In this blog post, we’ll take an easy-to-understand look at the design characteristics and aerodynamic pros and cons of the BWB (Blended Wing Body).
The B-2 strategic bomber recently gained widespread attention in major media outlets after participating publicly in joint U.S.-South Korea military exercises. Unlike typical passenger planes, the B-2 has a unique, manta ray-like shape that has captured the public’s attention; however, this design is not merely for visual effect but is the result of military and aerodynamic considerations.
In conventional aircraft (e.g., the B-747), the shapes of various components—such as the fuselage, main wings, vertical and horizontal stabilizers, and propulsion system—are clearly distinguishable. While shapes vary depending on the purpose, such as in fighter jets or twin-body aircraft, most allow for visual distinction between these parts. In contrast, aircraft like the B-2 lack separate components; the entire structure is integrated into a single large wing.
This type of aircraft is called a BWB (Blended Wing Body) or a flying wing. As the name suggests, the entire aircraft forms a single wing shape, and because the wing cross-section is thicker than that of a conventional aircraft, the crew and cargo can be accommodated inside the wing.
There are four main forces acting on an aircraft during flight: lift acts upward, weight due to gravity acts downward, thrust generated by the propulsion system acts forward, and drag acts backward. When flying horizontally at a constant speed, these four forces are in equilibrium.
Lift and drag are aerodynamic forces generated by airflow; the wing’s shape and area determine the magnitude of lift, while drag is influenced by the shape of the wing and the aircraft as a whole. The lift-to-drag ratio (L/D), which represents the ratio of lift to drag, is the most important figure for assessing an aircraft’s aerodynamic characteristics.
Thrust is determined by the performance of the propulsion system, and weight is determined by the structure and payload; therefore, these are not factors that directly represent aerodynamic characteristics. However, in aircraft of the same type, reducing drag allows for the use of a smaller propulsion system and reduces fuel consumption, while increasing lift enables the transport of more cargo with the same propulsion system, thereby improving efficiency. In other words, aircraft with a high lift-to-drag ratio have advantages in terms of fuel efficiency and performance.
Drag consists not only of pressure drag caused by the aircraft’s shape but also of significant surface friction drag. As high-speed airflow passes over an object’s surface, it creates friction, which generates drag; the larger the surface area, the greater the surface friction drag. Therefore, the aspect ratio—the ratio of the aircraft’s total surface area to the wing’s cross-sectional area—is a direct factor in determining the lift-to-drag ratio.
For example, while the B-747 passenger jet has an aspect ratio of approximately 6.5, a BWB like the B-2 has a very low aspect ratio of about 2. It is designed to maximize the lift-to-drag ratio by minimizing the surface area. In other words, the BWB is a structure focused on shape optimization to reduce drag.
In traditional aircraft, the fuselage, engines, and tail surfaces each perform important functions but are also major sources of drag. While the tail surfaces are responsible for attitude stability and control, they increase the surface area and thus generate drag. The BWB follows a design philosophy that eliminates these separate structures and integrates all components into the wings to increase the lift-to-drag ratio and improve aerodynamic performance.
Aircraft with high lift-to-drag ratios offer superior fuel efficiency. Since less drag is required to generate the same lift, fuel consumption is reduced, and consequently, the cost and energy required to transport the same cargo or passengers are lowered.
When applied to passenger aircraft, the BWB allows passengers to be seated in the spacious interior of the wing, enabling the accommodation of more passengers than traditional aircraft. The wider cabin enhances comfort and allows for the installation of additional amenities. Furthermore, it offers structural advantages by distributing loads over a wider area, and its small radar cross-section (RCS) provides excellent stealth capabilities for military aircraft. This is because, unlike traditional designs with many straight sections, radar waves are reflected in a direction opposite to the incoming wave, thereby reducing the amount of detectable radar energy.
However, there are also drawbacks. Since BWB technology is not yet fully mature, adopting this configuration carries significant risks. Furthermore, because the tail fins are removed, developing control systems to ensure attitude control and stability becomes a key challenge. Another issue that needs to be addressed is that, when used as a passenger aircraft, securing cabin windows becomes difficult, which could cause psychological resistance among passengers.
In summary, while BWB offers advantages such as excellent aerodynamic efficiency, expanded interior space, and stealth capabilities due to its low surface area-to-volume ratio and high lift-to-drag ratio, challenges related to stability and control technology, as well as passenger accommodation, remain. Consequently, it has not yet been widely adopted.
