We Claim:
1. A propulsion system for an aircraft (200) having a pair of wings (210) and
a tail section (208), the propulsion system comprising:
a plurality of primary engines including at least a first primary engine (252) and a second primary engine (254), the first primary engine (252) configured for mounting to a first of the pair of wings (210) of the aircraft (200), and the second primary engine (254) configured for mounting to a second of the pair of wings (210) of the aircraft (200); and
an aft engine configured for mounting at the tail section (208) of the aircraft (200), the plurality of primary engines sized to provide an amount of thrust sufficient for the aircraft (200) to takeoff without use of the aft engine.
2. The propulsion system as claimed in claim 1, wherein the first primary engine (252) and the second primary engine (254) are each configured as a turbofan jet engine.
3. The propulsion system as claimed in claim 3, wherein the aft engine is a boundary layer ingestion fan (256), wherein the boundary layer ingestion fan (256) includes a nacelle (106) defining an inlet (134) extending approximately three hundred and sixty degrees around a fuselage (202) of the aircraft (200) at the tail section (208) of the aircraft (200) when the boundary layer ingestion fan (256) is mounted to the aircraft (200).
4. The propulsion system as claimed in claim 1, wherein the first primary engine (252) and the second primary engine (254) are each sized to generate a maximum primary engine thrust when operated at maximum capacity, and wherein the aft engine is sized to generate up to about eighty-five percent of the maximum primary engine thrust when operated at maximum capacity.
5. The propulsion system as claimed in claim 1, wherein the first primary engine (252) and the second primary engine (254) are each sized to generate a
19

maximum primary engine thrust when operated at maximum capacity, and wherein the aft engine is sized to generate up to about seventy-five percent of the maximum primary engine thrust when operated at maximum capacity.
6. A method for operating an aircraft having a pair of wings, an aft engine
mounted at a tail section of the aircraft, and a plurality of primary aircraft engines,
at least a first of the plurality of primary engines mounted to a first of the pair of
wings and at least a second of the plurality of primary engines mounted to a
second of the pair of wings, the method comprising:
operating the plurality of primary aircraft engines to generate an amount of thrust sufficient for the aircraft to takeoff; and
operating the aft engine at less than full capacity during a takeoff operating mode of the aircraft.
7. The method as claimed in claim 7, wherein operating the aft engine less than full capacity during takeoff operating mode includes operating the aft engine at less than about seventy-five percent capacity during the takeoff operating mode.
8. The method as claimed in claim 7, further comprising
operating the aft engine at fifty percent capacity or more during at least one of a climb operating mode of the aircraft or a cruise operating mode of the aircraft.
9. The method as claimed in claim 7, wherein the plurality of primary aircraft engines together generate a cumulative maximum primary engines thrust when operated at full capacity, wherein the aft engine defines a maximum aft engine thrust when operated at full capacity, and wherein the maximum aft engine thrust is less than about thirty percent of the cumulative maximum primary engines thrust.
10. The method as claimed in claim 7, further comprising
20

providing energy from one or more of the plurality of primary aircraft engines to the aft engine to operate the aft engine after the takeoff operating mode of the aircraft is complete.
21