Abstract:
An inlet for an aircraft, missile or other high speed airborne mobile platform, to receive intake air and compress the intake air for delivery to an engine of the mobile platform. The inlet has an array of inlet elements placed in side-by-side arrangement. Each inlet element has a passage for delivery of intake air. The array provides for compact volume and effective aerodynamic performance. The inlet may be mounted for rotation to start the inlet when at a supersonic speed. The inlet is shorter in length than traditional inlets and can be integrated into a wider variety of airframes, or at locations on existing airframes that would be difficult or impossible to integrate a traditional inlet on.

Description:
TECHNICAL FIELD 
   This disclosure relates generally to air intakes for airborne mobile platform engines, and in particular to an inlet formed of multiple inlet elements arranged into an array. 
   BACKGROUND 
   Modern high-speed airborne mobile platforms, for example jet aircraft, must meet performance requirements which call for an air induction system of substantial complexity. The inlet must provide intake air to the engine at a quantity and quality necessary to meet thrust requirements throughout the aircraft flight envelope. Accordingly, it must have a configuration which can efficiently receive and compress intake air at a variety of speeds and altitudes. Further, the inlet should have a compact volume so that it fits within tightly limited space constraints. The configuration of the inlet should facilitate uniformity in the flow of intake air and minimize adverse impacts to the aircraft. That is particularly difficult in an aircraft which has a complex aerodynamic shape. For example, some aircraft have edges and/or surfaces which are angled in two directions (i.e., swept back with respect to both the vertical and horizontal planes). Ideally, the inlet should conform to that contour and minimize generation of secondary flows and shock waves which produce flow non-uniformities. 
   Unfortunately, previous inlets fail to fully meet these needs. For example, some inlets have required a length for accomplishing compression of intake air which is excessive for the space available in the aircraft configuration. That necessitates a substantial re-design effort or, alternatively, a degradation of performance. Other inlets have configurations which sharply limit the potential location or size relative to the surrounding aircraft fuselage. 
   Another constraint on certain aircraft which operate at supersonic speed is the need to “start” the inlet. As known to those skilled in the art, an inlet having internal compression or mixed compression is designed to compress intake air moving at a supersonic speed within the interior of the inlet duct. The inlet must initially “swallow” a structure of shock waves when exceeding its starting Mach number in order to establish a stable condition where the inlet operates as intended. When the inlet is “unstarted,” a phenomenon in which all shock waves remain outside of the inlet, the thrust produced by the engine is reduced substantially. A process for starting the inlet has typically required a variable geometry duct which provides a capability to increase flow passage size and receive a larger quantity of intake air, thereby swallowing the shock waves. Unfortunately, that capability requires additional complexity and weight. 
   SUMMARY 
   Generally, an inlet according to various embodiments of the present disclosure is for a high speed mobile platform to receive intake air and compress the intake air for delivery to an engine. In one example the inlet is used with a high speed jet aircraft. The inlet comprises a plurality of inlet elements placed in side-by-side arrangement defining an array. Each inlet element has a passage for delivery of intake air. The array includes two or more of the inlet elements forming a row and two or more inlet elements forming a column. Each inlet element has a forward end, a rearward end, and a flow area along the passage which is non-uniform between the forward end and the rearward end for compressing intake air as it flows therethrough. 
   In another aspect, an air induction system according to the disclosure is for a high speed mobile platform, for example an aircraft, to receive an adjustable quantity of engine intake air. The system comprises an inlet having at least one passage for receiving a flow of intake air. The inlet has a front face for facing generally in a forward direction and defining a frontal area. A mount is for connecting the inlet to the aircraft at an adjustable position. The inlet is selectively moveable between a first position wherein the front face has a frontal area which is relatively larger and a second position wherein the front face has a frontal area which is relatively smaller, such that the inlet at its second position is capable of receiving a smaller quantity of intake air than when the inlet is at its first position. 
   In still a further aspect of the disclosure, a method of starting an air induction system of a high speed mobile platform, such as an aircraft, is for operation at a supersonic speed. The method comprises the steps of connecting an inlet to the aircraft with a mount which permits controllable movement of the inlet relative to the aircraft. The inlet has a front face for facing generally in a forward direction and defining a frontal area, wherein movement of the inlet changes the frontal area of the inlet. The aircraft is accelerated to a supersonic speed. The inlet is placed at a position having a frontal area which is relatively smaller such that the inlet is capable of receiving a smaller quantity of intake air. The inlet is moved to a different position having a frontal area which is relatively larger such that the inlet is capable of receiving a larger quantity of air. The aircraft is operated with the inlet at said different position. 
   Other features of the present disclosure will be in part apparent and in part pointed out hereinafter. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present disclosure will become more fully understood from the detailed description and the accompanying drawings, wherein: 
       FIG. 1  is a perspective view of an aircraft incorporating an array inlet in accordance with one embodiment of the present disclosure; 
       FIG. 2  is a side elevational view of the array inlet 
       FIG. 3  is a front elevational view of the array inlet of  FIG. 1 ; 
       FIG. 4  is a lower perspective view of the array inlet of  FIG. 1  with a sidewall portion of the array inlet removed to show the construction of the flowpaths of several of the inlet elements; 
       FIG. 5  is a typical cross-sectional side view of the flowpath for one inlet element; 
       FIG. 6  is an enlarged fragmentary front view of an array inlet of a second embodiment; 
       FIG. 7  is an enlarged fragmentary front view of an array inlet of a third embodiment; 
       FIG. 8  is a perspective view of an aircraft incorporating an array inlet of a fourth embodiment; 
       FIG. 9  is a schematic side elevational view of the air induction system at a first position shown in dashed lines and at a second position shown in solid lines; and 
       FIG. 10  is a schematic front elevational view of the array inlet and its connection to the aircraft. 
   

   Corresponding reference characters indicate corresponding parts throughout the views of the drawings. 
   DETAILED DESCRIPTION 
   Referring now to the drawings and in particular to  FIG. 1 , an air induction system according to an embodiment of the present disclosure is indicated generally at  10 . There are two air induction systems  10  positioned on a mobile platform, in this example an aircraft  12 , forward of corresponding engines  16 . Each system  10  provides intake air to the corresponding engine  16  at a quantity and quality necessary to meet thrust requirements throughout the aircraft flight envelope. Although the aircraft  12  shown in  FIG. 1  is a supersonic manned vehicle, it is understood that the system  10  may be used at any speed regime and with any form of mobile platform or machine capable of atmospheric flight, including without limitation missiles and manned or unmanned aircraft. 
   The air induction system  10  includes an array inlet  20  which is received in a cavity of the airframe structure and is configured to compress the intake air for delivery to the engine. As shown in  FIG. 2 , the inlet  20  includes a plurality of inlet elements  22  placed in an arrangement defining an array. Each inlet element  22  has a passage  24  for delivery of intake air toward the engine. In one embodiment, all of the inlet elements  22  are placed directly adjacent in side-by-side, contiguous arrangement. That facilitates desirable aerodynamic performance by avoiding any regions of stagnant flow which could occur between inlet elements, as well as minimizes volume. However, it is understood that the inlet elements may be placed in a non-contiguous arrangement (along the entire or partial length) without departing from the scope of this disclosure. 
   The inlet elements  22  are arranged so that the array  20  is two-dimensional, that is, it forms a row  26  of inlet elements  22  in a first direction and a column  28  of inlet elements in a second direction which is non-collinear with the first direction. In the embodiment shown in  FIGS. 2 ,  3 , and  4 , there are ten rows and eleven columns of inlet elements  22 . However, any number of two or more inlet elements may define a row or column. Further, a row or column may be a non-linear or non-uniform assembly of irregularly shaped inlet elements. 
   An advantage of the array inlet  20  is that a designer may increase or decrease the number of inlet elements  22  (and corresponding size of the inlet) as is needed for a particular engine or speed/altitude sizing condition without degrading aerodynamic performance. Unlike an inlet which is a single cavity or a one-dimensional stack of elements, the array inlet  20  may be scaled to any size or shape without adding structural supports within the flowpath and without altering the geometry of each element  22 . Thus, it avoids losses from a wide flowpath (i.e., large width-to-height aspect ratio) or from shock waves and boundary layer interaction which would arise with conventional sidewalls. During design studies, the designer has the flexibility to place the inlet  20  at a greater variety of locations on the aircraft while maintaining effective aerodynamic performance. Consequently, an improved optimum location and size may be determined. 
   Referring to  FIG. 5 , each inlet element  22  has a forward end  30  which terminates at a front edge  32 . In the embodiment shown in the drawings, the front edges  32  of adjacent inlet elements are coterminous (i.e., they have a common front edge). This provides for smooth aerodynamic flow and improved pressure recovery. Each inlet element  22  extends from the forward end  30  to a rearward end  34  and has a non-uniform flow area along the passage configured to compress intake air. Thus, unlike a screen or filter which merely passes flow, the array inlet  22  is configured to increase pressure as a prelude to combustion. The passage  24  converges to a minimum area region  36  ( FIG. 5 ) which is positioned between the forward end  30  and rearward end  34 . As known to those skilled in the art, intake air received within the inlet at a supersonic speed is typically slowed to near sonic velocity (Mach  1 . 0 ) at the minimum area region  36 . The passages  24  of all inlet elements  22  are generally parallel to minimize volume. In the embodiment shown in the drawings, the inlet elements are substantially identical. However, it is understood that the passages may be non-parallel and/or substantially different without departing from the scope of this disclosure. In another embodiment (not shown), those inlet elements which are positioned along an outer periphery of the array (i.e., the outermost row or column) function as boundary layer diverters to eliminate air at low speed and/or lower pressure and thereby prevent its delivery to the engine. 
   The array inlet  20  is adapted to have a compact volume so that it fits within tightly limited space constraints. As known to those skilled in this art, a supersonic inlet typically requires a length which is significantly longer (e.g.,  6  to  12  times) than its effective exit diameter in order to achieve adequate compression of intake air. The multiple, smaller inlet elements  22  of the present disclosure provide an effective diameter which is smaller than that of a single duct inlet. Accordingly, the length of the array inlet  20  is correspondingly smaller (e.g., one-tenth) to achieve an equal length-to-diameter ratio and an equal compression. Because it is relatively short, compared to the length of a conventional inlet, the inlet  20  may be integrated at a greater variety of locations on the aircraft. In some instances, the significantly shorter overall length of the array inlet  20  may enable its integration on a mobile platform at a location that would be impossible for a conventional inlet to be integrated at. 
   The forward ends  30  of said plurality of inlet elements collectively define a front face  40  of the inlet. In one embodiment, the front face  40  is generally planar. The front face  40  of the inlet may be oriented at an oblique angle with respect to the forward direction of the aircraft  12  and at an oblique angle with respect to the vertical direction. When the aircraft is in level flight, the front face  40  is angled in two directions from the orientation of approaching intake air. 
   As shown in  FIG. 2 , the rows and columns of the array are arranged at the front face  40  in an orthogonal and generally perpendicular relation. However, the array may be constructed with any angular relation between rows and columns (i.e., any non-collinear arrangement), or with non-straight rows or columns. For certain mobile platforms, for example an aircraft (not shown), the front face may be integrated on the aircraft fuselage in a blended manner such that the front face meets and substantially conforms to a contour of the aircraft directly adjacent to the front face. 
   Each passage  24  of every inlet element  22  is configured to effectively compress the intake air flowing into it. The front face  40  and leading portion of each passage is constructed to be a “waverider.” As known to those skilled in the art, the inlet is shaped such that it will generate a planar shock wave in the plane of the front face  40 . That leads to a generally uniform pressure distribution and good pressure recovery as the intake air enters each inlet passage  24 , as it eliminates interaction between transverse shock waves and the boundary layer. Accordingly, the front face  40  is swept rearwardly with respect to the direction of flow. The passage  24  of each inlet element has, in one embodiment, four side walls  42 . Preferably, the side walls  42  have a “caret” shape which is an effective waverider. As known to those skilled in the art, a caret shaped surface is the surface of an isosceles triangle which has been folded along its base altitude line to form two mirror-image right triangles which meet along the altitude line. The advantages are minimization of pressure losses, and that the side wall surfaces of the passage function as both compression surfaces and wall boundaries. 
   The passage  24  of each inlet element  22  can be contoured to turn the flow and provide a desired direction of efflux of the compressed air. For example, the flow may be vectored for purposes of better alignment with the engine or to facilitate a better external aircraft contour (e.g., for lower drag) adjacent to the inlet. As shown in the embodiment of  FIG. 5 , the passage turns so that air exits the passage at a different flow direction than upon entering. The passage has a first turn relative to the direction of incoming air (indicated by arrow F) followed by a second turn opposite the first turn. The upwash or downwash of the flow is therefore changed by the passage. However, it is understood that the passage may be straight, providing no change in flow direction, without departing from the scope of this disclosure. 
   In the embodiment shown in the drawings, the inlet  20  has a one-piece construction. That provides for low cost, weight, and complexity. However, the inlet could, if necessary, be formed of multiple parts which are fastened together. The inlet  20  is made of a high-strength, low-weight material, with an exemplary material being titanium. It may be fabricated by a suitable process such as investment casting. 
   Referring to  FIGS. 9 and 10 , the inlet in one embodiment is connected to the aircraft  12  such that it is controllably movable. The inlet  20  can be moved between a first position (shown in dashed lines on  FIG. 9 ) wherein the front face  40  has a frontal area A 1  which is relatively larger and a second position (shown solid on  FIG. 9 ) wherein the front face has a frontal area A 2  which is relatively smaller. Consequently, the inlet  20 , at its first position, is capable of receiving a larger quantity of intake air than when the inlet is at its second position. As known to those skilled in the art, the inlet  20  at the second position has a smaller “capture ratio” (ratio of frontal area to minimum flow area) such that, when at supersonic speed, the shock waves in front of the inlet may be swallowed into the inlet. Further, when the inlet  20  is at its second position, the forward ends of the passages may be better aligned with the direction of flow of intake air to further aid the swallowing of the shock waves. It is understood that the inlet  20  may be at a fixed position relative to the aircraft without departing from the scope of this disclosure. 
   The air induction system  10  includes a support  44  (broadly, a “mount”) which connects the inlet  20  to the nearby structure of the aircraft. In one embodiment, the mount  44  comprises a pivot configured such that the inlet  20  is moveable relative to the aircraft by rotation about said pivot. Rotating the inlet  20  changes the orientation of the front face  40  to an angle which is either more or less nearly perpendicular to the incoming flow F of intake air. It is understood that the inlet  20  can have various types of mounts and may be moveable by translation to change position, or by a combination of translation and rotation, without departing from the scope of this disclosure. An actuator  46  engages the inlet  20  for controllably moving the inlet between the first and second positions. The air induction system  10  also includes a flexible conduit or seal  50  positioned rearward of the inlet  20  for receiving the compressed air which exits the inlet and delivering it to the engine  16 . Because the entire inlet  20  is moveable, it reduces mechanical complexities which accompany a variable geometry duct for changing minimum area to start an inlet. 
   A method of starting the inlet  20  for operation at a supersonic speed requires initially operating the aircraft, the mobile platform or, for example an inlet at the first position which has a relatively larger frontal area A 1 . When the aircraft  12  has accelerated to a supersonic speed, a pilot or an automated controller energizes the actuator  46  so that the inlet  20  moves to the second position having a relatively smaller frontal area A 2 . The seal  50  flexes with movement of the inlet  20  so that there is no leakage of intake air. The inlet  20  remains at the second position until such time as the shocks are swallowed. As known to those skilled in the art, that occurs typically in less than one second. Then the inlet  20  may be moved to a third position (not shown) which has a frontal area larger than A 2 , for continued operation at supersonic speeds with stable operation and good pressure recovery. The third position is similar to the first position but can vary with speed and altitude, such that the third position can have a frontal area which is greater than, less than, or about the same as the first position A 1 . But it will always be greater than A 2 . The sequence for starting is thus to move the inlet such that, in relative size, the frontal area is initially larger, then smaller, then larger again. 
   Referring to  FIG. 6 , a second embodiment  60  of the array inlet is shown which has passages with three walls  42 . The triangular shapes fit in a compact arrangement. A third embodiment  70  ( FIG. 7 ) of the array inlet has hexagonal inlet element passages with six walls  42 . These embodiments can provide advantages in manufacturing and strength for particular aircraft integrations. A fourth embodiment  80  is shown in  FIG. 8 , wherein the front face of the inlet is generally conical, producing a conical initial shock wave system rather than a planar one. In another embodiment (not shown), there is no seal  50  such that air is allowed to leak when the inlet is at the second position. 
   In view of the above, it will be seen that a number of significant benefits and advantages are achieved with the various exemplary embodiments disclosed herein. When introducing elements of the present disclosure or the described embodiment(s), the articles “a”, “an”, “the” and “said” are intended to mean that there are one or more of the elements. The terms “comprising”, “including” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements. 
   As various changes could be made in the above without departing from the scope of the disclosure, it is intended that all matter contained in the above description and shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.