The engineers conceived of the 180-passenger D “double bubble” series (Figure 3) by reconfiguring the tube-and-wing structure. Instead of using a single fuselage cylinder, they used two partial cylinders placed side-by-side to create a wider structure whose cross-section resembles two soap bubbles joined together. They also moved the engines from the usual wing-mounted locations to the rear of the fuselage. Unlike the engines on most transport aircraft that take in the high-speed, undisturbed airflow, the D-series engines take in slower-moving air that is present in the wake of the fuselage. Known as Boundary Layer Ingestion (BLI), this technique allows the engines to use less fuel for the same amount of thrust, although the design has several practical drawbacks, such as creating more engine stress.
The D Series travels about 10 percent slower than a 737. To further reduce the drag and amount of fuel that the plane burns, the D series features longer, skinnier wings and a smaller tail. (http://web.mit.edu/newsoffice/2010/nplus3-0517.html)
Boeing Drives New Horizons of Form and Function
Since the beginning of the jet age nearly 40 years ago, Boeing has succeeded in reducing the noise impact of airplanes. As Boeing continues development of the 787 Dreamliner, the plane’s noise improvement comes from a new generation of engines that have a very high bypass ratio, which allows more air to go through the engine. Boeing engineers also wrap the engines with special linings and other acoustic improvements. (www.newairplane.com/environment/)
Early data show the 787’s noise footprint will be as much as 60% smaller than today’s comparable airplanes, thanks to a host of design improvements, including advanced acoustic linings, new engine inlets and nozzles, lightweight composite materials, and a new, more aerodynamic wing.
Boeing has chosen to increase the use of composites in the design of the 787. It is, in fact, 50 percent composite by weight. Carbon Sandwich is a class of composites made by attaching two thin skins to a lightweight, thick core, similar to a honeycomb. The core material is usually a low-strength material, but its thickness provides the sandwich composite with high bending stiffness. Carbon Laminate is composed of layers of carbon fiber impregnated with a polymer. These structures on the 787 are composed of strands of carbon formed into a tape infused with resin. The layers are laminated to create a desired thickness and shape, and are cured through heat and pressure.
Engine enhancements include a more electric architecture. Today’s planes use pneumatic systems powered by high-pressure air diverted from the engines. The system requires manifolds, valves, and ducts to power other systems in the aircraft. The design of the 787 eliminates the pneumatic system. The electric system extracts only the power needed during each phase of flight.
Airbus Develops a Concept for the Future
Airbus is looking more than 40 years in the future to anticipate what the future of aviation will look like. One key part of the company’s research and technology efforts is to investigate, test, validate, and optimize the most advanced technologies, design features, configurations, and architectures.
The A380 is the first commercial aircraft to incorporate as much as 25% composites. The carbon-fiber-reinforced plastic composite center wing box has saved up to 1.5 tons. Airbus is also focusing on low-noise nacelle designs, acoustic treatments, and low engine noise technologies, including the “zero-splice” inlet technology for engine nacelles to reduce fan noise. It also contributes to the quiet flight of the A380, which satisfies the noise requirements of international airports.