Didn't want to loose this..........probably should be in its own thread.
From a post by Kent Porter (August 2009) on the IMAC web site forums regarding the 10% scale.
3. Open Events
3.1. The events accommodate aerobatic monoplanes and biplanes which are replicas of types known to have competed in International Aerobatic Club (IAC) competition, or replicas of types known to be capable of aerobatic competition within the airspace known as the “Box.”
3.2. All classes except Basic require that the pilot must meet the requirements defined in Rule 3.1. The Basic Class is open to all competitors with a monoplane or biplane aircraft. There is no minimum size requirement for any class. Contest Directors may make an exception for a model of a full-scale aircraft that was built for IAC competition, but has not yet competed. Proof of the latter is the responsibility of the contestant.
6. Proof of Scale
6.1. To prove that the model resembles a particular aircraft some proof of scale is required.
6.2. Proof of scale is the responsibility of the contestant.
6.3. The general outlines of the model shall approximate the full size outlines of the subject aircraft. Exact scale is not required. The model shall be judged for likeness at a distance of approximately 10 feet.
6.4. If the contestant presents no proof of scale material with the model, and the CD can determine that the aircraft is a replica of a full size aircraft, then the contestant will be allowed to have his/her entry considered.
6.5. Scale shall be determined by the wingspan. A change in wingspan will become a change in overall Scale. Fuselage width, height and aircraft planform or any other variations shall not exceed 10% of scale, with the exception of airfoils and size/shape of control surface within the scale outline rule.
Providing the above hasn't changed, the Viper will be IMAC legal providing the wingspan meets the 10% rule and the general outline of "X" model, in this case the MXS. I do believe the MXS has competed in IAC. The split ailerons, split cowl, cowl vents, etc. are not determining factors.
Obviously as stated at the beginning this plane was designed for "awesome" and 3D in mind so it's more for the freestyle segment of the IMAC to leave everyone else like this
