Synopsis of FAI Class F3A operation

by Bob Skinner, Chairman of the CIAM F3A Sub-committee (December 2000)

The FAI/CIAM class of F3A involves complex aerial manoeuvres with a radio controlled model aircraft, where utmost precision and skill in controlling the model aircraft in any attitude and under all conditions is required. The model aircraft is 100% influenced by the wind and all manoeuvres in the aerobatic schedules are judged relative to a point on the ground. The competitor must therefore compensate constantly for possible wind drift. Typically, an F3A model aircraft will have a fuselage length of no more than 2 metres, a wing span of less than 2 metres, and the weight must not exceed 5kg's. The motive power is usually an internal combustion engine, with no power limitations, but the engine has to be adequately silenced. The on-board radio control equipment, receiving signals from the competitor's transmitter, actuates the control surfaces to enable aerobatic performance.

The F3A class is a team as well as an individual competition. FAI member countries may enter a team of maximum three competitors as a national team for world- and continental championships. Team results are the sum of the three competitors' scores.

Flights are performed directly in front of the judges in an aerobatic zone or "box", which extends 60 degrees to the left and right of a centre line, and at an elevation of no more than 60 degrees. Each time the model aircraft crosses the centre line, a particular manoeuvre of a known (published) aerobatic schedule has to be performed, involving components such as loops, rolls, lines, spins, snap rolls, stall turns, and combinations of these. At the ends of the aerobatic box, the model aircraft is required to do turn-around manoeuvres to enable it to reverse its direction of travel. Typically an aerobatic schedule has 23 manoeuvres, including a take-off and a landing. Manoeuvres or parts performed outside of the box are penalised by loss of points, proportional to the degree of infraction. Generally the model aircraft is required to be flown at 150 metres from the pilot, in a plane perpendicular to the centre line. Each competitor will be entitled to four preliminary flights, of which the best three scores will determine his placing. Semi-final and final rounds are flown only for world- and continental championships, and involve more difficult known, and unknown manoeuvre schedules.

Each competitor's performance is assessed by a panel of judges who will award marks, independently from each other, between zero and ten for each manoeuvre, or figure. Manoeuvres are assigned a difficulty factor (K-factor) depending on the complexity of the particular manoeuvre. Judging is based on four basic criteria: precision (or geometry), smoothness and gracefulness, positioning (display), and size of manoeuvres. Points are subtracted for various types of defects observed by the judges, the severity of these defects, and the number of times these defects are observed. At the end of each flight the judges may award a penalty for an excessively noisy model aircraft, to discourage disturbance to the surroundings.