What emerged from these studies were several different configurations and technologies for further research – the majority of them propulsion and airframe technologies. As these areas of focus became more distinct, NASA’s research partnerships branched into two projects: one aimed at goals considered achievable by the mid-2020s (two generations beyond the existing generation of aircraft, or N+2); and another aimed at more ambitious goals for aircraft entering service around 2030 and 2035 (N+3).
N+2: The Environmentally Responsible Aviation (ERA) Project
In 2009, the six-year ERA Project was launched to create a faster track for the most mature and promising technologies being evaluated throughout ARMD’s green aviation research. The project involves partners from private industry and academia and is coordinated with system-level research in airframe and propulsion technologies performed by other ARMD programs, as well as other federal agencies.
Phase 1 of the project, conducted from 2010 to 2012, consisted of a series of smaller-scale experiments and studies of more than 20 different technologies. NASA funded studies of experimental aircraft configurations submitted by Boeing, Lockheed Martin, and Northrop Grumman.
At the conclusion of this first phase, project leaders analyzed the results to determine which technologies might be moved from the laboratory to larger-scale flight and ground tests, and beginning in 2013, NASA and its partners embarked on a series of demonstrations of the technologies that offered the greatest potential technical benefit to aircraft manufacturers.
“In Phase 2,” said Fay Collier, ERA project manager, “we whittled down to eight what we thought had the best chance of application in the near term – the next five, six, seven years. If we can mature the technology readiness on these eight, then we think there’s a pretty good chance we might see them on airplanes in the 2020-plus time frame.”
The demonstrations, launched in 2013, have focused on five areas:
- reduction of aircraft drag through innovative flow control concepts
- weight reduction through the use of advanced composite materials
- fuel and noise reduction with advanced engines
- emissions reductions from improved engine combustors and fuel consumption
- noise reduction through innovative airframe designs and engine integration
Like previous ERA activities, the demonstrations are carried out in partnership with federal and private-industry collaborators. In November 2013, for example, investigators from NASA and the Boeing Co. completed wind tunnel testing of a full-scale Boeing 757 vertical tail model equipped with active flow control technology: dozens of small sweeping jet actuators that blow air across the span of the tail section. By improving what aeronautical engineers call boundary layer control, or BLC, NASA engineers aim to enhance the performance and utility of the tail section – an airframe component that adds stability to an aircraft in flight but is also notorious for creating drag. On commercial aircraft, with active flow control it may be possible to reduce the size of the tail and reduce both drag and weight.
“We confirmed the flow rate,” Collier said, “and we confirmed the effectiveness of the actuators on the vertical tail. That gave us the confidence to launch a flight test aboard Boeing’s 757 ecoDemonstrator, which will occur next April or May [2015].”
Three proposed aircraft designs achieved varying levels of success in meeting tough NASA goals for reducing fuel use, emissions, and noise, all at the same time. NASA image
The ERA project, conducted under the leadership of ARMD’s Integrated Aviation Systems Program, is scheduled to end in 2015. As it winds down and the results of the demonstrations are published, Collier said, the next steps belong to the aircraft industry, which will decide how to integrate these technologies into future designs.
“Tech transfer has been a big part of the overall project goals,” said Ed Waggoner, who manages the Integrated Aviation Systems Program for ARMD. “In every one of these Phase 2 endeavors, we’ve been intimately involved with an industry partner that is interested in that technology. That’s a key part of this.”
N+3: The Advanced Air Transport Technologies Project
NASA researchers in the Advanced Air Transportation Technologies Project are testing propulsion and airframe technologies aimed at more ambitious “stretch” goals in the 2030-2035 time frame: a 60 percent reduction in fuel/energy consumption relative to the “best-in-class” aircraft from 2005; an 80 percent reduction in NOx emissions; and a cumulative 52-decibel noise reduction below the current FAA stage 4 noise standard.
The knowledge gained through such evaluations is incremental: By focusing on isolated elements of a design, said Rich Wahls, a scientist with the Advanced Air Transportation Technologies Project, NASA and aircraft manufacturers are gathering the data they’ll need to validate designs for the aircraft of the future.
One of the most effective ways to improve the efficiency of a turbofan engine, said project manager Ruben Del Rosario, is to increase its bypass ratio – the amount of air driven past the engine combustion core, relative to the amount driven through it. The traditional method of increasing a bypass ratio has been to expand the radius of the turbofan – but this method, Del Rosario said, is nearing its limits.
“The physics tell you that the higher the bypass ratio, the more efficient the propulsion system will be,” he said, “until the engine has gotten so large that the weight of the nacelle, and the drag generated from the nacelle, start eating the benefits that you get from a larger and larger bypass ratio.”
The Subsonic Ultra Green Aircraft Research, or SUGAR, Volt future aircraft design comes from the research team led by The Boeing Company. The Volt is a twin-engine concept with a hybrid propulsion system that combines gas turbine and battery technology, a tube-shaped body, and a truss-braced wing mounted to the top of the aircraft. NASA/The Boeing Company
NASA’s partnerships in exploring future turbofan technologies focus on highly efficient smaller engine cores. “The work we’ve been emphasizing,” said Del Rosario, “has been focused on shrinking components of the engine core: the compressor or turbine or combustor. We’re exploring how to get these very small core cycles that increase the bypass ratio without increasing the external diameter.” Commercial aircraft that depart from the tube-and-wing design will need such innovative propulsion systems if they are to outperform today’s aircraft by a large enough margin to be considered necessary.