This may surprise you to learn, but the fuel and wing mounted engines actually help to alleviate load from the wings.
When an aircraft is flight, the wings flex upwards as they carry the weight the of the aircraft (wing loading).
This flex causes compression forces on the top of the wing structure, and tensile forces on the bottom of the wing structure.
By mounting engines on the wing, and loading fuel into wing tanks, this helps to reduce the amount of flex that wings experience in flight, by weighing down the wing, and dampening flutter effects.
It is for this reason aircraft have a Maximum Zero fuel Mass (MZFM). I.e. the maximum mass the aircraft can be, before adding fuel. Again, is because the fuel in the wing tanks, actually helps the wing to absorb structural loads!
So, wing mounted engines, and wing fuel tanks, actually help to dampen out vibrations and flexing.
SOURCE: QUORA
