why is it better for the turbines on a jet to sit under the wing rather than over it?
In: Engineering
The top of the wing is where the lift is generated, it’s easier for maintenance and construction also some aircraft do have the jets mounted high and to the rear but it’s usually smaller aircraft.
Good in detail explanation.
It’s partially just easier to have the engines be below the wing from a construction and maintenance perspective.
In addition, with the engines below the wings, when the engines spool up that tends to pitch the nose of the plane *upwards*. Conversely, if you mount the engines above the wings, that’ll tend to pitch the plane *downwards*. The upward pitch is more preferable so long as you don’t stall the plane.
Edit: I should mention that the above comment on mounting the engines relates to when you mount the engines **directly over or under the wings**. There are aircraft with engines mounted above the wings in service, but they tend to have engines mounted as far back on the aircraft as possible (typically on the tail structure), which achieves the same kind of upward pitch because of how the engines interact with the planes center of lift and center of mass.
Aside from the aerodynamic shape of the wing, it’s simply easier to hang something heavy than to support something heavy on a stand.
When you hang the engine off the bottom of the wing you’re using gravity’s own force to keep the engine in position.
If it were mounted atop, then the forces of gravity would want to pull the engine downward and you’d likely require more material (weight) to support the engine in place.
Weight is the ultimate enemy of flight.
When I did ground school we talked a lot about parasitic drag [https://en.wikipedia.org/wiki/Parasitic_drag](https://en.wikipedia.org/wiki/Parasitic_drag)
I’m not an AeroEng but I’d think that you would not want to break the air flow over the top of the ~~where~~ wing where 80% of lift is generated.
Edit: typo
If engines basically just push air really fast. And lift is created by the air on top of the wing moving faster than the air under it, wouldn’t you want the thing that moves air fast on top of the wing with the other fast moving air?
Along with everyone else’s answers, the wing would act like a shield against the engine noise, making it quieter in the cabin. Of course, this really only applies to low-mounted wings.
Edit: spelling
An engine under the wing is a large vacuum cleaner sucking up all the dirt and debris off the runway. That’s another reason why the Boeing 737 is such a crap design. Ir should have been scrapped 40 years ago.
Don’t tell Honda!
[https://www.hondajet.com/](https://www.hondajet.com/)
[https://www.hondajet.com/otwem](https://www.hondajet.com/otwem)
The Honda Jet is unique but there can be an aerodynamic benefit to putting the pod above the wings. The Cirrus Jet mounts the engine in a weird location as well;
[https://cirrusaircraft.com/aircraft/vision-jet/](https://cirrusaircraft.com/aircraft/vision-jet/)
The big caveat to this is that these are small engines with (relatively) low fuel flow. It would be hard to fit a GE90 on top of the wing because of how cartoonishly huge the intake is. It would have to be up and out and the structure of the wing would have to be totally redesigned. Probably the most obvious reason is that maintenance is a lot easier with the turbine closer to the ground.
So you can walk easily in the wings if you need to evacuate the plane. There might be millions of reasons more I’m not aware of, but that one makes sense.
I’ll give two more reasons that I didn’t see other commenters add:
2. For commercial airliners, passenger comfort is a big deal. Having the engines below the wing and away from the cabin mitigates the noise.
3. If the engine were to detach in flight then it’s better for it to be able to fall away cleanly rather than potentially falling onto the wing or worse hitting the control surfaces at the rear.
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