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"I thought carbon-fiber composites were already being used in existing large commercial aircraft, specifically in the wings.... and even more extensively used in smaller aircraft."

Yes, carbon fiber has been used for control surfaces on large aircraft and more structural applications on smaller planes.

Bill Lear (of "Lear Jet" fame) discovered that carbon fiber composits tended to catch on fire when electrical current was passed through them. It sorta put the kabosh on carbon fiber for his company.

Now the entire fuselage and wing structure of the 787 is to be made from it. I just hope that they have learned from the experience of others in the industry.

I see a lot of talk of the use of composite structures here. Composites have been used for years, and is a fairly mature technology. That they’re going to be 50% (by weight) of the 787 is a major step up, but Boeing sees it as an evolutionary step.

What isn’t being talked about much, but is revolutionary IMO, is the fact that the 787 is basically an “electric jet”. Traditionally, just about everything on an airliner is powered by engine bleed air—vast amounts of ~70 PSI 350 deg+ air pulled from whatever stage of the engine’s compressor. This air is directed all over the plane in what’s known as the pneumatic system. This air is not available to propel the aircraft.

The 787 is doing away with almost all that, and is switching to electrical powered devices. This is no small task, as evidenced by the 787 having over twice the electrical generating capacity of the much-larger A380. I saw some numbers in Aviation Week magazine and was astounded to read it takes several hundred horsepower to simply pressurize the aircraft at cruise. Boeing feels pneumatic technology (not very efficient and over 50 years old) has progressed as far as it will go, but electrical technology (motors, motor controllers, etc) have plenty of room to evolve in size, weight and efficiency.

While the B787 and the A350 will use the same engine cores and technology, the 350 will use traditional bleed air while the 787’s engines will have huge, 500+ KVA generators on them. Anyways, something to chew on.