FAA Private Pilot Helicopter (PRH)Helicopter Aerodynamics and SystemsEasy
A mechanic points to a main rotor blade cross-section and explains that the imaginary straight line drawn from the leading edge to the trailing edge is used as a reference for measuring blade pitch and angle of attack. What is this line called?
- ASpan line
- BChord line
- CRelative wind line
- DCamber line
Show answer & explanationAnswer & explanation
Correct answer: B. Chord line
The chord line is the straight reference line connecting the leading edge to the trailing edge of an airfoil, used to measure both pitch angle and angle of attack.
Why the other options are wrong
- A. Span refers to the length of the blade from root to tip, not a chordwise reference line.
- C. Relative wind is the direction of airflow relative to the airfoil, not a fixed geometric line on the blade.
- D. The camber line is the curved line midway between the upper and lower airfoil surfaces, not a straight reference.
Chord Line
A straight imaginary line connecting the leading edge and trailing edge of an airfoil, used as the reference for measuring pitch angle and angle of attack.
- Straight line, unlike the curved camber line
- Basis for measuring blade pitch angle
- Basis for measuring angle of attack relative to relative wind
Memory trick: Chord is a straight cord tied leading-edge to trailing-edge