I'm getting a little heartburn, too many people in my opinion confuse hotliners with F5B airframes. There are a lot of nice hotliners, but few can really qualify as legal and reasonably competitive F5B airframes. When one talks of F5B, legal airframes are defined by the FAI.
Briefly (borrowing from UK F5B site http://www.f5b.co.uk
True F5B models (according to the FAI) must weigh at least 2000g, have a NiCd or NiMH battery weighing no more than 1100g and it must not exceed a wing loading of 75g/dm2. For 2005, the major ammendments are as follows.
Minimum model weight without battery will be 900g.
Maximum size of cylindrical cells will be 24mm diameter and 45mm long.
Maximum number of cells will be 16.
Minimum surface area 26.66 dm2
Alot of sites that claim to sell F5B models, are really selling what I would consider 10 cell hotliners. These 10 cell hotliners often do not legally fit into the provisional FAI 10 cell class because of having too little wing area.
F5F or F5B/10 (FAI provisional class) are the same rules as F5B except they are powered by 10 NiCd or NiMH cells, have a wing area of at least 36md2, and ready to fly weighs at least 1500g.
When I started this thread, I was thinking of true F5B airframes capable of using a 16-cell battery pack. But in retrospect, I am also interested in legal F5F airframes.