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PilotSchool Knowledge Base

Practical Application of Weight and Balance Calculations

In aviation, ensuring the proper weight and balance of an aircraft is crucial for safe and efficient flight operations. This section will guide you through extracting weight and balance information from a typical manual for a single-engine aircraft, like the Cessna 172N, and applying this knowledge to assess if the aircraft is safely loaded for flight.

Learning Outcomes

Upon completing this section, you will be able to:

  1. Extract weight and balance information from aircraft documentation.
  2. Calculate the center of gravity (CG) and assess loading configurations.
  3. Determine adjustments needed to maintain CG within specified limits.

Aircraft Weight and Balance Information

Baggage Lockers

  • Capacity and Arm Locations:
    • Area 1: Station 82 to 108 with a maximum capacity of 120 lbs.
    • Area 2: Station 108 to 142 with a maximum capacity of 50 lbs.
  • Maximum Combined Weight: 120 lbs for areas 1 and 2.

Seating Arrangements

  • Seating Configuration:
    • Total seating capacity: 4 (including the pilot).
    • Front seats: Adjustable (four- or six-way).
    • Rear seat: Fixed with options for solid or split-back configuration.
  • Arms for Seating: Provided in the Pilot’s Operating Handbook (POH), consult specific aircraft for detailed arm locations.

Fuel Systems

  • Capacity:
    • Standard tanks: 43 gallons total (40 gallons usable).
    • Long-range tanks: 54 gallons total (50 gallons usable).
  • Fuel Grade and Specific Gravity:
    • Approved grades: 100LL (Blue) and 100/130 (Green).
    • Specific gravity around 6 lbs per gallon.

Maximum Takeoff Weight (MTOW)

  • MTOW: The aircraft’s maximum takeoff weight is 2300 lbs.

Center of Gravity (CG) Calculations

Determining Forward and Aft Limits

  1. Identify the CG Range: Provided in the POH and typically plotted on a CG envelope chart.
  2. Calculate Total Moment and Weight:
    • Sum of all individual moments (weights multiplied by their respective arms).
    • Confirm that the total moment divided by total weight falls within the CG limits.

Assessing Aircraft Loading

To determine if the aircraft is safely loaded:

  • Step 1: Calculate empty weight and its associated moment.
  • Step 2: Add up the weights and moments for passengers, baggage, and fuel.
  • Step 3: Ensure the total weight remains within MTOW.
  • Step 4: Confirm CG is within the specified limits by comparing with POH charts.

Adjusting Load to Maintain CG

When the CG is out of limits:

  • Repositioning Load:
    • Shift weights forward or aft as needed, calculate new moments for changes, and recheck CG limits.
  • Adding Ballast:
    • Use ballast to help shift the CG within allowable limits.

Example Calculations

Suppose the Cessna 172N needs adjusting due to an aft CG:

  1. Initial Calculation: Determine all component weights and calculate the resultant CG.
  2. Identify Error: Consult the POH to see if the CG exceeds aft limits.
  3. Resolution Strategy: Shift a small amount of baggage or use additional fuel as ballast to adjust the moment arm.

Conclusion

Accurate weight and balance calculations are vital for aircraft safety and performance. By systematically calculating each component’s contribution to the total weight and balance, you can ensure that the aircraft is properly prepared for flight. Refer to the Cessna 172N Pilot’s Operating Handbook and the Weight and Balance Handbook (FAA) for detailed instructions and examples.