What is F3K?
Before we dive into what is what, check out this video. You see guys launching small gliders using a rotating throw method, into the sky. This in essence is F3K...
F3K is the FIA competition class of hand launched gliders (HLG) or more specifically discus launched gliders (DLG).
So what are DLG's?
A Discus Launch Glider (DLG) is a radio controlled model sailplane (or glider) which is launched using a spinning launch method or 'discus launch'. The glider is held by a peg on a wingtip and is rotated around the flyer by hand before release.
Using this method of launching the average flier (with as bit of practice) can achieve launch heights of greater than 50 metres with the best documented launch being around 100 metres. At competitions the average launches are in the 60 to 80 metre range.
The discus method of hand launching replaced the 'javelin style' launch, where a hand launched model glider would be launched over-arm, like a javelin. The discus launch is far easier, more efficient and less physically demanding than the javelin launch.
In the past DLG designs used a traditional built-up construction methodology using balsa wood and covering film. Although this style of building is not used much anymore, there are some current projects where planes like this are built and flown in special contests. There is an active 1m class in Holland with self-build plans available - check out this group on RCgroups.
Current DLG models are generally now constructed from composite materials - Kevlar, carbon fibre and glass fibre. Fuselages are moulded in Kevlar/carbon and epoxy, with wings either moulded as a hollow composite shell or with a composite covering over a foam core.
There are manufacturers who make 'foamie' DLG gliders too. Some examples are the Libelle from DreamFlight and the E-flite UMX™ Whipit™. Although these models are a lot of fun for casual use, they are very 'floppy' and launch heights are low. They are great as toys, and to learn the basics of flying on, but will frustrate anyone wanting to seriously get into DLG competitively. FlightTest also has plans for a DIY depron foam DLG. There is a growing list of 1m and 1.2m composite gliders coming onto the market too. They are cheaper and smaller (for travel and for shorter pilots).
DLG models are used for both general fun/sport flying and also for contest flying.
Most DLG 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 airbrakes for landing. A modern DLG model weighs in around the 200-260gram mark and has sophisticated aerodynamics. Pilots use 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 DLG models allow for the adding of extra weight or ballast. This is to increase the flying weight of the model, to increase its ability to fly into oncoming wind. This is important during competitions when wind speeds increase and pilots who have chased thermals down wind, need to return to the flying 'box' to land.
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 1970s, F3K is a relatively new aeromodelling discipline, becoming officially recognised by the FAI (international body responsible for aeromodelling competition disciplines) in 2007. The first F3K world championship was held in Sweden in 2011, and has been held every alternate year since then. The world champs in Ukraine in 2017 attracted teams from 32 countries comprising 87 seniors and 23 juniors.
F3K gliders are limited to a 1.5 metre wingspan. F3K competitions consist of a group of competitors completing a number of pre-defined flight tasks involving launching, flying and landing the model in a number of timed durations. Just the hand launch and thermal currents of rising air (thermals) are used to sustain the flight. Since thermals cannot be seen, F3K pilots rely on ground signs such as surface wind velocity, temperature and direction; signs such as circling birds, bugs, or rising particulates; and changes of direction or attitude of the glider due to the thermal itself. The pilot uses these signs to resolve the approximate location of the thermal. For F3K tasks where longer durations are needed, positioning and maintaining the model glider in thermal rising air is paramount. Contest strategy includes determining the location of thermals before the pilot launches.
