Students who often fly on the plane must have the impression that some of the plane's engines are hung on the wings, and some are installed on the buttocks. Can it be arranged casually?
In fact, aero-engines are not only very different in performance, but also in the specific location of installation. Generally speaking, in addition to the common wing hanger layout, jet engines also have wing root, tail hanger and wing tail hanger layouts.
Wing hanging layout
Let's start with the most common wing suspension layout. This layout first appeared on the bomber and was later adopted on the 707 aircraft that helped Boeing lay the foundation for the industry giant. Once adopted, this layout became the mainstream without hesitation. The reason why it is so popular is that it has many advantages. First of all, this layout is conducive to using the weight of the engine to offset part of the torsion at the connection between the aircraft wing and the fuselage, which plays an important role in "unloading".
During flight, the aircraft relies on the wings to generate upward lift, while the heavier fuselage generates a large downward force of gravity. In this way, at the connection between the wing and the fuselage, the lift generated by the wing and the gravity generated by the fuselage form a large torsion force, making the wing root the most important part of the aircraft structure. If you hang a very heavy engine under the wing, you can distribute some of the weight to the wing, which helps to balance the torque at the root of the wing.
Hanging the engine under the wing also reduces the discomfort caused by the noise. When the aircraft is in flight, the sound of the engine is very loud, which will bring a very noisy feeling to passengers near the engine area. The quiet cabin environment is an important criterion for measuring the comfort of an aircraft. For this reason, aircraft designers imagine that if the engine is hung under the wing, not only can the wing form a barrier to the noise of the engine, but also the engine can be kept as far away from the fuselage as possible, thereby reducing the impact of noise.
In addition, hanging the engine under the wing has the following advantages: the engine is closer to the ground, making maintenance and maintenance easier; the engine installed under the wing is closer to the center of gravity of the aircraft, making the aircraft easier to control; Large, so it is relatively easy to increase or decrease the number of suspended engines under the wings.
Hanging the engine under the wing is not just a matter of putting it casually. It needs to comprehensively consider various factors such as resistance and airflow during flight. Civil aviation aircraft are basically low-wing. In this case, the aircraft designer must ensure that the engine suspended under the wing cannot be too close to the ground, in order to prevent the engine from being sucked in by debris on the ground and damaged.
What we usually call a wing-suspended engine is to hang the engine under the wing, but there is also a reverse way to arrange the engine above the wing. In fact, from the point of view that the engine on the wing is not limited by the height above the wing and has the same unloading effect as the engine on the wing, the layout of the engine on the wing is very scientific. However, once the engine is placed above the wing, the wing's role in shielding the engine noise cannot be achieved. In addition, the over-wing engine layout makes engine maintenance difficult due to the elevated position of the engine. After comprehensive consideration of various factors, there are not many aircraft with wing-mounted engines at present.
wing root layout
The wing root layout is an engine layout with a long history. Beginning with early jetliners, the Comet and the Tu-104, designers have mounted engines at the root of the wing. The reason why designers choose this layout is that it can keep the shape of the aircraft formed by the three main aerodynamic components of the wing, fuselage and empennage, with the least wind resistance. Moreover, since the engine is relatively close to the central axis of the fuselage and the center of gravity of the fuselage, once one engine fails, the resulting thrust imbalance is relatively small, and the flight control is relatively simple. Therefore, most early jet airliners used this engine layout.
Of course, this layout also has obvious limitations. The layout of the wing root engine makes the engine close to the fuselage. This will firstly make the cabin noisy, and secondly, the hot airflow from the engine will easily cause damage to the fuselage. In addition, this layout allows the wing to pass through the engine nacelle and connect the fuselage, which complicates the design of the force-bearing system and increases the structural weight of the wing root. In addition, because the engine is installed within the wing structure, it increases the difficulty of engine maintenance.
Tail suspension layout
The tail-lift layout is to place the engine at the tail of the aircraft. The first jet airliner to adopt this engine layout was the Clipper, and later the Boeing 727 also adopted this layout.
The advantages of this layout are obvious: first, there are no redundant protrusions under the wing, which reduces the impact of the engine pod on lift and drag; second, there is no rigid requirement for the space under the wing, and the designer can shorten the height of the landing gear and save structure The third is that it can provide a quieter and more comfortable environment for the first class, business class, and even high-end economy class located in the front of the fuselage; the fourth is that the diameter of the engine is not limited by the space, and an engine with a very large bypass ratio can be used ; Fifth, due to the short distance between the engines, once a single engine fails, the impact on the yaw of the aircraft is far less than that of the underwing hanging layout.
This layout also has disadvantages, such as disintegrating the unloading effect of the engine on the wing; the layout of the tail engine requires a high-level tail, and the vertical structure needs to be strengthened in the design of the model; the number of engines cannot be increased or decreased at will.
"Wing Crane + Tail Crane" Layout
The "wing crane + tail crane" engine layout can be seen on some aircraft with 3 engines. Among them, the most representative ones are the DC-1 and MD-11 long-range wide-body airliners produced by McDonnell Douglas. At the beginning, the guiding ideology of adopting this engine layout method was to install an engine on the tail to increase the power of the aircraft and extend the flight distance. This "wing crane + tail crane" engine layout has gradually been eliminated with the increasing popularity of civil aircraft secondary engine hoisting.
