Abstract:
Hypersonic aircraft having a lateral arrangement of turbojet and SCRAMjet engines are disclosed. The SCRAMjet engines may be positioned laterally outboard of the turbojet engines. In one embodiment, the turbojet inlet and outlet openings may be covered during use of the SCRAMjets in order to provide compression and expansion ramps for the laterally adjacent SCRAMjet engines. The side-by-side arrangement of the turbojet and SCRAMjet engines reduces the vertical thickness of the aircraft, thereby reducing drag and potentially increasing performance.

Description:
FIELD OF THE INVENTION 
     The present invention relates to hypersonic aircraft, and more particularly relates to a lateral arrangement of turbojet and SCRAMjet engines for such aircraft. 
     BACKGROUND INFORMATION 
     Hypersonic aircraft may utilize a combination of turbojet engines and RAMjet or SCRAMjet engines. The turbojet engines are used at relatively low speeds and the RAMjet or SCRAMjet engines are used at relatively high speeds. For example, conventional hypersonic aircraft may use turbojets for flight up to approximately Mach 3 and RAMjets or SCRAMjets for flight at higher speeds. 
     In RAMjet engines, thrust is produced by passing hot exhaust from the combustion of a fuel through a nozzle. The nozzle accelerates the flow, and the reaction to this acceleration produces thrust. In a RAMjet, high pressure is produced by “ramming” external air into the combustor using the forward speed of the vehicle. SCRAMjet is an acronym for Supersonic Combustion RAMjet. SCRAMjets differ from RAMjets in that combustion takes place at supersonic air velocities through the engine. Since there are no compressors in RAMjets or SCRAMjets, they tend to be lighter and simpler than turbojets, which require a compressor to generate high pressure in the combustor. Since RAMjets and SCRAMjets cannot produce static thrust, other propulsion systems such as turbojet engines must be used to accelerate the vehicle to a speed where the RAMjets or SCRAMjets begin to produce thrust. 
     RAMjets and SCRAMjets typically include compression ramps at their inlets and expansion ramps at their outlets in order to provide the desired gas pressures entering and leaving the engines. Some hypersonic aircraft engines are equipped with movable inlet ramps. Examples of such movable ramps and their control mechanisms are disclosed in U.S. Pat. Nos. 3,430,640, 4,025,008, 4,307,743, 4,620,679 and 4,991,795, which are incorporated herein by reference. 
     SUMMARY OF THE INVENTION 
     The present invention provides a side-by-side or lateral arrangement of turbojet and SCRAMjet engines for hypersonic aircraft. As used in the following description and claims, the term “SCRAMjet” includes both SCRAMjet and RAMjet engines. Instead of positioning the SCRAMjet engine(s) vertically below the turbojet engine(s), the present design positions the SCRAMjet and turbojet engines laterally or spanwise beside each other. This arrangement provides improved hypersonic aircraft design and may result in improved performance. In one embodiment, inlet and outlet openings of the turbojets may be covered during SCRAMjet use in order to provide compression and expansion ramps for the SCRAMjet engines. 
     An aspect of the present invention is to provide a hypersonic aircraft comprising at least one turbojet engine mounted on the aircraft, and at least one SCRAMjet engine mounted laterally adjacent to the at least one turbojet engine. 
     Another aspect of the present invention is to provide a turbojet and SCRAMjet assembly for a hypersonic aircraft comprising a turbojet engine, and a SCRAMjet engine disposed laterally adjacent to the turbojet engine. 
     These and other aspects of the present invention will be more apparent from the following description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a partially schematic side view of a hypersonic aircraft including a conventional turbojet and SCRAMjet arrangement in which the SCRAMjet is positioned vertically below the turbojet. 
         FIG. 2  is a front view showing a portion of the hypersonic aircraft of  FIG. 1  and the vertical turbojet and SCRAMjet arrangement. 
         FIG. 3  is a top view showing a portion of the hypersonic aircraft of  FIG. 1  with the SCRAMjet positioned below the turbojet. 
         FIG. 4  is a partially schematic top view of a hypersonic aircraft having a lateral or spanwise turbojet and SCRAMjet engine arrangement in accordance with an embodiment of the present invention. 
         FIG. 5  is a partially schematic side view of the hypersonic aircraft of  FIG. 4  illustrating the laterally arranged turbojet and SCRAMjet engines. 
         FIG. 6  is a partially schematic front view of the hypersonic aircraft of  FIG. 4  further illustrating the lateral arrangement of the turbojet and SCRAMjet engines. 
         FIGS. 7 and 8  are sectional views of a turbojet engine taken through section A-A of  FIG. 4 . In  FIG. 7 , the inlet and outlet of the turbojet engine are uncovered when the turbojet engine is in use. In  FIG. 8 , the inlet and outlet of the turbojet engine are covered when the turbojet is not in use in order to provide compression and expansion ramps for the adjacent SCRAMjet engine. 
     
    
    
     DETAILED DESCRIPTION 
       FIGS. 1-3  schematically illustrate a hypersonic aircraft  10  having a conventional engine arrangement in which a turbojet engine  12  is mounted on the underside of the aircraft  10  and a SCRAMjet engine  14  is mounted vertically below the turbojet engine  12 . As shown in  FIG. 1 , the turbojet engine  12  has an inlet  16  which may be covered to provide a compression ramp above the inlet of the SCRAMjet  14 , which is located vertically below the turbojet  12 . The turbojet  12  also has an outlet  18  which may be covered to provide an expansion ramp above the outlet of the SCRAMjet  14 . 
     The conventional turbojet  12  and SCRAMjet  14  arrangement shown in  FIGS. 1-3  produces a thick airplane as shown in the side and front views. The thick body provides compression and expansion ramps that are necessary for the SCRAMjet to work. However, the thick body increases transonic forebody and base drag such that the turbojet engine(s) need a lot of thrust and fuel to get to Mach 3. This makes the aircraft heavy and may result in an impractical design. 
       FIGS. 4-6  schematically illustrate a hypersonic aircraft  20  in accordance with an embodiment of the present invention. The hypersonic aircraft  20  includes a body or fuselage  22 , wings  24   a  and  24   b , and a tail  26 . Turbojet engines  30   a  and  30   b  are provided within or laterally adjacent to the body  22  of the hypersonic aircraft  20 . SCRAMjet engines  40   a  and  40   b  are provided in a spanwise arrangement laterally outboard of the turbojet engines  30   a  and  30   b . As shown in  FIGS. 4-6 , the SCRAMjets  40   a  and  40   b  are provided in substantially the same horizontal plane as the turbojets  30   a  and  30   b . While this may be a preferred arrangement for many hypersonic aircraft designs, it may be desirable in some aircraft to provide the outboard SCRAMjet engines  40   a  and  40   b  in a horizontal plane slightly above or below the horizontal plane of the turbojets  30   a  and  30   b . Furthermore, although the SCRAMjets  40   a  and  40   b  as shown in  FIGS. 4 and 6  are spaced a lateral distance away from their corresponding turbojets  30   a  and  30   b , it may be desirable in some aircraft designs to move the SCRAMjets laterally inward and/or move the turbojets laterally outward in accordance with the present invention. 
     As shown in  FIG. 4 , the turbojets  30   a  and  30   b  have inlets which may be at least partially covered to serve as compression ramps  32   a  and  32   b  for the adjacent SCRAMjets  40   a  and  40   b . The turbojets  30   a  and  30   b  also include outlets which may be at least partially covered to provide expansion ramps  34   a  and  34   b  for the adjacent SCRAMjets  40   a  and  40   b . Thus, by selectively covering the turbojet inlets and outlets, compression and expansion ramps in the form of planform edges are provided for the laterally adjacent SCRAMjets. 
       FIGS. 7 and 8  are sectional views of the turbojet engine  30   a  taken through section A-A of  FIG. 4 . The turbojet  30   a  includes an inlet region  36  having two sharp leading edges and an outlet region  38 . In  FIG. 7 , the inlet  36  and outlet  38  are uncovered, e.g., when the turbojet  30   a  is being used at subsonic or relatively low hypersonic speeds. In  FIG. 8 , an inlet cover or panel  32   a  is provided over the inlet  36 , and an outlet cover or panel  34   a  is provided over the outlet  38 . The inlet cover  32   a  acts as a compression ramp which is positioned laterally adjacent to the inlet of the SCRAMjet  40   a . The outlet cover  34   a  acts as an expansion ramp which is positioned laterally adjacent to the outlet of the SCRAMjet  40   a . The inlet compression ramp cover  32   a  and outlet expansion ramp cover  34   a  may be moved to their deployed and stowed positions by any suitable mechanism, such as the mechanisms disclosed in U.S. Pat. Nos. 3,430,640, 4,025,008, 4,307,743, 4,620,679 and 4,991,795, which are incorporated herein by reference. 
     Thus, in the SCRAMjet mode, the leading  32   a  and trailing  34   a  panels deploy from the turbojet inlet and exhaust to close of the turbojet inlet and exhaust. The panels  32   a  and  34   a  create wide flat edges to compress and expand the flow for the SCRAMjet. The planform edges are thus used instead of the thick lower body on conventional aircraft configurations. Although the leading  32   a  and trailing  34   a  panels shown in  FIG. 8  are flat, alternate embodiments may have leading and trailing panels that have bends or curves in them to provide the desired performance. The SCRAMjet inlets and exhausts may also have similar deployable panels (not shown) if desired. 
     In accordance with the present invention, by providing the turbojet engines beside the SCRAMjet engines, a thinner airplane is possible in comparison with the conventional vertical arrangement shown in  FIGS. 1-3 . The present design decreases transonic forebody and base drag such that the turbojet engines need less thrust and fuel, e.g., to get to Mach 3. This makes the aircraft lighter and provides a more practical design. The body thickness no longer provides the compression and expansion ramps that are necessary for the SCRAMjet to work. Instead, the planform edges of the turbojet inlet and outlet covers and provide the compression and expansion ramps for the SCRAMjets. 
     Whereas particular embodiments of this invention have been described above for purposes of illustration, it will be evident to those skilled in the art that numerous variations of the details of the present invention may be made without departing from the invention as defined in the appended claims.