tsme-EatIt t1_ja6lyay wrote
There hasn't been a model designed with an engine on the vertical stabilizer since like the 70s/80s.
As for why, it has to do with reliability and the ability to make an emergency landing if 1 engine fails. Modern jet engines are reliable enough that only 2 of them are needed for the vast majority of airline flights. In the past, 3-engine or 4-engine designs would be used for airline routes that fly over oceans or over isolated areas where the nearest available airport in case of emergency is very far away. For further information about this, search for "ETOPS" (which is what the regulation is called). "4 engines 4 long haul" was also a phrase used in the past by certain airlines which preferred flying 4-engine planes, and by Airbus to market the A340 against competitors such as the Boeing 777.
And of course, with a 3-engine design, the only place to mount the center engine and still be balanced, is the vertical stabilizer.
dirschau t1_ja6wjm4 wrote
Pretty sure OP meant something like a business jet, with the two engines on the tail, compared to a big airliner with under wing engines. Not the old 3 engine liners.
tsme-EatIt t1_ja6wm82 wrote
Don't complain to me about assumptions you made about the OP
They very clearly said vertical stabilizer
critt385 t1_ja790sr wrote
There have in fact been at least two planes designed in the last decade (or so) with an engine in the vertical stabilizer
barrylunch t1_ja6pqgg wrote
What does ETOPS have to do with engine placement on the stab vs. under-wing? I don’t think you answered the question (which is about placement, not quantity).
tsme-EatIt t1_ja6rmp8 wrote
I answered how quantity is related to placement. You can't have 3 engines and have all of them under the wings, they wouldn't be balanced.
therealdilbert t1_ja6wrf1 wrote
But there have been several planes with all the engines in back, like the Boeing 727 witt three engines, or the MD80 with two engines
Target880 t1_ja72nlk wrote
Underwing versus on the back is not the same as why one on the vertical stabilizer or just the air intake there
If you have an odd number of engines you need to place one in the center line of the airplane and with a jet engine, you can put it in the front line with propellers.
You can but even the number of engines under the wing or on the body. 4 engines on the back have them placed side by side like a Vickers VC10
3 engines existed primarily because of ETOPS rating, you could fly longer over open water with 3 compared to 2 engines and the cost will be less than if you have 4 engines. A minor part is that it adds high-altitude takeoff performance in locations like Colorado which is at 1-mile altitude.
They have disappeared because engine performance and ETOPS regulations have changed so you are allowed to do the same flight with just 2 engines and it is a cheaper way to build and operate aircraft
Boeing 727 have all 3 engine in the rear, and McDonnell Douglas MD-11 had 2 under the wings and 1 in the back. So 2 engines under the wings or on the back are unrelated to the vertical stabilizer position of a third engine.
tsme-EatIt t1_ja6x2e2 wrote
That's outside the scope of the question asked by the OP. They asked about wing mounted and vertical stabilizer mounted engines.
NetworkLlama t1_ja7xsjm wrote
OP wasn't asking about 727, DC-10, or L1011-style engines. They were asking about DC-9-style mountings, or the common tail mountings on business jets. Unfortunately wording on their part.
Elios000 t1_ja7ildp wrote
E-jets and most business jets have tail mounted engines. the reason is mission. tail mounted engines let you have short landing gear and less chance of FOD damage on crappy airstrips. this lets you load pax and cargo with out needing extra equipment. even with under wing engines if you look at the 737 vs A320. the original 737 used turbo jets so they could keep the gear as short as possible when they change it to the CFM's they had relocate the some of the pumps and you ended up with the hamster pouch nacelles to keep the low gear. Airbus when they built the A320 years later airport infrastructure had improved a ton so they just keep the gear taller.
tsme-EatIt t1_ja8anrx wrote
I'm aware of that but OP specifically used the term "vertical stabliizer", which excludes fuselage-mounted tail engines.
Elios000 t1_ja8c1b9 wrote
to layperson it looks the same
tsme-EatIt t1_ja8ebxi wrote
Do layperson say "vertical stabilizer"? Most of them just say tail
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