Rocksim question concerning nosecone body diameter vs user reference number in stability calculations

Bill S

Well-Known Member
Aug 6, 2019
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I am working on a rocket, and while I was confirming that I was using Rocksim stability calculations, not Barrowman, I saw that there was an entry for static margin reference and one for user reference diameter. Under static margin reference you have a choice of nosecone base diameter (which I think is the default, which is what I normall use), maximal frontal diameter, or user reference number below.

The reason I am concerned is that I was not able to find the nosecone I used in the data base, and so had to construct it using a small diameter nosecone, and a transition with shoulder. I am thinking that the software might be using the diameter of the small frontal nosecone, because it doesn't recognize the transition shoulder as the nosecone base.

I've attached an image to illustrate what I am talking about. If the program uses the nosecone base diameter, stability with an E12 motor is 1.34, if I use the maximal frontal diameter its .64, and if I use the diameter of the widest body tube (1.64", BT-60), it says .64 as well.

So have I totally messed up, and need to adjust things to bring stability back to the good range from .64?

question on diameter.png