A propulsion system for an aircraft includes an electric propulsion engine. The electric propulsion engine includes an electric motor and a fan rotatable about a central axis of the electric propulsion engine by the electric motor. The electric propulsion engine also includes a bearing supporting rotation of the fan and a thermal management system. The thermal management system includes a lubrication oil circulation assembly and a heat exchanger thermally connected to the lubrication oil circulation assembly. The lubrication oil circulation assembly is configured for providing the bearing with lubrication oil. Such an electric propulsion engine may be a relatively self-sufficient engine.

A boundary layer ingestion fan system for location aft of the fuselage of an aircraft is shown. It comprises a nacelle (501) defining a duct, and a fan located therewithin. The fan comprises a hub arranged to rotate around a rotational axis (A-A) and a plurality of blades attached thereto. Each blade has a span (r) from a root at the hub defining a 0 percent span position (r=0) to a tip defining a 100 percent span position (r=1) and a plurality of span positions therebetween (r [0, 1]), and leading and trailing edges defining, for each span position, a chord therebetween to having a chord length (c). For each of said plurality of blades, the ratio of chord length at the 0 percent span position (c.sub.hub) to chord length at the 100 percent span position (c.sub.tip) is 1 or greater.

A boundary layer ingestion fan system for location aft of the fuselage of an aircraft includes a nacelle (501) defining a duct (502), and a fan (503) located therewithin. The fan comprises a hub which rotates around a rotational axis (A-A) and a plurality of blades attached thereto. Each blade has a span (r) from a root at the hub defining a 0 percent span position (r=0) to a tip defining a 100 percent span position (r=1) and a plurality of span positions therebetween (r [0, 1]), a leading edge and a trailing edge defining, for each span position, a chord therebetween having a chord length (c), and a blade thickness (t) defined for each span position thereof. For each blade, a ratio of thickness at the 0 percent span position (t.sub.hub) to chord length is 0.1 or greater.

A boundary layer ingestion fan system for location aft of the fuselage of an aircraft is shown. It comprises a nacelle (501) defining a duct (502), and a fan (503) located within the duct. The fan comprises a hub arranged to rotate around a rotational axis (A-A) and a plurality of blades attached to the hub. Each blade has a span (r) from a root at the hub defining a 0 percent span position (r=0) to a tip defining a 100 percent span position (r=1) and a plurality of span positions therebetween (r [0, 1]), and a stagger angle at the 0 percent span position (.sub.hub) relative to the rotational axis of 40 degrees or greater.

A boundary layer ingestion fan system for location aft of the fuselage of an aircraft is shown. It comprises a nacelle defining a duct, and a fan located within the duct. The fan comprises a hub arranged to rotate around a rotational axis (A-A) and a plurality of blades attached to the hub.

A blade blockage, which is the ratio of the blade thickness to the product of the circumferential pitch and the cosine of a blade inlet angle (t/s.Math.cos.sub.1), is 0.25 or greater at the 0 percent span position.

A boundary layer ingestion fan system for location aft of the fuselage of an aircraft is shown. It comprises a nacelle defining a duct, and a fan located within the duct. The fan comprises a hub arranged to rotate around a rotational axis (A-A) and a plurality of blades attached to the hub, each of which has a span from a root at the hub defining a 0 percent span position (r.sub.hub) to a tip defining a 100 percent span position (r.sub.tip) and a plurality of span positions therebetween (r[r.sub.hub, r.sub.tip]). A hub-tip ratio of the fan, defined as the ratio of the diameter of the hub to the diameter of the fan measured at the leading edge of the blades, is from 0.45 to 0.55.

A boundary layer ingestion fan system for location aft of the fuselage of an aircraft is shown. It comprises a nacelle defining a duct, and a fan located within the duct. The fan comprises a hub arranged to rotate around a rotational axis and a plurality of blades attached to the hub, each of which has a span from a root at the hub defining a 0 percent span position (r.sub.hub) to a tip defining a 100 percent span position (r.sub.tip) and a plurality of span positions therebetween (r[r.sub.hub, r.sub.tip]). The hub has a negative hade angle () with respect to the rotational axis at an axial o position coincident with the leading edge of the blades.

A boundary layer ingestion fan system for location aft of the fuselage of an aircraft is shown. It comprises a nacelle defining a duct, and a fan located within the duct. The fan comprises a hub arranged to rotate around a rotational axis and a plurality of blades attached to the hub, each of which has a span from a root at the hub defining a 0 percent span position (r.sub.hub) to a tip defining a 100 percent span position (r.sub.tip) and a plurality of span positions therebetween (r[r.sub.hub, r.sub.tip]). A plurality of outlet guide vanes are positioned aft of the fan. An afterbody is located aft of the plurality of outlet guide vanes and which tapers to an apex having an apex angle with respect to the rotational axis of between 35 and 45 degrees.

A cross flow fan to be incorporated into an aircraft comprises a cross flow fan rotor to be positioned in an aircraft, a drive arrangement for the cross flow fan rotor, and a plurality of vanes positioned downstream of the cross flow fan rotor. An aircraft is also disclosed.

In one aspect the present subject matter is directed to a gas-electric propulsion system for an aircraft. The system may include a turbofan jet engine, an electric powered boundary layer ingestion fan that is coupled to a fuselage portion of the aircraft aft of the turbofan jet engine, and an electric generator that is electronically coupled to the turbofan jet engine and to the boundary layer ingestion fan. The electric generator converts rotational energy from the turbofan jet engine to electrical energy and provides at least a portion of the electrical energy to the boundary layer ingestion fan. In another aspect of the present subject matter, a method for propelling an aircraft via the gas-electric propulsion system is disclosed.