Abstract:
A mechanism and methods for directing the flow of exhaust gases associated with a V/STOL aircraft. A pair of constant area nozzles are associated with a plenum chamber that receives and contains exhaust gases. The nozzles are independently rotatable within circular exhaust openings in the plenum chamber to direct, or vector, exhaust exiting from the plenum chamber in preselected directions such as vertically downward or directions forward or aft of the vertical plane.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to propulsion systems for vertical and short takeoff and landing (V/STOL) aircraft. More particularly, the invention relates to mechanisms for vectoring or directing the flow of exhaust from such propulsion systems. 
     2. Description of the Related Art 
     A class of V/STOL aircraft use lift fans or lift engines to generate the thrust needed to cause the aircraft to take-off vertically as well as to move laterally through the air. The exhaust gases from the lift fans are directed, or vectored, in various directions in order to move the aircraft laterally and longitudinally. 
     One method of directing exhaust flow requires the use of louvers that can be moved to direct the air flow forwardly or rearwardly away from the lift fan. Such an arrangement is described in U.S. Pat. No. 5,312,069. However, as louvers are moved, they tend to obscure or close off part of the exhaust area. This is disadvantageous as it will tend to cause a loss of thrust power. 
     Another approach is to use a ball and socket joint to provide flow deflection. If ball and socket joints are used for movement of a nozzle, the joints are subject to wear at the points where the joint attaches to the socket. Further, such joints may not seal properly leading to loss of thrust. 
     SUMMARY OF THE INVENTION 
     The present invention provides a novel mechanism and methods for directing the flow of exhaust gases associated with a V/STOL aircraft. In a preferred embodiment, the mechanism includes a pair of constant area nozzles associated with a plenum chamber that receives and contains exhaust gases. The nozzles are independently rotatable within circular exhaust openings in the plenum chamber to direct exhaust exiting from the plenum chamber in preselected directions such as vertically downward or directions forward or aft of the vertical plane. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side view, partially in cross-section, of the forward end of an exemplary V/STOL aircraft depicting placement of a lift fan, input power shaft and an exhaust system having a plenum with dual exhaust nozzles as constructed in accordance with the present invention. 
     FIG. 2 a  is a side view of portions of the exhaust system wherein the exhaust nozzles are configured to direct exhaust vertically downwardly. 
     FIG. 2 b  is an upward-facing bottom view of the components shown in FIG. 2 a.    
     FIG. 3 is a side view of portions of the exhaust system wherein the exhaust nozzles are configured to direct exhaust 20 degrees aft. 
     FIG. 4 a  is a side view of portions of the exhaust system wherein the exhaust nozzles are configured to direct exhaust 60 degrees aft. 
     FIG. 4 b  is an upward-facing bottom view of the components shown in FIG. 4 a.    
     FIG. 5 a  is a side view of portions of the exhaust system wherein the exhaust nozzles are configured to direct exhaust 15 degrees forward. 
     FIG. 5 b  is an upward-facing bottom view of the components shown in FIG. 5 a.    
     FIG. 6 is a side cross-sectional view of an exemplary nozzle shown apart from the remainder of the exhaust assembly. 
     FIG. 6A is an end-on view of the proximal end of the nozzle taken along lines A—A in FIG.  6 . 
     FIG. 6B is an end-on view of the distal end of the nozzle taken along lines B—B in FIG.  6 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     General details concerning the construction and operation of V/STOL aircraft and their propulsion systems are described in U.S. Pat. Nos. 5,209,428; 5,312,069; 5,320,305 and 4,901,947, all of which are assigned to the assignee of the present invention. These patents are each incorporated herein by reference. 
     FIG. 1 illustrates the forward portion of an exemplary V/STOL aircraft  10  having a fuselage  12  with a longitudinal axis  13 . The fuselage  12  contains a cockpit  14 , landing wheels  16  and other known features. The fuselage  12  defines an air intake vent  18  upon its upper surface. A vertically-disposed, bladed lift fan  20  is retained within the fuselage  12  to receive air from the intake bell mouth  18 . The lift fan  20  is a thrust engine that generates thrust for the aircraft  10 . It will be understood with reference to U.S. Pat. No. 5,209,428 that the lift fan  20  is operably interconnected with a more rearwardly-located engine section (not shown) that is also used for propulsion of the aircraft  10 . The details of the more rearwardly-located fan section will not be described here. An input power shaft  22  transmits rotational power from the main engine (not shown) of the aircraft  10  to the lift fan  20  for rotation of the blades within the fan  20 . The lift fan  20  is surrounded by a cylindrical housing  21  with exhaust flow tubing  23  disposed beneath. As a result, exhaust gases generated by the lift fan  20  are directed through exhaust flow tubing  23 . 
     A plenum chamber  24  is located below the lift fan  20  and exhaust flow tubing  23  for the collection of exhaust gases generated by the lift fan  20 . The construction of the plenum chamber  24  is best appreciated with reference to FIGS. 2 a  and  2   b  wherein the underside of the structure is shown in detail. The plenum chamber  24  has an outer shell that defines a pair of curved exhaust tubes  26 ,  28  that each terminate at a lower end in a circular exhaust opening  30 . The circular openings  30  are located one behind the other along the axis  13  of the aircraft  10 , as FIG. 2 b  of the drawings shows. The circular openings  30  are also angled laterally and longitudinally from the vertical plane. The two openings have the same angle longitudinally, but opposing matched angles laterally. A preferred angle of lateral offset from the vertical plane is 40 degrees. 
     A forward nozzle  32  and a rear nozzle  34  are rotationally affixed to the circular openings  30 . Due to the “one behind the other” arrangement of the circular openings  30 , the forward nozzle  32  is located forwardly from the rear nozzle  34  along the axis  13  of the aircraft  10 . A single nozzle  32  is depicted in FIGS. 6,  6 A and  6 B. It is noted that the nozzles  32 ,  34  are tubular and provide a transition from a circular cross section at the plenum (see FIG. 6A) to an oval shape at the exit, as shown in FIG.  6 B. The oval shape is advantageous and preferred as it helps the nozzles  32 ,  34  lie flatter against the lower surface of the plenum chamber  24  when the nozzles  32 ,  34  are rotated to more extreme angles, such as the 60 degree angle depicted in FIGS. 4 a  and  4   b . Each of the nozzles  32 ,  34  have a proximal end  36  having an opening that is circular in shape so as to complimentary to the circular openings  30 . The circular shape of the opening is created by cutting the nozzle at an angle from the longitudinal axis of the nozzle. The distal end  38  of each of the nozzles  32 ,  34  has an opening that is cut perpendicular to the longitudinal axis of the nozzle (see FIGS. 6 and 6B) and, therefore, has a substantially oval shape. Vanes  40 , of a type known in the art, are retained within the proximal ends  36  of the nozzles  32 ,  34  to assist exhaust flow through the nozzles  32 ,  34 . 
     The plenum chamber and nozzles  32 ,  34  can be considered collectively to provide an exhaust assembly or system  42  for vectoring exhaust gases generated by the lift fan  20 . It is noted that the plenum chamber  24  and the nozzles  32 ,  34  are located beneath the aircraft  10  and centrally between the two lateral sides of the aircraft  10 . Thus, the nozzles  32 ,  34  are located proximate the center of gravity for the aircraft  10 . 
     Each of the nozzles  32 ,  34  are rotatable on a bearing assembly (not shown) within their respective circular openings  30  by toothed gearing, which is not shown in detail as the construction and operation of such is well known. It is noted that various styles of bearing assemblies and gearing, including rack-and-pinion and worm gearing may be used to actuate the nozzles  32 ,  34  and cause them to selectively rotate within the circular openings  30 . 
     In operation, the nozzles  32 ,  34  may be oriented, or directed, to various angled positions by rotation of the nozzles  32 ,  34  within their openings  30 . FIGS. 2 a  and  2   b  depict the nozzles  32 ,  34  oriented so that the distal end  38  of each nozzle  32 ,  34  is directed in a vertically downward position as would be used during the take-off phase of operation for the aircraft  10 . 
     FIG. 3 illustrates the exhaust assembly  42  in a configuration wherein the nozzles  32 ,  34  are oriented to direct exhaust from the plenum chamber  24  at an angle of about 20 degrees rearward of vertical plane  44 . To achieve this position, the nozzles  32 ,  34  have been rotated within their respective circular openings  30  until the nozzles  32 ,  34  are oriented at the appropriate angle. The orientation of the circular exit plane determines the range of motion for the nozzles  32 ,  34 . 
     FIGS. 4 a  and  4   b  show the exhaust assembly  42  in a configuration wherein the nozzles  32 ,  34  are oriented so that exhaust from the plenum chamber  24  is directed rearwardly from the vertical plane at an angle of approximately 60 degrees. To achieve this position, the nozzles  32 ,  34  have again been rotated within their respective circular openings  30  until the nozzles  32 ,  34  are oriented at the appropriate angle. 
     In FIGS. 5 a  and  5   b , the exhaust assembly  42  in a configuration wherein the nozzles  32 ,  34  are oriented so that exhaust from the plenum chamber  24  is vectored forwardly from the vertical plane at an angle of approximately 20 degrees. To achieve this position, the nozzles  32 ,  34  have been further rotated within their respective circular openings  30  until the nozzles  32 ,  34  are oriented at the appropriate angle. 
     From the above description, it can be seen that the exhaust assembly  42  permits exhaust gases to be vectored from the plenum chamber  24  at angles within a range from 20 degrees forward of vertical plane  44  to 60 degrees aft of vertical plane  44 . Generally, 180 degrees of rotation will vector the thrust from stop to stop. 
     During adjustment of the nozzles  32 ,  34  from position to position, the nozzles  32 ,  34  are rotated in opposite directions from one another so that the lateral thrust forces generated by the exhaust gases being emitted from the nozzles  32 ,  34  will offset one another and, thereby, reduce or eliminate the inducement of yawing moments to the aircraft  10 . It is also noted that the nozzles  32 ,  34  provide a constant area for exhaust of gases regardless of the orientation of the nozzles  32 ,  34  with respect to the plenum chamber  24 , in contrast to arrangements like louvers, which vary exhaust area with deflection angle. 
     It will be apparent to those skilled in the art that modifications, changes and substitutions may be made to the invention shown in the foregoing disclosure. Accordingly, it is appropriate that the appended claims be construed broadly and in the manner consisting with the spirit and scope of the invention herein.