TANDEM FAN FOR BOUNDARY LAYER INGESTION SYSTEMS

1 . A tandem fan for a boundary layer ingestion engine, comprising:

a fan disk configured for rotation about a longitudinal axis;

a primary fan blade extending radially from the fan disk, the primary fan blade having a primary fan blade span; and

a secondary fan blade extending radially from the fan disk, the secondary fan blade having a secondary fan blade span within about ninety percent to about one-hundred percent of the primary fan blade span.

2 . The tandem fan of claim 1 , wherein the secondary fan blade span is about equal to the primary fan blade span.

3 . The tandem fan of claim 1 , wherein the primary fan blade includes a primary fan blade tip configured for disposition a primary tip distance away from a radially inner surface of a fan case within about one percent to about five percent of the primary fan blade span.

4 . The tandem fan of claim 3 , wherein the secondary fan blade includes a secondary fan blade tip configured for disposition a secondary tip distance away from the radially inner surface of the fan case within about one percent to about five percent of the secondary fan blade span.

5 . The tandem fan of claim 4 , wherein both the primary tip distance and the secondary tip distance are equal.

6 . The tandem fan of claim 1 , wherein the primary fan blade includes a primary fan blade trailing edge and the secondary fan blade includes a secondary fan blade leading edge and the secondary fan blade leading edge is positioned axially forward of the primary fan blade trailing edge by a first distance.

7 . The tandem fan of claim 6 , wherein the first distance is within about zero percent to about thirty percent of a primary fan blade chord.

8 . The tandem fan of claim 1 , wherein the primary fan blade includes a primary fan blade leading edge and the secondary fan blade includes a secondary fan blade trailing edge and the secondary fan blade trailing edge is positioned axially aft of the primary fan blade leading edge by a second distance and wherein the second distance is within about one-hundred percent to about two-hundred percent of a primary blade chord.

9 . The tandem fan of claim 4 , wherein at least one of the primary fan blade tip and the secondary fan blade tip is connected to a shroud.

10 . A boundary layer ingestion engine, comprising:

a fan case;

a spool operably coupled to at least one of an electric motor and a gas turbine engine; and

a tandem fan operably coupled to the spool, the tandem fan comprising

a fan disk configured for rotation about a longitudinal axis,

a primary fan blade extending radially from the fan disk, the primary fan blade having a primary fan blade span, and

a secondary fan blade extending radially from the fan disk, the secondary fan blade having a secondary fan blade span within about ninety percent to about one-hundred percent of the primary fan blade span.

11 . The boundary layer ingestion engine of claim 10 , wherein the secondary fan blade span is about equal to the primary fan blade span.

12 . The boundary layer ingestion engine of claim 11 , wherein the primary fan blade includes a primary fan blade tip configured for disposition a primary tip distance away from a radially inner surface of the fan case within about one percent to about five percent of the primary fan blade span.

13 . The boundary layer ingestion engine of claim 12 , wherein the secondary fan blade includes a secondary fan blade tip configured for disposition a secondary tip distance away from the radially inner surface of the fan case within about one percent to about five percent of the secondary fan blade span.

14 . The boundary layer ingestion engine of claim 13 , wherein both the primary tip distance and the secondary tip distance are equal.

15 . The boundary layer ingestion engine of claim 10 , wherein the primary fan blade includes a primary fan blade trailing edge and the secondary fan blade includes a secondary fan blade leading edge and the secondary fan blade leading edge is positioned axially forward of the primary fan blade trailing edge by a first distance.

16 . The boundary layer ingestion engine of claim 15 , wherein the first distance is within about zero percent to about thirty percent of a primary fan blade chord.

17 . The boundary layer ingestion engine of claim 10 , wherein the primary fan blade includes a primary fan blade leading edge and the secondary fan blade includes a secondary fan blade trailing edge and the secondary fan blade trailing edge is positioned axially aft of the primary fan blade leading edge by a second distance.

18 . The boundary layer ingestion engine of claim 17 , wherein the second distance is within about one-hundred percent to about two-hundred percent of a primary blade chord.

19 . The boundary layer ingestion engine of claim 10 , wherein the fan disk comprises a forward fan disk and an aft fan disk and both the forward fan disk and the aft fan disk are configured for rotation by the spool.

20 . A boundary layer ingestion system configured for mounting to or downstream of a fuselage of an aircraft, comprising:

a fan case configured for attachment to or downstream of the fuselage;

a tandem fan rotationally disposed within the fan case, the tandem fan including:

a fan disk configured for rotation about a longitudinal axis,

a primary fan blade extending radially from the fan disk, the primary fan blade having a primary fan blade span, and

a secondary fan blade extending radially from the fan disk, the secondary fan blade having a secondary fan blade span within about ninety percent to about one-hundred percent of the primary fan blade span; and

a power source configured to rotate the tandem fan.