If there’s one thing common about most commercial jet aircraft, it’s that their engines are mounted on the wings, and usually lower than the wings. When jet engines first appeared on commercial aircraft like the de Havilland Comet, they were mounted on the wings itself, or perhaps, at the same level as the wings. However, with the introduction of the Boeing 707 and later the Douglas DC-8, the engines are mounted below the wings.
Of course, one might think that a reason for this could be that it would be harder to repair an engine when it is mounted directly on the wing than under, which is actually easier to remove and replace too. However, there are simply more reasons than that.
Aerodynamics
Aerodynamics are the lifeblood of efficient movement through the air. Placing engines under the wings streamlines airflow and minimizing drag. The wing’s curved profile creates an area of low pressure above it, where the engine sits comfortably. This pressure differential helps “suck” the engine’s exhaust upwards, away from the wing, reducing turbulence and drag. Additionally, the engine placement contributes to lift generation, creating a symbiotic relationship between wing and engine.
Think of it like a perfectly coordinated waltz: the wing generates lift, the engine’s thrust adds to it, and the low-pressure zone above the wing “lifts” the exhaust, minimizing its disruptive impact. This aerodynamic ballet results in a smoother, more fuel-efficient flight for everyone onboard.
Mounting engines under the wings however offers more than just aerodynamic synergy; it maintains structural balance and stability. By placing the engines below the wings, engineers effectively distribute weight evenly, preventing the aircraft from tilting excessively. This balanced weight distribution contributes to a smoother flight experience and reduces stress on the wing structure, ensuring the safety of everyone onboard.
Furthermore, the wings themselves provide a robust platform for the engines. Their sturdy construction can withstand the weight and vibrations of the engines, unlike other potential locations like the fuselage or the tail, which might require significant structural reinforcements.
Safety and Ease of Maintenance
Anyone who’s ever worked on a car knows the importance of accessibility. The same principle applies to aircraft maintenance. Mounting engines under the wings makes them readily accessible for inspections, repairs, and routine maintenance. This ease of access translates to quicker turnaround times, reduced maintenance costs, and ultimately, improved operational efficiency for airlines.
Jet engines are not immune to technical problems. In such scenarios, Engines under the wings helps mitigate the impact of an engine failure. If one engine malfunctions, the thrust from the remaining engine(s) is countered by the weight distribution, minimizing the aircraft’s tendency to roll or yaw excessively. This balanced configuration allows pilots to maintain better control and navigate the situation more effectively, prioritizing the safety of passengers and crew.
Challenges
While under-wing engine placement offers numerous advantages, it’s not without its challenges. The need to reinforce the wings to handle the weight and vibrations of the engines adds complexity to the design process. Additionally, larger engines can pose ground clearance issues, requiring careful design to prevent contact with the runway during takeoff, landing, and taxiing.
High bypass engines, like those found on the Boeing 737 MAX, pose a challenge. The MAX’s CFM LEAP 1B engines are so large that they do not fit under the wing of a 737, which was originally designed to sit low to the ground. Consequently, Boeing decided to mount the huge engines forward of the wing and a bit higher, causing the plane to pitch upward quickly. This was the reason why Boeing created the MCAS (Maneuvering Characteristics Augmentation System) to counter this upward pitch. However, the MCAS proved to be another challenge at the start, which led to the crash of two 737 MAX 8 planes, resulting in the loss of more than 300 lives.
Indeed, balancing these challenges with the benefits requires meticulous engineering and design optimization to ensure optimal performance, safety, and efficiency.
First love never dies. I fell in love with airplanes and aviation when I was a kid. My dream was to become a pilot, but destiny led me to another path: to be an aviation digital media content creator and a small business owner. My passion for aviation inspires me to bring you quality content through my website and social accounts. Aviation is indeed in my blood and blog!
