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      01-28-2020, 03:45 PM   #38
sethwas
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Quote:
Originally Posted by GtiGyver View Post
That's not why they were moved forward. At least not what from what I understand. It's more to do with the fact that the basic 737 design (dating back to mid 1960s) has its wings far closer to the ground than, say, the A320.
That's right - the efficiency gains have nothing to do with engine location - it's the engines themselves.
The more efficient engines have larger fans which have larger nacelles which simply don't fit on a plane with short legs. (the 757 has long legs because of this).
They can't get longer landing gear so the solution was to just move the engine forward until it reaches a point that it fits under the wing.

Of course at certain angles of attack (when the plane raises its nose which changes the airflow across the wing) this puts the top of the engine right in the airflow over the front of the wing which causes the nose to rise farther than the pilot had commanded. The MCAS adjusts trim in back to keep the nose still (again it's not the nose that's the issue, I'm just simplifying, but the airflow over the wing when nose is high). And we all know about MCAS.

The 777x is just making advancements to the 777 (specifically the ER model). Aside from the airline side benefits like modern interior/width and more seating (10 across), the benefit is again the engines and a redesigned wing which save in fuel cost (to compete with Airbus A350). Because the wingspan is so long, (it's a 787 wing that doesn't sweep as much which means its wider (you can picture a F14 wing or B1 wing sweep to get the idea)) it doesn't fit in standard gates and that would hurt sales since it limits customers, so they are able to fold (in about 20s) at the tips so it can be parked next to other planes.

Seth
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