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It's pretty shocking how giant that engine is. Is that really how big they are on the biggest jumbo jets? Or is it for one of those super giant planes that carr

It's pretty shocking how giant that engine is. Is that really how big they are on the biggest jumbo jets? Or is it for one of those super giant planes that carry tanks for the military or whatever?

_ph_ 3y ago
The 747 actually had rather small engines. First of all, it had 4 and they were older-style with low bypass ratio. The 777 isn't that far from 747 capacity, but only sports 2 gigantic engines, they not only need to be more powerful, but have high bypass ratios to improve efficiency. They are even wider than the body of a 737.
masklinn 3y ago
It’s pretty normal for modern turbofans to look huge, they’re so-called “high bypass” turbofans: the power is provided by a turboreactor-ish core, but that drives a large ducted fan which pushes air through, most of that air bypasses the core (hence high-bypass). A model turbofan might have a bypass ratio of 10, aka for every kilo of air going through the core 10 are pushed around it by the fan. That applies to all airliners e.g. the reason for the 737 max’s issues is that the plane is very low to the ground, so it didn’t have room under the wings for modern turbofans. The 2nd and 3rd gen 737 (Classic and NG) worked around it with peculiar flattened nacelles (they’re circular on every other plane), and moving some of the components to the sides (from their usual position at the bottom). For the Max Boeing wanted even wider engines, and there was no way to flatten things further, so they moved the engines forwards and using long struts (check out comparison pics from the side). The result however is that the thrust vectors are different than on “normal” 737 giving the aircraft a tendency to pitch up in certain conditions, which is what the MCAS was supposed to automatically remedy. For reference, the original 737 had engines with a width of ~1m (40 inches), the second generation (“classic”) had fans 1.5m (60in) in diameter, the 737-NG is a minor bump to 1.55m (61in). The Max’s CFM Leap has a 1.76m (70in) fan. And that’s a specially reduced and less efficient version, on the 320neo the same engine has a 2m (78in) fan.

It's pretty shocking how giant that engine is. Is that really how big they are on the biggest jumbo jets? Or is it for one of those super giant planes that carry tanks for the military or whatever?

_ph_ 3y ago

The 747 actually had rather small engines. First of all, it had 4 and they were older-style with low bypass ratio. The 777 isn't that far from 747 capacity, but only sports 2 gigantic engines, they not only need to be more powerful, but have high bypass ratios to improve efficiency. They are even wider than the body of a 737.

masklinn 3y ago

It’s pretty normal for modern turbofans to look huge, they’re so-called “high bypass” turbofans: the power is provided by a turboreactor-ish core, but that drives a large ducted fan which pushes air through, most of that air bypasses the core (hence high-bypass). A model turbofan might have a bypass ratio of 10, aka for every kilo of air going through the core 10 are pushed around it by the fan. That applies to all airliners e.g. the reason for the 737 max’s issues is that the plane is very low to the ground, so it didn’t have room under the wings for modern turbofans. The 2nd and 3rd gen 737 (Classic and NG) worked around it with peculiar flattened nacelles (they’re circular on every other plane), and moving some of the components to the sides (from their usual position at the bottom). For the Max Boeing wanted even wider engines, and there was no way to flatten things further, so they moved the engines forwards and using long struts (check out comparison pics from the side). The result however is that the thrust vectors are different than on “normal” 737 giving the aircraft a tendency to pitch up in certain conditions, which is what the MCAS was supposed to automatically remedy. For reference, the original 737 had engines with a width of ~1m (40 inches), the second generation (“classic”) had fans 1.5m (60in) in diameter, the 737-NG is a minor bump to 1.55m (61in). The Max’s CFM Leap has a 1.76m (70in) fan. And that’s a specially reduced and less efficient version, on the 320neo the same engine has a 2m (78in) fan.