Boeing Near-Elliptical Cross-Section Aircraft
Current "small" commercial airplanes such as the Boeing 737 and 717, the Airbus A320 family, and regional jets in the less-than-100-seat class being designed by Bombardier, Embraer and Fairchild Dornier, all feature a passenger cabin with a single-aisle. A single-aisle configuration used in current airplanes in these smaller classes minimizes drag, weight, fuel bum, and economic penalties. However, the single-aisle fails to provide spacious cabins, desirable ambiance and interior architecture, and easy mobility in flight for both passengers and cabin crew. As a result, the passenger appeal of single-aisle aircraft is significantly less than that of larger twin-aisle aircraft.
Current larger commercial airplanes such as the Boeing 747, 767, and 777, and the Airbus A340 family feature a passenger cabin with a twin-aisle. A twin-aisle configuration used in current airplanes in these larger classes provides increased passenger comfort over a single-aisle configuration. Due to economic and performance constraints, small aircraft currently known in the art are limited to single-aisle configurations at the expense of increased passenger comfort, such as that available in twin-aisle configurations. Therefore, there exists a need to improve passenger comfort in small commercial aircraft while minimizing drag, weight penalties, fuel burn, and economic penalties.
Certain classes of internally pressurized aircraft fuselages, such as are found in passenger planes, can beneficially employ near-elliptical cross-sections. For example, an aircraft having a fuselage with a quasi-elliptical, or near-elliptical cross-section that is wider than it is tall, wherein the fuselage comprises a rigid, light weight shell having respective opposite, closed nose and tail ends. This cross-section efficiently encloses a main deck cabin, typically provisioned as a spacious and comfortable twin-aisle, seven-abreast cabin, together with a cargo container (typically a LD-3-46W or similar, standardized type of container) in a pressurized lower deck hold.
This twin-aisle fuselage cross-sectional shape has also been shown to provide a perimeter-per-seat ratio comparable to that of a corresponding single-aisle, six-abreast, conventional aircraft fuselage having a circular or "blended circular arc" cross-section, and consequently, can also provide a cross-section-parasite-drag-per-seat ratio and an empty-weight-per-seat ratio that, in a first-order analysis, are comparable to those of the corresponding single-aisle fuselage cross-section, while offering better passenger comfort and owner revenue options.
However, achieving an optimized, lightweight structure for such near-elliptical cross-section fuselages when they are constructed of composite materials, i.e., reinforcing fibers embedded in resin matrices, presents substantial engineering design challenges, not only because of the application of such materials to this relatively new application, but also because of the structural and weight penalties involved in moving from a fuselage design having a conventional circular cross-section to a fuselage design having a non-circular cross-section, especially those associated with the internal pressurization effects inherent in the design of high-altitude jet airliners.
Advantageously, the shell of the fuselage can function as a pressure vessel in which the design loads of major interest include internal pressurization loads. The shell can comprise a circumferential outer skin and circumferentially spaced longitudinal stringers, disposed adjacent to an inner surface of the skin, and the at least one tailored structural attribute can comprise at least one of a cross-sectional shape and size, number, and material of the stringers. Each of at least one of the circumferential skin and the stringers can comprise a "composite" of a plurality of plies, each having a selected angular orientation relative to the others, the at least one tailored structural attribute can comprise at least one of the number, relative angular orientation, and material of the plies.
Alternatively, the shell can comprise a "sandwich" structure, i.e., circumferential outer and inner skins attached to a rigid core, which can comprise either of a continuous rigid foam or of interconnected cells, and the at least one tailored structural attribute can comprise at least one of a thickness of the core, a core density or core cell density and a core material. The skins can be made from either thermosetting or thermoplastic material, and by hand lay up, machine lay up or resin infused.
In another embodiment, the shell can comprise an "isogrid" structure having at least one external face sheet attached to a grid comprising internal stiffening members, and the at least one tailored structural attribute can comprise at least one of grid spacing, grid geometry, grid material and face sheet material.
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