Weight and Balance

Private Pilot License (PPL) Notes

This section covers the importance of understanding weight and balance in aircraft operation, including how it affects performance and safety, and the methods for calculating and ensuring proper weight and balance before flight.

Importance of Weight and Balance

1. Weight and balance significantly affect aircraft performance and handling.
   1. Exceeding maximum weight limits compromises structural integrity.
   2. Improper balance can lead to unsafe flight conditions.
2. In many four-place or larger aircraft:
   1. You can either fill the fuel tanks or fill the seats, but not both at the same time.

Basic Empty Weight

1. Includes:
   1. Airframe and engine.
   2. All permanently installed equipment or accessories.
   3. Unusable fuel.
   4. Full engine oil (unless specified otherwise in the POH).
2. Note:
   1. Some aircraft do not include full oil in the empty weight; always check the Pilot’s Operating Handbook (POH).

Calculating Weight

1. Add the following to the basic empty weight:
   1. Weight of people (pilot, passengers).
   2. Usable fuel (gasoline weighs 6 pounds per gallon).
   3. Baggage.
2. Example with a Cessna 172:
   1. Basic empty weight: 1,600 pounds.
   2. Pilot and passenger: 282 pounds.
   3. Fuel: 53 gallons x 6 pounds/gallon = 318 pounds.
   4. Total weight: 1,600 + 282 + 318 = 2,200 pounds.
   5. Maximum takeoff weight: 2,450 pounds (so we're under the limit).

Center of Gravity (CG)

1. The CG is the point where the airplane balances.
   1. If CG is too far forward:
      1. Elevator control may be insufficient to rotate nose up during takeoff.
      2. May result in nose-wheel-first landings.
   2. If CG is too far aft:
      1. The airplane becomes less stable in pitch.
      2. Risk of stalls and spins due to pitch instability.
2. Maintaining CG within limits is critical for safe flight.

Key Terms

1. Datum:
   1. A reference point on the aircraft for balance calculations.
      1. Example: On a Cessna 172, the datum is the front face of the firewall.
2. Arm:
   1. The horizontal distance from the datum to the weight.
      2. Example: Pilot's seat is 37 inches behind the datum.
3. Moment:
   1. The product of weight and arm.
      1. Moment = Weight x Arm.
   2. Expressed in inch-pounds.
   3. Moment Index:
      1. Moment divided by a reduction factor (e.g., 100 or 1,000) to simplify numbers.

Calculating Weight and Balance

1. Steps to calculate balance:
   1. Calculate individual moments (Weight x Arm).
   2. Sum all weights to get total weight.
   3. Sum all moments to get total moment.
   4. Calculate the CG: Total Moment ÷ Total Weight.
   5. Ensure the CG is within limits specified in the POH.
2. Manufacturers may provide:
   1. Moment charts or tables to simplify calculations.
   2. Different methods for presenting weight and balance data.

Weight and Balance Calculations (Examples)

1. Cessna 172 Example:
   1. Total weight and moment calculated during takeoff planning.
   2. Check CG at both takeoff and landing (consider fuel burn).
   3. In this aircraft, fuel burn-off barely affects CG.
2. Piper Cadet Example:
   1. Using an electronic calculator (e.g., Sporty's E6B) to compute weight and CG.
   2. Initial calculation may show CG out of limits.
   3. Adding ballast or adjusting loading can bring CG within limits.
3. Beechcraft Example:
   1. Using tables and moment indexes provided in the Pilot's Operating Handbook.
   2. Swapping passenger positions to adjust CG within limits.

Other Weight Terms

1. Maximum Ramp Weight:
   1. Slightly higher than maximum takeoff weight.
   2. Accounts for fuel burned during start and taxi.
2. Maximum Landing Weight:
   1. The greatest weight allowed at landing.
   2. May be lower than maximum takeoff weight.
3. Useful Load:
   1. Difference between maximum takeoff weight and basic empty weight.
4. Zero Fuel Weight:
   2. Basic empty weight plus crew, passengers, and baggage.
   3. Some aircraft have a maximum zero fuel weight limitation.
5. Basic Operating Weight:
   1. Empty weight plus standard items like crew and equipment.
   2. Used in jets and larger aircraft.

Final Tips

1. Use basic math (Weight x Arm = Moment) to calculate weight and balance.
2. Always ensure the aircraft is within weight and CG limits before flight.
3. Be cautious when flying unfamiliar aircraft or with unusual loading conditions.
4. Refer to the POH for specific weight and balance data for each aircraft.
5. Proper weight and balance calculations are essential for safe flight operations.

Understanding and calculating weight and balance is crucial for ensuring aircraft performance and safety. Always take the time to perform accurate weight and balance calculations before each flight.