Design Con 2015

Boeing 787 battery/charging system solutions---Good design or not?

-March 16, 2013

Boeing officials have detailed their proposed fixes for the lithium-ion batteries aboard its 787 planes, and the changes include better insulation between the eight cells in the battery, gentler charging to minimize stress and a new titanium venting system.

But to prevent any new fire and smoke episodes like the ones that have grounded its fleet, Boeing proposed that the battery itself will be sealed inside a steel box that would serve as the last safety rampart if everything else fails.

As design engineers, you and I know that the solution is to prevent failure, not contain smoke and fire after the fact. At least Boeing designers have made an attempt at modifying the charging system. It’s difficult to zero in on a solution when investigators have not determined the root cause of a problem that has grounded all 50 Dreamliners worldwide since January. So Boeing said it can assure federal authorities, airlines and the public that its flagship aircraft is safe, and there is no chance of a battery fire.

First let’s look at the way an aircraft power management system works and we ask readers to give us their comments and possible solutions.

The following is complements of Boeing Corporation:

Airplane power basics                  
On an airplane, the electrical system produces, controls and distributes power to all the other systems that need it — flight deck displays, flight controls, in-flight entertainment and more. It’s much like the electrical system in your house, which carries electricity throughout the rooms to power your lights, television and so forth.

Unlike your house, though, the airplane generates electricity as it flies. Airplanes don’t fly on battery power. Generators on the engines make power in flight.

The traditional airplane: electrical and pneumatic systems
On a traditional airplane, power is extracted from the engines in two ways to power other airplane systems:

  • Generators driven by the engines create electricity.
  • A pneumatic system “bleeds” air off the engines to power other systems (e.g., hydraulics).

Modern jet engines are very efficient, but removing that high-energy air robs them of some energy. A pneumatic system means that the engines produce less thrust, so they must be bigger, work harder and use more fuel. The system also means more weight, fuel burn and maintenance due to the heavy ducts and equipment needed to manage that hot air.

 


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