Originally Posted by
ruddman
Rather then converting older airframes into something modern, why not design something that flies faster? At the end of the day, that’s what we we all want.
How did engineers go from designing aircraft with higher speeds like a 727 M80-84 to the current dawdling along .76-77 on CI of nearly nought 737/A320’s?
Surely the technology can design something to fly 0.86-0.88 with ease. Costs a little more but it evens out.
Actually, pretty much all the aircraft
designed to be medium to long range have cruise Mach numbers over 0.80. 767/777/787 are in the 0.80 to 0.84 ranger - the 747-400 and -8 are in the 0.82-0.86 range (I believe the A380 is similar to the 747).
The 737/A320 series were designed for short haul - so another 0.02 Mach wasn't much of a time difference. But with the newer, more powerful and more fuel efficient engines the 737/A320 are being increasingly used for medium range flights - where the speed difference is becoming meaningful.
The other things that's changed is the new generation of very high bypass engines. With a JT8D, slowing down didn't save much fuel - no longer true with the very high bypass engines. Going slower does make a meaningful difference in fuel burn, so there is more of a carrot for going slower.
As another poster noted, the Boeing Sonic Cruiser was going to be fast - Mach 0.94 - 0.97 range, with operating costs (per seat mile) similar to a 767. Initially the airlines liked the idea, but after 9/11, they became increasingly concerned about costs, so instead of going 15% faster with the same fuel burn, they got the 787 with ~20% better fuel burn at the same speed.
Oh, and while the Sonic Cruiser's engines were going to mounted far aft - they were still going to be mounted under the wings...