Links to competition classes

S4 Boost Glider duration

This is a challenging class in which a model must be boosted vertically as high as possible under rocket power and then glide back gently to earth. During ascent it must stay within a defined cone and not use the lifting surfaces (wings). In other words it must go up as a rocket! On descent it must be in stable flight. There are three rounds, each with a maximum time of 180 seconds. If after the three rounds there is a tie, then those competitors have a fly off with no maximum

There are many different approaches to building models for this class from simple balsa wood chuck gliders with a motor pod added, to complex folding models. The motor may be ejected in a pod or part of the airframe at apogee, in which case it must come down on a streamer. The rules changed in 2009 to permit the motor to be retained in the model during the glide part of the flight. Some competitors have inserted flying wings into rocket bodies and polystyrene "darts" have also been seen at recent championships. In this case the body descends on the streamer leaving the wing or dart to do the gliding portion of the flight

The most popular current design turns the wing through 90 degrees for boost. The wing tips are then folded under and are held in place against the body spar. A thread runs under the motor to hold the wings in the boost position. When the motor burns out the thread holding the wings in place is released and the wings un-fold back to the glide position, normally using the power of elastic bands, although springs are sometimes used.

A more advanced version of this is the "Jacomb" special where the wings don't just turn through 90 degrees but they actually fold around the central spar for best aerodynamic shape for boost. This design helped Nigel Bathe to a silver medal at the 2008 World Championship.

One other issue with boost gliders is the DT. Once they are up and gliding in good buoyant air they don't want to come down. After the 180 second flight it is important to destabilize the glider so it will stall and tumble from the sky to be used in the next round.