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 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 MZFW. This is usually done for large airplanes.
Most small airplanes do not have a MZFW 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.
Read more about this topic: Zero-fuel Weight
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“the uncomfortable angels that rot
On the slabs, a wing chipped here, an arm there:
The brute curiosity of an angel’s stare
Turns you, like them, to stone....”
—Allen Tate (1899–1979)
“No ray is dimmed, no atom worn,
My oldest force is good as new,
And the fresh rose on yonder thorn
Gives back the bending heavens in dew.”
—Ralph Waldo Emerson (1803–1882)
“The hill farmer ... always seems to make out somehow with his corn patch, his few vegetables, his rifle, and fishing rod. This self-contained economy creates in the hillman a comparative disinterest in the world’s affairs, along with a disdain of lowland ways. “I don’t go to question the good Lord in his wisdom,” runs the phrasing attributed to a typical mountaineer, “but I jest cain’t see why He put valleys in between the hills.””
—Administration in the State of Arka, U.S. public relief program (1935-1943)