Ballast and its Use in Mass and Balance

What is Ballast and Why is it Used?

Ballast is any extra weight—such as lead bars or sandbags—added to an aircraft to adjust the centre of gravity (CG) without affecting the useful load. It is commonly used when the aircraft's loading, after accounting for crew, passengers, cargo, and fuel, results in a CG outside the permitted envelope. Ballast ensures the CG is brought back within limits for safe flight.

How to Use Ballast

• Identify the CG Problem: Check if the calculated CG is forward or aft of the allowed range after loading.
• Determine Ballast Location: Ballast should be placed as far from the CG as practical, typically in the nose (for aft CG correction) or tail (for forward CG correction), to maximize its effect with minimal mass.
• Calculate Ballast Mass: Use the moment equation: Mass × Arm = Moment. To move the CG to a desired position, calculate the required mass and its position using:
  • Required moment change = Desired CG shift × Total aircraft mass
  • Ballast mass = Required moment change ÷ Ballast arm (distance from datum)
• Update Documentation: Ballast becomes part of the Basic Empty Mass if fixed, or is included in the load sheet if temporary.

Ballast Calculation Example

Suppose the CG is too far aft. Placing ballast in the nose will move the CG forward. Calculate how much mass is needed and at what position to achieve the desired CG, making sure the new CG falls within the envelope.

Effects on Aircraft Performance

Improper CG (too far forward or aft) can degrade stability, control, and performance. Ballast corrects these issues, but always check that total mass and structural limits are not exceeded.

Operational Considerations

• Fixed ballast is included in Basic Empty Mass.
• Removable ballast must be secured and documented.
• Always verify the new CG and mass against the aircraft's limitations before flight.