Why is the belly of C919 bulging?

The presentation of this question shows that the questioner's observation is relatively detailed. In fact, the fusion of the wing and fuselage of the C919 is rather "drum", or it is because of the overall and aerodynamic design requirements. Let Eagle Airlines simply answer it:

1. The C919 adopts the lower single wing design;

modern civil aviation aircraft, whether it is a medium-and long-range wide-body passenger aircraft (such as 777/747), a medium-and short-range trunk passenger aircraft (such as 737/32), or regional aircraft (such as CRJ9/ERJ-19), all adopt the lower monoplane design.

The advantage of this method is that it can release the space inside the fuselage, which does not interfere with the cabin. The overall advantage is better than that of the middle monoplane and the upper monoplane, thus becoming the mainstream design of civil aircraft.

2. The additional influence brought by the lower single wing design;

For a passenger plane with a lower wing, the joint between the wing and the fuselage is below the central part of the fuselage. On the one hand, in order to reduce aerodynamic drag, it is often necessary to install fairing around it. On the other hand, considering that this is also the installation position of the main landing gear, it is necessary to provide a landing gear cabin so as to accommodate the folded landing gear. Under the requirements of these two aspects, this foreskin will appear more "drum".

in addition, the position here is where the center of gravity of the aircraft is located, and it is more suitable to set up the central fuselage fuel tank, so that the fuel consumption has relatively little influence on the center of gravity of the aircraft during flight, which is conducive to maintaining flight stability.

There are many reasons * * * about the same, which makes the intersection of fuselage and wing generally "fat" in appearance.

-that's the end of the question-

Friends who are interested in aviation may wish to pay attention to Eagle Airlines.

not only does the belly of the C919 passenger plane look bulging, but basically all the belly of the civil aviation passenger plane that we can see now with the lower wing and the engine hanging under the wing are bulging. For example, Airbus A32 and Boeing B737, which are of the same class as C919, are all the same, including many large passenger planes with two engines or even four engines.

There are also reasons for deliberately designing such a bulge. Specifically, the main reasons are as follows:

First, modern passenger aircraft generally adopt the lower wing design, so in order to avoid the wing box at the connection point between the lower wing and the fuselage from encroaching on the lower cargo hold of the fuselage, the wing box adopts the external design, so it needs additional aerodynamic compensation, so when viewed from the front, the belly of the passenger aircraft will look bulging.

Second, modern passenger aircraft generally adopt the main landing gear design of the fuselage. Except for some regional aircraft, which still retains the traditional landing gear design of the wing pod module, most passenger aircraft choose to design the main landing gear on both sides of the fuselage. Similarly, in order to avoid the main landing gear storage module from encroaching too much on the internal space of the fuselage, especially the small trunk passenger aircraft like C919, in order to have a cabin with larger internal clear height and larger seat spacing, The vertical clear height and horizontal width of the cabin will be increased as much as possible, so for the fuselage with a small diameter, the height of the landing gear cabin must be as low as possible, so the landing gear cabin must be designed closer to both sides of the fuselage, so in order to leave enough room for the main landing gear, the belly of the fuselage will also protrude a lot.

third, not only small trunk passenger planes such as C919, but also many large passenger planes often design a main fuel tank at this position in order to increase their flight range. One reason is that the central wing box connecting the fuselage and the wing is closer to the mass center and aerodynamic center of the whole machine, so the built-in main fuel tank with larger capacity can be designed at will. In addition, the design of the main fuel tank at this position will not occupy the space of the front and rear cargo holds in the lower fuselage, which is more conducive to the passenger plane to load more standard containers.

For example, the A38 passenger plane has designed a main fuel tank capable of loading 53 tons of fuel at this position, and this main fuel tank is directly integrated into the central wing box made of carbon fiber. Of course, because the wingspan of A38 is too large, the central wing box is also designed to meet the structural strength, and the whole fuselage looks more like it is directly located on the integrated fuselage, which is of course the case.

The lower wing design is commonly used in civil airliners, which is convenient for engine maintenance. The lower wing has a good aerodynamic shape and is more stable than the upper wing design.

Generally, a passenger plane has a single wing, and the wing and fuselage are butted under the fuselage, which requires high stress. In addition, the landing gear cabin is below, so there is a bulge under the fuselage for rectification. Only by repairing the aerodynamic shape at the butt joint of the landing gear and the central wing can there be a bulge shape!

Look at the butt joint between the center wing and the fuselage of Yun-2, and the thickness is also increased. The butt joint between the wing and the fuselage needs to bear all the forces!

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