Books written by Ray Sullivan

Tuesday, 5 February 2013

The Lithium Ion Flying Club Cunundrum

There's no doubt that Lithium Ion batteries have revolutionised our use of electronic equipment.  For one thing, they have liberated our cameras, with the batteries recharging quickly and efficiently.  No more dragging packets of replacement batteries on every trip.

And the same goes for for other electronic devices.  My Kindle runs for a month of intermittent use without the need for a recharge in-between; in fact, in some ways the extended period between needing a charge can be viewed as a drawback as it lulls you into forgetting to check the charge is up to speed before you set off on that long flight/train journey/bus ride/wait at the dentist.

It allows the tablet computers we all use to pack so much punch into each and every day and it powers a multitude of other devices in a similar way.  Even  mundane items like cordless hedge trimmers and power drills use the technology - in fact I have both of these devices manufactured by Bosch and they both use the same battery so if I'm running low I can borrow off the other device to complete the job.

And aircraft are getting in on the act.  It's hardly surprising as there is a move towards fly-by-wire technology and an increasing dependence on electrical power.  Of course the engines drive generators when they are running in the same way as they power hydraulic pumps.  But like the hydraulic systems, which utilise physical energy reserves called accumulators to power them in the absence of engine power, so do the electrical systems.

On the Boeing Dreamliner aircraft it has two Lithium Ion batteries installed as part of its electrical installation. The methodology is increasingly popular with the Airbus A350, due to be launched next year, will also use this technology.  Other models are being looked at with a view to retro-fit them with Lithium Ion batteries as they are generally a lot lighter than conventional alternatives.

That isn't to say that the Lithium Ion batteries are light, though.  We tend to think of the batteries used in our pocket cameras and Kindle eReaders when we talk about Lithium Ion batteries, although the units in my Bosch power drill and hedge trimmer are fist sized and would make the archetypal blunt instrument as a handy club in a defensive situation.  But the batteries used in the Dreamliner weigh in at 63 pounds, approximately 28.5 Kg, about the baggage allowance for a transatlantic trip.  However, they are lighter than the equivalent batteries using other technologies.

But there is a problem.  Lithium Ion batteries are known to overheat and burn, especially if stored incorrectly or subjected to damage.  And when I say burn, I mean they reach the melting point of aluminium pretty quickly, which could be a bit worrying as that is what the Dreamliner is clothed in, like most aircraft.  The Boeing designers knew this and believed they had designed in suitable protections to prevent the batteries overheating - it looks like they may not have achieved that fully in hindsight.

Now it turns out that the aviation authorities have been concerned about the risk to aircraft, particularly passenger aircraft, from carrying Lithium Ion batteries and set a rule, ironically on the day that the Dreamliner was cleared for commercial use, that  limited the maximum weight of Lithium Ion batteries that could be transported in a passenger aircraft to 11 pounds.  So, technically, the Dreamliner couldn't technically carry the batteries it was designed to be used with, as cargo anyway.

However it is clear that the regulatory bodies involved realised that the rules were unrealistic, given the direction of the technology and the impact their rule could have on major manufacturers such as Boeing.  I'm sure there was a little industry leaning going on as well, it's what  makes commerce go round.  The point was made that if an aircraft that depended on one of these batteries was grounded due to a failure then allowing the batteries to be shipped on passenger aircraft would allow a more rapid recovery of the airframe.  Mitigation was alluded to by reference to very stringent extra checks carried out on these types of batteries, however the point that the checks were related to performance, not safety, doesn't appear to have made as much impact as maybe it should have.

Anyway, almost as soon as the weight restriction was varied upwards to allow for Dreamliner sized batteries to be flown as cargo on passenger planes that the current grounding of Dreamliner aircraft took place, due to concerns about their battery safety.

So we are left with the conundrum that when the Dreamliner was approved for flight, the batteries it used were effectively outlawed, but once the batteries were accepted, the aircraft was grounded because of the batteries it used.


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