|Quoting Sh0rtybr0wn (Reply 34):|
Quoting Flipdewaf (Reply 26):
I expect it to go slightly slower than the 737NG.
What? No Chance.
Why not? On short/medium sectors cruise speed has a fairly small effect on sector time but a quite significant effect on fuel burn. You could probably get ~4% fuel burn improvement for a 2% drop in cruise speed, which would work out to about 4 minutes on a typical flight.
|Quoting HUbsnotDubs (Reply 35):|
Why not mount the engines on top of the wing?
It can be done (Honda Jet) but maintenance is more difficult and the aerodynamics are extremely difficult. Nacelle/wing interaction is a difficult problem when the engine is under the wing on the high pressure side. It's even more difficult when you're dealing with the low pressure flow above the wing.
|Quoting Osiris30 (Reply 37):|
Quoting Tdscanuck (Reply 31):
It's not a given that composites will scale down to the 737 size in all applications. Wings almost certainly, but fuselage skins is a little less clear. The skin gauge could become so small that you'd bump up against durability issues.
That's the whole reason why composites are likely to be a player in the short-haul, high-cycle world.. they 'mature' more gracefully than AL (supposedly).
I think you're thinking fatigue, and you're right as far as that goes. I was thinking durability in terms of ramp rash. A 0.005 CFRP skin might be fine for the flight loading but you could probably poke a pencil through it if you weren't careful.
|Quoting Flipdewaf (Reply 38):|
Quoting Sh0rtybr0wn (Reply 34):
I don't think the fan diameter will be much larger than it is now
Of course it will.
I don't think a large fan will help, particularly because of the short sectors it will likely do.
About the only way you can increase engine effiency in any major way is:
1) Increase temperature (pressure ratio): strongly limited by materials
2) Improve turbine efficiency: GTF
3) Increase bypass ratio: Bigger fan and/or UDF
1 is very limited right now and 2 is just starting to be tested at the right thrust ratings (and has a bigger fan anyway). So if you really want to improve fuel burn you end up with 2 or 3, which leads to a bigger fan.
|Quoting Cloudy (Reply 44):|
With a composite airframe, the fuselage skin is not as thick. With a plane only a little wider than the A320, one could easily have 2-2-2 seating
Except it's not the skin thickness that's the problem, it's the frame thickness, and that doesn't go down very much at all when you switch materials.