4.3.2: Wing and tail loads
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The lift produced by the wing creates a shear force and a bending moment, both of which are at their highest values at the root of the wing. Indeed, the root of the wing is one (if not the most) structurally demanding elements of the aircraft. The structure at this point needs to be very strong (high strenght) to resist the loads and moments, but also quite stiff to reduce wing bending. Thus, the wing is quite thick at the root.
Another important load supported by the wing is, in the case of wing-mounted engines, that of the power plant. Moreover, the jet fuel is typically located inside the wing. Therefore, an appropriate location of the power plant weight together with a correct distribution of the jet fuel (note that it is being consumed during the flight) contribute to compensate the lift forces during the flight, reducing the shear force and bending moment at the wing root. Fuel load close to the tips reduces this moment. Therefore the order in which the tanks are emptied is from the root to the tip. Nevertheless, when the aircraft is on the ground the lift is always lower than weight (when the aircraft is stopped, there is no lift), and all three forces, i.e., its structural weight, fuel, and power plant, can not be compensated by upwards lift. Therefore, the wing must also be design to withstand these loads which requires a design compromise.
The tailplane, rudder, and ailerons also create lift, causing a torsion in the fuselage. Since the fuselage is cylindrical, it can withstand torsion very effectively.