the upper and lower surfaces of the rotor blades.

A completely symmetrical airfoil will intersect the vertical axis of the graph at the origin (0) and generates zero lift at zero alpha.

A positively cambered airfoil will generate more lift at the same speed (thus, has a higher CL), than a symmetric airfoil and, therefore, intersects the vertical axis above the origin generating zero lift even at a negative angle of attack.

A negatively cambered airfoil will generate less lift at the same speed (thus, has a lower CL at a certain speed), than a symmetric airfoil and, therefore, intersects the vertical axis below the origin. An example of a negatively cambered airfoil is the tail's horizontal stabilizer.

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