How to Calculate Stability of a Model Rocket

Model rockets have several important factors that determine how they fly. A stable model rocket can resist force to reach maximum altitude in flight. Model rockets have the capability of causing serious injuries, especially during an unstable flight. There are several methods that can be used to calculate model rocket stability.

Difficulty: Moderately Easy

Instructions

Things You'll Need:

• String
• Piece of cardboard
• Pencil
• Scissors

1. Locate the Center of Gravity (CG) on a model rocket. The CG is the point around which your rocket rotates. Tie a string around the middle of your rocket.

2. Move the string back and forth until the rocket is able to balance horizontally. Take note at what point it balances.

3. Find Center of Pressure (CP) which represents the point on the model where drag or air pressure is acting. Use a piece of thin cardboard and pencil to trace the profile of your rocket.

4. Cut out a flat profile with scissors and balance model on edge of ruler. Mark the point where it balances--that's the CP.

5. Complete a swing test by tying a string around the CG. Swing the rocket around in circles while holding end of string in your hand. A stable rocket usually points in the direction in which you swing it.

6. Implement information into software program. Stability can be tested with use of specially designed software programs, some are available for free online (see Resources).

Tips & Warnings

• CP can be adjusted by making fins smaller or larger. To change CG add weight or make body tube of rocket longer.
• CP can also be calculated using the "Barrowman Method," a detailed mathematical formula (see Resources.
• Understand different states of stability. Many factors can influence this when in flight including the size of the engine, fins and the weight of the materials used to create the model rocket.
• A model rocket should only be flown when it shows stability, meaning the CG should be ahead of the CP. Rockets that demonstrate dynamic instability are unsafe to fly and changes should be made to the design.

Resources

• Use the Barrowman Equation to find CP of your model rocket.
• Popular rocket stimulation software RockSim has a free demo.
• Use SpaceCad to design model rockets and predict stability.