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How nickel contributes to more sustainable air transportation
By Carroll McCormick
Nickel Magazine, March 2008 -- Airlines are constantly striving to burn
less fuel. Doing so both reduces costs (fuel consumption accounted for 26% of airlines’ operating expenses
globally in 2006) and lessens the impact of air travel on the environment (the industry remains a major
emitter of nitrous oxide and carbon dioxide).
In response, aircraft manufacturers are building more fuel-efficient planes. Fast and flash designs, such
as the Sonic Cruiser concept The Boeing Company unveiled in 2001 and dropped just a year later, are being
replaced by aircraft that are slower but more economical. There will likely never be another Concorde.
The fuel efficiency of aircraft designs has improved by 70% in the past 40 years, and 20% of those
improvements were achieved in the past decade. Since the 1960s, carbon monoxide levels have dropped by 50%,
and unburned hydrocarbons and smoke, by around 90%. The International Air Transport Association (IATA)
reports that, by 2020, nitrogen oxide emissions could be reduced by 80% and fuel efficiency improved by 25%
-- all as a result of investing in new aircraft. Combined, these improvements should eliminate 345 million
tonnes of carbon dioxide emissions during the next 13 years.
Aircraft manufacturers have increased fuel efficiency by improving aerodynamics, particularly in the area
of winglets, those vertical appendages at the ends of wings that, among other things, reduce drag. Better
engine design has also played a role, an example being the use of higher-temperature nickel alloys to raise
operating temperatures.
But the most striking gains are being made by lowering the weight of airframes. This is achieved by
replacing aluminum with ever-increasing amounts of composite materials: layers of carbon fibre and other
types of cloth, impregnated with epoxy resin. Three aircraft illustrate the trend:
When the Boeing 777 first flew in 1994, it was 9% composite by weight (another source cites 12%).
Composites accounted for about 23% of the airframe weight of the Airbus A-380, which made its maiden flight
in 2005. Boeing has pushed that to 50% for its newest commercial airplane, the 787, also known as the
Dreamliner, which will make its maiden flight in 2009.
The Dreamliner is the first commercial airplane with an airframe completely made of carbon fibre
composites rather than aluminum. Such a high percentage of composites, coupled with improved engine design
and aerodynamics, will make the Dreamliner 20% more fuel efficient than the B-767 or Airbus A330, according
to Boeing.
Composite construction depends on a 36% nickel alloy called Invar, developed by Charles-Édouard Guillaume
(1861-1938) in the late 19th century. Its most important property, a near-zero coefficient of thermal
expansion, makes it the material of choice for the construction of molds, or mandrels, on which composite
parts are laid up and then cured in autoclaves at temperatures as high as 375-425 °C. Invar’s exceptional
stability ensures composite parts maintain precise tolerances of just fractions of a millimetre while being
cured.
Boeing is using composites for the skin of the Dreamliner (fuselage, wings and tail, and other structures
such as the wing box). For example, one of the fuselage sections, which measures 6.7 metres (m) long and 5.8
m wide, is made by laying down epoxy-soaked carbon fibre tape on a rotating mandrel made from smaller,
interlocking mandrels. A one-piece fuselage section eliminates 1,500 aluminum sheets and 40,000-50,000
fasteners.
The wing span of the 787-3 Dreamliner version is 52 m. The wing skins are made of composite material laid
up on two different Invar mandrels, one of which is 31 m long and weighs 36 tonnes.
Altogether the use of composites means the Dreamliner weighs 4,536 kilograms less than it would have had
Boeing used aluminum.
Both the A-380 and Dreamliner are super-efficient in terms of fuel consumption per passenger mile, but
they also contribute to the efficient use of airports while reducing local pollution. The A-380, with 555
seats for a typical configuration and a range of 15,000 kilometres, fits the hub-and-spoke model of air
transport wherein large planes fly between central airports while smaller planes ferry passengers to and from
regional ones. One way to reduce the congestion and delays that plague large airports is to fly fewer planes
carrying more passengers.
The Dreamliner has a range of 4,650-5,650 km for the 787-3 version, 14,200-15,200 km for the 787-8, and
14,800-15,750 km for the 787-9. It can carry as many as 290 passengers on long-haul flights and as many as
330 on shorter routes. Since the 787 is a mid-sized plane (unlike the A-380, which requires wider runways and
taxi ways, oversized gates, and special ground handling equipment), it can reduce airport congestion by
avoiding hubs.
By late January 2008, Boeing had received orders for 857 of the Dreamliner from 56 customers, making it
the world’s fastest-selling commercial airplane, according to the company.
Carroll McCormick is a Montreal-based freelance writer.
Photos: The Boeing Company
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