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Flying Green, What Does it Mean?
June 25, 2010



You're talking with your friends at a backyard barbecue. An airplane landing at a nearby airport passes overhead. It's so loud you can't hear a thing.

You look up at a blue sky and see that straight line of fluffy white following an airplane. Looks pretty, but contrails are being studied to see if they are harmful to the atmosphere.

You're waiting to board. You watch the fuel tanker servicing your airplane and find yourself wondering if the plane gets anywhere near the equivalent level of fuel efficiency as your new hybrid car.

Reducing noise, emissions and fuel consumption are the targets of NASA's work on green aviation. We're looking at ways to improve the airplanes and also the system in which they fly.

When might you fly in an airplane that's considered "green"?

Join our green aviation expert, Fay Collier, on Friday, June 25, 2010 at 3:00 p.m. ET for a chat about what NASA is doing to make air travel better.

More About Chat Expert Fay Collier
Fay is the project manager for NASA's Environmentally Responsible Aviation Project. He's leading a team of researchers who are testing everything from unusual aircraft designs that provide greater lift, to composite (nonmetallic) materials that reduce weight, to advanced combustor technologies that can reduce engine NOx emissions.

Fay graduated from Virginia Tech and the Massachusetts Institute of Technology.

Chat Transcript
(Moderator) Jason: Today's Chat is scheduled to begin at 3pm ET. Please begin to ask your questions by typing them into the box at the bottom of the screen and clicking the 'Ask' button on the right. We'll begin answering them in a few minutes. Thanks for your patience. I'd like to welcome Fay Collier today. He's an expert on green aviation here at NASA and will be fielding your questions over the next hour. Please go ahead and ask your questions.

Patrick: Good afternoon Fay! In your opinion, which U.S. based airline is the most environmentally friendly and which airline(s) need the most improving on? Thanks!

Fay: Honestly, this issue isn't something we're focused on. We're focusing on new aircraft designs which eventually the airlines will have available to you - the flying public.

Abishek: Aare prototype rockets considered to be green? Ecofriendly?

Fay: Our project is focused on environmentally friendly aircraft and the benefits to the flying public.

AkarshValsan: Sir, how can the sound of airplanes be reduced?

Fay: One way to do this is to build larger diameter turbofan engines and this slows down the fan and the jet and that results in an overall quieter jet engine. We also use devices called chevrons to modify the jet noise in such a way that it is quieter. Chevrons are devices that cause more mixing in the jet exhaust, therefore reducing noise levels.

AkarshValsan: Sir is 71decibel voice less for airplanes to fly?

Fay: Hi Arkash. I don't quite understand your question. Can you clarify?

(Moderator) Jason: Just a reminder to folks, today's topic is about making passenger carrying airplanes more environmentally friendly. Feel free to ask Fay your questions about greening aviation. Thanks for your patience as we work to answer your questions.

AkarshValsan: What is 2030-era aircraft?

Fay: It is an aircraft that burns 50 percent less fuel than today's aircraft. It also makes one-sixth of the noise of today's aircraft. That's what we're aiming for by then.

Malcolm: You mentioned the use of new open-rotor technology for use on some future aircraft concepts. How do these engines compare to the traditional turbofans employed on most commercial aircraft today?

Fay: They're about ten percent more fuel efficient on the plus side. On the minus side, they make a whole lot more noise. Our research is focused on reducing the noise of open-rotor engines.

Remy: When will the design of commercial planes change significantly for environmental purposes? And what will it look like? Fay: Commercial airplanes have been changing over the last 50 years to be more environmentally friendly - since 1975 they've really become about 90 percent more friendly and conventional aircraft are near their limit. The NASA research is focused on moving to a new technology curve and working designs where significant reductions in noise are possible with significant reductions in carbon emissions combined. *Combined* is the important part of this - it's even harder to achieve both of those goals simultaneously. That's the challenge.

Malcolm: How exactly do they enhance efficiency and cut back on fuel use?

Fay: For the airframe, we are exploring drag reduction techniques. Less drag means less fuel burned. There are many ways to do this - two ways we are exploring include a configuration change to something like a hybrid wing body (wing blends into the fuselage); another approach is laminar flow boundary layers, which have much less skin friction and drag. This technique is applicable to either current configurations or to future configurations. On the engine side, higher bypass ratio engines can be more fuel efficient (higher bypass ratio allows more air to move over the core; more air makes it more efficient). The challenge is reducing the weight and drag of the increased nacelle size (the nacelle is the covering of the engine - like the hood of a car engine). A second approach is the open rotor, on the engine side. That's the ultimate UHB engine. Its propulsive efficiency is close to the high limit. The open rotor has no nacelle; it consists of open fans.

(Moderator) Jason: We're working to get through all of the great questions you've asked us. Keep them coming! To submit your own question, please type it in the box at the bottom of the window and click the 'Ask' button on the right side of the box. Thanks for your patience as we answer your questions.

AkarshValsan: Sir, how does aircraft fuel affect the Earth?

Fay: Aircraft burn fuel; therefore they emit carbon dioxide into the atmosphere. However, the aircraft industry is responsible for about 2 percent of carbon emissions in total. Even so, the industry is taking a serious position in reducing their contribution.

StacyM: What are the incentives for industry to switch to these new designs of aircraft?

Fay: The cost of fuel has become the largest element of cost for operating an aircraft. Therefore, the industry is always exploring options for reducing fuel burned, thereby reducing their cost for fuel. When it comes to reducing noise, many airports have strict noise rules or, in some cases, a curfew after which planes can't fly. This has an economic cost. There are recent cases where aircraft manufacturers have given up fuel efficiency for reduced noise so that they can fly into and out of airports like Heathrow.

Jims: Will "green" airplanes will change their physical appearance in the next 20 to 20 years?

Fay: In the near future (next 10 years) airplanes will likely keep their current tube-and-wing shape. The NASA research is exploring other configurations which may enter the fleet in the 2025 and out timeframe.

AkarshValsan: Sir, what is SELECT? Was it introduced by Northop Grumman team?

Fay: We have info on SELECT here: www.nasa.gov/topics/aeronautics/features/future_airplanes.html

AkarshValsan: What is Subsonic Ultra Green Aircraft Research?

Fay: Same URL answer for this question as for SELECT.

AkarshValsan: What is the meaning of the line "A 71-decibel reduction below current Federal Aviation Administration noise standards, which aim to contain objectionable noise within airport boundaries".

Fay: The intent is to contain all objectionable noise from aircraft taking off and landing *within* airport boundaries.

StacyM: How environmentally hazardous are contrails? Is NASA developing technology to reduce the formation of contrails?

Fay: We don't really know for sure. The hazard is not as well known as carbon hazards and is an area that needs much more research. There are experimental methods which allow pilots to sense areas in the atmosphere that would be conducive to contrail formation. The pilot could then choose to avoid those areas by maneuvering the aircraft either above or below them. This could be a line of research that needs to be followed. Another approach would be to design the aircraft to always fly below about 27,000 feet where the formation of contrails is not an issue. There are research teams looking into these ideas.

(Moderator) Jason: Just a reminder to folks, today's topic is about making passenger carrying airplanes more environmentally friendly. Feel free to ask Fay your questions about greening aviation. Thanks for your patience as we work to answer your questions.

maria33: Looking at the open rotor technology with the exposed blades, even though they have the potential for reducing fuel consumption, is there a concern that these types of engines might be susceptible to bird strikes?

Fay: Yes. Other hazards include preventing a broken blade from passing through the cockpit, so there are technical challenges that will have to be addressed.

Abishek: Will an aircraft [ever] be [as] noiseless like a kite in the sky?

Fay: It will never be that quiet. But the goal is to reduce the noise to levels that blend in to typical airport background noise.

Timototje: What percentage of C02 will be reduced If bio-fuel is used in a plane instead of regular fuel?

Fay: Biofuel, when burned, will produce the same amount of carbon. The attraction is that while the feedstock is growing, carbon is removed from the atmosphere. The feedstock - like algae - is used to generate the biofuel. In that process, we surmise that the net carbon output is near zero. There are studies at places like MIT to more accurately determine the life cycle carbon output of this approach.

(Moderator) Jason: We're still working on answering all the questions you've asked. If you haven't seen yours yet, give us a few minutes to get to all of your questions. To submit your own question, please type it in the box at the bottom of the window and click the 'Ask' button on the right side of the box. Thanks for your patience as we answer your questions.

Clay: Are there any aircraft designs under consideration for the future that would be significantly more environmentally friendly, but are not conventional take-off vehicles. I am thinking of vertical take off vehicles...?

Fay: My project isn't focused toward vertical takeoff vehicles, but rather more conventional takeoff and landing passenger- and cargo-carrying vehicles.

KnightVision3D: Hi there fay, I just saw your reply on making a larger turbo fan, however I have been paying attention to what NASA and the military have been doing with scram jet technology, it does seem a very promising design, and while it's far from commercialisation (I would assume) would it be viable for passenger travel in the future? I am not sure of its environmental impact compared to a standard turbofan, but I would also assume that it is an appealing thought to be able to carry passengers (and lets dumb this down to paying customers) across the world in a few hours with such a design?

Fay: The scramjet is focused on hypersonic flight, where this project is focused on subsonic/transonic flight. Hypersonic flight for the flying public is a long ways off.

breenap33: Would these planes be more or less expensive than a typical plane? Would they cost more to produce?

Fay: Hard to tell. The economics right now have fuel costs playing a major role in the operation of passenger-carrying aircraft. So the trade would be efficiency gained against the cost of a new airplane and this is typically a business decision made by the airlines whenever new technology is introduced.

Remy: Is it just NASA doing research or is it multinational? I am from the UK, so do our scientists also help?

Fay: NASA, industry, other govt agencies are all working this problem. Including industry and govt in the UK. See "Greener by Design," by John Green for a UK treatise on this subject.

Izno: When will we begin seeing composite materials used commercially? I would imagine that lighter frames will have an effect on greening.

Fay: Current aircraft designs are on the order of about 50 percent composite, so you're actually seeing them in use already. It may be possible to increase the composite content of future aircraft, reducing the weight even further and cutting the fuel burn even more. NASA's approach in this regard is a technology known as PRSEUS. To save time, I recommend you search online for that acronym and you'll find lots of info.

maria33: Is there a plan in place on how we might incorporate these new configurations into the airspace? I would imagine there will be a transition phase where you still have the old tube and wing designs flying along with the hybrid wing designs.

Fay: We're working with NASA's Airspace Systems Program to study this very issue; the introduction of new vehicles into the airspace to identify where the challenges lie. So check back later! :)

(Moderator) Jason: We've got about ten minutes left in today's chat and time to get answers for a few more questions. Fay is working hard to get through all the questions in the queue and answer as many as possible. Thanks for your patience.

Erik_Richter: Does the research also include a better fuel non carbon based or any other kind of energy?

Fay: Yes. Our research currently includes exploring the benefits of biofuels.

Timototje: Will a 2030-era aircraft fly faster than the modern aircraft?

Fay: Not necessarily. Could actually fly a little bit slower, especially for *short-haul routes*. Studies have shown that reducing speed could save quite a bit of fuel.

(Moderator) Jason: And now for the last few questions for today's chat...

maria33: Was the hybrid wing design inspired at all by nature? i.e. the way geese fly in order to reduce drag?

Fay: Formation flight, as geese fly, is an area of interest and has been shown to potentially reduce fuel burn by as much as 20 percent (akin to the benefits that come from drafting behind a larger vehicle or Lance Armstrong). The challenge comes in how to do this safely. This approach might be useful for long-haul/transoceanic flights.

(Moderator) Jason: Thanks to everyone who posed questions today. We hope you found this to be very interesting and that you got some great answers. And a big thanks to Fay for taking some time to sit down with everyone and answer your questions! Have a great weekend.

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Image of a green field with a tree and a blue sky. There is a computer illustration of a hybrid wing flying in the sky.
Finding ways to reduce airplane noise, emissions and fuel consumption are NASA's goals for green aviation.
Image Credit: 
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Dr. Fayette Collier.
Dr. Fayette Collier.
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