What is the role of the datum when defining LEMAC and TEMAC?

• A. A point on the aircraft used to fix components
• B. A measurement system for aerodynamic data
• C. A reference point used to measure distances for LEMAC and TEMAC
• D. A type of datum line passing through the aircraft

Answer: (C)

The datum is the fixed reference from which all measurements are taken when locating wing geometry. For LEMAC and TEMAC, you need a consistent origin to define where the leading-edge mean aerodynamic chord and the trailing-edge mean aerodynamic chord lie. By measuring distances from this datum point (or from a datum plane/line defined from that point), engineers can specify the exact positions of LEMAC and TEMAC so drawings, manufacturing, and analysis all align. Without this common reference, the locations of those mean chords would be ambiguous. In short, the datum provides the measurement origin used to determine where the LEMAC and TEMAC lines sit on the wing.