Here’s Why The McDonnell Douglas MD-11’s Tail Engine Is Different Than Other Trijets

When one observes a trijet on the ramp at an airport, their eyes will be naturally drawn directly to the aircraft’s tail. On the McDonnell Douglas MD-11, the center engine is not fed in the same way that most traditional trijets are. The Boeing 727 and the Lockheed L-1011 both use a pronounced S-duct, with an intake on top of the fuselage that curves down to an engine buried deeper in the jet’s tail. The MD-11’s tail engine, by contrast, is a much more direct and straight-through arrangement carried at the base of an aircraft’s vertical stabilizer. This leads the inlet, ducting, and fan presentation to differ in significant aerodynamic and maintenance-related ways from that of a traditional three-engine aircraft.