The zero-fuel weight (ZFW) of an aircraft is the total weight of the airplane and all its contents, minus the total weight of the
usable fuel In aviation, usable fuel is the Aviation fuel, fuel on board an aircraft that can actually be used by its engines. The opposite of usable fuel is unusable fuel.Websters dictionary oUnusable fuel visited 19 March, 2012
The unusable fuel figure is ca ...
on board. Unusable fuel is included in ZFW.
Remember the takeoff weight components contributions:
:
Where OEW is the Operating Empty Weight (that is a characteristic of the plane), PL is the Payload actually embarked, and FOB the Fuel actually embarked and TOW the actual take-off weight.
ZFW is also defined as OEW + PL. The previous formula becomes:
:
.
For many types of airplane, the
airworthiness
In aviation, airworthiness is the measure of an aircraft's suitability for Air safety, safe flight. Initial airworthiness is demonstrated by a certificate of airworthiness issued by the civil aviation authority in the state in which the aircraft ...
limitations include a maximum zero-fuel weight.
This limitation is specified to ensure
bending moment
In solid mechanics, a bending moment is the Reaction (physics), reaction induced in a structural element when an external force or Moment of force, moment is applied to the element, causing the element to bending, bend. The most common or simplest ...
s on the wing roots are not excessive during flight. When the aircraft is loaded before flight, the zero-fuel weight must not exceed the maximum zero-fuel weight.
Maximum zero fuel weight
The 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) are 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.
If the limitations applicable to a
transport category airplane type include a maximum zero-fuel weight it must be specified in the Airplane Flight Manual
FAA Advisory Circular AC25.1581-1, paragraph 2.b.(1) "Weight Limitations".
Retrieved 13 December 2022 and the type certificate data sheet for the airplane type.
Maximum zero fuel weight in aircraft operations
When an aircraft is being loaded with crew, passengers, baggage and freight it is most important to ensure that the ZFW does not exceed the MZFW. When an aircraft 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 permissible weight of an aircraft with no disposable fuel or oil.
:
where FOB is Fuel On Board.
For any aircraft with a defined MZFW, the maximum payload () can be calculated as the MZFW minus the OEW (operational empty weight)
:
Maximum zero fuel weight in type certification
The maximum zero fuel weight is an important parameter in demonstrating compliance with gust design criteria for transport category airplanes.
Wing bending relief
In fixed-wing aircraft
A fixed-wing aircraft is a heavier-than-air aircraft, such as an airplane, which is capable of flight using aerodynamic lift. Fixed-wing aircraft are distinct from rotary-wing aircraft (in which a rotor mounted on a spinning shaft generate ...
, fuel is usually carried in the wings. While the aircraft is in the air, weight in the wings does not contribute as significantly to the bending moment
In solid mechanics, a bending moment is the Reaction (physics), reaction induced in a structural element when an external force or Moment of force, moment is applied to the element, causing the element to bending, bend. The most common or simplest ...
in the wing as does weight in the fuselage
The fuselage (; from the French language, French ''fuselé'' "spindle-shaped") is an aircraft's main body section. It holds Aircrew, crew, passengers, or cargo. In single-engine aircraft, it will usually contain an Aircraft engine, engine as wel ...
. 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.
Considering the bending moment at the wing root, the capacity for extra weight in the wings is greater than the capacity for extra weight in the fuselage
The fuselage (; from the French language, French ''fuselé'' "spindle-shaped") is an aircraft's main body section. It holds Aircrew, crew, passengers, or cargo. In single-engine aircraft, it will usually contain an Aircraft engine, engine as wel ...
. Designers of airplanes can optimise the maximum takeoff weight
The maximum takeoff weight (MTOW) or maximum gross takeoff weight (MGTOW) or maximum takeoff mass (MTOM) of an aircraft, also known as the maximum structural takeoff weight or maximum structural takeoff mass, is the maximum weight at which the p ...
and prevent overloading in the fuselage by specifying a MZFW. This is usually done for large airplanes with cantilever
A cantilever is a rigid structural element that extends horizontally and is unsupported at one end. Typically it extends from a flat vertical surface such as a wall, to which it must be firmly attached. Like other structural elements, a cantilev ...
wings. (Airplanes with strut-braced
In aeronautics, bracing comprises additional structural members which stiffen the functional airframe to give it rigidity and strength under load. Bracing may be applied both internally and externally, and may take the form of struts, which act in ...
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 MZFW specified for an airplane with a strut-braced wing.)
Most small airplanes do not have an MZFW specified among their limitations. For these airplanes with cantilever wings, the loading case that must be considered when determining the maximum takeoff weight
The maximum takeoff weight (MTOW) or maximum gross takeoff weight (MGTOW) or maximum takeoff mass (MTOM) of an aircraft, also known as the maximum structural takeoff weight or maximum structural takeoff mass, is the maximum weight at which the p ...
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
* Index of aviation articles
Aviation is the design, development, production, operation, and use of aircraft, especially heavier-than-air aircraft. Articles related to aviation include:
A
Aviation accidents and incidents
– Above Mean Sea Level (AMSL)
– ADF
– Acces ...
* Aircraft gross weight
The aircraft gross weight (also known as the all-up weight and abbreviated AUW) is the total aircraft weight at ''any moment'' during the flight or ground operation.
An aircraft's gross weight will decrease during a flight due to fuel and oil co ...
* Dry weight
Vehicle weight is a measurement of wheeled motor vehicles; either an actual measured weight of the vehicle under defined conditions or a gross weight rating for its weight carrying capacity.
Curb or kerb weight
Curb weight (American English) or k ...
- The equivalent term for automobiles
References
{{reflist
Aircraft weight measurements