If you take
a long international flight ten years from now, there's a good chance the
airliner carrying you will be made as much out of plastic as metal.
But not just any plastic. Tomorrow's airliners will make extensive use of advanced
carbon-fiber composite materials, much stronger and lighter than the
aluminum parts they replace.
The entire
fuselage skin of Boeing's new 787 twin-engined widebody jet, due to enter service in 2008, will
consist of composites. The skin and spars of the 787's wings are made of
composite material too, though the ribs that shape and stiffen the wing from
front to back are aluminum.
"We looked
at how every part of the aircraft was [stress] loaded, and we chose
the right part for every given application," said Tom Cogan, chief project
engineer on the Boeing 787. For instance, Boeing used titanium for the large
fittings joining the 787's wings to its fuselage, because "it's very light and
it does very well in a highly loaded situation."
Today's
airliners make use of composite materials, but not to the degree that the 787
and its future rival the Airbus
A350 XWB will. Composite materials make up "roughly 50 percent" of the 787,
said Cogan. The A350 XWB, which won't enter service until 2013, will
be more
than 60 percent composite.
Airbus was
the first manufacturer to use composite materials for load-bearing parts and
flight control surfaces in airliners, but Boeing chose to use composites for
the 777's floor beams when designing the big twinjet in the 1990s.
Composite
materials confer several major design advantages. Apart from being very light
and very strong, they don't corrode and they aren't subject to metal fatigue.
The
earliest-built 777s have recently undergone their first "heavy checks"--major structural inspections
during which the aircraft essentially were taken apart, examined extremely
thoroughly and rebuilt-- and their floor beams were "pristine," said Cogan. "We
haven't sold a single spare floor beam."
This is
great news for airlines. In the course of normal operations their jets are
subject to extremes of heat and cold and--particularly on transoceanic flights--fly
for long periods in moist, salt-laden, corrosive air.
Employing
composites to a greater degree will make airliners more reliable, letting
airlines fly them more while keeping maintenance costs down. It will also make
airliners lighter, reducing fuel costs and allowing them to carry more
passengers and cargo--or fly longer distances--at their maximum takeoff weights.
Tomorrow's
largely composite airliners also will improve the flying experience for
passengers.
Making
airliner fuselages out of composites banishes the fear of metal fatigue and
corrosion that has constrained designers until now. Passenger-cabin air can be
moister and kept at higher pressure, so passengers feel less dehydrated and
don't find themselves gasping for breath.
Breathing in today's
jets is like breathing at the top of an 8,500-foot mountain. But the 787 will have a 6,000-foot cabin
altitude, making it much easier to breathe.
Passenger
windows can be much larger, too. Each 787 window is some 30 percent bigger than
today's cabin windows and window-height difference is particularly noticeable.
The 787's windows will extend above seatback height, so passengers sitting
between the aisles can look across and see outside.
"We like to
say every seat is a window seat," said Cogan.
Building on
these advantages, Boeing has adopted other technologies to make passengers feel
comfortable on 787s.
It is using
LED lighting to create a cabin lighting environment that can vary with the time
of day from a restful pastel-colored glow at dawn and dusk to brighter daytime
lighting and a subdued midnight-blue shade in late evening.
Additionally,
not only does the 787 cabin environmental control
system employ HEPA filters to keep the air free of particles as small as
viruses, but Boeing also has incorporated a gaseous air purification system to scrub
out even smaller molecules, to keep the air aroma-free.
"Actually,
the air onboard will be cleaner than the outside air," said Cogan.
Since
outside air at high altitude is very dry but people generate humidity, Boeing
787 pilots will tell the aircraft's computers how many people are on board and
the computers will manage cabin humidity levels by drawing in greater or lesser
amounts of air from outside. The 787 won't need cabin humidifiers.
Passengers
won't notice all the advanced technologies used in the 787 and the A350 XWB.
But one they will notice is the use of dynamic load alleviation to reduce gust
forces.
Sensors in
the aircraft's nose will sense lateral and vertical wind gusts as it begins to
encounter them, allowing its flight computers instantly to move the aircraft's
flight control surfaces to reduce the loads. This means the aircraft can have a
lighter design structure--but more importantly for passengers, the flight will
feel less bumpy.
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