Variable Geometry in Rocksim?

[PunkRocketScience]

Does anyone know of a good way to deal with a rocket with variable geometry in Rocksim?

I am working on a project where the upper stage of the rocket has pop out fins that will deploy at staging.

I have simmed the rocket with the fins retracted to test stability when stacked, and simmed the upper stage by itself as well. Both are stable, but I am looking for a way to test for altitude of the full stack.

Without the pop out fins, the upper stage goes unstable. Lighting the upper stage on the ground doesn't take into account the velocity and altitude that the rocket has from the booster....

[powderburner]

I sure ain't no rocsim driver, but if all else fails--

You could create parallel analysis runs, one with the rocket modeled as a single stage (weight, size, drag, first stage motor, etc) and see where that gets you in the sky at the second stage ignition point.

Then you could run the rocket as a two-stage, with fins deployed, with whatever booster motor you need to fake to get you to that same staging condition (altitude, velocity).

Kind of a PITA way to have to do it, but if you have no other choices....