If you were to make an engine in the wing or at least closer to it in commercial airliners such as the 747, 737 and A380 etc. Would it increase efficiency?
Yes, mounting jet engines in the wing root increases aerodynamic efficiency due to:
- No drag from engine pods
- Smaller yawing moment upon engine fail, and resulting smaller vertical tail.
But that is about it. There is a host of disadvantages to mounting the engines in the wing root, one of them being that high lift devices cannot be used and the wing is bigger, causing more drag.
Three huge advantages of mounting the engines in pods, underneath the wing, in front of the aeroelasitc axes are:
- High bypass engines can be mounted, vastly improving fuel efficiency.
- The engines are within easy reach for maintenance.
- The weight of the engines provides both bending relief, and reduces structural weight to prevent flutter.
Also see this question.