The World Championships class F1D permits rubber motors of up to 0.6 gram in an aircraft with a minimum weight of 1.2g the without rubber motor. Dimensional limits are maximum wing span of 550mm, maximum chord of lifting surfaces 200mm, and maximum tail span 450mm. Models are usually made of a balsa frame covered with a lightweight transparent covering, either microfilm or plastic. Flights of up to 40 minutes are possible with F1D models.
There are two other rubber powered classes for smaller models:
For all 3 rubber-powered classes competitors are allowed six official flights, from which the total of the best two count for the final classification. At the World Championships there is also an award for the longest single flight in the Championships.
A different type of indoor class is F1N for hand-launched gliders. In competitions for this class flyers are allowed 9 flights from which the total of best 3 times count for the final classification.