For static stability, where must the center of pressure be relative to the center of gravity?

For static stability, where must the center of pressure be relative to the center of gravity?

• A. Center of pressure behind the center of gravity
• B. Center of pressure in front of the center of gravity
• C. The rocket must have fins
• D. The length of the body tube must be at least 5 times the model diameter

Answer: (A)

Static stability comes from having the aerodynamic force act behind the weight’s location so a disturbance creates a restoring torque. The weight acts through the center of gravity, and the aerodynamic force acts through the center of pressure. If the center of pressure is behind the center of gravity, a small tilt produces a moment that tends to realign the rocket back to upright. If the center of pressure were in front of the center of gravity, the same tilt would push the rocket further away from its original orientation, making it unstable. So, for static stability, the center of pressure must be behind the center of gravity.

Static stability comes from having the aerodynamic force act behind the weight’s location so a disturbance creates a restoring torque. The weight acts through the center of gravity, and the aerodynamic force acts through the center of pressure. If the center of pressure is behind the center of gravity, a small tilt produces a moment that tends to realign the rocket back to upright. If the center of pressure were in front of the center of gravity, the same tilt would push the rocket further away from its original orientation, making it unstable. So, for static stability, the center of pressure must be behind the center of gravity.