This article explains the various elements of the Boeing QTD2 noise reduction program on the 77W run during 2005.
Now the question is this:
When Boeing proposed the 7E7, it was a true 8Y plane. They drew it with engine chevrons, but they did not know the impact of those chevrons yet as the testing was not yet done on the flying test aircraft, and wouldn't be for some time.
Once Boeing completed this test program in 2005, they learned that chevrons + engine lining reduced noise so much that they could reduce the amount of insulation used in the fuselage to protect passengers from in flight engine noise. They determined it would reduce dB levels ahead of the engine by as much as 15 and behind the engines of 4-6 dB. They estimated 800 pounds of insulation could be removed.
It was not too long after the QTD2 tests that Boeing was able to offer the 787 at 9Y due to a suprise ability to thin out the 787 insulation. IIRC, it was attributed to the lack of condensation on the CFRP, but I now wonder if that is only part of the story, or possibly a ruse to obscure the genius of the real reason for most of the savings.
It seems to follow that the QTD2 program allowed Boeing to thin out the insulation on the jet by 600-800 pounds which was enough to gain 2" and widen the cabin, allowing for 9Y seating.
Once 9Y seating was offered, sales of the 787 took off and the A350, as proposed at that time, was no longer competitive. It was so dramatic a change, that Airbus was forced to redesign the A350 at great expense, billions of dollars, and offer an XWB version that can also fit 9Y seating.
So it would seem that the use of CFRP for weight and manufacturing reasons, and the introduction of noise abatement measures on the engines, had positive unintended consequences for Boeing, so much so that they allowed Boeing to redefine the CASM of the aircraft and send Airbus into a spiral of Leahy spin followed by a costly redesign that they are still struggling to recover from.
"We see this technology making a big difference on the 787, the 747 Advanced, the next-generation single-aisle airplane, and all new generations of aircraft from here forward," says Walt Gillette, Boeing Commercial Airplanes vice president for 787 Engineering, Manufacturing, and Partner Alignment.
The impact on the 787 truly does seem to be dramatic, but not just in the ways the engineers first imagined...