I competed in Spain a few months ago on behalf of the US Team. Prior to going I did at least a few hundred practice flights. I spent an enormous amount of time testing my entire recovery system so that it would not fail. I did achieve three qualified flights. I noticed the same thing that Chan has. That is, that DQ'd flights are way too common with this event. The best chance for doing well is to make sure that you can even get in 3 qualified flights to begin with and that will put you in the top group of competitors. My best advice is to keep your recovery system simple. Reduce your fasteners and knots to an absolute minimum. Also, if you are really into this event then you'll want to know precisely how much force your various components can take before failing. I did a lot of material testing on basically every critical functional part of the rocket. I absolutely love pistons to push out the recovery hardware. I used foam plugs that were hollowed out and capped with jap tissue. Some of the foreign teams actually used thin aluminum foil that was pressed into a cup pattern. It has to be made very precisely in order to slide smoothly within the airframe. It really requires some machining of a male and female mold in order to punch them out in any quantity.