What does static stability mean
Static stability is the relationship of the CG and CP when the rocket is sitting still... ready for launch, with the parachute and motor(s) loaded and ready to go. It is generally considered to be considered 'safe' if the CG is AHEAD of the CP by at least one body diameter (one caliber stability). Usually stability of up to three calibers is better (safer) but going much over that and you start running into 'overstable' problems (which usually just rob altitude but can have bad effects like 'corkscrewing' and 'wobbling' in flight).
Now, the problem is, neither CG NOR CP are CONSTANTS!!! As the propellant burns, the rear of the rocket is getting lighter, so that moves the CG forward. With liquid propellant rockets, the opposite is true-- as the propellant burns, the TOP of the propellant tanks gets lighter, so the CG moves backwards, but this doesn't really apply to us modellers so we'll just keep that in the trivia dept.
Now, the CG moving forward helps to increase stability during flight, but the CG generally doesn't move a WHOLE lot... If you want to see the effect, balance the rocket in a loop of string at the CG with a loaded motor, remove the motor and install a spent casing, and rebalance-- that's how much the CG moves and where the CG is at the instant of ejection.
CP, on the other hand, is a VERY dynamic 'point' and moves around considerably more. Generally speaking, CP moves forward as the angle of attack increases. In other words, once the rocket starts to 'tip over' in flight, the CP moves forward more and more, which can put it ahead of the CG pretty quickly. The CP moving forward means that there is less and less corrective force to straighten the flight path back to 'normal' and if the CP passes the CG, the rocket INSTANTLY goes unstable because the corrective forces are now pulling the rocket OFF COURSE. Any wind at liftoff artificially creates an 'angle of attack' since the body of air surrounding the rocket is moving perpendicular to the rocket as it sits on the pad, and when the rocket is travelling at precisely the wind's speed, the 'effective angle of attack' is 45 degrees. As the rocket accelerates, this 'effective angle of attack' becomes less and less, since the rocket is moving upward MUCH faster than the wind is blowing sideways. This is why rockets weathercock and some marginally stable designs can go unstable in higher wind conditions, and overstable rockets can weathercock excessively, and why a higher power motor that really "kicks" a rocket off the pad at high speed reduces weathercock.
Now, since CP moves around, how do we know if the CP we calculated (or got from Rocksim) is correct?? When in flight is it correct?? That depends on the method used to calculate it, and the assumptions inherent in the method used. The Barrowman and "Rocksim" methods calculate the 'static' CP for a rocket sitting on the pad and moving in a more or less 'straight up' (low angle of attack) direction. SO, when you actually FLY the rocket, if it gets rod whip, or a sudden gust of wind at liftoff when the speed is slow causes high induced angle of attack, bad things CAN happen. The "cardboard cutout" method, on the other hand, 'calculates' CP as "the center of lateral area" (balance point of the area that would be exposed to the airflow if the rocket WERE FLYING NINETY DEGREES TO THE AIRFLOW (sideways). This is the MOST conservative method, since it will show the CP as far forward as it's basically possible for it to go! So it would be the best method to use for a finless rocket. It does tend to be 'overly conservative' for finned rockets though, because fins 'flat' structure create lift differently than the round body tube does at high angles of attack, but then you REALLY get into some deep math, as Barrowman (and Rocksim AFAIK) ignore the effects of body tube lift from the cylindrical tube moving through the airflow at an angle of attack, and the effects of fins 'stalling' at high angles of attack (which moves the CP forward).
All this helps explain why rockets sometimes do some of the crazy things they do in flight, like sometimes 'mysteriously' going unstable, yet then becoming 'stable' again, sometimes pointed in directions we'd rather they didn't.
Hope this helps! OL JR