Friday 23rd June, 2017
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Breathe easy: nose shape was influenced by local climate

Breathe easy: nose shape was influenced by local climate

Some close-quarter flying has provided new insights into air­craft pollution.
US space agency-led scientists flew small, in­strumented, chase planes directly in the exhaust plume of a big jet to mea­sure the sorts of gases and particles being thrown out.
The data suggests air­craft burning a mix of avi­ation kerosene and biofuel could reduce their climate impact.
This would come from a substantial reduction in the production of the sooty particles that make contrails.
“Those soot particles serve as nuclei for water vapour in the very cold at­mosphere to condense on and for the artificial-look­ing linear contrails that we see when we look out the window,” explained Rich­ard Moore from NASA’s Langley Research Centre.
“You’ll then see those lines spread and form cirrus clouds that weren’t there before the plane flew through the airspace.
“We know these con­trails and cirrus clouds have a warming effect on the Earth’s climate, and it’s currently thought the warming effect associated with those clouds is more significant than all of the carbon dioxide emitted by aviation since the first powered flights began,” he told the Science In Action programme on the BBC World Service.
Dr. Moore’s team de­scribes its research in this week’s edition of the jour­nal Nature.
It involved flying a DC-8 at cruising speed and altitude - to try to simulate real-world con­ditions.
Much of the data pre­viously obtained in stud­ies is the result of ground tests, where a jet has been locked down and its en­gines throttled up. But the team wanted to see what really happened at 30,000 - 36,000ft (9,000 - 11,000m), where the air temperatures and pres­sures are much lower.
The DC-8’s engines were fed either Jet A fuel, one of the convention­al kerosenes used by the world’s airlines, or a 50-50 blend of Jet A and a fuel derived from the Cameli­na oilseed plant.
To be sure they were sampling only the exhaust plume from a particular engine, the chase planes - from Nasa, the German space agency (DLR), and the National Research Council of Canada - had to fly extremely close to the back of the DC-8, just 30-150m behind each en­gine and directly in the plume.
This called for military levels of skill and very good communication be­tween the pilots.
“It’s very exciting,” re­called co-worker Berna­dett Weinzierl from DLR and the University of Vi­enna.
“You have to imagine the plane in front is trav­elling at something like 200m/s and you are less than 100m behind. But in fact it’s quite safe to go very close or indeed very far away. It is in between where it is very dangerous: there is an area where the wave vortex is so strong it would destroy the follow­ing plane.”
What the team found was that the blended fuel, taking account of vary­ing flying conditions, was producing 50% less black carbon by number and up to 70% by mass.
“We were testing in what we call the soot-rich regime,” Prof Weinzi­erl said.
“Models tells us if you reduce the number con­centration of black carbon then you will reduce the number concentration of ice crystals. So this could be a way to mitigate the climate impacts of avia­tion,” she told BBC New

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