Environmental Engineering Reference
In-Depth Information
aluminum and 10% steel were used in their construction. This reduction in
weight allows for 30% fuel saving along with associated benefits of avoided
GHG emissions. Compared to an Airbus A300-200 of similar size, the 787
is 30,000-40,000 lbs lighter and uses 20% less fuel in spite of having
45% more cargo space. The corresponding carbon emissions are also lower
by approximately 20%, thanks to lightweight carbon-reinforced plastic
composite construction.
As with conventional aircraft manufacture, numerous metal panels no
longer have to be painstakingly applied to the fuselage using rivets. Large
sections of it can instead be fabricated as single molding using composite
material. Maintenance costs are also about 30% less with composite
structures. These benefits, however, come at the cost of several inherent
drawbacksofcompositesasamaterialofconstruction.Plasticsburnreadily,
and burning poly(vinyl chloride) (PVC) and thermoset resins generally
releases copious amounts of noxious toxic fumes. Adequate fire retardancy
and other design features must be built-in to minimize this risk. Also, if
subjected to a sudden impact in a crash landing, composites can crack
and shatter rather than bend or dent (like malleable metals). Engineering
designs need to ensure the integrity of the frame against catastrophic failure
in such situations to ensure passenger safety. Concerns have been also
raised on the crash survivability of 787's novel composite-wing fuel tanks
(US General Accountability Office, 2011).
Ocean-going vessels have also benefited greatly from composite technology.
In small pleasure vessels and fishing boats, fiber-reinforced unsaturated
polyester (glass-reinforced polyester (GRP)) has been widely used. This
allows for a light and reliable craft that better resists environmental
corrosion relative to the wooden or metal crafts they replaced. However,
the benefit of energy saving when using composites are best illustrated in
larger vessels. The Visby-class stealth vessel used by the Swedish Navy is
a 600 ton vessel that relies heavily on plastic composite construction to
achieve good fuel efficiency, high speed, and low signature. Its hull is a
sandwich construct where the foam core of PVC is covered with stiff surface
laminates of carbon-fiber-reinforced poly(vinyl ester) composites (Burman
et al., 2007). A vessel using composite hulls will naturally be lighter by
approximately 50% compared to their metal counterpart and therefore less
expensive to operate.
