Maximum Zero-Fuel Weight
The Zero Fuel Weight (ZFW) of an airplane is the total weight of the airplane and all its contents, minus the total weight of the fuel on board.
For example, if an airplane is flying at a weight of 5,000 lb and the weight of fuel on board is 500 lb, the Zero Fuel Weight is 4,500 lb. Some time later, after 100 lb of fuel have been consumed by the engines, the total weight of the airplane is 4,900 lb, the weight of fuel is 400 lb, and the Zero Fuel Weight is unchanged at 4,500 lb.
Note that, as a flight progresses and fuel is consumed, the total weight of the airplane reduces, but the Zero Fuel Weight remains constant (unless some part of the load, such as parachutists or stores, is jettisoned in flight).
For many types of airplane, the airworthiness limitations include a Maximum Zero Fuel Weight.
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Maximum Zero Fuel Weight (MZFW)
Is the maximum weight allowed before usable fuel and other specified usable agents (engine injection fluid, and other consumable propulsion agents) must be loaded in defined sections of the aircraft as limited by strength and airworthiness requirements. It may include usable fuel in specified tanks when carried in lieu of payload. The addition of usable and consumable items to the zero fuel weight must be in accordance with the applicable government regulations so that airplane structure and airworthiness requirements are not exceeded.
Maximum Zero Fuel Weight in airplane operations
When an airplane is being loaded with crew, passengers, baggage and freight it is most important to ensure that the Zero Fuel Weight does not exceed the Maximum Zero Fuel Weight.
When an airplane is being loaded with fuel it is most important to ensure that the Takeoff Weight will not exceed the maximum permissible takeoff weight.
MZFW : The maximum weight of an aircraft prior to fuel being loaded.
For any aircraft with a defined Maximum Zero Fuel Weight, the maximum payload can be calculated as the MZFW minus the OEW (Operational Empty Weight)
Wing bending relief
In an airplane, fuel is usually carried in the wings. Weight in the wings does not contribute as significantly to the bending moment in the wing as does weight in the fuselage. This is because the lift on the wings and the weight of the fuselage bend the wing tips upwards and the wing roots downwards; but the weight of the wing, including the weight of fuel in the wing, bend the wing tips downwards, providing relief to the bending effect on the wing.
When an airplane is being loaded, the capacity for extra weight in the wing is greater than the capacity for extra weight in the fuselage. Designers of airplanes can optimise the Maximum Takeoff Weight and prevent overloading in the fuselage by specifying a Maximum Zero Fuel Weight. This is usually done for large airplanes.
Most small airplanes do not have a Maximum Zero Fuel Weight specified among their limitations. For these airplanes, the loading case that must be considered when determining the Maximum Takeoff Weight is the airplane with zero fuel and all disposable load in the fuselage. With zero fuel in the wing the only wing bending relief is due to the weight of the wing.
References
See also
- Aircraft Gross Weight
- Dry weight - The equivalent term for automobiles