Today's installment of Apogee's Newsletter contains instructions/guidance on how to build two interesting, out of the ordinary simulations in RockSim: water and ducted rockets.
The airframe of a water rocket is straightforward, but simulating the 'motor' is not. Tim found that Clifford Heath provides an on-line calculator that simulates a water rocket's flight and even provides a thrust-curve (sample shown to the right). From there you use the TCtracer (hat tip to John Coker and ThrustCurve.org) to capture the data and import it into RockSim. Tadah - you have a water rocket simulation in RockSim! Tim provides a link to his simulation as a starting point. You can even refine the thrust curve to account for the shift in CG due to the spewing of the H2O.
Next, he describes how to design a ducted rocket, as shown below.
This technique was developed by BrianC in response to this TRF thread. Tim describes the technique and, of course, provides a sample file. Since RockSim wasn't designed to handle such sims, the results may be questionable. Tim thinks the CP looks about right, but I doubt if RockSim will simulate the effects of the internal airflow. I could be wrong. yes or no, this is pretty cool and I've already used it.