F5J is an electric motor launch version of F3J. You don't need a high cost motor/battery combination, the maximum wing span is 4 metres which allows many types of models the are readily available from manufacturers. 

Each model has a device installed that records the launch motor run time and height. The maximum motor run is 30 seconds. The motor can only be run once during the working time. There is a launch height penalty in place. Each metre of the recorded Start Height results in a deduction of half (0.5) a point up to 200m and three (3) points above it.

There is a 10 minute working time from the moment the model leaves the hand to the time it touches the ground or any object in contact with the ground. A landing bonus of 50 points is available.

The aim is to use the minimum launch height possible to achieve the maximum flight time within the 10 minute working time. With launch height penalties in place the best flights are a judgement on pilot skills and risks using short motor runs and low launches.

The full rules are available below.

BARCS F5J Forum

Contest Eurotour Website

sc4_vol_f5_electric_22.pdf