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Free Flight World Championships and many major competitions are flown with the following model classes:
F1C power model - minimum loading 20 g/dm2, minimum total weight 300 g/cc, maximum volume of motor 2.5cc, maximum motor run 5 seconds. Typical models have a wing span of 2m and reach altitudes of well over 100m in the 5 seconds of climb.
The outline specifications are shown here, the full details are available in Volume F1 of the Sporting Code section 4.
These classes are flown to a maximum flight time of 3 minutes on each of 7 flights. Fly-off flights are flown to decide the final winner when there is a tie, with the maximum duration increasing by 2 minutes between each flyoff round.
Smaller model classes are defined which have a lower performance and are flown in competitions with 5 flights and the shorter maximum flight times of 2 minutes. These are:
The World Championships class F1D permits rubber motors of up to 0.6 gram in an aircraft with a minimum weight of 1.2g the without rubber motor. Dimensional limits are maximum wing span of 550mm, maximum chord of lifting surfaces 200mm, and maximum tail span 450mm. Models are usually made of a balsa frame covered with a lightweight transparent covering, either microfilm or plastic. Flights of up to 40 minutes are possible with F1D models.
For all 3 rubber-powered classes competitors are allowed six official flights, from which the total of the best two count for the final classification. At the World Championships there is also an award for the longest single flight in the Championships.
Free Flight models are flown without any form of mechanical or radio control over the model in flight. This is the earliest form of aeromodelling, a particular milestone being the first model powered by a rubber band built and flown by Alphonse Penaud in 1871. Always present since that time has been the joy and achievement of releasing a model and seeing it soar overhead in its planned flight pattern.
Free Flight competitions are solely determined by the total flight duration achieved over a set number of flights, the stopwatch is the only judge of success. Competitors always strive to improve models by design and trim adjustments to achieve the longest flight time.
There are two fundamental categories of free flight model - indoor and outdoor - with various types and specifications in each category. These classes will now be described, with outline of main points of the rules (see Sporting Code for full specifications).
Most indoor models are powered by twisted rubber motors, with a maximum weight of rubber permitted in each class along with limitations on the airframe size and minimum weight. Championships are flown in large buildings, particularly airship hangars (old or new), exhibition halls, and also the salt mines in Romania. Smaller models or local competitions may be flown in local buildings such as sports halls. Rubber powered models have the motor driving the propeller during the entire flight, climbing up to close to the ceiling and then descending slowly during the rest of the flight as the torque of the motor reduces. The indoor classes recognised by FAI are the World Championships class F1D, two other rubber powered classes for smaller models F1L and F1M, and hand-launched gliders F1N.
Outdoor models are in 3 major forms - gliders, rubber powered, or powered by motors. Rubber models are powered by a twisted rubber motor driving a propeller which folds to leave the model to glide when the turns have unwound. Power models have a limited size of internal combustion motor or electric motor and this is allowed to run for a short time, after which the model glides. There are two types of glider, one launched by towing them up on a line 50m long and the other flown from hills with steering to keep them facing into wind.
Traditional models were constructed from balsa wood and covered with tissue paper, but for competition models this has largely been superseded by new technologies for making lighter stronger structures. Many models have airframes made mainly from carbon fibre and covered with plastic film. A common feature of all outdoor models is that they are subject to the wind and rising or descending air currents. Competitors work to understand the air motion and to keep their models up best by launching into thermals.
Major competitions are flown with the aim of flying for at least 3 minutes on each of 7 flights. Fly-off flights with increasing maxima are flown to decide the final winner when there is a tie. Clockwork or electronic timers are used to make pre-set adjustments to controls during the flight and to bring the aircraft down when the maximum time has been reached. Models are trimmed to circle during the gliding flight, which circles then drift downwind with the prevailing wind. Smaller models classes are defined which are flown to the shorter maximum time of 2 minutes.
The World Championships class for rubber powered models is the oldest type of aeromodelling international competition. The F1B World Champion is awarded the Wakefield Trophy, which has been competed for since 1928.