Angle of incidence is measured from which line to the rotational relative wind?

• A. Measured from chord line to rotational relative wind
• B. Measured from leading edge to trailing edge
• C. Measured from center of gravity to wind
• D. Measured from trailing edge to wind direction

Answer: (A)

Angle of incidence is the angle between the blade’s chord line and the relative wind the blade sees as it rotates. The chord line runs from the blade’s leading edge to its trailing edge, so measuring from that line to the rotational relative wind defines how the blade is oriented to the oncoming flow. This orientation governs how much lift the blade can produce, up to stall limits, and ties directly to how the pitch (incidence) is set. The other ideas don’t reference the wind direction properly—one describes just the chord line, and the others refer to unrelated reference points—so they don’t define the blade’s actual angle to the flow.