Abstract:
An apparatus comprising is provided including an auxiliary power unit positioned within an aircraft. A reverse thrust assembly is driven by the auxiliary power unit to provide reverse thrust during landing of the aircraft. An air flow surface having a first boundary layer of moving fluid when external air is flowed along the airflow surface which could be a nacelle, pylon or any other aircraft surface. A movable member is configured to move between a first position to direct the boundary layer to the auxiliary power unit during climb and cruise of the aircraft, and to a second position to direct a free stream air feed to the auxiliary power unit during landing of the aircraft. Further, the movable member may switch to a third conduit to extract the boundary layer from the interior surface of an engine air intake to reduce the main engine inlet losses and distortion.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to U.S. Provisional Patent Application No. 62/091,962 filed Dec. 15, 2014, the contents of which is hereby incorporated in its entirety. 
     
    
     FIELD OF TECHNOLOGY 
       [0002]    The present disclosure relates to gas turbine engines, and more particularly, but not exclusively, to an auxiliary power unit configured within an aircraft fuselage configured to remove boundary layer flow from an air flow surface to reduce drag. More particularly, a design and method to utilize the auxiliary power unit to selectively remove boundary layer flow or a freestream air feed is disclosed. 
       BACKGROUND 
       [0003]    Aircraft utilize gas turbine engines for propulsion as well as energy generation utilized in aircraft operation. In addition, it is known to utilize auxiliary power units to provide additional energy generation needed by the aircraft to power electrical power demands in the aircraft including landing gear actuation and control surface actuation. In addition, composite aircraft construction will likely require powering heat pumps to pump out heat as they may be substantially more insulated from the outside atmosphere. Finally, it may be desirable to power reverse thrust assemblies directly from an auxiliary power unit for improved effectiveness over conventional thrust reversers. 
         [0004]    As the number of systems that utilize the auxiliary power unit expand, and their corresponding energy draw increases, the need for larger and more powerful auxiliary power units will increase. The use of powerful auxiliary power units in ultra-bypass ratio turbofans to power dedicated thrust reverse assemblies may further their increase. The larger and often heavier auxiliary power units may decrease the efficiency of the aircraft operation if not counterbalanced by increases in efficiency elsewhere. 
         [0005]    Overcoming the efficiency concerns associated with the use of larger auxiliary power units would be helpful, could provide for improve aircraft operation, and could provide for the continued expansion and development of systems that rely on the auxiliary power unit for operational electrical power. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    While the claims are not limited to a specific illustration, an appreciation of the various aspects is best gained through a discussion of various examples thereof. Referring now to the drawings, exemplary illustrations are shown in detail. Although the drawings represent the illustrations, the drawings are not necessarily to scale and certain features may be exaggerated to better illustrate and explain an innovative aspect of an example. Further, the exemplary illustrations described herein are not intended to be exhaustive or otherwise limiting or restricted to the precise form and configuration shown in the drawings and disclosed in the following detailed description. Exemplary illustrations are described in detail by referring to the drawings as follows: 
           [0007]      FIG. 1  schematically illustrates some aspects of one non-limiting example of a gas turbine engine in accordance with one non-limiting exemplary embodiment of the present disclosure; 
           [0008]      FIG. 2  schematically illustrates some aspects of one non-limiting example of an aircraft assembly according to one non-limiting exemplary embodiment of the present disclosure; 
           [0009]      FIG. 3  schematically illustrates some aspects of one non-limiting example of an aircraft assembly illustrated in  FIG. 2 , the aircraft assembly illustrated showing flow to an auxiliary power unit removing a boundary layer from an airflow surface; 
           [0010]      FIG. 4  is an illustration of the aircraft assembly illustrated in  FIG. 3 , the aircraft assembly illustrated showing flow to an auxiliary power unit from a freestream air feed; 
           [0011]      FIG. 5  is an illustration of the aircraft assembly illustrated in  FIG. 3 , the aircraft assembly illustrated showing a variable moving member proportioning flow to an auxiliary power unit from the airflow surface and the freestream feed; and 
           [0012]      FIG. 6  schematically illustrates some aspects of one non-limiting example of an aircraft assembly illustrated in  FIG. 2 , the aircraft assembly illustrated showing removal of a boundary layer from an engine intake surface. 
       
    
    
     DETAILED DESCRIPTION 
       [0013]    An aircraft assembly is described herein and is shown in the attached drawings. Gas turbine engines are utilized as exterior engines for propulsion. An auxiliary power unit, which itself may comprise a gas turbine engine, is positioned within the fuselage of the aircraft. The auxiliary power unit is selectively fed intake air from a freestream air feed during landing when thrust reversing is required or during high power requirements, from the low pressure regions of the main engine inlets during high angle of attack operations to reduce inlet distortion losses, or from aircraft/nacelle boundary layer ports to reduce drag during climb and cruise of the aircraft. The present disclosure describes such a system. In addition, the present disclosure describes a method of balancing the reduction of drag with the need for electrical power production from the auxiliary power unit. 
         [0014]      FIG. 1  illustrates a gas turbine engine  10 , which includes a fan  12 , a low pressure compressor  14  (“LP compressor”), intermediate pressure compressor  16  (“IP compressor”), a high pressure compressor  18  (“HP compressor”), a combustor  20 , a high pressure turbine  22  (“HP turbine”), an intermediate pressure turbine  24  (“IP turbine”) and low pressure turbine  26  (“LP turbine”). The HP compressor  18 , the IP compressor  16  and the LP compressor  14  are connected to a respective one of an HP shaft  28 , an IP shaft  30  and an LP shaft  32 , which in turn are connected to a respective one of the HP turbine  22 , the IP turbine  24  and the LP turbine  26 . The shafts extend axially and are parallel to a longitudinal center line axis  34 . Additionally, two or more of these shafts and an outer body structure  36  (“body”) are rotatably connected to one another by an intershaft bearing assembly  38 . While  FIG. 1  illustrates a three shaft engine, it will be appreciated that other embodiments can have configurations including more or less than three shafts. During general operation of the engine  10 , ambient air  40  enters the fan  12  and is directed across a fan rotor  42  in an annular duct  44 , which in part is circumscribed by fan case  46 . The bypass airflow  48  provides a fraction of engine thrust while the primary gas stream  50  is directed to the combustor  20  and the turbines  20 ,  22 ,  24 , and then exhausted through a nozzle  52  generating thrust. 
         [0015]      FIG. 2  illustrates an aircraft assembly  100  incorporating the gas turbine engine  10  of  FIG. 1 . The aircraft assembly  100  utilizes gas turbine engines  10  in the form of external engines  102  mounted on the aircraft assembly  100  to produce propulsion for flight. The external engines  102  may be mounted directly to a wing  104  as illustrated or may be mounted to a variety of aircraft structures, such as the fuselage  106  or tail assembly  108 . The external engines  102  may even be mounted to these structures indirectly such as through the use of a pylon  110  as illustrated in  FIG. 3 . The external engines  102 , in one non-limiting exemplary example, may be housed within nacelles  112 . In addition to the external engines  102 , the aircraft assembly may include at least one auxiliary power unit  114  for producing electrical power to a variety of aircraft assembly systems  116 . These systems may include, but are not limited to battery storage  118 , landing gear systems  120 , environmental control systems  122 , heat pumps  124 , and reverse thrust assemblies  126 . The auxiliary power unit  114  may be comprised of a gas turbine engine  10  coupled to a generator  128 . In one non-limiting exemplary example, it is contemplated that the auxiliary power unit  114  may be positioned within the fuselage  106  of the aircraft. 
         [0016]    As the number of aircraft assembly systems  116  that rely on the auxiliary power unit  114  increase, the required size and capacity of the auxiliary power unit  114  may increase as well. In addition, composite fuselage materials may require the use of heat pumps  124  to expel excess heat within the cabin. Dedicated reverse thrust assemblies  126  may rely on the auxiliary power unit  114  for power during the landing of the aircraft  100 . It would be desirable to counterbalance the effects of a larger and possibly heavier auxiliary power unit  114  by improving the efficiency of the aircraft performance. The present disclosure, therefore, contemplates utilizing the auxiliary power unit  114  to improve aircraft efficiency by harnessing its suction to remove the aircraft surface/engine inlet boundary layer. 
         [0017]      FIG. 3  is a non-limiting exemplary embodiment of the current disclosure. The auxiliary power unit  114  is positioned within the fuselage  106  of the aircraft. The outer surface of the aircraft  100  defines an airflow surface  130  over which air  132  flows during operation of the aircraft  100 . The air  132  forms a boundary layer  134  along the airflow surface  130 . The airflow surface  130  may include a plurality of boundary layer bleed slots  136  formed therein. In 
         [0018]      FIG. 3 , the boundary layer bleed slots  136  are formed in the nacelles  112  and the pylons  110 . It should be understood, however, that the boundary layer bleed slots  136  may be formed in any of the aircraft  100  exterior surfaces including, but not limited to the wings  104  and the fuselage  106  itself. A first conduit  138  is positioned between the airflow surfaces  130  and the auxiliary power unit  114 . A second conduit  140  is positioned between the auxiliary power  114  and a freestream air feed  142  (see  FIG. 4 ). A movable member  144  is positioned between the auxiliary power unit  114  and the first and second conduits  138 ,  140  to switch from one source to the other. 
         [0019]    The movable member  144  is configured to be moved between a first position  146  that provides for the passage of at least a portion of the boundary layer  134  from the airflow surface  130 , through the first conduit  138 , to the auxiliary power unit  114  (see  FIG. 3 ) and a second position  148  that provides passage of the freestream air feed  142 , through the second conduit  140 , to the auxiliary power unit  114  (see  FIG. 4 ). When the movable member  144  is in the first position  146 , the auxiliary power unit  114  is fed from the boundary layer  134 . The suction from the auxiliary power unit  114  pulls in the boundary layer  134 , which in turn reduces aerodynamic drag of the aircraft  100 . Although this may be desirable in any number of situations, one exemplary example contemplates configuring the movable member  144  into the first position  146  during climbing and cruising of the aircraft  100 . In another exemplary example, the movable member  144  may be in the first position  146  anytime the maximum output of the auxiliary power unit  114  is not desired. The auxiliary power unit  114  will generate power at a lower rate when fed from the first conduit  138  and may therefore be utilized to charge the batteries  118  or power other systems not requiring peak output. 
         [0020]    As shown in  FIG. 4 , when the movable member  144  is in the second position  148 , the auxiliary power unit  114  draws air from a freestream air feed  142 . The freestream air feed  142  is contemplated to include any free flow of air from the exterior of the aircraft  100 . This allows the auxiliary power unit  114  to operate unimpeded and maximize electrical power generation. Although this may be desirable in a variety of situations, one exemplary example contemplates configuring the movable member  144  into the second position  148  during takeoff and landing of the aircraft  100  when electrical demands of aircraft assembly systems  116  may be highest. In another exemplary example, the movable member  144  may be in the second position  148  anytime the maximum output of the auxiliary power unit  114  is desired. In one exemplary example, the auxiliary power unit  114  is used to power a dedicated reverse thrust assembly  126  such as a dedicated reverse thrust fan  150  during landing of the aircraft. The auxiliary power unit  114  may power the dedicated reverse thrust fan  150  either electrically or through a mechanical connection. In another exemplary example, it is contemplated that such a dedicated reverse thrust fan  150  may be powered by the auxiliary power unit  114  and operated in a positive thrust direction, in combination with the external engines  102 , during periods when increased thrust is desired. 
         [0021]      FIG. 5  illustrates an alternate exemplary example, wherein the movable member  144  is comprised of a variable position member  152 . The variable position member  152  is configured to proportion the flow of air into the auxiliary power unit  114  from both the first conduit  138  and the second conduit  140 . This allows the boundary layer  134  to be at least partially removed during all periods of operation when short of the maximum power from the auxiliary power unit  114  is required. Additionally, it allows proportioned flow from the second conduit  140  to be supplied in amounts sufficient for the auxiliary power unit  114  to provide current draw requirements at all times. The use of a proportioned flow allows the reduction of friction, through boundary layer removal, and the generation of power from the auxiliary power unit  114  to be optimized continuously during aircraft  100  operation. 
         [0022]      FIG. 6  illustrates still another alternate exemplary example, wherein the auxiliary power unit  114  is in further communication with a third conduit  154  in communication with an engine intake surface  156 . The engine intake surface  156  has a second boundary layer  158  of air moving across it. The moveable member  144 , which may comprise a variable position member  152 , is positioned between the third conduit  154  and the auxiliary power unit  114 . The moveable member  144  is configured to allow the second boundary later  158  of air to feed the auxiliary power unit  114  during takeoff of the aircraft. By removing the second boundary layer  158 , the engine intake air  160  is conditioned and can reduce inlet flow distortion during takeoff to increase thrust and stall margin. In an exemplary example, the variable position member  152  proportions the feed into the auxiliary power unit  114  from both the third conduit  154  and the first conduit  138  during climb of the aircraft. This allows proper conditioning of the engine intake air  160  while additionally reducing drag. 
         [0023]    It will be appreciated that the aforementioned method and devices may be modified to have some components and steps removed, or may have additional components and steps added, all of which are deemed to be within the spirit of the present disclosure. Even though the present disclosure has been described in detail with reference to specific embodiments, it will be appreciated that the various modifications and changes can be made to these embodiments without departing from the scope of the present disclosure as set forth in the claims. The specification and the drawings are to be regarded as an illustrative thought instead of merely restrictive thought.