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Use the comp sim and set the material of the fins to carbon fiber and figure out how much it thinks those fins weighed
This value is 1.5 lbs which seems high but going with it.
Subtract that number from the section mass and make a copy of cycle 2.2 1a-c using this new number and see that it makes sense
Make a new file with four fins and dial in stability first
Then do flutter calcs and thickness back into openrocket and check stability again and iterate.