Aviation experts said the energetic quality of lithium-ion can be a concern onboard aircraft. "One of the issues with lithium batteries is they get very hot," Freiwald said. "When they ignite, they can burn so hot that Halon 1301 won't extinguish a fire."
Automakers, many of whom use lithium-ion chemistries in hybrids and electric cars, typically operate their batteries with cooling systems. The Chevy Volt, for example, employs a fluid coolant that circulates through 1mm thick channels machined into 144 metal plates sitting between the battery's cells. Other automakers have employed air cooling on hybrids.
Even with cooling, however, lithium-ion automotive batteries have been known to have problems on rare occasions. In 2011, a fire started in a Chevy Volt weeks after government crash testing, causing a ripple of concern. "The chemistry is edgy," Donald Sadoway of MIT wrote in an email to Design News after the incident. "The electrolyte is an organic fluid that is flammable, highly volatile at even moderately elevated temperature and in the presence of metallic lithium, which can form on the negative electrode at high charging rates."
Although it's not known whether the Dreamliner employs battery cooling systems, its batteries are smaller than those of plug-in hybrid cars. A National Transportation Board (NTSB) examination of an auxiliary power battery unit from the JAL Boeing 787 that caught fire in Boston's Logan Airport on January 7 showed that it measures 19 inches x 13 inches x 10 inches and weighs just 63 pounds. In contrast, electric vehicle batteries can weigh more than 400 pounds.
Freiwald said he doubts the two reported fuel leaks are related to the overheating incidents. Those were more likely to have been caused by human error, he said.
Experts who spoke with Design News emphasized that the cause of the problems isn't fully understood yet, and that such incidents need to be put into perspective. "None of these were catastrophic failures," Dietz told us. "The engineering systems provided an alert to the failures and action was taken. There should be some solace in that."
Seems like the batteries are the culprit, but as of now no one knows why. They've x-rayed the batteries, put them through CT scans, disassembled them and checked the associated wiring bundles and battery management circuit boards. As of now, regulators have said that overcharging doesn't seem to be the issue, but we don't know much more than that. We'll have more coverage on this coming up.
@Ervin- I'm a pilot and engineer, and your aerdynamic theory is more or less correct. As you state, planes don't fly by converting PE to KE by falling. But without gravity there won't be a lift vector; a subtle but important distinction. BTW an airliner is a surprisingly efficient glider...I'd guess a 20:1 glide ratio is typical.
Airflow over the top contour of the wing is critical while the underside of the wing less so. (Next time you see a plane, look at the designed-in smoothness of the top of the wing compared to the bottom). Frost, insect contamination, or a paint step can drastically or completely destroy lift if it "trips" the laminar flow over the top of the wing. So will going too fast if airflow over the top of the wing accelerates to supersonic, called a "Mach stall". (The 777 and other newer planes use a "supercritical" airfoil that allows it).
"The thinner the air the faster you need to go to maintain the same amount of lift"..this is called Indicated Airspeed and True Airspeed. For a constant amount of lift, IAS will be the same at sea level or 40,000 feet. As the term implies, it's the number of air molecules the plane encouters per unit of time. That produces a ram pressure that the pilot sees on the airspeed indicator. But, in thinner air the plane can go faster before it encounters the same ram pressure and drag. IAS to TAS is a pretty complicated equation. A 767 at cruise altitude may have a TAS of 500 knots (= groundspeed with no wind) while IAS is 325 knots.
Airliners are one of the most high-tech machines you will encounter in daily life. It's amazing they perform so reliably and safely. The 4th anniversary of US passenger airlines being fatality-free is a few weeks away. About 3 billion people carried on 40 million flights!
@Jennifer Campbell: Yes, I remember reading about the 787 in Design News back when I was in college. It was called the 7E7 then, and it was supposed to be the next big thing. Over the past few years, the news has been a lot less positive.
Another major aerospace project that got lots of "gee-whiz" press around that time, the Joint Strike Fighter, has also met with lots of delays, cost overruns, and technical problems. Now it seems more and more likely that the Department of Defense will pull the plug on the whole program.
Speaking as an outsider: what's going on with the U.S. aerospace industry? Are we just not capable of executing these kinds of big projects anymore? Are the projects just too big these days (the mutually-conflicting requirements for the Joint Strike Fighter come to mind)? Or has the development process always been this messy?
Given that the highest-profile civilian and military aircraft projects of the last decade have wound up scandalously late, over-budget, over-weight, and full of bugs, it almost seems like there is a systemic problem in the industry. But maybe this is just "normal," and I shouldn't have been naive enough to believe the hype in the first place. Or maybe things aren't as bad as they seem.
Any industry insiders care to weigh in on this quesion?
You are right I was thinking more in line with 777 and 787 since they are still flying.
Some basic info on how a plane flies. This is a physicist's view (so most likely incorrect). You transfer enough kinetic energy to potential energy (exhaust of the engine is kinetic, plane flying is potential energy) and the object flies. The reason the object flies is because the air flowing around the wing provides lift hence the plane does not convert the potential energy to kinetic by falling. The downside and the reason engines need to remain on during flight is drag on the plane. Drag (air friction) slows down the plane converting some of the potential energy into heat. The engine has to burn fuel and input more energy into the system to insure we don't loose enough potential energy to loose altitude. As far as thin or thick air that only effects drag and efficiency of the airplane. The thinner the air the faster you need to go to maintain the same amount of lift or more wing span (seeing that wingspan is fixed we tend to make airplanes go faster). Also keep in mind that these engines output 240-330 kN of force. That force is enough to suspend 60 tons of mass. Now yes an airplane is far greater than 60 tons I think Dreamliner tops at 500. Keep in mind that we only have to defeat drag to make it fly we don't have to supply enough force to lift it straight up.
This is a very interesting article. Great information Charles. I'm sure a company such as Boeing has a procedure similar to FEMA (Failure Mode Effect Analysis ). I would love to see the failure mode "tree" for the lithium-ion battery application. Of course, the FEMA does NOT take the place of testing, bench and flight but it can be an indicator of "things to come" realtive to failure. In looking at the possible failure modes, severity, probability and detctability are given a number to quantify and pritorize each possible occurance. From these multiples, rankings of high, moderate and low are addressed. I have not idea if Boeing does this but if so, it would be very interesting to see.
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There’s a good chance that a few of the things mentioned here won't fully come to fruition in 2015 but rather much later down the line. However, as Malcolm X once said, "The future belongs to those who prepare for it today."
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