At the March 2007 meeting of CIAM the FAI passed new rules to allow lithium polymer cells to be used in F5B in 2008. I think the rules are as follows:

  • Minimum model weight without battery will be 1000g.
  • Maximum 6s (no parallel) lithium polymer cells.
  • Battery must weigh between 450g and 600g .
  • Power limited to 1750 Watt-minutes by an electronic device that stops the motor.
  • Minimum surface area 26.66 dm2
  • Maximum surface loading 75g/dm2

The running of the competition is as before. F5B is a multitask event for radio controlled electric gliders. The three tasks that have to be completed in one flight are Distance, Duration and Landing.

Distance: You have 200 seconds (3min and 20s) from the moment the model is launched to complete as many 150 metre 'legs' as possible. Each completed leg scores 10 points. You can use the motor to climb up to 10 times but all legs must be completed with the motor off.

Duration: At the end of the distance task you have to fly for a further 600 seconds (10 minutes). Each second airbourne scores 1 point but one point is deducted for every second of motor you use. You also lose a point for every second you fly in excess of the 10 minutes.

Landing: The flight ends when the model comes to rest on the ground. A landing bonus of 30 points is added if the nose of the model is within 5 metres of a pre-determined landing spot. 20 points are added if the nose is within 10 metres, and 10 points if it is within 15 metres.

More detailed rules can be found on the FAI website. You can also download the F5 sporting code in pdf format.

In the UK we run an F5B league with approximately one competition each month from April to October. Your model will fall into one of the following classes.

F5B-800: Your model is powered with no more than 7 NiCd or NiMH cells OR up to 3s lithium polymer, with a MINIMUM mass of 275g. In any case the power is limited to 800Wmin. ("Trust" limiting will be allowed in 2008.)

F5F No-one is flying F5F (10-cell) anymore, so this class does not really exist in the UK

F5B (open): If your model is not powered by 7-NiMH or 275g lipo it must be this class. True F5B models (according to the FAI) must weigh at least 1000g (without battery) and use a lithium polymer battery (6s max.) weighing at least 450g but no more than 600g. NiMH are banned in F5B (open) as of January 1st 2008. Power is limited to 1750Wmin. The wing loading of the model (ready to fly) must not exceed 75g/dm2.