Apogee Newletter #158, which is available on newstands today, presents Part 2 to Bruce Levison's Simulating Short, Wide Rockets in RockSim 8. I reported earlier on Part 1, which showed how to improve the simulations of short, stubby rockets like the Estes Fat Boy by adding a mass-less cone at its base. However, it turns out that this technique was only applicable to designs with flat bases, i.e. it wouldn't work properly on a design with a tail cone. Such rockets still exhibit a base vortex effect, but the tail cone partially interrupts it. Well, Bruce doesn't like partial answers, so he tweaked his method for rockets with rear transitions. The tweak is trivial - you just add a properly dimensioned, truncated cone. In part 2, he shows how he simulated a Fat Boy-like rocket with a tail cone, and also a 'Sputnik' style rocket.
As a bonus, he indicates how to simulate a tumble design in RockSim. First off, RockSim must have a recovery device installed in order to complete the second half (recovery) part of the sim. All you do is add a 'chute with a cross-sectional area the same as your model, with a single, minimally thin shroud line, and a Cd which is set to that of the rocket itself. (But you know the real trick is finding the correct Cd in the first place! :eek:)