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F5B is an international competition class for electrically powered radio controlled model gliders. It is a multitask event which means you have to fly more than one 'task' per flight. The following description is an interpretation of the rules.

In the UK they use a handicap system to allow different models to compete on more equal terms. I propose we adopt that system to allow more pilots to compete with a chance of winning.

The F5B Competition Rules 

Before reading these rules you might like to take a look at this image of the course that F5B is flown on.  This image is taken from the FAI sporting code.

Task 1 - Distance 

From launch you have 3 minutes (180 seconds) to fly as many 150 metre legs as possible. You score 10 points for every leg completed in this time. There are 2 sighting lines called ‘base A’ and ‘base B’ that are 150m apart. Spotters at base A and base B sound a buzzer when the model has crossed the line. The pilot turns the model when the buzzer is sounded. The area between base A and base B is called ‘the course’. The area beyond base A or B is ‘off the course’. The electric motor is used to gain height ‘off the course’. The motor must be switched off before the model enters ‘the course’. The model must always enter ‘the course’ at base A. This is the end where the pilot stands.

The model must make a minimum of 2 and a maximum of 10 climbs in the 3 minutes.  Each time the motor is switched on counts as a climb.

Most pilots fly 4 legs from a single climb. The current record (October 1999) for legs flown in the 3 minutes is 39. That is 5.85km in just 180 seconds, which is 117km/h! This calculation does not include the time taken to climb or the time taken to turn the model at base A or B.

Task 2 - Duration 

At the end of the distance task the model must complete a 5 minute (300 second) duration. You score 1 point for every second that the model stays airborne, up to a maximum of 300 (5 minutes). The duration task starts when the model completes a ‘limbo’ below 3 metres at base A. One point is deducted for every second of motor used during the duration task. If you land before or after the 5 minutes you lose 1 point for every second. In other words, over-flying the task by 5 seconds loses 5 points in the same way that under-flying by 5 seconds does.

The top pilots are able to complete the duration with 2 or 3 seconds of motor in zero lift conditions. They achieve this by completing the limbo very fast. One option is to climb before the limbo and dive through at great speed. Another is to use the motor to accelerate the model just before the limbo. Several have managed to complete the task without using any motor, but this required thermal assistance.

Task 3 - Spot landing 

The flight ends with a precision landing.  30 points are added to the score if the nose of the model is within a 7.5 metre radius of the spot. 15 points are added if the nose is within a 15 metre radius.

Handicap system 

In the UK they use a handicap system to allow FAI models, FAI 10 cell models, 7 cell models and 7 cell Speed400 models to compete against each other. The handicap is adjusted at the end of the season if necessary. The following table indicates how points are awarded for the distance task and the duration task. The landing bonus is not affected by the handicap.

Complete FAI Rules

General rules affecting all F5B models (OPEN RULES)

• The battery must not exceed 1100g. This mass to include all connections but not the electronic speed controller (ESC).
• Wing loading must not exceed the FAI limit of 75 g/dm².
• The model must climb more than once but not more than 10 times in the distance task. This means that most now fly 4 legs each climb in the 3 minutes. You're shooting for a target of around 40 legs to be "world class".

Rules for the 10-cell competition (F5B-600)

• The model must conform to all of the open rules.
• The battery can be made with no more than 10 cells and must not exceed 600g.  Most pilots are using 10 Sanyo RC2000's.
• The total projected area (wing and tail) must be at least 36dm². It is still an advantage to go for light models so they climb quicker. Obviously this results in quite lightly loaded models (compared to open) and the flying is quite different.

Rules for the 7 cell competition

There is no international class for 7 cell F5B. The following are local rules applied in the UK only.

• The model must conform to all of the open rules.
• The battery may not exceed 7 cells. We do not apply a weight limit for the battery in 7 cell competition. Most pilots use 7 Sanyo RC2000's.
• There is no wing area limit for the 7 cell competition. Very small models, like pylon racers, could be used to good effect in the distance task. The thermalling ability of such small models would possibly put them at a disadvantage in the duration task. The best results have been using models designed for open F5B, i.e. Approximately 24dm²

Rules for F5B-S400

F5B-S400 is an experimental class of F5B which was run for the first time in 1999. The provisional rules below may have been adapted and amended in the light of experience gained since then.

These simple rules will allow plenty of scope for the would-be competitor to fly any available kit. You also have complete freedom to design whatever takes your fancy.

• Only ferrite motors with a 2.3mm shaft, permanently affixed rear end-bell and non-replaceable brushes will be permitted. (This permits all of the cheaper motors such as Graupner Speed 400, Robbe Power 400 and other variants of the Mabuchi 380, but excludes more expensive motors such as the Graupner 480 Race and Kyosho equivalents).
• Only one of these motors allowed per airframe.
• The motors can be retimed but no other reworking is allowed.
• Gearboxes are allowed if desired.
• The battery that powers the motor must not exceed 7 cells. These can be either NiCd or NiMH and can be any capacity.
• No other restrictions apply.