Triangular-frame connection between fan case and core housing in a gas turbine engine

1. A gas turbine engine comprising:

a fan rotor driven by a fan drive turbine about an axis through a gear reduction to reduce a speed of said fan rotor relative to a speed of said fan drive turbine;

a fan case surrounding said fan rotor, and a core engine with a compressor section, including a low pressure compressor;

said fan rotor delivering air into a bypass duct defined between said fan case and said core engine, and a rigid connection between said fan case and said core engine including three triangular-frame connecting members rigidly connected to said fan case at a fan case connection point, and to said core engine at a core engine connection point, the triangular-frame connecting members each being defined by two rigid legs which extend between said fan case and to said core engine, along directions each have a component extending radially inwardly and a component in opposed circumferential directions to each other; and

a plurality of non-structural fan exit guide vanes and said non-structural fan exit guide vanes being provided with an acoustic feature to reduce noise, said non-structural fan exit guide vanes being rigidly mounted to at least one of the fan case and the core engine.

2. The gas turbine engine as set forth in claim 1 , wherein said acoustic feature includes said non-structural fan exit guide vanes being formed with chambers and a covering perforated face sheet.

3. The gas turbine engine as set forth in claim 1 , wherein there are also structural fan exit guide vanes rigidly secured to both said fan case and said core engine, and said structural fan exit guide vanes include greater than 0 and less than 55% of a total number of fan exit guide vanes including the non-structural fan exit guide vane.

4. The gas turbine engine as set forth in claim 3 , wherein said structural fan exit guide vanes include 15-30% of the total fan exit guide vanes.

5. The gas turbine engine as set forth in claim 1 , wherein said low pressure compressor has four to six stages.

6. The gas turbine engine as set forth in claim 1 , wherein there is an outer diameter to the core engine at the location of the connection points to the rigid legs of said three triangular frame connecting members and there is a distance between the legs in each triangular frame connecting member at the connection points where the legs are attached to the core engine, and the distance is greater than the outer diameter.

7. The gas turbine engine as set forth in claim 1 , wherein said core engine includes a fan intermediate case forward of said low pressure compressor, and said structural fan guide vanes are rigidly connected to said fan intermediate case.

8. The gas turbine engine as set forth in claim 7 , wherein said core engine including a compressor intermediate case intermediate said low pressure compressor and a high pressure compressor, and said connection points between said triangular frame connecting members are to said compressor intermediate case.

9. The gas turbine engine as set forth in claim 1 , wherein said core engine including a compressor intermediate case intermediate said low pressure compressor and a high pressure compressor, and said connection points between said triangular frame connecting members are to said compressor intermediate case.

10. The gas turbine engine as set forth in claim 1 , wherein the connection point between one of said three triangular frame connected members and said fan case is at a top dead center position, and the connection point to the fan case for the other two of the triangular frame connecting member are on circumferentially spaced sides of a bottom dead center position.

11. The gas turbine engine as set forth in claim 1 , wherein the connection point between one of said three triangular frame connecting members and said fan case is at a bottom dead center position and the connection points for the other two of the three triangular frame connecting members are on circumferentially spaced side of a top dead center position.

12. The gas turbine engine as set forth in claim 1 , wherein two rigid links connect one of said legs from two of said three triangular frame connecting members spaced circumferentially about said top dead center position to said fan case, with said two rigid links being on opposed sides of said top dead center position.

13. A gas turbine engine comprising:

a fan rotor driven by a fan drive turbine about an axis through a gear reduction to reduce a speed of said fan rotor relative to a speed of said fan drive turbine;

a fan case surrounding said fan rotor, and a core engine with a compressor section, including a low pressure compressor;

three triangular frame connecting members, the triangular-frame connecting members being defined by two rigid legs which extend between said fan case and to said core engine, along directions each have a component extending radially inwardly and a component in opposed circumferential directions to each other the two rigid legs being fixed to both the fan case and the core engine at connection points;

a plurality of fan exit guide vanes rigidly connected to said fan case, and connected to said core engine; and

said two rigid legs in each said triangular frame connecting members extend from said fan case to said core engine extend in a direction with a radially inward component and an axially aft direction.

14. The gas turbine engine as set forth in claim 13 , wherein said low pressure compressor has four to six stages.

15. The gas turbine engine as set forth in claim 13 , wherein said core engine includes a fan intermediate case forward of said low pressure compressor, and said structural fan guide vanes are rigidly connected to said fan intermediate case.

16. The gas turbine engine as set forth in claim 13 , wherein the connection point between one of said three triangular frame connected members and said fan case is at a top dead center position, and the connection point to the fan case for the other two of the triangular frame connecting member are on circumferentially spaced sides of a bottom dead center position.

17. The gas turbine engine as set forth in claim 13 , wherein the connection point between one of said three triangular frame connecting members and said fan case is at a bottom dead center position and the connection points for the other two of the three triangular frame connecting members are on circumferentially spaced side of a top dead center position, and wherein two rigid links connect one of said rigid legs from two of said three triangular frame connecting members spaced circumferentially about said top dead center position to said fan case, with said two rigid links being on opposed sides of said top dead center position.

18. The gas turbine engine as set forth in claim 13 , wherein said core engine including a compressor intermediate case intermediate said low pressure compressor and a high pressure compressor, and said connection points between said triangular frame connecting members to said core engine are to said compressor intermediate case.

19. The gas turbine engine as set forth in claim 13 , wherein there is an outer diameter to the core engine at the location of the connection points to the rigid legs of said three triangular frame connecting members and there is a distance between the legs in each triangular frame connecting member at the connection points where the legs are attached to the core engine, and the distance is greater than the outer diameter.

20. The gas turbine engine as set forth in claim 13 , wherein said plurality of fan exit guide vanes include structural and non-structural fan exit guide vanes.