|Quoting Cingularity (Reply 21):|
it seems to me that you are eventually going to run out of room to fit one large engine under the wing
This assumes bypass ratio can only be increased with greater diameter fans. But the bypass ratio is the ratio of "mass flow rate (meansured in mass of air per unit of time)" of what goes around the core divided by what goes through the core. Widening the blade chord could increase the ratio as well, which negates needing a larger diameter. There is more about an engine's efficiency than just the bypass ratio.
|Quoting KC135TopBoom (Reply 16):|
The way I see it, the B-747-800i will be the last 4 engine passenger liner
You mean subsonic?
Assuming all variables in question were accounted for, I'm less inclined to believe a supersonic/hypersonic as a twin or even a quad set. Most transport designs I've seen have 4-6 engines, some even have over 20 (not rockets).
But yeah, I agree and think that most subsonic airliners from here on out may be twins; we've covered all thrust ranges, now it's just a matter of making them even more efficient to satisfy future requirements, customer and regulatory.