AboutDave Combs Expertise Can: Nearly all low-power and some high-power rocketry questions.
Can't: Anything that approaches violations of NAR/TRA safety codes; advanced high-power rocketry questions beyond L1 (I'm still learning those myself).
Experience NAR Level 1 high-power certification; BSA Space Exploration Merit Badge counselor; many years of experience in building and flying rockets from mini-motors (A3-4T) up to H impulse.
Organizations National Association of Rocketry; NAR Section 703 TORC in Dayton, OH.
Question Im just trying to figure out whats better about using 3 fins and whats better for using 4 fins.
Answer The simple answer: There really isn't much difference.
The complex answer: The purpose of the fins on a rocket are to provide what is called the Corrective Moment force. Simply put, if the rocket is "pushed" out of its normal flight path, by a gust of wind for example, it's up to the fins to provide the aerodynamic forces to counter the force of the wind gust and straighten the rocket's flight path. Assume you are using fins all of the same shape and dimensions. If you have 4 fins on the rocket, it may be able to straighten out the flight path a little quicker than a rocket with 3 of the same fins, but you are paying a penalty of the drag of the 4th fin. So it comes down to a matter of trade-offs.
Rockets most often used for high performance have 3 fins. The BSD Thor series, Giant Leap Talon series, and the vast majority of LOC/Precision high-power kits have 3 fins.
