Abstract:
The present invention relates to a low signature jet engine outlet comprising movable border segments forming at least one circular arc and being movable radially for controlling the form and area of the outlet, at least one stationary border element for defining the form and area of the outlet, and movable coupling means for connecting the at least one circular arc to the at least one stationary border element. The coupling means are movable along a connection part of the at least one stationary border element, and the connection part of the at least one stationary border element is substantially flat and extending in a substantially radial direction of the at least one circular arc.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a low signature jet propulsion motor outlet. 
       BACKGROUND ART 
       [0002]    Stealth technology is a sub-discipline of military tactics, which aims at designing e.g. aircrafts, ships and missiles which are difficult to detect with e.g. radar, infrared or sonar. This can be done by developing a particular shape for the surfaces that tends to reduce detection, by redirecting electromagnetic waves from radars. Another way is to cover the construction with a radar absorbent material that reduces or blocks radar signals. Shields that hide a heat source can be effective against infrared detectors. 
         [0003]    When designing an aeroplane with a low signature the jet motor outlet causes problems. Motor outlets that are designed to have a low signature normally have a constant cross section area, i.e. the size of the outlet cannot be changed. This makes it very difficult to adapt them to velocities above the speed of sound or to use an after-burner. Some outlets have a rectangular cross section, which leads to a heavy and expensive construction that is not optimal in a stealth perspective. 
         [0004]    Conventional aeroplanes normally use an outlet with a circular cross section since they have high performance and a low weight. However, from a signature point of view, a circular cross section is ineffective, since the curved outer surfaces give reflexes within wide angles. One solution to combining a low signature with a circular outlet is to hide the outlet with e.g. stabilizers or tail booms on both sides of the outlet. GB 2428414 A shows an aircraft which engines are mounted forward of the trailing edge of a wing and between two vertical stabilizers. The benefit with this location is to reduce ground detectable acoustic signatures and infra red signatures. The construction suffers from the drawback of aerodynamic problems like e.g. large surfaces and a large cross section area in the rear parts of the aeroplane and a squeezed flow. 
         [0005]    The form and size of a circular motor outlet can be adjusted to different flight situations by providing controllable border surface elements at the periphery of the outlet. Those border surface elements can be hinged in the fixed channel of the motor outlet and be controlled by e.g. hydraulic means. A problem that arises with these variable circular outlets is the leakage of noise and heat from the edges and from the gap between the border surface elements. 
       DEFINITIONS 
       [0006]    It shall be noted that through this application “front” parts of the outlet refers to the parts that are located upstream from an engine point of view and the “rear” parts are located downstream. 
       SUMMARY OF THE INVENTION 
       [0007]    The present invention tries to overcome the above mentioned weaknesses of the known technology. 
         [0008]    The object of the invention is to create a jet engine motor outlet with a low signature. Another object with the present invention is to create a jet engine motor outlet which has a low weight. Still a further object of the present invention is to create a jet engine motor outlet with good propulsion and aerodynamic characteristics. 
         [0009]    The solution has been to design a jet engine motor outlet according to the characterizing parts of claim  1 . The invention defines a jet engine outlet comprising:
       movable border segments forming at least one substantially circular arc and being movable radially for controlling the form and area of the outlet,   at least one stationary border element for defining the form and area of the outlet, and   movable coupling means for connecting the at least one circular arc to the at least one stationary border element,
 
wherein the coupling means are movable along a connection part of the at least one stationary border element, and the connection part of the at least one stationary border element is substantially flat and extending in a substantially radial direction of the at least one circular arc.
       
 
         [0013]    The present invention further defines the movable border segments and the movable coupling means being hingedly connected to a fixed part of the outlet channel. It also provides pressure inducing means acting in the main direction of the outlet and affecting the movable border segments and the movable coupling means by means of a linkage system. 
         [0014]    This invention has the effect that the technology used for varying the area of circular outlets can be applied to outlets with other forms having a lower signature than a circular outlet. This means that the outlet is light, it is difficult to detect, it can be directed and still has acceptable propulsion and aerodynamic characteristics. 
         [0015]    The present invention further defines that the movable coupling means comprise an upper part that is positioned on one side of the stationary border element, a lower part that is positioned on the other side of the stationary border element, and a connection element for connecting the upper part with the lower part. The connection element is moved in a guide channel in the stationary border element. The upper part of the movable coupling means is formed as an oblong segment that is bent approximately 90° in a lengthwise direction. 
         [0016]    The advantages of the movable coupling means being bent and being movable in a guide channel is that the coupling means seal to the stationary border element so that no leaks of engine gases occur. The pressure acting on the movable border segments and the movable coupling means in the radial direction of the circular arcs is handled by the pressure inducing means and the linkage system, whereas the pressure from the engine gases acting on the movable coupling means in the direction towards the stationary border element is handled by the resistance of the stationary border element. 
         [0017]    According to one embodiment of the invention the movable border segments form a semicircle. This has an advantage that the outlet can be integrated into the construction lines of the aircraft. By letting the stationary border element protrude behind the circular arc and by providing stabilizers, which can be substantially vertical, or inward or outward leaning, on both sides of the outlet, the outlet can be shielded both from below and from the sides. 
         [0018]    According to another embodiment of the invention the movable border segments form two circular arcs, which arcs are located symmetrically on the same vertical axis, one above the other, and with the concave sides of the arcs directed towards each other. This has the advantage that the outlet can be shielded from the sides by e.g. two tail booms, integrated with the outlet, one tail boom on each side. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    Further advantages and features of the invention can be can be derived from the following detailed description of exemplary embodiments of the invention, with reference to the drawings. 
           [0020]      FIG. 1  is a schematic cross section rear view of a circular jet engine outlet according to the state of the art. 
           [0021]      FIG. 2  is a schematic cross section side view of a convergent-divergent circular motor outlet according to the state of the art. 
           [0022]      FIG. 3A  is a schematic cross section rear view of a jet motor outlet with a variable area according to one embodiment of the invention. 
           [0023]      FIG. 3B  is a schematic cross section rear view of a jet motor outlet with a variable area according to one embodiment of the invention. 
           [0024]      FIG. 3C  is a schematic cross section rear view of a jet motor outlet with a variable area according to one embodiment of the invention. 
           [0025]      FIG. 4  is a side view of the outlet according to one embodiment of the invention. 
           [0026]      FIG. 5  is a schematic cross section rear view of a jet motor outlet according to the invention provided with shielding stabilizers. 
           [0027]      FIG. 6  is a detailed view of the movable coupling means. 
           [0028]      FIG. 7  is a cross section view of a semicircular outlet, seen from above, according to the cut A-A seen in  FIG. 3 . 
           [0029]      FIG. 8  is a schematic side view of a cross section of a circular convergent-divergent outlet of the state in the art. 
           [0030]      FIG. 9  is a schematic side view of a cross section of a circular convergent-divergent outlet according to the invention. 
           [0031]      FIG. 10  is a schematic side view of a cross section of a variable ejector outlet according to the state in the art. 
           [0032]      FIG. 11  is a schematic side view of a cross section of a variable ejector outlet according to the invention. 
           [0033]      FIG. 12  is a schematic side view of a cross section of a fixed ejector outlet according to the state in the art. 
           [0034]      FIG. 13  is a schematic side view of a cross section of a fixed ejector outlet according to the invention. 
           [0035]      FIG. 14  is a schematic rear view of a jet motor outlet according to one embodiment of the invention. 
           [0036]      FIG. 15  is a schematic rear view of a jet motor outlet according to one embodiment of the invention. 
           [0037]      FIG. 16  is a schematic rear view of a jet motor outlet according to one embodiment of the invention. 
           [0038]      FIG. 17  is a schematic rear view of a jet motor outlet according to one embodiment of the invention. 
           [0039]      FIG. 18  is a schematic rear view of a jet motor outlet according to one embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0040]    With reference to  FIG. 1 , a circular jet engine outlet  1  according to the state of the art is generally depicted.  FIG. 1  shows a schematically cross section image of a circular outlet seen from a point behind the outlet. The outlet is constructed by two layers of overlapping, slightly bent movable border segments  3   c,    3   d.    
         [0041]    The outlet area can be varied by moving the border segments  3   c,    3   d  in and out along the radius. An enlarged state of the outlet  5  is shown in dashed lines in  FIG. 1 . The front edge of the border segments are hinged on the fixed part  13  of the outlet and the rear ends of the border segments can be moved by e.g. hydraulic means. This cannot be seen in  FIG. 1 . 
         [0042]    The two layer overlapping structure of the border segments  3   c,    3   d  generates a variable but tight construction. Since the underlying segments  3   c  are pressed outwards towards the overlying segments  3   d  by the pressure from the gases, the underlying segments  3   c  automatically seal towards the overlying segments  3   d  so it is not necessary to control them, although it is possible. The overlying segments  3   d,  however, must be steered inwards, towards the underlying segments  3   c,  and outwards. It is also possible to use a one layer overlapping structure where one end of each segment overlaps the next segment. Some outlets are further provided with outer segments  11  which surround and protect the outlet, but they are not shown in  FIG. 1 . 
         [0043]      FIG. 2  shows a schematic side view cross section of a convergent-divergent circular motor outlet  1  according to the state of the art. Hot air flow from the left fixed part  13  of the outlet and continues through the convergent-divergent outlet to the opening  15  on the right side in the figure. The outlet has inner movable divergent border segments  3   b,  inner movable convergent border segments  3   a  and outer segments  11 . The inner movable convergent border segments  3   a  are hinged at  17  to the fixed part  13  and can be turned to widen or narrowing the passage. This is performed by pressure inducing means  19 , like e.g. hydraulic, electric or pneumatic means acting on a ring formed structure  21 , which in turn affects a linkage system  23  that turns all the inner movable convergent border segments  3   a.  The ring formed structure  21  makes it possible to reduce the number of pressure inducing means  19 , to only a few. Evidently, it is possible to have one pressure inducing means  19  for every border segment  3 , but then it is difficult to regulate the pressure evenly and the system will be more complicated. The inner movable divergent border segments  3   b  are linked to the inner movable convergent border segments  3   a  and mainly follow them with approximately the same angle  25 . The outer segments  11  can be fixed or movable and are not discussed here. 
         [0044]    One embodiment of the new invention is drawn in  FIGS. 3A ,  3 B and  3 C. These figures shows a jet motor outlet  1  with a variable area that principally works in the same manner as the circular motor outlet of the state of the art as drawn in  FIGS. 1 and 2 . The difference is that one half of the outlet is replaced by a stationary border element  27  which gives the outlet a cross section profile in the form of a semicircle with an upper substantially semicircular arc  29  and a substantially flat bottom. The stationary border element  27  can be a separate element or it can be integrated into the aircraft fuselage. The figures shows the outlet in a retracted state  1  and an enlarged state  5 . 
         [0045]    The outlet is provided with movable coupling means  31  located adjacent the stationary border element  27 . The coupling means connect the movable border segments  3  with the stationary border element  27 . They comprise a first flat part that can glide along the stationary border element  27  and a second part that fits to the movable border segments  3 . The two parts are bent approximately 90° in regard to each other, so that they fit tightly to both the stationary border element  27  and the adjacent movable border segments  3 . 
         [0046]    In most of the figures in this application the movable coupling means  31  are overlapped by an overlying movable border segment  3   d.  It is to be understood that, instead, the movable coupling means  31  can overlap an underlying movable border segment  3   c.  See  FIG. 3B . 
         [0047]    In  FIG. 3C , the movable coupling means  31  are extended and overlap each other. 
         [0048]    This semicircular outlet can easily be integrated into the contour of the aircraft while still being light and having good propulsion and flight characteristics. It is also easy to direct the outlet to obtain thrust vectoring. 
         [0049]      FIG. 4  shows a side view of the outlet  1 . From the figure it can be seen that the outlet is provided on a protruding shelf  33  on the frame  35 . This shelf  33  protects the outlet from detection from the ground. 
         [0050]    The outlet can also be sheltered from the sides by providing stabilizers  37  on both sides of the outlet  1 . Such stabilizers are shown in  FIG. 5  and are already known in the art. The stabilizers can be substantially vertical, or outward or inward leaning. When stabilizers and a horizontal surface between them are used together to shield a circular outlet, the outlet will be placed over the horizontal surface and the air will be squeezed between the horizontal surface and the lower part of the outlet unless the distance between the outlet and the horizontal surface is large, which is hard to achieve on a fighter aircraft. With a semicircular outlet, the air passing in the corners  39  has more open space, resulting in less turbulence and better flight characteristics. 
         [0051]    One construction example of the movable coupling means  31  is shown in  FIG. 6 . It is important that the movable coupling means  31  seal against the stationary border element  27  so that no pressure or heat leaks appear. The movable coupling means  31  comprises a bent upper part  31   c  being located on the upper side of the stationary border element  27  and a lower part  31   d , which is positioned on underside of the stationary border element  27 . The upper and lower parts of the movable coupling means  31   c,    31   d  are connected by a connection element  41  which is movable in a guide channel  43  in the stationary border element  27 . 
         [0052]    The parts of the stationary border element  27 , which are connected to the movable coupling means  31  is hereafter referred to as the connection parts  45 . If these connection parts  45  are substantially flat and directed substantially radially, towards the midpoint of the semicircle, a half of the ring formed structure  21  and the pressure inducing means  19 , described together with  FIG. 2 , can be used also for controlling the movable coupling means  31  and the movable border segments  3  of a semicircular outlet. 
         [0053]    The pressure inside the channel is directed normally to the border surfaces. Consequently the pressure on the movable border segments  3  and the parts of the movable coupling means  31  adjacent the movable border segments  3  is directed radially outwards and this pressure is resisted by the linkage system  23  and the pressure inducing means  19 . The pressure on the stationary border element  27  and the parts of the movable coupling means  31  which is in contact with the stationary border element  27  is resisted by the strength of the stationary border element  27 . This construction has the benefit that the movable coupling means  31  always seal towards the stationary border element  27 , which reduces the risk of leaks or hot gases. 
         [0054]    The outer side of the movable coupling means  31  can be curved (dashed lines) in order to further minimize the outlet signature and improve the aerodynamics. The strength of the movable coupling means ( 31 ) will also increase, which is advantageous since the pressure on the movable coupling means  31  is high and acts in many directions. 
         [0055]    If the movable coupling means  31  are extended and overlapping, as in  FIG. 3C , it is possible to let the movable coupling means  31  rest upon the stationary border element  27 . The inner pressure from the gases presses the movable coupling means  31  outwards toward the stationary border element  27  and seals the seam between the movable coupling means  31 . This makes the lower part  31   d  and the connection element  41  superfluous. 
         [0056]      FIG. 7  shows schematically a cross section of the movable coupling means  31  of a convergent-divergent semicircular outlet and the guide channels  43  seen from the cut (A-A) in  FIG. 3 . The figure shows the stationary border element  27 , the fixed part of the outlet  13 , and the movable convergent and divergent coupling means  31   a,    31   b  in a retracted and a widened state. The dashed lines show how a point on the movable convergent and divergent coupling means  31   a,    31   b  moves. As the movable convergent coupling means  31   a  are hinged, a point at the edge will move in a circular arc. Hence, the connection element  41  of the movable coupling means  31   a  can glide in a narrow glide channel  43  in the stationary border element  27 . The divergent coupling means  31   b  are linked to the convergent coupling means  31   a . Therefore a point at the divergent coupling means  31   b  will move over an area  47 , so the glide channel for the divergent coupling means  31   b  must be wider. 
         [0057]      FIG. 8  displays schematically a cross section of a circular convergent-divergent outlet of the state in the art. A similar outlet is shown in  FIG. 2 . This type of outlet can be used on aircrafts flying above the speed of sound. The striped parts in the figure show the fixed channel and the unfilled parts show the movable border segments  3   a,    3   b.    
         [0058]      FIG. 9  displays a cross section of a variable convergent-divergent outlet according to the invention with the movable border segments  3   a,    3   b  forming the upper semicircular border of the outlet and the stationary border element  27  protruding behind the outlet and shielding the semicircular arc. 
         [0059]      FIG. 10  presents a cross section of an ejector outlet with a variable circular outlet which can be used on aircrafts flying above the speed of sound. In this kind of outlets a secondary air stream  49  passes between the inner  3  and the outer segments  11  and the secondary air stream  49  affects the primary air stream  51  in a way similar to a divergent surface. 
         [0060]      FIG. 11  shows that the invention can be applied to other outlets than a convergent-divergent outlet.  FIG. 11  displays a cross section of a variable ejector outlet according to the invention with the movable border segments  3  forming the upper border of the outlet and the stationary border element  27  protruding behind the outlet and shielding the semicircular arc. 
         [0061]      FIGS. 12 and 13  show a cross section of an ejector with a fixed outlet. In  FIG. 12  the outlet is circular and in  FIG. 13  the outlet is semicircular according to the invention. 
         [0062]    In another embodiment the cross section of the outlet has approximately the form of a circular segment  53 , which is depicted in  FIG. 14 . As can be seen in the figure, the stationary border element  27  is constituted by two substantially flat connection parts  45  with a curved surface  55  between them. It is important that the connection parts  45  are flat and directed substantially radially, related to the circular segment, if the ring formed structure  21  and pressure inducing means  19  described earlier in the application is to be used. It should be realized from the figure that the movable coupling means  31  can slide on the stationary border element  27  in a guide channel  43  in the same manner as in a semicircular outlet. 
         [0063]    The curved surface  55  has no restrictions and can principally have any form. The curved surface  55  shown in  FIG. 14  can e.g. be formed as straight extensions of the flat connection parts  45 , which would result in a cross section in the form of a circle section (dashed lines). The angle  57  of the circular segment in the figure is about 135°. The angle of the segment is, however, not limited to 135° but could principally have any angle between 0° and 360°. 
         [0064]    This embodiment has the advantage that the outlet can be partly integrated in the structure of e.g. two tail booms  59  located under each side of the outlet. This is another way to hide the outlet from the sides and make it difficult to detect the aircraft while still having good flight properties and a low weight. 
         [0065]    In the further embodiments the outlet is supposed to be integrated in the structure of e.g. two tail booms  59 , which restricts the size and form of the outlet. These embodiments are presented in  FIGS. 15-18 . In these figures the cross section is built of two circle segments  53  pointing at each other, connected in some way. The two stationary border elements  27  comprise flat connection parts  45  in the areas which come in contact with the movable coupling means  31 . This has the benefit that the movable coupling means  31  and the movable border segments  3  can be steered by two arcs of the ring formed structure  21  and the pressure inducing means  19  described earlier (not shown in  FIG. 15 ). The stationary border elements  27  can be separate elements or they can be integrated into the aircraft fuselage. 
         [0066]    The principle of the movable coupling means  31  gliding in guide channels in the stationary border elements  27  can be applied to these embodiments. The form of the parts of the stationary border elements  27  that do not belong to the connection parts  45  are not limited by the invention. They can e.g. be straight as seen in  FIG. 15  or curved as in  FIG. 16 . 
         [0067]    The crosses show the circular midpoint  61  of the two segments. In  FIG. 17  the two segments overlap. Still though, the connection parts  45  are substantially flat and directed substantially radially related to the adjacent circular segment. 
         [0068]      FIG. 18  presents an additional form of the outlet that is covered by the invention. The circular segments  53  are in the form of two semicircles with separate circular midpoints  61  and located at a distance from each other. Even here the two stationary border elements  27  comprise flat connection parts  45  in the areas which come in contact with the movable coupling means  31  and these connection parts  45  are directed substantially radially in regard of their adjacent semicircles. 
         [0069]    It should be obvious to the reader that the form of the outlet is not intended to be limited by the examples shown in the figures. Instead, the scope of the invention is limited by the technical features described in the claims. 
         [0070]    Features of the above mentioned different embodiments may be combined with each others.