Integrated pusher turbofan for aircraft

A propulsion system for a transport aircraft employs a gas turbine core coupled to a wing. A ducted fan is coupled to the core gas turbine extending downstream from and integrated in a trailing edge of the airplane wing.

REFERENCE TO RELATED APPLICATIONS

This application is copending with application Ser. No. 14/032,163 now U.S. Pat. No. 9,835,093 issued on Dec. 5, 2017 entitled Contra-rotating open fan propulsion system having a common assignee with the present application, the disclosure of which is incorporated herein by reference.

BACKGROUND INFORMATION

Field

Embodiments of the disclosure relate generally to power plants for transport aircraft and more particularly to a two stage pusher turbofan arrangement wherein the propulsor and associated shroud are mounted integrally aft of the trailing edge of the wing.

Background

High bypass ratio propulsor systems for large transport aircraft provide significant fuel efficiency and thrust increase over conventional turbojet power plants. Ducted fans enhance the qualities of high bypass aerodynamics by allowing aircraft operation at higher speeds and reduction of noise over unducted propulsors. Integration of ultra-high bypass ratio turbo-fan engines into a low-wing airplane with conventional landing gear in order to deliver reduced emissions and improved fuel efficiency, while avoiding the high noise traditionally associated with ultra-high bypass ratio unducted engines (often described as open-fan, open-rotor, or propfan engines) has not been accomplished.

It is therefore desirable to provide a structural design for integration of an ultra-high bypass ratio turbofan engine into a low-wing airplane.

SUMMARY

Exemplary embodiments provide a propulsion system for a transport aircraft employing a gas turbine core coupled to a wing. A ducted fan is coupled to the core gas turbine, extending downstream from and integrated in a trailing edge of the airplane wing.

A method of fabricating an airplane propulsion system is accomplished for the disclosed embodiments by coupling a ducted fan to a gas turbine core such that the ducted fan extends downstream from the gas turbine engine in a pusher configuration. A fairing is then employed for integration of the ducted fan into the wing structure.

DETAILED DESCRIPTION

The system and methods described herein provide embodiments for an ultra-high bypass ratio (cruise bypass ratio >15) turbofan engine, which has the core in front of the main propulsive fan in a pusher configuration to provide major improvements for aircraft emissions, performance and operating economics. The ratio of the mass-flow of air bypassing the engine core compared to the mass-flow of air passing through the core is referred to as the bypass ratio. Various embodiments demonstrate airplane level solutions to integrating such engines with a conventional airframe wherein the propulsor and the shroud (or duct) are mounted on the trailing edge of the wing. The core of the engine is mounted under or above the wing or is integral or embedded within the wing. The engine core can be made with any number of spools, with or without fixed or variable gearing in order to deliver power to the propulsive fan with both the propulsive fan and the core operating at proper rotational speeds. The engine core, while described herein as a gas turbine may alternatively be a direct or alternating current electrical motor, steam turbine or other prime mover. Additionally, the propulsor may be a two stage contra-rotating fan arrangement as depicted for the embodiments disclosed but may be a single stage fan as well.

Referring to the drawings,FIG. 1shows an aircraft10, having a conventional configuration of low mounting of wings12with respect to fuselage13and having main landing gear14and nose gear16arranged in a conventional manner. An engine core18is mounted under wing12closely coupled for direct structural attachment to the wing spars as will be described in greater detail subsequently. The engine core18drives counter rotating fans or propulsors20aand20b. A shroud or duct22closely receives the propulsors20aand20bfor enhanced aerodynamic performance of the propulsors and for noise reduction. Additionally, the shroud provides containment for released blades in the event of an engine failure. The thickness, structural design and fabrication for the shroud will incorporate containment requirements. The duct and propulsor arrangement may be, for example, the ducted fan coupled to the core gas turbine engine using a gear box as described in copending patent application Ser. No. 14/032,163 entitled Contra-rotating open fan propulsion system. The arrangement as shown for the port or left wing inFIG. 1is duplicated on the starboard or right wing.

As seen inFIG. 2A, the duct22housing propulsors20aand20bemploys a fairing24for aerodynamic and structural integration with the wing12. The fairing24and duct22are located between moving surfaces on the wing such as inboard flap26and outboard or main flap28. In alternative embodiments one or both of the moving surfaces may be aerodynamic control surfaces or may be primarily high-lift devices but with secondary function as primary control surfaces. For the embodiment shown, fairing24has a sculpted leading edge30with extending lateral points32integrating into the wing upper surface34and lower surface.

As shown inFIG. 2B, the fairing24is interconnected into the wing structure with partial chord ribs36which may mate with the structural ribs38of the wing structure extending aft from the aft spar40. The partial chord ribs36may be attached to the aft spar or structural ribs to support the duct22without direct support from the engine core. The attachments of the partial chord ribs36may be through pinned or resilient connections to allow flexing of the wing12without deforming of the fairing24and duct22. In a desirable embodiment shown inFIG. 2Band shown in detail inFIG. 2C, the duct attachment structure provided by the fairing24is free to “float” inside the wing mold line. The fan duct22is attached through the fairing24to struts25that attach to a pylon48supporting the core18similar to known turbofan engines but much shorter. The fairing24is supported by struts25engaging the partial cord ribs36only with clearance apertures through any intervening ribs. A deformable membrane39made of synthetic material seals the gap between the partial cord rib36and the wing interior to reduce aerodynamic drag. This allows wing deformations (due to aerodynamic or inertial loads acting on the wing) to be decoupled from the any deformation of the duct22. Additionally, decoupling the shroud from the wing isolates structural damage in event of a blade loss. If the propulsor sheds a blade, the fan duct22deforms to absorb the energy and contain the blade, to preclude the blade from penetrating the fuselage or the wing. If the fairing24is tightly coupled with the wing structure, the deformation of the duct22in the event of a blade loss might be transmitted to the wing box via the aft spar40resulting in potential structural damage. In the desired embodiment, the strut25transfers such loads to the pylon48which is attached securely to the wing structure and surrounded by a “dry-bay” to prevent any potential for the wing fuel tanks to rupture. The dry bay is the volume constrained by the two ribs49aand49bon either side of the pylon48.

Alternatively or in addition, the structural rigidity of the fairing24may be predetermined comparative to the structural rigidity of the duct22to absorb or mitigate flexing allowing the duct to remain circular and undistorted. The core18may be integrated into the wing with the short pylon48using thrust links50at the front and aft spars40,46.

As shown inFIGS. 3A-3L, the gas turbine core18may be mounted externally to the wing12via a pair of pylons44and48connected to the front spar46and aft spar40or, alternatively, the core18may be coupled directly to the wing spars46and40, such that a portion of the core is at least partially within the airplane wing as shown inFIGS. 3A, 3D, 3G and 3J. The pylon connection may be accomplished with the core18in an overwing position as shown inFIGS. 3B, 3E, 3H and 3Kor with the core18in an underwing position as shown inFIGS. 3C, 3F, 3I and 3L. The configuration ofFIG. 3Iis substantially as disclosed for the detailed embodiment described inFIGS. 2A and 2B.

As previously described, the propulsor may be interconnected to the core18with a gear box52. The gear box52may incorporate vertical and/or lateral displacement of the propulsor and duct22from an axis54of the core18using flexible joints and shafts.

A first general configuration of the propulsor duct22is shown inFIGS. 3A-3Cwherein the duct is substantially located over the wing upper surface34with the partial chord ribs36located in a bottom portion of the duct22. For the wing embedded mounting of the core18as shown inFIG. 3A, the gear box52provides an upward vertical offset for the propulsor. For the overwing mounting of the core18as shown inFIG. 3B, the gear box also provides a modest upward vertical offset. In various alternative configurations, the diameter of the propulsor and duct22or the length of the pylons44,48may be adjusted to allow axial alignment of the core18and propulsor and duct. For the underwing mounting of the core as shown inFIG. 3C, the gear box52provides a large upward vertical offset.

A second general configuration of the propulsor duct22is shown inFIGS. 3D-3Fwherein the duct is located with a midline54above but proximate to the wing top surface34. For the wing embedded mounting of the core18as shown inFIG. 3D, the gear box52and core18are substantially aligned with the propulsor. For the overwing mounting of the core18as shown inFIG. 3E, the gear box provides a modest downward vertical offset. In various alternative configurations, the diameter of the propulsor and duct22or the length of the pylons44,48may be adjusted to allow axial alignment of the core18and propulsor and duct. For the underwing mounting of the core as shown inFIG. 3F, the gear box52provides a modest upward vertical offset.

A third general configuration of the propulsor duct22is shown inFIGS. 3G-3Iwherein the duct is located with the midline54below but proximate to the wing lower surface56. For the wing embedded mounting of the core18as shown inFIG. 3G, the gear box provides a modest downward vertical offset for the propulsor. For the overwing mounting of the core18as shown inFIG. 3H, the gear box provides a large downward vertical offset. For the underwing mounting of the core as shown inFIG. 3I, the gear box52provides a small upward vertical offset. In various alternative configurations, the diameter of the propulsor and duct22or the length of the pylons44,48may be adjusted to allow axial alignment of the core18and propulsor and duct.

A final configuration of the propulsor duct22is shown inFIGS. 3J-3Lwherein the duct is substantially located under the wing lower surface54substantially even with or aft of the trailing edge with the partial chord ribs36located in an upper portion of the duct22. This configuration would be applicable primarily to high wing mounting. For the wing embedded mounting of the core18as shown inFIG. 3J, the gear box provides a large downward vertical offset for the propulsor. For the overwing mounting of the core18as shown inFIG. 3K, the gear box provides a very large downward vertical offset. For the underwing mounting of the core as shown inFIG. 3I, the gear box52provides a modest downward vertical offset.

Due to the operation of the propulsor behind the wing trailing edge the propulsor may be slightly less efficient in generating thrust due to the ingestion of the low-energy wing boundary layer and wake behind the trailing edge. Additionally, in some of the embodiments illustrated inFIGS. 3A-3I, there may be an increase in fan noise due to ingestion of the wake by the propulsor. In exemplary embodiments, increase in fan noise may be partially or wholly mitigated by ejecting air to fill the wake (or the air velocity deficit) behind the trailing edge of the wing adjacent to the propulsor as shown schematically inFIG. 4A.

As shown inFIG. 4Aengine core ventilation air may be employed to energize the boundary layer. For thermal and safety reasons, the engine core nacelle is typically vented using air either from the early stages of the engine core, or with scoops60using outside air. The source air circulates in the volume62between the engine core64and the core nacelle66and is typically combined with and ejected via the core nozzle68. This flow can then be ejected proximate the wing trailing edge69to fill the wake behind the wing trailing edge facing the propulsor duct22.

An alternative embodiment is shown inFIG. 4Bthe wing trailing edge wake and boundary layer are substantially removed, before being ingested into the propulsor duct22, via perforations70in the wing upper surface34and a suction chamber72. A vacuum system74attached to the suction chamber72provides pressure differential to draw the boundary layer into the suction chamber and then discharge the flow overboard at a location not interfering with the propulsor.

A method of fabricating an airplane propulsion system is provided by the disclosed embodiments as shown inFIG. 5. A ducted fan having a bypass ratio of greater than 15 is coupled to a gas turbine core with a gear box such that the ducted fan extends downstream from the gas turbine engine in a pusher configuration, step502. The ducted fan located to extend downstream from a trailing edge of the airplane wing, step504, and the ducted fan is located between a pair of movable wing surfaces, step506. A fairing for the ducted fan is integrated into the wing structure, step508and the gas turbine core is coupled to the wing, step510. The gas turbine core is substantially axially aligned with the ducted fan, step512, or the gas turbine core is offset from the ducted fan, step514. The gas turbine core may be mounted on an upper surface of the wing, step516, a lower surface of the wing, step518, or at least partially integrated within the wing, step520. The mounting the gas turbine core to the wing may be accomplished with a pair of pylons, step522, and the pair of pylons may be attached to the forward and aft spars in the wing, step524.

Having now described various embodiments of the disclosure in detail as required by the patent statutes, those skilled in the art will recognize modifications and substitutions to the specific embodiments disclosed herein. Such modifications are within the scope and intent of the present disclosure as defined in the following claims.