FAI Competition Codes
The FAI (www.fai.org) who are the world organising body for all sports aviation including model flying have system of codes for sporting classes for competition aircraft.
In aero modelling competitions, these are given the designation 'F'. So there is F1 to 6. Each of these designations are split into groups A up to K (at the moment). Each class comforms to strict rules.
F1 = Free Flight Models
(With various sub sections)
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F2 = Control Line Circular Flight
F2A = Speed Models
F2B = Aerobatic Models
F2C = Team Racing Models
F2D = Combat Models