Stability and Control characteristics of the Early Mark Spitfires

[Crumpp]

Lenght of aerodynamical mean chord (MAC): 78.54"

The rest is simple math:
Aft limit behind datum line at MAC: 26.7036" - 18.65" = 8.05"
Datum line behind leading edge at wing root: 31.656" - 8.05" = 23.6024"
NACA CoG behind datum line: 31.4" - 23.6024" = 7.7976"
NACA CoG location at MAC behind leading edge: 18.65" + 7.7976" = 26.4476"
NACA CoG % at MAC: 26.4476" / 78.54 * 100 = 33.6741%