Cp issues in open rocket and rocksim

[flynfrog]

I am having trouble getting my cp to model correctly in both open rocket and rocksim. I am modeling a 4inch V2 with .25 think fins. I keep getting my cp to almost midrocket when it should be about the top of the fins. Any idea what I am missing here.

 

[mwtoelle]

The mathematics of the Barrowman equations do not work work very well with the V-2. The problems occurs when you have the fins on the tail cone that have a short span. As long as it balances about 1/2 of the body diameter ahead of the tail cone, it should be stable. Please note that this assumes that you are using scale fins instead of the enlarged fins supplied with most V-2 kits (i.e. Estes K-22 (BT-55) and Estes 1926/1904 (BT-80)).

 

[flynfrog]

That sounds exactly like my problem. I went with the balance exactly where you and say and the rocket flew fine. Thanks!