This is a question for anyone in the "aircraft business." I have noticed that, as far as I know, all

commercial air planes being built for airline service these days have engines in the wings and none have engines on the tail, like the old MD-80, the 727, DC-10 (one on rear), and the Tristar 1011, ( also one on rear). But small private jets continue to have twin engines mounted at the rear instead of on the wings. Can you explain when larger planes have moved away from engines in the rear, whild smaller planes still put their engines there.

There's a limit to the size of the engine that can be mounted on the tail, when referring to a 2-engine airplane.

Airframes like the 767, 777 and so on have engines that are too large for rear mounting.

When I say too large, I mean in terms of diameter as well as weight.

The DC10 and L1011 were actually anomalies in design when you consider the history of jetliners. If those airplanes had two engines instead of three, the engines would have been larger and therefore impractical to mount on the tail.

Also, with the increase in engine reliability over time, airlines no longer were averse to 2-engine operations overwater and other limitations related to ETOPS (Extended Twin Operations) which the regulatory agencies enforced upon two-engine transports. So, the third engine became effectively obsolete.

Another factor is the increase in the bypass, and therefore the fan size and diameter, of modern engines when compared to their older counterparts.

The exception to the two-engine model of airliner design today is the 747 series, the A340 series, and the A380 series- all very large aircraft.

Many smaller aircraft currently in production continue to employ rear-mounted engines, especially business jets.

The main advantage to rear-mounted engines include much less complex wing structure, and shorter landing gear and related air-stair issues, and quieter cabin.

Two engines are preferred for reduced costs compared with three or four smaller engines. Airliners mount them under the wings so they will be closer to the ground and not so far away from the mechanics when they require maintenance or inspection.

Smaller jets carry the engines in the rear and mount them high enough and shielded by the wings to reduce the risk of sucking up damaging debris on the runway. They won't fit under the wings and they're still close enough to the ground to be accessible to the mechanics and for inspections.

actually they just phased out as engines became more powerful there were less need for 3 engines, a 737 with 2 engines has the same fuselage as a 727. Boeing canned the 717 line the last of the rear mounted engines which were
basically a dc-9.. Airtran airways went to boeing and ordered more 717,s and wanted one stretched longer, which would have basically put another whole series of dc-9,s to be stretcthed. I think there was the 10,20,30,40,50,etc and boeing said no,,and shoved the 737 on them,
.
Private jets have to small of a wingspan and not as strong to hold an engine but one day in the future we may see it,,
I missed the big ones like the l-10-11 and dc-10,s are are about freighters now,, Actually some of those md80,s are not as old as some of the twin jets like some 757,and 767,s..
The first airbus i saw was the a300 like in the early 70,s??

Tough to beat the answer from Kansas Engineer.

The only thing I might add is that putting engines on the wings has the added advantage of moving the C/G (center of gravity) forward, which allows the airplane to have its main and tail wings further apart, and that provides the benefit of giving the aircraft more stability. And putting the engines in the rear has the benefit of making the cabin quieter.

In short, there is no perfect location for the engines.