eli5: Why do small jet aircraft, like regional jets and private jets, have engines on the rear, but larger jet planes have engines on the wings?
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Jet engines have to be placed a certain distance above the runway. This is both so it does not scrape the runway on touchdown when the body and wing flexes but also so that any debris and dust is not sucked into them. And these smaller aircraft do not have enough room under their wings for the engines and the clearance to the ground. If you put the engine on top of the wing you will be disrupting the airflow over the wings a lot more and you lose a lot of the wing surface. Putting the engines anywhere else on the body will put the exhaust right onto the rest of the airplane. So the only good place to put the jet engines is in the tail.
For larger airplanes the added complexity of having the engines in the tail is not worth the effort. Not only do you need to bring the fuel from the wing tanks all the way to the tail but the weight of the engines will also have to be carried by the wings so you need stronger beams between the wings and tail to carry the weight. So it is much better to have the engines mounted under the wings.
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