How is “unusual” sail area (such as inflated kites, wingsails, or Flettner rotors) measured?
Typically, measurement of wingmasts, wingsails and inflated kites or other structures is taken as half the total surface area of both “skins” of the structure. This is in accordance with the IRYA standards, for measuring wingmasts and wingsails. Note that this is not the “projected” area of the rig. In addition, in measuring rig or rig elements capable of accelerating independently of the craft (such as kites, windmill or auto-gyro rigs), and also for ultra-high lift rigs (Flettner or Thom rotors), the sail area measured is the “blade” or rotor area only, and not the “swept,” “disc” or “effective” area. This is a distinct advantage for these types of craft, and is currently allowed in order to encourage their development.
