Frequent flyers are likely familiar with the fact that airplane engines are sometimes mounted on the wings and sometimes on the fuselage. Is this arrangement arbitrary?
Actually, aircraft engines differ significantly not only in performance but also in their specific mounting locations. Generally, jet aircraft engines, besides the common wing-mounted configuration, also have wing-root, tail-mounted, and wing-tail-mounted configurations.
Wing-mounted Configuration
Let's start with the most common wing-mounted configuration. This configuration first appeared on bombers and was later adopted on the Boeing 707, which helped Boeing establish its industry dominance. Once adopted, this configuration quickly became the mainstream. Its popularity stems from its numerous advantages. First, this configuration effectively utilizes the engine's weight to offset some of the torque at the wing-fuselage junction, playing a crucial "unloading" role.
During flight, the aircraft generates upward lift through the wings, while the heavier fuselage generates significant downward gravity. This creates a significant torque at the wing-fuselage junction, where the lift from the wing and the weight from the fuselage combine to form a substantial torque, making the wing root the heaviest structural point on the aircraft. Suspending the very heavy engines under the wings distributes some of the weight across the wings, helping to balance the torque at the wing root.
Suspending the engines under the wings also reduces noise discomfort. Aircraft engines are very loud during flight, creating a disturbing experience for passengers near the engine area. A quiet cabin environment is a crucial standard for aircraft comfort. Therefore, aircraft designers envisioned that suspending the engines under the wings would not only allow the wings to act as a noise barrier but also keep the engines as far away from the fuselage as possible, thus reducing noise impact.
Furthermore, suspending the engines under the wings offers the following advantages: the engines are closer to the ground, making maintenance and repair easier; engines mounted under the wings are closer to the aircraft's center of gravity, making the aircraft easier to control; and due to the larger area of the wings, it is relatively easy to add or remove engines under the wings. Mounting an engine under the wing is not a simple matter; it requires careful consideration of factors such as drag and airflow during flight. Commercial aircraft are mostly low-wing monoplanes. In this case, aircraft designers must ensure that the engines mounted under the wing are not too close to the ground to prevent the intake of ground debris and damage.
While we commonly refer to wing-mounted engines, they are typically mounted under the wing. However, there are also cases where the reverse is true, with the engine positioned above the wing. In fact, from the perspective of overwing engines not being limited by ground clearance and having the same unloading function as underwing engines, the overwing engine layout is very scientific. However, once the engine is placed above the wing, the wing's noise shielding effect is lost. Furthermore, the elevated position of the engine in the overwing layout makes maintenance more difficult. Considering all these factors, aircraft currently using the overwing engine layout are not very common. [Advertisement: Super addictive and stress-relieving mini-game, click to play! Legend of the Artifact - Grass-Mowing Version Enter Mini-Game]
Wing Root Layout
The wing root layout is a historically significant engine layout. From early jet airliners like the Comet and Tu-104, designers have mounted engines at the wing roots. This layout was chosen because it allows the aircraft to maintain its shape, formed by the three main aerodynamic components: wings, fuselage, and tail, minimizing drag. Furthermore, because the engines are close to the fuselage centerline and center of gravity, the thrust imbalance in the event of a unilateral engine failure is smaller, simplifying flight control. Therefore, early jet airliners mostly adopted this engine layout.
However, this layout also has significant limitations. The wing-root engine layout places the engines close to the fuselage, resulting in increased cabin noise and the potential for the hot exhaust gases to damage the fuselage. Additionally, this layout requires the wing to pass through the engine nacelle and connect to the fuselage, complicating the stress system design and increasing the structural weight at the wing roots. Moreover, mounting the engines within the wing structure increases the difficulty of engine maintenance. MBTI Test Entry (2025 Official Website New Version) Qianyingzhi Personality Test View
Tail-mounted Layout
The tail-mounted layout places the engines at the rear of the aircraft. The first jet airliner to adopt this engine layout was the "Crossfire," and the Boeing 727 later followed suit.
The advantages of this layout are obvious: First, there are no extra protrusions under the wings, reducing the impact of engine nacelles on lift and drag; second, there are no strict requirements for underwing space, allowing designers to shorten the landing gear height and save structural weight; third, it provides a quieter and more comfortable environment for the first-class, business-class, and even premium economy classes located at the front of the fuselage; fourth, the engine diameter is not limited by space, allowing for engines with very high bypass ratios; fifth, because the engines are closer together, the impact of a single engine failure on the aircraft's yaw is far less than with an underwing-mounted layout. This layout also has drawbacks, such as undermining the engine's load-bearing capacity on the wings; requiring a high-mounted horizontal stabilizer for the tail-mounted engines, necessitating strengthened vertical structures during aircraft design; and limiting the number of engines.
"Wing-mounted + Tail-mounted" Layout
