Asa2fly Aircraft Weight and Balance Calculator

Aircraft Weight & Balance Calculation

Calculation Results

Total Moment = (Empty Weight * Empty Moment Arm) + (Pilot Weight * Pilot Arm) + … + (Additional Payload Weight * Additional Payload Arm)
Total Weight = Empty Weight + Pilot Weight + … + Additional Payload Weight
Current CG = Total Moment / Total Weight

Center of Gravity (CG) Range

Visual representation of the aircraft's current CG relative to its allowable limits.

Weight and Moment Summary

Item	Weight (kg)	Arm (m)	Moment (kg-m)
Empty Aircraft	—	—	—
Pilot	—	—	—
Front Passenger	—	—	—
Rear Passenger	—	—	—
Fuel	—	—	—
Additional Payload	—	—	—
TOTAL	—	—	—

What is Aircraft Weight and Balance?

Aircraft weight and balance is a critical aspect of aviation safety and performance. It involves calculating the total weight of an aircraft and determining the location of its center of gravity (CG). The CG is the point where the aircraft would balance if suspended. Maintaining the CG within specified limits, as defined by the aircraft manufacturer, is paramount for stable and controllable flight. An out-of-balance aircraft can be difficult or impossible to fly safely, potentially leading to stalls, spins, or loss of control.

Who should use it: Pilots, flight instructors, aircraft owners, and maintenance personnel all need to understand and utilize weight and balance calculations. Before every flight, pilots are responsible for ensuring their aircraft is loaded correctly and within its operational CG limits. This is especially important when carrying different numbers of passengers, varying amounts of fuel, or cargo.

Common misconceptions: A frequent misconception is that as long as the total weight is below the maximum takeoff weight, the aircraft is safe. However, the distribution of that weight is equally, if not more, important. Another myth is that weight and balance is a complex, one-time calculation; in reality, it's a dynamic process that must be re-evaluated for each flight based on the specific load.

Aircraft Weight and Balance Formula and Mathematical Explanation

The core of weight and balance calculation relies on the principles of moments. A moment is the product of a weight and its distance from a reference point, known as the datum. The datum is an arbitrary zero point established by the aircraft manufacturer, typically located at the aircraft's nose or firewall.

The fundamental formulas are:

• Moment = Weight × Arm
• Total Moment = Sum of all individual moments
• Total Weight = Sum of all individual weights
• Center of Gravity (CG) = Total Moment / Total Weight

The "Arm" is the horizontal distance from the datum to the center of gravity of the specific item (e.g., pilot, fuel, baggage). This distance is usually measured in meters (m) or inches. The weight is measured in kilograms (kg) or pounds (lbs). The resulting moment is expressed in kg-m or lb-in.

The aircraft's operating manual (Aircraft Flight Manual – AFM or Pilot's Operating Handbook – POH) specifies the allowable CG range, which is critical for safe flight. This range is typically expressed in meters or inches from the datum.

Variables Table

Weight and Balance Variables

Variable	Meaning	Unit	Typical Range
Weight	Mass of an item or the entire aircraft	kg (or lbs)	10 – 2000+
Arm	Horizontal distance from the datum	m (or in)	-5 to 5+ (depends on datum)
Moment	Weight multiplied by its arm	kg-m (or lb-in)	Varies widely
Datum	Reference point for measurements	N/A	Fixed by manufacturer
CG	Center of Gravity location	m (or in)	Specific range defined by AFM/POH
Allowable CG Range	The operational limits for the CG	m (or in)	e.g., 2.0m to 3.0m

Practical Examples (Real-World Use Cases)

Let's illustrate with two scenarios for a typical light aircraft. Assume the datum is at the firewall (0m), the empty weight is 500 kg with an empty moment of 10000 kg-m. The allowable CG range is 2.0m to 3.0m.

Example 1: Solo Flight with Full Fuel

A pilot weighing 75 kg is flying solo. They plan to carry 100 kg of fuel.

• Pilot: Weight = 75 kg, Arm = 2.5 m. Moment = 75 * 2.5 = 187.5 kg-m.
• Fuel: Weight = 100 kg, Arm = 3.0 m. Moment = 100 * 3.0 = 300 kg-m.
• Total Weight = 500 (empty) + 75 (pilot) + 100 (fuel) = 675 kg.
• Total Moment = 10000 (empty) + 187.5 (pilot) + 300 (fuel) = 10487.5 kg-m.
• Current CG = 10487.5 kg-m / 675 kg = 15.54 m.

Interpretation: In this scenario, the calculated CG of 15.54m is far outside the allowable range of 2.0m to 3.0m. This indicates a significant loading issue, likely due to the pilot's arm being too far forward or the fuel arm being too far aft relative to the empty weight's moment. The pilot would need to adjust the fuel load, passenger arrangement, or baggage to bring the CG within limits. This highlights the importance of precise arm measurements.

Example 2: Two Passengers and Light Baggage

The same aircraft (500 kg empty, 10000 kg-m empty moment, CG range 2.0m-3.0m) is carrying two passengers and 15 kg of baggage.

• Pilot: Weight = 80 kg, Arm = 2.5 m. Moment = 80 * 2.5 = 200 kg-m.
• Front Passenger: Weight = 70 kg, Arm = 2.8 m. Moment = 70 * 2.8 = 196 kg-m.
• Rear Passenger: Weight = 60 kg, Arm = 3.5 m. Moment = 60 * 3.5 = 210 kg-m.
• Baggage: Weight = 15 kg, Arm = 4.0 m. Moment = 15 * 4.0 = 60 kg-m.
• Fuel: Assume 50 kg of fuel onboard. Arm = 3.0 m. Moment = 50 * 3.0 = 150 kg-m.
• Total Weight = 500 + 80 + 70 + 60 + 15 + 50 = 775 kg.
• Total Moment = 10000 + 200 + 196 + 210 + 60 + 150 = 10816 kg-m.
• Current CG = 10816 kg-m / 775 kg = 13.95 m.

Interpretation: Again, the calculated CG of 13.95m is significantly aft of the allowable limit. This suggests that with this passenger and baggage configuration, the aircraft is likely to be tail-heavy. The pilot might need to reposition the baggage further forward, reduce passenger weight, or carry less fuel if possible, or consider a different aircraft if the mission requires heavier loads or different configurations. This demonstrates how passenger and cargo placement dramatically affects the CG.

How to Use This ASA2FLY Aircraft Weight and Balance Calculator

Using the ASA2FLY Aircraft Weight and Balance Calculator is straightforward. Follow these steps to ensure your flight is safe and within operational limits:

1. Gather Aircraft Data: Locate your aircraft's Pilot's Operating Handbook (POH) or Aircraft Flight Manual (AFM). You'll need the aircraft's empty weight and empty moment, as well as the minimum and maximum allowable CG values. These are usually found in the Limitations or Performance sections.
2. Input Basic Aircraft Information: Enter the Empty Weight (kg) and Empty Moment (kg-m) into the corresponding fields. Also, input the Minimum Allowable CG (m) and Maximum Allowable CG (m).
3. Enter Occupant and Fuel Details: Input the weight (kg) and arm (m) for the pilot, front passenger, rear passenger(s), and any fuel onboard. The arm is the distance from the aircraft's datum (usually marked in the POH).
4. Add Payload: Enter the weight (kg) and arm (m) for any additional payload, such as baggage or equipment.
5. Calculate: Click the "Calculate" button. The calculator will instantly compute the total weight, total moment, and the resulting current center of gravity (CG).
6. Interpret Results:
   • Primary Result (Current CG): This is the calculated center of gravity for your current load configuration.
   • Total Weight (kg): The sum of all weights entered. Ensure this is below the Maximum Takeoff Weight (MTOW) specified in your POH.
   • Total Moment (kg-m): The sum of all moments.
   • CG Status: This will indicate whether your current CG is "Within Limits," "Forward of Limits," or "Aft of Limits" based on the minimum and maximum CG values you entered.
   • Table: The table provides a detailed breakdown of each item's contribution to the total weight and moment.
   • Chart: The chart visually displays your current CG relative to the allowable range.
7. Decision Making:
   • If the CG Status is "Within Limits," your aircraft is balanced correctly for flight.
   • If the CG Status is "Forward of Limits," you need to shift weight aft (e.g., move baggage to the rear, have lighter passengers in front) or reduce forward weight.
   • If the CG Status is "Aft of Limits," you need to shift weight forward (e.g., move baggage forward, have heavier passengers in front) or reduce aft weight.
8. Reset: Use the "Reset" button to clear all fields and start a new calculation.
9. Copy Results: Use the "Copy Results" button to copy the key calculated values for documentation or sharing.

Always double-check your inputs against your POH and ensure all calculations are performed correctly before flight. This calculator is a tool to aid in that process.

Key Factors That Affect Aircraft Weight and Balance Results

Several factors significantly influence the weight and balance calculations and the resulting CG position. Understanding these is crucial for safe flight operations.

• Empty Weight and Moment Changes: Over time, aircraft empty weight and moment can change due to modifications, repairs, or equipment additions/removals. It's essential to keep the aircraft's weight and balance records up-to-date and perform a re-weigh periodically as recommended by regulations or the manufacturer. An inaccurate empty weight is the foundation for all subsequent calculations.
• Fuel Load: Fuel is often the most variable weight component. As fuel is consumed during flight, the aircraft's total weight decreases, and the CG shifts forward (assuming fuel tanks are located forward of the main wing's CG). Pilots must calculate weight and balance for both the takeoff configuration (full fuel) and the landing configuration (minimum planned fuel) to ensure the CG remains within limits throughout the flight.
• Passenger and Cargo Distribution: The location (arm) of passengers and cargo is critical. Placing heavier items or passengers further aft will move the CG aft, while placing them further forward moves the CG forward. Even small changes in arm can have a significant impact on the CG, especially in aircraft with tight CG envelopes.
• Aircraft Configuration: Different flight phases or mission types might require different configurations. For example, a ferry flight with only the pilot and maximum fuel will have a very different CG than a sightseeing flight with four passengers and minimal fuel. Each configuration requires a separate, accurate calculation.
• Datum Location: The choice of datum by the manufacturer affects the numerical values of the arms and moments. While the datum itself doesn't change the physical CG location, it dictates how the arms are measured, influencing the intermediate calculations. Always use the datum specified in the POH.
• Maximum Takeoff Weight (MTOW): While this calculator focuses on CG, the total weight must also be considered. Exceeding the MTOW reduces aircraft performance, increases takeoff and landing distances, and can lead to structural failure. The CG must be within limits *and* the total weight must be below MTOW.
• Arm Measurement Accuracy: Precise measurement of the arm for each item is vital. Even a small error in measuring the distance from the datum can lead to a significant error in the calculated CG, potentially placing the aircraft outside its safe operating envelope.

Frequently Asked Questions (FAQ)

Q: What is the datum in weight and balance calculations?

A: The datum is an imaginary vertical line or plane established by the aircraft manufacturer from which all horizontal distances (arms) are measured. It's the zero reference point for calculating moments.

Q: How often should I re-calculate weight and balance?

A: You must calculate weight and balance before every flight, especially if the load (passengers, fuel, cargo) differs from the previous flight. Significant changes to the aircraft (e.g., modifications) also require recalculation.

Q: What happens if my aircraft's CG is outside the allowable limits?

A: Flying an aircraft with its CG outside the specified limits is extremely dangerous. It can lead to reduced controllability, increased stall speed, and potential loss of control, especially during critical phases of flight like takeoff and landing.

Q: Can I use this calculator for any aircraft?

A: This calculator is a general tool. You MUST use the specific empty weight, empty moment, arm measurements, and allowable CG range provided in the Pilot's Operating Handbook (POH) or Aircraft Flight Manual (AFM) for YOUR specific aircraft model. Using incorrect data will yield inaccurate and potentially unsafe results.

Q: What is the difference between weight and balance and maximum takeoff weight (MTOW)?

A: MTOW is the maximum permissible weight of the aircraft at takeoff. Weight and balance refers to the distribution of that weight, specifically the location of the center of gravity (CG). Both must be within limits for safe flight.

Q: My POH lists CG in inches, but this calculator uses meters. How do I convert?

A: You need to convert consistently. 1 inch = 0.0254 meters. If your POH uses inches, convert all arm and CG measurements to meters before entering them into the calculator, or vice versa. Ensure all units are consistent.

Q: What if I have multiple baggage compartments or fuel tanks?

A: You should calculate the combined moment for all items in a similar location. For example, if you have two fuel tanks with different arms, calculate the moment for each tank and sum them to get the total fuel moment. Treat each distinct payload location as a separate entry if their arms differ significantly.

Q: Does the weight of the pilot and passengers include clothing and equipment?

A: Yes, the weight entered should be the total weight of the person, including clothing, personal items they are carrying, and any equipment they might have (e.g., flight bag). It's better to slightly overestimate than underestimate.