I wanted to get a sample of Tim Van Milligan's kits, so I included a Centrix and its booster when I ordered some items from Apogee Components.I call this version a "sport" model because it uses a launch lug. For competition (AL14-98?), I'll build an extended one (for tracking powder) without the lug and use a tower for the launch. The Centrix is a minimum diameter 3FNC model designed for Apogee's 10.5mm micro-motors. It has nicely die-cut balsa fins and some interesting construction details. It uses a length of Kevlar® line for its shock cord (no elastic, but at the light weight of this model it's not really needed) that is attached to the nose cone by gluing a plastic bead into a hollow in the base of the balsa cone, trapping the line. I suppose if you wanted to be SURE the shock cord wouldn't separate from the nose cone, you could tie the cord thru the bead before gluing it into place. The booster (what makes it a Super Centrix) is gap-staged (the gap varies depending on how big a motor you use) and vented to improve the odds of lighting off the upper stage motor.

Note: Be SURE to use the Apogee staging igniters to get the upper stage lit. Depending on just the blow-by from the lower stage going into that *tiny* nozzle is an invitation to failure.