Constant TUMBLE_FIN_DRAG_COEFFICIENT 

pub const TUMBLE_FIN_DRAG_COEFFICIENT: f64 = 1.42;

The drag coefficient of a tumbling fin set, on its effective fin area (the same source; it sits between a flat plate’s 1.17 and an open hemispherical cup’s 1.42, and the documentation says it is the less reliable of the two).