On the flip side...
Tail-mounted engines are more protected from runway FOD on unimproved surfaces, thus their use on Russian airliners and the A-10 (and may have figured in Canadair's thinking, for use in the "Siberia of the West").
And of course the "three-holers" had to have at least one (L-1011, DC-10, MD-11) or more (727, Trident) engines in the tail anyway, as a stepping-stone before engines were powerful enough for two to be sufficient on heavier long-range planes.
With wing-mounted engines, the wing root carries less weight load in flight - but more thrust loads.
There was a design "cachet" to T-tail designs in general in the 60's + 70s, beyond simple functionality. They had that F-104 "Starfighter coolness", even if they were pedestrian planes otherwise (Tomahawk, Skipper, Seminole, Duchess).
But absent any of those "special needs", two or four under the wing is likely the pattern for the future except for small planes that don't have room there. Or have one engine.
Last edited by pattern_is_full; 23rd Jul 2012 at 21:35.