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The CG is at 25% MAC. Where is it located in relation to LEMAC and TEMAC?

  • A

    25% of the MAC is measured behind the LEMAC and is calculated with reference to the LEMAC

  • B

    25% forward of the Leading Edge of the Mean Aerodynamic Chord (LEMAC).

  • C

    25% of the MAC is measured behind the LEMAC and is calculated with reference to the TEMAC

  • D

    25% forward of the Trailing Edge of the Mean Aerodynamic Chord (TEMAC).

Refer to figure. 
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Generally, the Centre of Gravity (CG) is expressed as a distance (L) relative to a datum or reference point, but CG is usually expressed in swept wing aircraft as a distance relative to the Mean Aerodynamic Chord (MAC) of a wing. The MAC (Mean Aerodynamic Chord) represents the chord of an imaginary airfoil that has the same aerodynamic characteristics as the actual wing. To be more specific, the CG is expressed as a percentage of its position along the MAC (%MAC) from the leading edge (Le), also called LEMAC.

  • LEMAC: This is the Leading Edge of the Mean Aerodynamic Chord. It represents 0% of the MAC.
  • TEMAC: This is the rear edge of the MAC and is considered 100% of the MAC.

If the CG is at a distance L from the datum, then the correct formula to calculate the CG position as a percentage of the MAC is:

  • ((L - LEMAC)/MAC) x 100.

The CG is at 25% MAC, which means it is 25% of the chord length back from the LEMAC. This means that the CG is located behind the Leading Edge of the Mean Aerodynamic Chord (LEMAC).

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