Blended Wing Body
Since the introduction of the legendary X-1 in 1946, scientists have used the X-plane designations to identify experimental aircraft and rockets used to explore new aerospace technologies. As of late 2018, an X designator for this designator to this aircraft is conjectural.
In 2016 NASA announced a 10-year plan by NASA Aeronautics to achieve ambitious goals in reducing fuel use, emissions, and noise by the way aircraft are designed, and the way they operate in the air and on the ground. One exciting piece of this 10-year plan is New Aviation Horizons – an ambitious undertaking by NASA to design, build and fly a variety of flight demonstration vehicles, or “X-planes.” The New Aviation Horizons X-planes will typically be about half-scale of a production aircraft, although some may be smaller or larger, and are likely to be piloted. Design-and-build will take several years, with vehicles going to flight starting around 2020 depending on funding.
One of the first X-planes is expected to be a hybrid wing body shape, where the familiar tube-and-wing instead becomes a wing that blends into the body. It flies the same speeds as commercial transport aircraft. Engines are on top of a fuselage that is itself revolutionary because of the shape and what’s required to build it to withstand the stresses of flight. For the past decade, NASA and partners have studied the performance and benefits of the hybrid wing body configuration using computers, wind tunnels and even subscale unpiloted flight tests. A lot of data is already in hand to inform an X-plane that will test the highest number of advanced technologies.
Besides a number of aircraft configurations being investigated by both large aircraft manufacturers to comply with the strict requirements, the Blended Wing Body (BWB) is closest to realization with a reasonable chance to enter the market by 2030, being discussed by both large aircraft manufacturers.
The flying wing idea that emerged around 80 years ago anticipates the elimination of all surfaces that are not generating lift in order to minimize wetted area with a simultaneous increase of airlifting area, thus increasing the lift capacity, as well as minimizing aerodynamic drag and fuel consumption of aircraft. There have been two main obstacles that resulted with such outcome including difficulties related to attaining the efficient longitudinal stabilization and pitch control of a large airlifting body, as well as the effective accommodation of bulky payload within the airlifting body that is designed with thin efficient airfoils.
The Blended Wing Body aircraft is one of the most recent attempts to apply tailess flying wing concept to civil applications. Intensive research since around 1990 has involved a significant number of experts in the areas of theoretical and applied aerodynamics, as well as computational analysis and wind tunnel testing have not produced a desirable outcome to simultaneously satisfy a required level of flight safety and competitive aerodynamic efficiency for civil air transportation at high subsonic speeds.
Blended Wing Body aircraft like the B-2 achieve lower drag than a pure flying wing by minimizing the surface area exposed to the airflow. They do this by having a center body that is as close as practical to circular in planform but usually with a pointed nose on the front to reduce compressibility drag and with wings attached to the sides to increase the wingspan for reduced induced drag which is drag due to creating lift. A wing with a circular planform has the least amount of surface area to internal volume for the same reason that a circle has the smallest circumference to the enclosed area or a sphere has the largest volume to surface area. The Blended Wing Body aircraft also can have inherent pitch stability at a farther aft center of gravity due to the aft swept wings that can act like horizontal tail surfaces.
A BWB is an airframe design that incorporates design features from both traditional fuselage and wing design, and flying wing design. Advantages of the BWB approach include efficient high-lift wings and a wide airfoil-shaped body. BWB aircraft have a flattened and airfoil shaped body (i.e., relative to a conventional aircraft), which produces lift (i.e., in addition to wing lift) to keep itself aloft. Flying wing designs comprise a continuous wing incorporating the functions of a fuselage in the continuous wing. Unlike a flying wing, the BWB has wing structures that are distinct and separate from the fuselage, although the wings are smoothly blended with the body. The efficient high-lift wings and wide airfoil-shaped body enable the entire craft to contribute to lift generation with the resultant potential increase in fuel economy.
In the art of commercial airplanes, it is highly desirable to design airplane and engine configurations that yield reduced fuel burn to increase efficiency and lower cost. In addition, carbon trading regulations comparable to those already enacted in the European Union may also likely to be adopted in other industrialized nations including the United States. These environmental considerations become even more important in economic scenarios in which fuel cost increases. This motivates a need for step- change technologies to reduce fuel consumption.
Conventional military cargo airplane configurations address two disparate missions: devise a military cargo airplane that provides more fuel-efficient transport of cargo in typical operations; and provide a means to load large wheeled vehicles into the airplane without the use of ground-based equipment. In general, these airplanes have a requirement to carry a large, dense and heavy payload. For example, an existing cargo plane can carry a main battle tank that
weighs about 160,000 lb and has floor space to carry 18 cargo pallets. These pallets typically have a weight limit of about 10,000 lb each, but in actual service are typically loaded with a weight of about 5000 lb each for a typical payload weight of about 90,000 lb. This means that the existing cargo plane may not have sufficient floor area (or payload volume) to carry a pallet payload weight approaching the airplane's actual capacity. Therefore, it may be typical that too much airplane is used to fly too little payload, resulting in a relatively large fuel burn per unit of payload. A typical metric of airplane fuel efficiency and carbon dioxide emissions is payload multiplied by range divided by fuel burned (ton-miles per pound of fuel). A way to address these challenges is to take advantage of the inherent fuel efficiency of a blended wing body (BWB) configuration.
BWB freighter designs are not currently being manufactured. Of the existing designs, most use large cargo doors in the centerbody leading edge. The chief disadvantage and limitation of this arrangement is that rolling stock can only be loaded with extensive ground-based cargo handling equipment. It would be preferable to have a rear (aft) cargo ramp in order to load large wheeled vehicles that can drive up the ramp. Existing BWB designs lack an airframe design that can incorporate a rear cargo door and ramp into the BWB configuration without disrupting aerodynamic performance. Integration of a rear cargo door and ramp into a BWB configuration may require preserving favorable lift distribution, avoiding separation of airflow over the BWB, and preserving pitch trim stability and control capability.
BWB designs being considered by the EC Framework 6 project NACRE (New Aircraft Concepts REsearch) are capable of carrying in excess of 1000 passengers on a single deck with 20 exits and eight longitudinal aisles. Furthermore, BWB layouts will mean that cabin crew at exits will not be able to assess the situation at opposite exit locations making redirection of passengers difficult. Indeed, the restricted and complex visual access and complex spatial connectivity offered by these aircraft configurations make wayfinding by passengers and redirection by cabin crew difficult and challenging.
The experimental results highlight the importance of situational awareness and visibility in navigating a successful exit path within the complex layout of the BWB. Improving the passenger’s knowledge of the cabin layout and the location of the exits and providing them with good visual access of the exits and aisles will be essential in achieving an efficient evacuation of complex BWB configurations.
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