Karela Fry

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Waking from a dream(liner)

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Harper’s carries an interesting piece on three things which make a dreamliner unsafe:

A primary Dreamliner selling point is its 20 percent savings on fuel compared with the plane it replaces, the 767. Since today’s jet engines burn fuel at more or less the same rate, efficiency depends on reducing the weight of the plane, and “composite materials” (i.e., plastic) are an increasingly popular means to this end. Even though plastic has yet to achieve the same predictability and reliability as metal, the Dreamliner team opted to make greater use of plastic than ever before in an airliner, even employing it for the load-bearing joint that connects the wings to the fuselage, which bears more stress than any other part of the plane. Sure enough, in final static tests, the wing failed and had to be stiffened, at great cost. Boeing’s risky choice prompted one aerospace structural engineer to remark, “Friends don’t let friends fly in plastic airplanes.”

Boeing’s other major weight-reduction initiative was to make the 787 an “all-electric” airplane, which meant that rather than having hydraulic motors drive control surfaces on the wings and tail, along with other components, they would be controlled by large generators backed up by powerful batteries — the lighter the better. Lithium-ion batteries are indeed extremely powerful for their weight, but they are also extremely dangerous, as lithium is notorious for burning with an intense, unquenchable heat. Model-airplane enthusiasts have learned the wisdom of keeping their lithium batteries in an asbestos box when recharging them; too many have seen homes and garages go up in smoke. Nevertheless, that was the route Boeing took. The overheating batteries that prompted the global grounding back in January were a harsh reminder of the risk this choice entailed.

Boeing also made the copper wire that distributes power around a plane, another major contributor to overall weight, as thin as possible. The thinner the wire, however, the higher the voltage at which current must flow along it. As a result, the 787 is laced with miles of ultrathin copper wire, bearing current that runs at 230 volts AC and 270 volts DC, which would require only a scratch in the insulation to spark a fire (a likely cause of the Heathrow blaze). A fire is especially bad news in a plastic plane, since not only do the flames cause far more damage (the design-temperature limits of composite materials are half those of aluminum), but the fumes are highly toxic to passengers.


Written by Arhopala Bazaloides

July 21, 2013 at 11:52 am

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