portion of the project in a timely manner, either by appropriately using a sub-scale test vehicle or by dedicating major funding levels to a “flagship” effort.

THE ENVIRONMENTALLY RESPONSIBLE AVIATION PROJECT

The ERA project is a part of NASA’s Integrated Systems Research Program. The ERA project is an effort to substantially improve the fuel efficiency and environmental performance—and therefore competitiveness—of the U.S. aviation industry. U.S. aircraft must operate not only at a time when fuel prices are increasing but also in areas such as Europe that have been tightening environmental restrictions on noise and emissions. According to NASA, the ERA project was created to “explore and document the feasibility, benefits and technical risk of vehicle concepts and enabling technologies that will reduce the impact of aviation on the environment.” This impact reduction will be accomplished by reducing noise, nitrous oxide (NOx) emissions, and fuel burn. The ERA project’s primary focus is to enable the design of aircraft that can accomplish all three of those goals simultaneously. With air traffic expected to double by 2025, the work of the ERA project will be crucial for reducing the air transportation system’s emission of greenhouse gases and decreasing its susceptibility to volatile aviation fuel prices.1

The ERA project’s 2020 goals, as outlined in the National Aeronautics Research and Development Plan, are to reduce noise by 42 dB, reduce NOx emissions by 75 percent, and reduce aircraft fuel burn by 40 percent.2 To meet these goals the ERA project plans to explore and mature unconventional aircraft designs in the areas of airframe and propulsion technology as well as vehicle systems integration. The project plans to invest in certain technologies for meeting its goals.

One challenge facing almost every aircraft is how to reduce noise. The ERA project will specifically concentrate on mitigating propulsion noise and airframe noise and the interaction between the two, referred to as propulsion airframe aerodynamics. Propulsion noise mostly consists of fan and jet noise, and airframe noise is primarily caused by flaps and landing gear. Engine noise can be reduced by employing ultra-high bypass engines such as a geared turbofan engine, soft vane, over-the-rotor foam metal lines, distortion-tolerant fans with active noise control, variable area fan nozzles, and combination metallic and polyimide foams or aerogel materials. Airframe noise can be reduced with the use of continuous mold-line wing structures, drooped leading edge, active flow control, adaptive and flexible wing structures, smart chevrons, and a toboggan fairing for landing gear noise reduction.

For example, to demonstrate noise reduction, NASA is conducting flight tests with a Gulfstream G550 at NASA’s Wallops Flight Facility. This will be used to demonstrate noise reduction capabilities with a focus on aircraft design as a whole and specifically on landing gear.

Another challenge is to reduce landing and takeoff NOx emissions. There are three current plans to address these types of emissions. One of them, the ERA CMC (ceramic matrix composite) combustor liner, will be able to tolerate high engine temperatures. Another one is active combustion instability control that will focus on trying to reduce combustor instabilities. Finally, the low-NOx, fuel-flexible combustor offers a high bypass ratio and advanced combustion with fuel/air mixtures. An example of this propulsion technology research is the development of fuel injector designs that will meet the emission standards.

NASA’s plan to tackle fuel burn is composed of three parts: reducing drag via laminar flow, reducing weight via advanced structures, and reducing specific fuel consumption via ultra-high bypass ratio engines. Drag reduction can be achieved by using many tools and techniques, such as aircraft design and propulsion (see Figure 2.1). For example, the hybrid laminar flow control will use a suction technique, and the natural laminar flow will consist of a thin wing design that reduces friction drag. The Gulfstream G-III “Gloved Wing” aircraft is being developed by a partnership with Texas A&M University, Gulfstream Aerospace, and the Air Force Research Laboratory. This project will demonstrate drag reduction by using discrete roughness elements. It will also be working on a compliant flap in which changes are made to the curvature of the flap to create more lift. Weight reduction will

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1 NASA Aeronautics Research Mission Directorate, “Environmentally Responsible Aviation Project: Integrated Systems Research Program,” available at http://www.aeronautics.nasa.gov/isrp/era/index.htm, last updated February 3, 2011.

2 NASA Aeronautics Research Mission Directorate, “Fundamental Aeronautics Program: Subsonic Fixed Wing,” available at http://www.aeronautics.nasa.gov/fap/sfw_research_overview_feature.html, last updated September 9, 2009.



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