Zero-fuel weight

The Zero-Fuel Weight of an aircraft is the total weight of the airplane, minus the total weight of usable fuel on board.

For example, with the following givens:

• Maximum takeoff weight 6,000 lb
• Operating empty weight 4,000 lb
• Maximum zero-fuel weight 5,500 lb

The aircraft can be loaded with only 1,500 lb of non-fuel payload; the remainder must be fuel.

Wing bending relief

In fixed-wing aircraft, 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 wings, including the weight of fuel in the wings, 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 wings is greater than the capacity for extra weight in the fuselage. Designers of airplanes can optimize the maximum takeoff weight and prevent overloading in the fuselage by specifying a Zero-fuel weight. This is usually done for large airplanes with cantilever wings. (Airplanes with strut-braced wings achieve substantial wing bending relief by having the load of the fuselage applied by the strut mid-way along the wing semi-span. Extra wing bending relief cannot be achieved by particular placement of the fuel. There is usually no zero-fuel weight specified for an airplane with a strut-braced wing.)

Most small airplanes do not have a zero-fuel weight specified among their limitations. For these airplanes with cantilever wings, 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.

See also

• Aircraft gross weight
• Empty weight
• Dry weight - The equivalent term for automobiles

References

• Aircraft Weight and Balance Handbook (FAA-H-8083-1A)
• Zero fuel weight