F3K is the international contest class for radio controlled, hand-launched model gliders.
Although the roots of RC hand-launched gliders can be traced back to the late 1970′s, F3K is a relatively new aeromodelling discipline, becoming officially recognised by FAI CIAM (the international body responsible for aeromodelling competition disciplines) with full official status in 2007. The first official FAI F3K world championships will be held in July 2011 at Arboga Airport in Sweden. The UK is sending a full senior team (3 pilots) and one junior pilot.
F3K gliders are 1.5 metre wingspan, radio controlled models, launched using a ‘discus launch’ in which the glider is held by a wingtip and rotated around the flyer by hand before release. Using this method of launching the average flier can achieve launch heights of greater than 140 feet, with the top fliers exceeding 200 foot high launches.
F3K competitions consist of a group of fliers completing a number of pre-defined flight tasks, centred around launching, flying and landing the model in a number of timed durations, using just the hand launch itself and thermal currents of rising air to power the flight.
In competitions, flight times range up to 5 minutes duration, in practice sessions F3K gliders are capable of flying for upwards of an hour in the right hands on a good day… not bad for a small, radio controlled glider, launched only by hand.
F3K models are generally constructed from composite materials, in the form of Kevlar, Carbon Fibre and Glass Fibre. Fuselages are moulded in Kevlar/Carbon, with wings either moulded as a hollow composite shell, or vacuum bagged over a wire-cut foam core. Most models use aileron, rudder and elevator control, with the ailerons also being used as camber changing flaps for different modes of flight and also as air-brakes for landing. A modern F3K model weighs only approx 9 ounces (255g) and has extremely sophisticated aerodynamics, thanks largely to the work of Dr Mark Drela of MIT who has developed most of the popular wing sections and plan-forms for these low-Reynolds number models. Many competitors use computer radio transmitters with full mixing and flight mode capabilities in order to optimise performance and set up the models for flight as near perfectly as possible.
Most F3K models are purchased as a ready made composite model, with all main components near-finished. This leaves the builder only having to assemble a few main parts and fit radio gear. Therefore the build time is minimal compared to a traditional wood-built RC model, with an average model ready to fly after only six or seven evening’s building work.
As well as out-and-out composite competition models, F3K (or DLG as it is sometimes called)models can be bought in the form of simpler and less expensive models for fliers wishing to partake in ‘sports’ flying, but still enjoy the superb launch and performance characteristics of F3K models…. in the right hands on the right day, they have been known to win competitions as well !
To a newcomer to F3K, on first sight, the discus launch can look both difficult and physically challenging. This is certainly not the case. The whole point regarding a F3K discus launch is that it can be achieved easily and with a minimum of physical stress. After a few practice sessions most new fliers start producing good launches. We have competitors in the UK who are over 70 years old and yet can throw to 140 feet altitude. Obviously the more effort and skill that is put into the launch the higher the model will go, with some competitors breaking the 200 foot launch barrier. However, for the average flier it is relatively easy after some practice, to achieve a good launch height, which will enable them to enjoy the sport and compete well.
When not being used to compete in F3K competitions these models offer very accessible sport flying. With no noise issues to worry about and a quick hand launch as a method of getting airborne, F3K models can be safely flown on the average large playing field or local park. One of the great benefits of flying this type of model is that they can easily be flown during a lunch break, as there is no lengthy setup, bungee layout or winch to worry about. Easily transported in the average car, it’s just a case of find a suitable field, throw and enjoy.