Dedicated fans for boundary layer ingestion

Abstract

A propulsion system for an aircraft including at least two main gas turbine engines and a plurality of dedicated boundary layer ingestion fans. The propulsion system is arranged such that a combined thrust produced by the boundary layer ingestion fans is less than 20 percent of a total thrust of the main engines and the boundary layer ingestion fans. The boundary layer ingestion fans are controllable and selectively turned off at lower speeds.

Claims

1. A propulsion system for an aircraft comprising: at least two main gas turbine engines and a plurality of dedicated boundary layer ingestion fans; wherein a total thrust provided by a combination of said at least two main gas turbine engines and said dedicated boundary layer ingestion fans is such that a combination of a thrust provided by said dedicated plurality of boundary layer ingestion fans is less than 20 percent of said total thrust; wherein a control selectively turns said dedicated boundary layer ingestion fans off at lower aircraft speeds; and said dedicated boundary layer ingestion fans are driven by a motor, said motor controlled by said control, and said motor being separate from said at least two main gas turbine engines.

2. The propulsion system as set forth in claim 1, wherein said total thrust provided by said combination of said at least two main gas turbine engines and said dedicated boundary layer ingestion fans is such that said combination of said thrust provided by said dedicated plurality of boundary layer ingestion fans is less than 10 percent of said total thrust.

3. The propulsion system as set forth in claim 2, wherein there are more than five of said dedicated boundary layer ingestion fans.

4. The propulsion system as set forth in claim 3, wherein a diameter of said dedicated boundary layer ingestion fans is less than 15 inches and a fan pressure ratio at cruise condition is less than 1.5.

5. The propulsion system as set forth in claim 1, wherein said lower aircraft speeds include takeoff of an associated aircraft.

6. The propulsion system as set forth in claim 1, wherein a curved surface provides an inlet to said dedicated boundary layer ingestion fans.

7. The aircraft as set forth in claim 6, wherein said total thrust provided by a combination of said at least two main gas turbine engines and said dedicated boundary layer ingestion fans is such that said combination of said thrust provided by said plurality of dedicated boundary layer ingestion fans is less than 10 percent of said total thrust.

8. An aircraft comprising: a wide fuselage and having a tail section, with a plurality of main gas turbine engines mounted at a location outside said wide fuselage; and a plurality of dedicated boundary layer ingestion fans mounted in said tail section of said aircraft to ingest boundary layer air created by said wide fuselage; and wherein a total thrust provided by a combination of said at least two main gas turbine engines and said dedicated boundary layer ingestion fans is such that a combination of a thrust provided by said plurality of dedicated boundary layer ingestion fans is less than 20 percent of said total thrust.

9. The aircraft as set forth in claim 8, wherein there are more than five of said dedicated boundary layer ingestion fans.

10. The aircraft as set forth in claim 9, wherein a diameter of said dedicated boundary layer ingestion fans is less than 15 inches and a fan pressure ratio at cruise condition is less than 1.5.

11. The aircraft as set forth in claim 9, wherein a control selectively turns said dedicated boundary layer ingestion fans off at lower aircraft speeds.

12. The aircraft as set forth in claim 11, wherein said lower aircraft speeds include takeoff.

13. The aircraft as set forth in claim 11, said dedicated boundary layer and ingestion fans are driven by a motor, said motor controlled by said control, and said motor being separate from said at least two main gas turbine engines.

14. The aircraft as set forth in claim 8, wherein a control selectively turns said dedicated boundary layer ingestion fans off at lower aircraft speeds.

15. The aircraft as set forth in claim 14, wherein said lower aircraft speeds include takeoff.

16. The aircraft as set forth in claim 14, said dedicated boundary layer and ingestion fans are driven by a motor, said motor controlled by said control, and said motor being separate from said at least two main gas turbine engines.

17. The aircraft as set forth in claim 8, wherein said wide fuselage is defined as having a height and a width with said width being greater than one and a half times said height.

18. The aircraft as set forth in claim 17, wherein a curved surface on said fuselage provides an inlet to said dedicated boundary layer ingestion fans.

19. The aircraft as set forth in claim 8, wherein said main gas turbine engine each have a fan independent of said boundary layer ingestion fans.

20. The propulsion system as set forth in claim 8, wherein said main gas turbine engine each have a fan independent of said boundary layer ingestion fans.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1A shows an aircraft.

(2) FIG. 1B shows a detail of the FIG. 1A aircraft.

(3) FIG. 2 shows a detail of a propulsion system.

(4) FIG. 3 shows a rear view of the FIG. 2 propulsion system.

DETAILED DESCRIPTION

(5) FIG. 1A shows an aircraft 20 having a wide fuselage 22.

(6) As shown, a tail section 24 is provided. Gas turbine engines 26 are positioned outwardly of the tail section. It should be understood that this is not the only location for the main gas turbine engines 26 and they could be mounted in other locations, such as under the wings of the aircraft 20.

(7) As shown in a callout, the main gas turbine engines 26 include an engine fan 30 delivering air into a bypass duct and into a low pressure compressor 32 which is driven by a low pressure turbine 34. Downstream of the low pressure compressor 32 is a high pressure compressor 38. The high pressure compressor 38 is driven by a high pressure turbine 36. Air from the compressor 38 is delivered into a combustor 40, where it is ignited as known.

(8) To remove the boundary layer air from atop the fuselage 22, a plurality of dedicated boundary layer ingestion fans 28 are positioned in the tail section 24. As shown in the callout, the dedicated boundary layer ingestion fans 28 may include a control 25 for a motor 27 driving a dedicated fan rotor 29, all shown schematically. That is, the fans 28 are driven by a motor 27 independent of the engines 26. In one embodiment, there are seven boundary layer ingestion fans 28 positioned adjacent the tail section 24.

(9) In embodiments, the thrust provided by all of the dedicated boundary layer ingestion fans 28 combined is less than 20 percent, and in other embodiments less than 10 percent, of the overall thrust provided by the propulsion system including the dedicated boundary layer ingestion fans 28 and the main gas turbine engines 26.

(10) FIG. 1B shows a detail of the fuselage 22. A height h is defined and a width W is defined between opposed sides of the fuselage 22. In embodiments, the width W is more than one and a half times the height h.

(11) FIG. 2 shows a detail including a scoop inlet 42 leading into the dedicated boundary layer ingestion fans 28. As can be seen, the scoop inlet includes a curved surface moving into an inlet for the boundary layer ingestion fans 28 (See FIG. 1A).

(12) FIG. 3 is a rear view showing the dedicated boundary layer ingestion fans 28 having an exhaust 60 rearward of the aircraft.

(13) In embodiments, it may be desirable to substitute a gear connection between a gas turbine engine 26 to drive the dedicated fan rotors 29, rather than the dedicated motor 27. In other embodiments, the motor 27 is utilized and may be an electric motor or a gas turbine engine (power turbine).

(14) The boundary layer air is less problematic at low aircraft speeds. As such, in order to increase efficiency, the dedicated boundary layer ingestion fans 28 may be turned off during takeoff, but utilized at higher speed operation, such as cruise or climb conditions.

(15) In embodiments, the dedicated boundary layer ingestion fan rotors 28 may have a diameter of less than 15 inches and may be approximately 10 inches. Each dedicated boundary layer ingestion fan may provide propulsion of less than 50 lbf of thrust and may be approximately 34 lbf. Also, the fans may operate at a fan pressure ratio of less than 1.5 and in one embodiment approximately 1.25 at cruise condition.

(16) Although an embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.