NASA’s Environmentally Responsible Aviation team was put into place in 2009 as a six-year project. It had a fixed budget of around $420 million spread over six years.  The project touched over a thousand researchers around the United States with several university partnerships. AeroTime had the chance to talk NASA’s Fay Collier about ERA’s findings and ways in which they can make air transport a greener industry overall.


What were the main goals of NASA’s Environmentally Responsible Aviation team?

The objective of the project was to focus on some promising technologies that were emerging from the base program within NASA Aeronautics. The time was right to do some focused research, to mature those technologies to the point where the industry could then begin to pick them up and transition them to products. So that was the overall objective. Concrete goals involved noise, carbon footprint, and nitrogen oxide (NOx) reduction. NASA had set those targets prior to the project. This big team, this funding was all put in place to mature technologies to help us reach those goals.

 

What is “green aviation” in the eyes of NASA?

For us, green aviation is essentially reducing the overall footprint of aviation, the carbon footprint, and the noise footprint, reducing the impact of aviation on the community. It’s not only carbon and noise but also local air quality around airports.  We wanted to reduce the overall emissions footprint associated with day-to-day life in communities that support airports.

 

Why is noise footprint as important as carbon emissions?

It has to do with the impact that aviation makes on the quality of life. There’s a large demand for aviation. The noise around airports is a constraint on being able to grow the aviation system to meet that demand. That’s number one. Number two – it’s well documented that there is a health impact associated with noise in communities around airports. It’s kind of a twofold strategy where, in the long run, we want to contain noise from aircraft movements within the airport boundaries.

 

What were the changes undertaken in the direction of more environmentally friendly aircraft throughout the years?

Between 1960, when the jet age began, and 2010 there was a lot of improvement in the areas I’ve mentioned – noise and fuel burning, carbon footprints, a lot of improvements in the overall efficiency of the plane. The airplanes have gotten quieter over time, improvements in the engine technology and the airframe have led to lower emissions around airports as well, so there’s a long history of making gradual improvements and that’s well documented.

So one of the things we wanted to do was establish what the state of the art was in 2010, what were the most promising technologies. We then wanted to mature them so that the industry and the aircraft manufacturers themselves could continue these improvements. It is a long-term endeavor. And we want to continue that trend.  And actually more and more of the public are in favor of this as well as time has gone on.

 

Could elaborate more on the findings of the project and the X-48B demonstrator aircraft?

There’s an equation called the Breguet range equation. And in that range equation, there are three factors that we like to focus on because if you can increase the range of an aircraft while operating on these three factors it is more efficient. The three factors are drag, weight and the specific fuel consumption of the engine. So the overall efficiency of an airplane is really related to these three factors.

We’ve worked on ways to reduce the overall drag of these transport aircraft. We worked on methods to reduce the weight and we actually worked on engine technology to make the engines themselves burn less fuel and emit less NOx.  Those are the three parameters that we operate on and we really focused on them during the ERA project.

One hypothesis that we carried into the project was that to meet some of these targets we needed a different configuration than the turbine wing. While there are some improvements left behind there and we’re working on that. To really get a transformation we needed to look at alternative configurations, things that are different than the turbine wing. And one of those configurations is something we call a hybrid wing body or a blended wing body.

They are quite different than the traditional turbine wing airplane that we fly in every day.  The blended wing body has a whole lot less drag and therefore it reduces fuel burn.  The way the engines are placed has a dramatic effect on community noise.  So we get fuel burn reduction and noise reduction simultaneously. 

For the X-48 B flight test to begin to mature the hybrid wing body concept in a low-speed environment.So whenever you’re working on an airplane or a new concept you’ve got low-speed concerns and that will be landing and take-off operations. And then you’ve got high-speed concerns which are when the airplane has been cruised when you're moving along at altitude. So there's high speed and low-speed concerns. The X-48B was focused on a low-speed regime of the airplane so we did a series of wind tunnel tests with our partner Boeing and Air Force and actually Cranfield University was involved as well. And then we took those same vehicles that we tested in the wind tunnel and we flew them out of Armstrong Flight Research Center. And in that way, we were able to characterize the low-speed aerodynamics of the hybrid wing body. That was centrally a hurdle but needed to be overcome to mature that concept.

The second hurdle and it is something we also look on in ERA was the structure. The traditional airplane that we fly on has a circular fuselage, basically, it’s a circle, it’s the most efficient shape that we could employ for the turbine wing. It’s easy to pressurize the circular fuselage.  But the hybrid wing body has a flat circular section and that’s very difficult to pressurize. And you need to pressurize it because we need the right environment to transport passengers.  This was a big problem, a big challenge to develop the structure necessary to meet the design requirements of the airplane. And so another area of research for hybrid wing body was this area known as PRSEUS –Pultruded Rod Stitched Efficient Unitized Structure.

It’s a concept that we've matured over a period of about 12 years and the last six years in the ERA we rapidly mature the concepts so that we're quite confident now that we have a structure that will work for that type of configuration.
 


Fay Collier is a graduate of Virginia Tech (Ph.D., 1988) and the Massachusetts Institute of Technology (M.B.A., 1997) where he participated as a NASA Sloan Fellow. He serves on numerous committees for the Agency, including the JPDO’s Environmental Working Group, and the AFRL Fixed Wing Executive Council, and was a contributor to the development of the National R & D Plan for Aeronautics. He is an advisor to many students across the country. Dr. Collier is an Associate Fellow of the AIAA.

He directs the planning and execution of NASA’s integrated system research project focused on the subsonic transport sector, working in partnership with Industry, FAA, AFRL and other government agencies. The research project is focused on development and integration of engine and airframe technologies that will enable dramatic improvements in noise, emissions, and performance characteristics of future subsonic aircraft operating in the air transportation system.