Comanche 250 Weight and Balance Calculator

Piper PA-25 Pawnee 250 Weight & Balance Calculation

Safely operate your Comanche 250 by ensuring your aircraft is within its approved weight and balance limits. Use this calculator to determine your current center of gravity (CG).

Weight & Balance Summary Table

Item	Weight (lbs)	Arm (inches)	Moment (in-lbs)
Empty Weight	—	—	—
Pilot	—	—	—
Passenger	—	—	—
Baggage	—	—	—
Usable Fuel	—	—	—
Total	—		—

What is Comanche 250 Weight and Balance?

The Comanche 250 weight and balance calculation is a critical process for pilots of the Piper PA-25 Pawnee agricultural aircraft. It involves determining the aircraft's total weight and the location of its center of gravity (CG) for a given flight configuration. This ensures that the aircraft remains within its certified operating limits, which are essential for safe flight, stability, and controllability. Flying an aircraft outside its weight and balance limitations can lead to a loss of control, reduced performance, and potentially a stall or spin. Understanding and correctly calculating this ensures the aircraft performs as designed and can be safely maneuvered by the pilot.

Who should use it: Pilots, aircraft owners, and maintenance personnel responsible for the operation of a Piper PA-25 Pawnee (often referred to colloquially or in specific contexts as a "Comanche 250" due to its engine, though technically distinct from the Piper Comanche line) should use this calculation before every flight, especially when the aircraft's loading configuration changes significantly. This includes pilots carrying different amounts of fuel, passengers, or cargo.

Common Misconceptions: A common misconception is that weight and balance is only important for large airliners or during ferry flights. In reality, it is a fundamental aspect of flight safety for all aircraft, including specialized types like the Pawnee. Another misconception is that simply staying under the maximum takeoff weight is sufficient; the location of that weight (the CG) is equally, if not more, critical for stability.

Comanche 250 Weight and Balance Formula and Mathematical Explanation

The calculation of weight and balance for any aircraft, including the Comanche 250, relies on fundamental principles of physics and aviation regulations. The core idea is to ensure the aircraft's center of gravity (CG) remains within a specific range defined by the manufacturer.

The process involves calculating the total weight of the aircraft and the total moment generated by that weight. The moment is the product of weight and its horizontal distance (arm) from a reference datum. The datum is an arbitrary vertical plane forward of the aircraft, used as a reference point for all measurements.

Key Steps and Formulas:

1. Calculate Individual Moments: For each item (empty aircraft, pilot, passengers, baggage, fuel), multiply its weight by its respective arm (distance from the datum).
   Moment = Weight × Arm
2. Sum All Weights: Add up the weight of the empty aircraft, pilot, passengers, baggage, and usable fuel to find the total weight.
   Total Weight = Empty Weight + Pilot Weight + Passenger Weight + Baggage Weight + Usable Fuel Weight
3. Sum All Moments: Add the moment of the empty aircraft (which is pre-calculated and provided by the manufacturer) to the moments calculated for the pilot, passengers, baggage, and fuel.
   Total Moment = Empty Moment + Pilot Moment + Passenger Moment + Baggage Moment + Fuel Moment
4. Calculate Center of Gravity (CG): Divide the total moment by the total weight.
   CG = Total Moment / Total Weight

The result of this calculation is the aircraft's center of gravity, typically expressed in inches aft of the datum. This value must then be compared against the aircraft's specified CG limits (forward and aft) found in its Aircraft Flight Manual (AFM) or Pilot's Operating Handbook (POH).

Variables Table:

Variable	Meaning	Unit	Typical Range (Comanche 250 / PA-25)
Empty Weight	Weight of aircraft excluding crew, passengers, fuel, and baggage.	lbs	~1300 – 1450 lbs
Empty Moment	Moment of the empty aircraft.	in-lbs	~47000 – 52000 in-lbs
Pilot Weight	Weight of the pilot.	lbs	150 – 220 lbs
Pilot Arm	Horizontal distance from datum to pilot's CG.	inches	80 – 100 inches (varies by seat position)
Passenger Weight	Weight of the passenger(s).	lbs	150 – 220 lbs
Passenger Arm	Horizontal distance from datum to passenger's CG.	inches	90 – 110 inches (varies by seat position)
Baggage Weight	Weight of baggage in the baggage compartment.	lbs	0 – 100 lbs (check POH for limits)
Baggage Arm	Horizontal distance from datum to baggage's CG.	inches	120 – 140 inches
Usable Fuel Weight	Weight of usable fuel onboard. (Fuel density ~6 lbs/gallon)	lbs	0 – 150 lbs (approx. 0-25 gallons)
Fuel Arm	Horizontal distance from datum to the fuel tank's CG.		inches	94 – 114 inches (varies by tank)
Total Weight	Sum of all weights.	lbs	Max Gross Weight: 2500 lbs
Total Moment	Sum of all moments.	in-lbs	Varies based on loading
Center of Gravity (CG)	Calculated CG position of the aircraft.	inches aft of datum	Typical range: ~86 to ~96 inches aft of datum (check POH for exact limits)

Practical Examples (Real-World Use Cases)

Accurate weight and balance is crucial for safe agricultural operations. Here are two examples for a Comanche 250 (PA-25).

Example 1: Standard Operations with One Pilot and Full Fuel

Scenario: A typical day for crop dusting. The aircraft has its standard empty weight and moment. The pilot is boarding, along with 15 gallons of usable fuel.

• Empty Weight: 1380 lbs
• Empty Moment: 49680 in-lbs
• Pilot Weight: 180 lbs
• Pilot Arm: 88 inches
• Passenger Weight: 0 lbs
• Passenger Arm: N/A
• Baggage Weight: 0 lbs
• Baggage Arm: N/A
• Usable Fuel: 15 gallons (approx. 90 lbs)
• Fuel Arm: 100 inches

Calculation:

• Pilot Moment: 180 lbs * 88 in = 15840 in-lbs
• Fuel Moment: 90 lbs * 100 in = 9000 in-lbs
• Total Weight: 1380 + 180 + 0 + 0 + 90 = 1650 lbs
• Total Moment: 49680 + 15840 + 0 + 0 + 9000 = 74520 in-lbs
• CG: 74520 in-lbs / 1650 lbs = 45.16 inches aft of datum

Interpretation: With a calculated CG of 45.16 inches aft of datum, the aircraft is well within the typical forward CG limits for the PA-25. This configuration is safe for flight.

Example 2: Ferry Flight with Maximum Payload and Reduced Fuel

Scenario: The aircraft needs to be repositioned. It's loaded with the maximum allowable baggage, a pilot, and only the minimum required fuel for the ferry flight.

• Empty Weight: 1380 lbs
• Empty Moment: 49680 in-lbs
• Pilot Weight: 200 lbs
• Pilot Arm: 90 inches
• Passenger Weight: 0 lbs
• Passenger Arm: N/A
• Baggage Weight: 100 lbs (Max allowed)
• Baggage Arm: 130 inches
• Usable Fuel: 10 gallons (approx. 60 lbs)
• Fuel Arm: 104 inches

Calculation:

• Pilot Moment: 200 lbs * 90 in = 18000 in-lbs
• Baggage Moment: 100 lbs * 130 in = 13000 in-lbs
• Fuel Moment: 60 lbs * 104 in = 6240 in-lbs
• Total Weight: 1380 + 200 + 0 + 100 + 60 = 1740 lbs
• Total Moment: 49680 + 18000 + 0 + 13000 + 6240 = 86920 in-lbs
• CG: 86920 in-lbs / 1740 lbs = 49.95 inches aft of datum

Interpretation: The calculated CG of 49.95 inches aft of datum is still within the acceptable forward limits for ferry operations. This indicates that even with a concentrated load towards the rear (baggage), the aircraft remains stable. However, it's crucial to always refer to the aircraft's specific POH for exact CG limits.

How to Use This Comanche 250 Weight and Balance Calculator

Using this calculator is straightforward and ensures you maintain safe flight parameters for your Piper PA-25 Pawnee.

1. Gather Aircraft Data: Locate your aircraft's POH (Pilot's Operating Handbook) or Weight and Balance manual. You'll need the exact 'Empty Weight' and 'Empty Weight Moment' for your specific aircraft. These are usually found on the aircraft's weight and balance sheet.
2. Determine Occupant and Cargo Weights: Accurately estimate or weigh the pilot, any passengers, and baggage.
3. Identify Arms: From your POH or the aircraft's weight and balance data, find the correct 'Arm' (distance from the datum) for the pilot's seat, passenger seat(s), baggage compartment, and fuel tanks. The calculator provides common arm values; select the ones that match your aircraft's configuration and POH.
4. Input Values: Enter the gathered weights and selected arms into the corresponding fields on the calculator. For 'Usable Fuel', enter the number of gallons you plan to carry and the calculator will convert it to pounds (assuming 6 lbs/gallon).
5. Calculate: Click the "Calculate" button. The calculator will instantly display your 'Total Weight', 'Total Moment', 'Center of Gravity (CG)', and indicate if it's within the standard CG range.
6. Interpret Results:
   • Total Weight: Ensure this is below the maximum gross weight for the PA-25 (typically 2500 lbs).
   • Center of Gravity (CG): Compare the calculated CG (in inches aft of datum) to the forward and aft CG limits specified in your POH. The calculator shows a common range, but your POH is the ultimate authority.
7. Review Table and Chart: The table provides a breakdown of each component's contribution to the total weight and moment. The chart visualizes your CG position relative to the aircraft's operating envelope.
8. Reset and Re-calculate: If you need to change values or calculate for a different loading scenario, click "Reset" to clear the fields and start again, or simply change the numbers and recalculate.
9. Copy Results: Use the "Copy Results" button to save or share your calculation details.

Key Factors That Affect Comanche 250 Results

Several factors significantly influence the weight and balance calculations for a Comanche 250 (PA-25), impacting its safety and performance. Understanding these is vital for responsible operation.

1. Empty Weight and Moment Variation: Every aircraft is unique. Modifications, repairs, or installed equipment can alter the empty weight and its moment from the manufacturer's original specifications. Regularly updating the aircraft's weight and balance records is crucial. Small changes in these baseline figures compound over time and affect all subsequent calculations.
2. Crew and Passenger Weights: The weight of individuals on board is a direct input. Higher weights mean higher total weight and potentially shift the CG. Standard weight assumptions (e.g., 170 lbs) may not be accurate for all pilots and passengers, necessitating actual weighing for critical operations.
3. Fuel Load: Usable fuel is a significant variable weight. The PA-25 carries a substantial amount of fuel, and the amount onboard directly affects both total weight and the CG position. Fuel burn during flight also changes the CG dynamically, though pre-flight calculations are based on the initial load. The location of fuel tanks (arm) also matters.
4. Baggage and Cargo Loading: While the PA-25 is primarily designed for agricultural spraying, it can carry baggage or specialized equipment. The weight and, critically, the placement (arm) of this cargo directly impact the CG. Loading heavy items far aft can push the CG beyond its limits. Always adhere to the specific baggage compartment weight and location limits outlined in the POH.
5. Datum Point Selection and Arm Measurements: The accuracy of the entire calculation hinges on the correct 'arm' values. These arms are distances from the datum specified in the aircraft's POH. Incorrect arm values, whether due to misreading the manual or inaccurate measurement of cargo placement, will lead to erroneous CG calculations, potentially compromising safety.
6. Maximum Gross Weight Limit: The PA-25 has a maximum certified gross weight (typically 2500 lbs). Exceeding this limit reduces aircraft performance, increases stall speed, lengthens takeoff distance, and can lead to structural failure. The total calculated weight must always be at or below this limit.
7. CG Limits (Forward and Aft): Even if the total weight is within limits, the CG must also fall within the specified range (e.g., 86 to 96 inches aft of datum, though specific limits must be confirmed in the POH). An aft CG can make the aircraft unstable and difficult to control, while a forward CG can result in excessive control forces and reduced maneuverability. The purpose of weight and balance calculations is to ensure the aircraft remains within these crucial CG boundaries throughout its flight envelope.

Frequently Asked Questions (FAQ)

Q1: What is the maximum takeoff weight for a Piper PA-25 Pawnee?

A1: The maximum takeoff weight for the Piper PA-25 Pawnee is typically 2500 lbs. Always verify this with your aircraft's specific POH.

Q2: What is the typical CG range for the Comanche 250 (PA-25)?

A2: The normal CG range for the PA-25 is approximately 86.0 inches to 96.0 inches aft of the datum. However, exact limits are published in the aircraft's Pilot's Operating Handbook (POH) and must be followed.

Q3: What does "moment" mean in weight and balance?

A3: Moment is a measure of the turning effect of a weight at a distance from a reference point (the datum). It's calculated as Weight × Arm. Summing moments helps determine the overall balance point of the aircraft.

Q4: How do I find the "Arm" for different items?

A4: The "Arm" is the horizontal distance from the aircraft's datum line to the center of gravity of an item (like a person, baggage, or fuel tank). These values are specified in the aircraft's POH or Weight and Balance manual.

Q5: What happens if I fly outside the CG limits?

A5: Flying outside the CG limits can lead to serious safety issues. An aft CG can make the aircraft unstable and difficult to control, potentially leading to a stall or loss of control. A forward CG can increase control forces and reduce maneuverability.

Q6: Does fuel burn affect the CG during flight?

A6: Yes. As fuel is consumed, the total weight decreases, and the CG typically shifts forward, as fuel is often located forward of the aircraft's empty CG. Weight and balance calculations are performed for the *start* of the flight, but pilots should be aware of how fuel burn affects CG, especially on long flights.

Q7: What if my calculated CG is slightly outside the POH limits?

A7: If your calculated CG is outside the published limits, the aircraft should not be flown in that configuration. You must adjust the loading (e.g., redistribute weight, remove items, carry less fuel) until the CG falls within the acceptable range.

Q8: How often should I update my aircraft's weight and balance records?

A8: You should update the weight and balance records whenever a change occurs that could affect the aircraft's empty weight or empty moment. This includes major repairs, modifications, or the installation/removal of equipment.

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