Modeling Fin Cutouts in OpenRocket

[tjkopena]

What's the best way in OpenRocket to model fins with cutouts? For my purposes, "best" means most accurate stability modeling, which is by far what I care about most, followed by most accurate performance simulation. The visual rendering isn't important.

I can create such a shape out of multiple sets of fins capturing different sections, which is how I've seen it done in files I've found. Doing so permits an accurate visual representation, but is that best practice for stability & performance modeling? I've looked around a bit and haven't found any discussion on that. I'm (naively) assuming the calculations don't really account for wake, etc., in such closely positioned shapes. So I could envision it being reasonable to just model the outer shape as if it were solid, but then that might meaningfully change the CG, and around we go in circles.

So, any accepted practices or conventions other than taking both approaches, evaluating those as ballpark assessments, and then giving it a whirl in flight?

E.g., for a shape like this from Bill S' thread:


Or an Estes Luna Bug:


Thx

 

[neil_w]

There's nothing you can do that will get a "perfect" sim, because OR doesn't understand geometries like that. I think that multiple separate fins are going to get you the closest.

 

[Handeman]

There's nothing you can do that will get a "perfect" sim, because OR doesn't understand geometries like that. I think that multiple separate fins are going to get you the closest.

Is there enough difference in how the fin affects CP when it has cutouts vs. solid to make going through the trouble of modeling it worth while? I've never tried that to find out, so I'm curious. Of course, my use of OR is to get an accurate CP to compare against a measured CG to determine stability. If the CP is accurate with solid vs. cutouts, that's pretty much all I care about.