Why are jet engines hung forward of the wing leading edges?

Question

In other words, why aren't engines hung directly underneath the wings? It seems like weight would be saved through less mass of structural components. You'd also have less potential vibration problems with the wobbling up and down of the engine. However, I remember that older 737s had the engines directly under the wings, but that's all.

Answer 1

Ease of installation/removal and access for maintenance are major considerations. There has never been a 737 with engines mounted as you "remember". The older models had smaller engines but were mounted the same as is done currently.

Answer 2

Got it wrong Mr. B. Very, very wrong. Once all other considerations have been made for the overall aircraft design such as tail or wing monted engines, CG has everything to do with the engine placement. Our executive 727 with three engines on the tail has roughly the same CGMAC, mean aerodynamic cord, as does a 737 with the engines mounted underwing. It absolutely has to be. How can that be you ask? Simple, move the wings back on the fuselage of the 727 to keep CGMAC comparable. Your new CG station on the airplane will have moved aft of datum along with the wings.

Answer 3

The placement of the engines is dictated by center-of-gravity considerations.  Setting the engines further forward helps offset the weight of the rear fuselage and tail.

Can't remember a 737 with engines right under the wing.  What model was that?

Answer 4

The -100 and the -200 had the engines(JT8D-1) directly under the wings. But you should remember that these were low by-pass turbofans and hence of a smaller dimension (circumference) than its high by-pass turbofan successor CFM56. The larger dimension of the CFM56 turbofan (B737 Classic and NG series) meant that there could be ground clearance issues if fixed directly to the wing. Hence the nifty forward hanging placement. It was the increased diameter of the engines that necessitated this change.

And the B737 models are example that the engine placements are more of practicability and design considerations than absolute weight savings.

Answer 5

Center-of-gravity does not dictate engine placement as previously answered, otherwise there would be no aircraft with engines on the tail, or on aft end of the fuselage or in the wing like the comet (or the Nimrod).  They are in front of the wing for safety.  If there is an un-contained turbine failure (turbine comes apart and blades fly out of the engine) there won't be any damage to the wing with the engine out front.  Also, if the engine comes off the wing due to structural failure when there is lots of power on, it will tend to rise up in front of the wing, and go backwards over it (yes this has happened a few times) rather than rise up and hit it.

Also, having it away from the wing helps efficiency as the air under the wing is not disturbed by an engine stuck to it (like the 737-200).

And yes, there was a 737 (the -100 and the -200) with engines stuck on the bottom of the wings.

see:

http://images.google.com/imgres?imgurl=h...

Just one example, the first one I found.

Cheers,

B