It's a simple goal, really. A silent airplane that sends no carbon into the atmosphere.
Getting there is the quest on which NASA embarked years ago and figures to continue working on into mid-century. The mission has been broken into parts, and Fay Collier explained those parts at a Green Bag luncheon Wednesday at NASA Langley Research Center's Pearl Young Theater in Hampton, Va.
"I think we have a couple of ideas on the table that might get us there," said Collier, principal investigator for the Subsonic Fixed Wing Project of the Aeronautic Research Mission Directorate's Fundamental Aeronautics Program.
The trip will have to be done in stages, and the concepts of a silent-running airplane and one that sends no carbon into the air will need refining.
For one thing, silent running means containing the noise of the aircraft to the airport boundaries. "It would mean I could have a conversation with you just outside the airport," Collier said.
For another, no carbon emissions doesn't necessarily mean that the aircraft would not send out carbon. Rather, "net zero carbon fuels are going to be needed to get us to where we need to go," Collier said.
Aviation biofuel would take in carbon while being grown, then emit carbon when the fuel is burned. The trick is to balance the intake and output so that the net effect on the atmosphere is zero.
Hydrogen also could be part of the future of fuel.
Collier outlined three stages to coming close to that goal. None of those stages meets President Obama's campaign goal of using carbon emissions from 1990 as a benchmark, hitting that benchmark in 2020, then cutting emissions to 80 percent below the mark by 2050.
"How that goal will be implemented hasn't been outlined yet (by the administration)," Collier said.
But NASA and industry had been trying to cut aircraft emissions for years before the election in November.
The three stages of the process are "N-plus-1," "N-plus-2" and "N-plus-3." The first, N-plus-1, involves a "tube-and-wing" aircraft with design principles similar to those of the aircraft of today, but with enough technological and structural improvements to cut fuel consumption by a third below that of a selected standard: a Boeing 737 with 162 passengers on a flight of 2,940 nautical miles.
Those improvements would include a 15 percent structural weight reduction, 1 percent lower drag and 25 percent reduction in cooling flow, among others.
"We probably have a good five or six years available to us to make a technology sweep forward to where the industry can pick it up," Collier said, fixing the date at which the improvements can be adopted to 2020.
Then there is "N-plus-2," in which design modifications show airplanes that are hybrids: less fuselage and much more wing. Continued technological improvements and weight and flow reductions would produce aircraft that burn 40 percent less fuel and emit 75 percent less carbon with a prototype available by 2020.
No one improvement will optimize the results.
"A 70 percent better fuel burn? Is that even possible?" Collier said. "Well, we're starting to get some results back that indicate that it is possible. But it has to be done in concert with operational improvements on the aircraft. It's not just technology. Operational improvements have to be factored in.
The final step, N-plus-3, has Collier most excited.
"It's wide open," he said. "We're just now getting our arms around it."
Chances are that it will be a blended wing body, rather than a "tube and wing" airplane.
"I inherited this four years ago," Collier said of his job with the program. "I was not a blended wing body guy. But it didn't take me long to figure out that it is a good idea."
How good is yet to be proved.
"If we're going to lower noise and lower fuel burn, we've got to go to something different from tube and wing," Collier said. "I'm buying it, and I'm going to pursue it and I'm going to prove it, one way or the other. It's either going to work or it's not, and we're going to prove it. That's our strategy."
It's also the strategy of at least four industry and academic teams. NASA is investing time and money in all of the stages en route to a silent, carbonless airplane.
"I'm investing in those three concepts, proportionally," Collier said. "N-plus-1, maybe 35 percent. N-plus-3 is emerging, a small amount, maybe 10 percent. That leaves about 55 percent for the middle."
The ideas are ambitious, but then again, so are the goals.
"I've got many stakeholders and they want it all," Collier said. "If anybody can do it, NASA can do it."
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