Abstract:
Diverter assemblies for aircraft air inlets include a diverter structure at least substantially surrounding the air inlet, and a fairing mounted to an upper edge of the diverter structure forwardly of the air inlet.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based on and claims domestic priority benefits under 35 USC §119(e) from U.S. Provisional Patent Application Ser. No. 61/580,969 filed on Dec. 28, 2011, the entire content of which is expressly incorporated hereinto by reference. 
    
    
     FIELD 
     The embodiments disclosed herein relate generally to aircraft inlet structures, and more particularly, to aircraft fuselage inlets provided with diverter structures having improved aerodynamic characteristics. 
     BACKGROUND 
     Commercial aircraft (e.g., regional jets) are usually equipped with an Auxiliary Power Unit (APU) that provides shaft and pneumatic power to different aircraft systems, including electronics and on-board electrical equipment, avionics, main engine air starters, air conditioning units and the like, before and during the flight. The conventional APU is a small gas turbine engine often located in the aircraft tail, fuselage wing root or fuselage wheel well area. Historically, the first commercial aircraft to have an APU installed was an early (circa  1963 ) model Boeing 727. At that time there were no ground support equipment at smaller airport facilities to support aircraft operations. Since then, different APUs have been installed in different types of aircraft that operated in smaller and less sophisticated airports. Since the APU allowed aircraft to operate independently from ground support equipment, the APU has contributed to air traffic expansion. The APU has thus been consolidated in civil and also military aircraft. Its function in the aircraft through many decades has progressed from main engine start on the ground to providing a source of electrical and pneumatic power while the aircraft is on ground or during flight. 
     Due to the increase of APU importance for aircraft operations, it has continually been subjected to improvement and sophistication of its components to achieve improved performance with reduced operational costs, within safe conditions. In order to reach this goal, the integration of the APU in the aircraft is one important aspect that must be considered by both aircraft manufacturer and APU supplier. This integration of the APU in the aircraft constitutes an important and relatively difficult challenge related to an attempt to find an optimal design through a very large number of design constraints. 
     Every APU has technical specifications that must be observed and complied with during its installation in the aircraft so that the APU can provide its minimum performance during any operational condition. One of these requirements is strongly correlated with the air intake that is necessary for APU functionality. The embodiments disclosed herein are therefore directed toward optimizing air intakes for not only on-board APUs but also air intakes for other related aircraft components, for example an aircraft APU Air Cooling Oil Cooler (ACOC). 
     A diverter is typically provided with APU air inlet ducts and serves as a shielding device to prevent undesired fluids (e.g., inflammable fluids) from being ingested by the duct. However, the diverter is a fixed structure which thus generates additional aerodynamic drag to the aircraft. In the worldwide context of development of “green technologies” with the aim to reduce pollutant emissions, many research efforts are underway to identify improved solutions to reduce the aircraft aerodynamic drag and therefore lower the fuel consumption. 
     On prior example to address this problem is disclosed in US Published Patent Application No. 2007/07106479 (expressly incorporated hereinto by reference) which proposes instead of a fixed structure to use a moveable door that is opened only when the APU is operating. Although this prior proposal appears to provide for reduced fuel consumption and noise, there are many technical problems that are associated with such proposal. First, it is a relatively high cost solution due to the mechanical actuators needed to open and close the door. Second, the solution is not simple, due to the electrical or pneumatic system required to install and power the actuators. Third, there is a relatively high impact on aircraft weight as compared to a fixed diverter already existing and installed on many commercial aircraft. Finally, and perhaps most importantly, due to the system complexity, there can be aircraft dispatch reliability issues in the event of a component failure associated with the moveable door. 
     SUMMARY 
     In order to further reduce the aircraft drag in the region of the APU air inlet, there are disclosed herein various embodiments of improved diverter structures that achieve a geometry profile having more efficient aerodynamic characteristics. In addition, the new and innovative diverter provided by the embodiments disclosed herein improve the air flow distribution and increase the APU pressure recovery due to the addition of an aerodynamic fairing. Moreover, these improved aerodynamic characteristics are achieved while observing all of the APU design constraints and maintaining the same functionality of the diverters currently in service (i.e., to avoid any undesired fluid from reaching the APU compressor). 
     The aerodynamically improved diverter structures of the embodiments disclosed herein were developed for the APU air inlets and generally include a leading edge that avoids airflow stagnation in the front region of the aircraft and defines a relatively smooth ramp in the aft region, thereby avoiding airflow detachment and increasing the average total pressure recovery. From numerical simulations and from flight-tests it has been confirmed that the diverter structures in accordance with the embodiments disclosed herein decreased the excrescence drag of the aircraft and therefore contributed to a decreased fuel burn. The embodiments of the diverter structures disclosed herein also improved the inlet total pressure recovery, which benefits the efficiency of the machine, in this case the APU. 
     According to some embodiments, diverter assemblies for an aircraft air inlet are provided which comprise a diverter structure at least substantially surrounding the air inlet, and a fairing mounted to an upper edge of the diverter structure forwardly of the air inlet. The fairing may be a solid structure which defines a relatively smooth ramp which slopes aftward toward the in the air inlet to thereby avoid airflow detachment forwardly of the air inlet. The diverter structure may have a substantially S-shaped cross-sectional configuration. 
     A fairing bracket may also be provided which is positioned along a forward edge of the air inlet such that the aft edge of the fairing is attached to the fairing bracket. In certain embodiments, the fairing may comprise a forward apex region, a concavely curved aft region defining a corresponding concavely curved aft edge and laterally divergent side regions joining the forward apex and aft regions. 
     The fairing bracket may itself have an S-shaped cross-sectional configuration. In such a configuration, the fairing bracket may include a lower base flange, an upper support flange and an intermediate support member which rigidly joins the lower base and upper support flanges to one. In some embodiments, the upper support flange is positioned rearwardly of the lower base flange so that the aft edge of the fairing overhangs a forward edge of the air inlet. 
     According to other embodiments, the air inlet includes an air scoop extending outwardly therefrom. The diverter may thus have a generally U-shaped member which substantially surrounds the air inlet and includes a base member connected to the aircraft, a support member and an upright member joining the base and support members to one another. In such embodiments, the fairing may include an aft region which slopes downwardly and rearwardly towards the air inlet. 
     These and other aspects and advantages of the present invention will become more clear after careful consideration is given to the following detailed description of the preferred exemplary embodiments thereof. 
    
    
     
       BRIEF DESCRIPTION OF ACCOMPANYING DRAWINGS 
       The disclosed embodiments of the present invention will be better and more completely understood by referring to the following detailed description of exemplary non-limiting illustrative embodiments in conjunction with the drawings of which: 
         FIG. 1  is a bottom perspective view of an aircraft tail section provided with an APU air inlet and diverter structure; 
         FIG. 2  is a schematic exploded view of an air inlet diverter assembly according to one embodiment of the invention; 
         FIG. 3  is a plan view as viewed from below the aircraft tail depicted in  FIG. 1  of the air inlet diverter assembly as shown in  FIG. 2 ; 
         FIG. 4  is a greatly enlarged partial cross-sectional view of the fairing region associated with the diverter assembly depicted in  FIG. 3  as taken generally along lines  4 - 4  therein; 
         FIGS. 5 and 6  are schematic bottom front and rear perspective views, respectively, of an APU Air Cooling Oil Cooler (ACOC) which employs a diverter assembly according to an and its associated conventional diverter structure; and 
         FIGS. 7 and 8  are front and side elevational views, respectively of the APU ACOC and its associated diverter assembly as shown in  FIGS. 5 and 6 . 
     
    
    
     DETAILED DESCRIPTION 
     Many of the details, dimensions, angles and other features shown in the figures of the present patent application are merely illustrative of particular embodiments of the invention. Accordingly, other embodiments can have other details, dimensions, angles and features, without departing from the spirit or scope of the present inventions. 
     Accompanying  FIG. 1  shows an APU inlet associated with an APU (e.g., APU APS  2300  model manufactured by Hamilton Sundstrand, not shown) installed in the tailcone fuselage of an aircraft AC, e.g., inside a dedicated compartment surrounded by a firewall (not shown). The APU is mounted in relation to an inlet  10  which allows inlet airflow to be received through an inlet silencer duct SD (positioned at 6 o&#39;clock as shown in  FIG. 3 ), and to discharge exhaust through an acoustic muffler that is mounted to exhaust ducts ED of the APU to reduce associated noise. The external perimetrical edge  10 - 1  of air inlet  10  is entirely surrounded by a contiguous fluid diverter in order to prevent ingestion of inflammable liquids by the APU compressor. 
     A conventional APU air inlet diverter  12  is typically installed as depicted in  FIG. 2  in a manner which completely bounds the air inlet  10 . More specifically, the diverter  12  is a generally S-shaped structure in cross-section having a base member  12 - 1  rigidly attached to the fuselage skin FS of the aircraft  10  immediately adjacent of the inlet  10 , an upper member  12 - 2  and an upright support member  12 - 3  which rigidly joins the base and upper support members  12 - 1 ,  12 - 2  such that the latter is outwardly and angularly disposed relative to the inlet  10  (see  FIG. 4 ). 
     The diverter  12  will typically include a forward apex region  12 - 4  relative to the flight direction FD of the aircraft AC in order to improve its aerodynamic flow characteristics with an aft region  12 - 5  that is generally transverse to the airflow during flight. However, due to its geometry characteristics, for instance its width (W) and attack angle (α), the diverter  12  acts as an obstacle to the air flow that passes through the region of the air inlet  10  and hence increases the excrescence drag of the aircraft AC. 
     As shown, e.g., in  FIGS. 2 and 3 , according to some embodiments of the present invention, a fairing assembly  20  is provided forwardly of the air inlet  10  in aerodynamic cooperation with the fluid diverter  12 . In this regard, the fairing assembly  20  is preferably an arcuately curved piece of solid material (e.g., aluminum sheet) having a forward apex end  20 - 1  conforming to the apex region  12 - 4  of the diverter  12  and a aft end  20 - 2  having a curved rear edge conforming to the curvature of forward section  10 - 1   a  of edge  10 - 1  of the inlet  10 . The fairing assembly thus provides a relatively smooth aerodynamic ramp which slopes aftward (relative to the flight direction FD of the aircraft AC) toward the air inlet  10  to thereby avoid airflow detachment forwardly thereof. The side edges  20 - 3  of the fairing assembly  20  diverge outwardly and rearwardly from the forward apex end  20 - 1  to the aft end  20 - 2  of the fairing  20 . 
     As is shown in  FIGS. 2 and 4 , the forward apex end  20 - 1  and side edges  20 - 3  of fairing assembly  20  is supported physically by an underlying portion of the diverter  12 . More specifically, the forward apex end  20 - 1  and side edges  20 - 3  are joined rigidly (e.g., via flush rivets) to the upper support member  12 - 2  of the diverter  12 . An S-shaped fairing support bracket  22  (or Z-shaped as viewed in the orientation of  FIG. 4 ) is positioned adjacent the forward edge  10 - 1   a  of the inlet  10  in order to support the rear edge  20 - 2  of the fairing  20 . As shown, e.g., in  FIG. 4 , the fairing support bracket  22  includes (relative to the aircraft AC) a lower base flange  22 - 1 , an upper support flange  22 - 2  and an intermediate support member  22 - 3  which rigidly joins the lower base and upper support flanges  22 - 1 ,  22 - 2  to one another such that the latter is rearwardly positioned relative to the former and relative to the flight direction (FD) of the aircraft. The rear edge  20 - 2  of the fairing  20  may thus be joined rigidly to the upper support flange  22 - 2  (e.g., via flush riveting). As is shown in  FIG. 4 , this rearward positioning of the rear edge  20 - 2  of the fairing  20  by means of the fairing support  22  creates an overhang in an aft direction of the rear edge  20 - 2  relative to the forward edge  10 - 1   a  of the inlet  10  (and relative to the inlet  10  itself). This overhang thus improves the aerodynamic characteristics of the inlet  10  by reducing drag in the region thereof. 
     As can be seeing in  FIGS. 5-8 , the aerodynamic principles discussed above may similarly be applied to an APU Air Cooling Oil Cooler (ACOC) air inlet assembly  50  which may typically be mounted in an upper tail cone region of the aircraft AC. In this regard, the APU ACOC air inlet assembly  50  will typically include an air scoop  52  positioned over the ACOC air inlet  54 . For aerodynamic purposes, the air scoop  52  will include a larger surface area entrance opening  52 - 1  and will slope rearwardly relative to the flight direction FD of the aircraft AC to a smaller surface area exit opening  52 - 2 . Since the air scoop  52  covers the ACOC air inlet  54 , some of the air flowing between the entrance and exit openings  52 - 1 ,  52 - 2 , respectively, will enter through the ACOC inlet  54  to serve as cooling air. 
     The ACOC inlet  54  is surrounded forwardly and laterally by a generally outwardly directed (relative to the inlet  54 ) U-shaped diverter  56  having a base member  56 - 1 , an upper support member  56 - 2  and an upright support  56 - 3  joining the base and upper support members  56 - 1 ,  56 - 2 . A solid sheet (e.g., aluminum) fairing  60  is mounted rigidly (e.g., via riveting) to a portion of the upper support member  56 - 2  forwardly of the entrance opening  52 - 1  of air scoop  52 . The fairing  60  has a forward apex end  60 - 1  and lateral side edges  60 - 2  which diverge outwardly and rearwardly relative to the flight direction FD of the aircraft AC. The apex end  60 - 1  and the lateral divergent side edges  60 - 2  are rigidly joined (e.g., via riveting) to respective underlying portions of the upper support member  56 - 2  of the diverter  56 . An aft end  60 - 3  of the fairing  60  slopes downwardly and rearwardly so as to terminate in generally flush and adjacent to the ACOC inlet  54 . In such a manner, airflow through the scoop  50  and into the inlet  54  is improved while decreasing aerodynamic draft associated with the diverter  56 . 
     While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope thereof.