Eli5: why are some airplane jet engines under the wings and some on the vertical stabilizer?

Question

Eli5: why are some airplane jet engines under the wings and some on the vertical stabilizer?

In: 3

Answer 1

The planes with single engines in the vertical stabilizer are due to a law that required twin-engine aircraft to always be within 60 minutes of an airport.This regulation came to be known as ETOPS: Extended range Twin engine Operation Performance Standards. (Or, “Engines Turn Or Passengers Swim)

This law did not apply to jets with 3 or more engines. If carriers wanted to fly longer, over-water routes, they had to follow coastlines, or fly planes with more engines. It’s cheaper to operate 3-engined aircraft than 4-engined, so the market made 3-engined aircraft.

Planes with an odd number of engines can’t divide them between the wings; they need the odd one in the fuselage. It has to point aft, so the tail is the natural choice.

With improved jet engine reliability, ETOPS standards have been extended from 60 minutes to 120 minutes in 1985, and 180 minutes in 1988. Some twin-engine aircraft are now certified to fly up to 370 minutes from a diversion airport. The era of trijets is rapidly coming to a close.

Answer 2

The planes with single engines in the vertical stabilizer are due to a law that required twin-engine aircraft to always be within 60 minutes of an airport.This regulation came to be known as ETOPS: Extended range Twin engine Operation Performance Standards. (Or, “Engines Turn Or Passengers Swim)

This law did not apply to jets with 3 or more engines. If carriers wanted to fly longer, over-water routes, they had to follow coastlines, or fly planes with more engines. It’s cheaper to operate 3-engined aircraft than 4-engined, so the market made 3-engined aircraft.

Planes with an odd number of engines can’t divide them between the wings; they need the odd one in the fuselage. It has to point aft, so the tail is the natural choice.

With improved jet engine reliability, ETOPS standards have been extended from 60 minutes to 120 minutes in 1985, and 180 minutes in 1988. Some twin-engine aircraft are now certified to fly up to 370 minutes from a diversion airport. The era of trijets is rapidly coming to a close.