Abstract:
A scramjet has a cowl, a center structure, and a plurality of wide pylons connecting the cowl to the center structure, with scramjet engines positioned between adjacent pylons. Leading surfaces of adjacent pylons converge to one another to provide side wall compression to air entering the engines. The center structure includes a fore body, a center body and an aft body that, with the pylons, define a basic structure either formed entirely from one piece or several securely connected pieces. A method of testing the scramjet projectile comprises using a gun to accelerate the scramjet projectile to the takeover velocity of the engines.

Description:
GOVERNMENT INTEREST  
       [0001] This invention was developed in part under a Phase II Small Business Innovation Research Contract. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    Embodiments of the invention relate to high velocity engines and projectiles. More particularly, embodiments of the invention relate to testing procedures and apparatuses for high velocity engines and projectiles.  
           [0004]    2. Description of Related Art  
           [0005]    Ramjet and supersonic combustion ramjet (scramjet) technology has been the subject of extensive research and development. In this application, the term ramjet is intended to include scramjets, where appropriate. Scramjet engines provide propulsion at hypersonic speeds (i.e. above Mach 5) by capturing atmospheric air to bum onboard fuel. For hypersonic propulsion, these air breathing engines are more efficient than rocket motors and can allow longer duration hypersonic flight with greater payload.  
           [0006]    Testing scramjet engines has, in the past, been an extremely expensive undertaking. This is due to the need to accelerate a scramjet to its takeover velocity, the velocity at which the engine begins to be able to operate. The takeover velocity is at supersonic or hypersonic speeds. One mainstream thought regarding methods of accelerating a scramjet engine to the takeover velocity involves a first stage vehicle being lifted to flight level by a jet aircraft and released. The first stage vehicle then accelerates the scramjet vehicle beyond the takeover velocity, at which point the scramjet engine ignites and testing can begin. The costs associated with one such test can be on the order of magnitude of $10 million. The high cost of such testing has proved to be prohibitive in many cases, resulting in insufficient testing of scramjet technology.  
           [0007]    As a low cost alternative, it has been proposed to use a gas gun to accelerate to supersonic speeds a projectile having a scramjet engine. Many problems exist with the prior art ramjet test projectile and with methods for launching such a ramjet test projectile from a gas gun. For example, the acceleration forces to which a ramjet, and particularly a scramjet, projectile is subjected during a gas gun launch is more than 5000 G&#39;s and is more typically on the order of 10,000 G&#39;s, that is, 10,000 times the force of gravity, or more. Launches from other types of guns can subject a scramjet or other projectile to 60,000 or 70,000 G&#39;s. At accelerations as high as these, the projectile must be G-hardened to withstand the loads resulting from the acceleration. Conventional mechanical fasteners often used in the prior art cannot withstand such forces. Moreover, the basic structural design of prior art ramjet projectiles is incapable of withstanding such forces. Prior ramjet test projectiles typically include a heavy center body surrounded by a cowl. Thin pylons are used to hold the center body and cowl together. When a projectile having such a construction is subjected to the high acceleration forces present during gun launch, the thin pylons break and the test projectile disintegrates.  
         SUMMARY OF THE INVENTION  
         [0008]    A projectile structure is provided. In an exemplary embodiment, the projectile structure comprises a cowl and a center structure. A plurality of wide pylons connects the cowl to the center structure. At least one engine is provided, the engine being located between adjacent pylons. The cowl, the center structure and the plurality of pylons form an integral structure. The pylons define, in part, the inlet to the engine, providing side wall compression to a fluid provided to the engine.  
           [0009]    Embodiments of the invention greatly increase the feasibility of ramjet, and particularly scramjet, technology research and development. By using a gas gun to launch a scramjet projectile, embodiments of the invention reduce the launch cost of a scramjet projectile by two orders of magnitude compared to aircraft-released and/or rocket acceleration.  
           [0010]    Exemplary embodiments of the present invention overcome the problems in the prior art. Embodiments of the invention use strong materials, such as titanium, for the projectile. The scramjets of the invention have a basic structure formed from a single piece or constructed from a small number of parts connected securely, such as by welding or threaded connections. For example, particular embodiments of the invention are constructed from four titanium parts welded together.  
           [0011]    Exemplary embodiments of the present invention utilize wide pylons as structural members of the projectile. The use of wide pylons as structural members is enabled by also using the pylons to form part of the scramjet engine inlet. Otherwise, wide pylons would adversely affect engine performance. When used as part of the scramjet engine inlets, the pylons provide tangential compression to the inlet airflow. The arrangement of the pylons at the inlet, along with a tapered fore body, provides a radial and tangential flow to incoming air, that is, flow of air radially outward from the longitudinal axis of the scramjet and in directions tangential to the scramjet. Thus, the arrangement of the pylons in the scramjet according to the present invention provides a three-dimensional airflow. The three-dimensional air flow leads to improved scramjet performance compared to the two-dimensional air flow achieved by the high aspect ratio slit used for the inlet flow area in the prior art. Thus, the structure and design of the pylons in the present invention provide structural integrity to the test projectile, as well as improved scramjet engine performance. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    [0012]FIG. 1 is a perspective view of a projectile structure in accordance with embodiments of the invention;  
         [0013]    [0013]FIG. 2 is a sectional view of an embodiment of the invention shown in FIG. 1;  
         [0014]    [0014]FIG. 3 is a front view of the embodiment of the invention shown in FIG. 2;  
         [0015]    [0015]FIG. 4 is a rear view of the embodiment of the invention shown in FIG. 2;  
         [0016]    FIGS.  5 - 8  are schematic views of an example of a testing apparatus of the invention; and  
         [0017]    [0017]FIG. 9 is a rear view of another embodiment of the invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0018]    FIGS.  1 - 4  show an example of a scramjet projectile in accordance with an embodiment of the invention. As can be seen from FIGS. 1 and 2, a projectile structure  100  has primary structural members including: a conical fore body  110 , a center body  114 , an aft body  125 , together defining a center structure, and an annular member, or cowl,  140 . The conical fore body  110  is connected to the center body  114 . The conical fore body  110  includes an external surface  115  extending from its tip towards the cowl  140 . The external surface  115  is configured to compress the fluid (air) through which the projectile passes. The aft body  125  is connected to the center body  114  at an end opposite the conical fore body  110 . A plurality of pylons  120  extend radially from the center body  114  and aft body  125  to the cowl  140 . The pylons serve to segregate adjacent internal flow passages  200 , each of which is part of a respective scramjet engine. The cowl  140  encloses the scramjet engines. In this example, each pylon  120  has a leading edge  124 , two side surfaces  126  and an aft end adjacent to the aft end of the projectile structure  100 . The flow passages  200  are each defined by side surfaces  126  of adjacent pylons  120 , center body  114 , aft body  125 , and cowl  140 . Although described herein as separate members connected together by, for example, welding or threaded connections, the fore body  110 , the center body  114 , the aft body  125  and the pylons  120 , or combinations thereof, can be formed as a monolith, that is, a single piece, for example, by casting or by machining a billet.  
         [0019]    Two flow passages  200  are shown in cross-section in FIG. 2. The flow passages  200  extend longitudinally through the projectile. Inlets  190  to flow passages  200  are each defined by leading portions of side surfaces  126  of adjacent pylons  120  and by center body  114 . The inlets  190  are preferably not enclosed by the cowl  140 . As shown in FIG. 3, leading portions of side surfaces  126  of adjacent pylons  120  are arranged opposite each other to define inlets  190 . The side surfaces  126  of the pylons  120  are arranged to converge toward opposing side surfaces of adjacent pylons and thereby provide sidewall compression to the air entering inlet  190 . Accordingly, the air entering the inlet of flow passages  200  is compressed by the external surface  115  of the conical fore body  110  and also by leading portions of the side surfaces  126  of the pylons  120 . Preferably, the external surface of the conical fore body  110  and leading portions of the side wall surfaces  126  are configured to have certain angles to compress and turn the air as it enters the inlets  190 , thus, raising the pressure of the air flow.  
         [0020]    In the illustrated embodiment, the pylons  120  and the leading edge of cowl  140  define notches  130  at the inlets  190 . The notches  130  here are V-shaped and have leading points  134 , at the leading edges  124  of the pylons  120 , and rear points  132 . The notches  130  may have other shapes, for example, U-shape, elliptical or hyperbolic, but are usually generally scalloped in shape. The objective of the shape of the leading edge of the cowl  140  is to achieve a shock wave at the rear points  132  for the design Mach number, and allow self-starting inlet. The leading edge of the cowl  140  is arranged to intersect a conical shock wave set up by the conical fore body  110 . The shapes of the notches  130  are designed such that the leading edge of the cowl  140  also conforms to planar shock waves set up by the leading portions of the side wall surfaces  126  of the pylons  120 . These provisions maximize the performance of the engines. Each notch  130  is the leading edge of an exterior surface  210 . Although exterior surfaces  210  are shown as having both concave and convex surfaces, other shapes for exterior surfaces  210  are also appropriate.  
         [0021]    Utilizing the pylons  120  to compress the incoming air flow allows the pylons to be made wider than in prior art scramjet projectiles. In previous projectile structures, wide pylons would have inhibited air flow into the scram jet engines and affected the performance of the engines. However, by using the pylons to compress the air entering the engines in accordance with the present invention, it is possible to have wide pylons that provide structural integrity to the projectile. For example, a profile width of the pylons  120 , the width between adjacent flow passages at the throat of the flow passages, can be made as great as and even greater than a profile width of the engines, the width of the flow passages  200  between adjacent pylons  120  being from 1 to 12 times as great, preferably 2 to 5 times as great. These relative widths, as described, are taken at the throat, the minimum flow area of the flow passages  200 . Pylons having such thicknesses provide the structural integrity needed for the test projectile to withstand the high acceleration forces, G forces, generated during gas gun launch. The key is to have wide pylons to give structural integrity while at the same time using those wide pylons constructively to yield high engine performance.  
         [0022]    [0022]FIG. 3 is a frontal view of the projectile structure  100  shown in FIGS. 1 and 2. FIG. 4 is a rear view of the projectile structure  100  shown in FIGS. 1 and 2. As can be seen from FIGS. 1, 3 and  4 , the illustrated embodiment has eight pylons  120  and eight flow passages  200 . As can be seen from FIGS. 3 and 4, the thickness of the pylons  120  in a circumferential direction about the center line of the projectile structure is preferably greater than the width of the flow passages  200  along the same direction. As discussed further below, in alternate embodiments, this relatively large volume of the pylons  120 , can be used, in part, for additional storage. For example, if the pylons  120  are made hollow adjacent leading edges  124 , these volumes can be used to store fuel or munitions, including explosives,  215 , or boosters  400  (FIG. 9).  
         [0023]    As can be seen in FIGS. 2 and 4, each flow passage  200  has at its rearmost portion a nozzle  150 . In addition, each flow passage  200  has a flame holder  160  and fuel supply ports  170 . Primary storage area  180  is provided in aft body  125 . Fuel can be stored in primary storage body  180  and supplied to each of the flow passages  200  by fuel valve  220  and fuel system  230 . Fuel valve  230  may be an inertially activated valve of a known type that is triggered by high G forces to allow fuel to flow. The fuel can be a compressed or liquefied gas or a solid fuel. In this example, fuel system  230  supplies fuel through apertures  240  and passages (not shown) through the center body  114  and the pylons  120  to fuel supply ports  170  in the pylons. The throat of each flow passage  200  is preferably located upstream of the point at which fuel is introduced into the flow passage. Also shown in FIG. 2 is a secondary storage volume  190 , which can store, for example, additional fuel, navigational or communications instrumentation, or munitions.  
         [0024]    In operation, air is compressed, turned and introduced to flow passages  200 . As discussed above, the pylons  120  are arranged to provide side wall compression. The turning of the air is performed by the pylons  120  and conical fore body  110 , with the pylons preferably providing about two-thirds of the turning and the conical fore body  110  providing the remaining one-third. The external surface of the conical fore body  110  can have an angle, from the longitudinal axis to the surface, of, for example, about 8 degrees to perform compression and turning of the air.  
         [0025]    The temperature of the air rises due to the heat of compression. As the compressed air passes fuel supply ports  170 , fuel is introduced by fuel supply ports  170  and ignited, for example, by spontaneous combustion due to compression or by other ignition. As the burning air/fuel mixture progresses along flow passages  200 , it expands and exits projectile structure  100  through nozzles  150 , thereby creating thrust to move the projectile forward. In the illustrated embodiment, each flow passage  200  is an independent scramjet engine. The fuel supply ports  170  of all of the flow passages  200  can be controlled together so that, when fuel flows, it flows to all of the flow passages simultaneously. Thus, the outputs of all of the engines can be controlled together. In preferred embodiments, the fuel supply ports  170  of each flow passage  200  are independently controlled so that the amount of thrust generated by each flow passage is controllable independently of the thrust of other flow passages. As a result, the output of each engine is controllable independently, and the projectile structure  100  can be steered during flight by independently controlling the amount of fuel supplied to each flow passage  200 .  
         [0026]    FIGS.  5 - 8  illustrate an example of a testing apparatus  300  used to economically test ramjet and scramjet technology. The testing apparatus is able to simulate flight and operation of the scramjet test projectile at altitude. A two-stage gas gun  305  employing a light gas may be used as the testing apparatus. The gas gun  305  is used to accelerate the test projectile to supersonic speeds necessary to test the scramjet engines. The gas gun  305  has a pump tube  310  in which a piston  320  is arranged. The piston  320  moves in the longitudinal direction of pump tube  310 . A gun barrel  330  is connected to pump tube  310  by a transitional section  315 . Transitional section  315  transitions between the cross-sectional area of pump tube  310  and the smaller cross-sectional area of gun barrel  330 . The gun barrel has, for example, a diameter of about 4-8 inches and a length of about 80-130 feet.  
         [0027]    Gun barrel  330  is connected to a blast tank  340 , which is, in turn, connected to a range tank  350 . A membrane  360  separates blast tank  340  and range tank  350 . When the gas gun is fired, the air in the gas gun gets extremely hot. An inert gas should be provided in blast tank  340  to prevent any unwanted combustion during the firing of the gun. The air pressure in range tank  350  is reduced to simulate flight at altitude, for example, about 100,000 feet. Membrane  360  may include a fast acting valve that opens to allow the test projectile to pass through, then closes quickly to maintain the separation between blast tank  340  and range tank  350 .  
         [0028]    In operation, the test projectile  100  is arranged in gun barrel  330 . Piston  320  is accelerated to the right in FIG. 5 to compress a light gas in pump tube  310 . Examples of the gas that can be used in pump tube  310  are hydrogen and helium. Piston  320  can be accelerated by, for example, a gunpowder explosion behind piston  320  (to the left of piston  320  in FIG. 5) or any other appropriate means. FIG. 6 shows piston  320  being moved toward the right and compressing the gas in pump tube  310 . Projectile structure  100  begins to move to the right under the force created by the compressed gas in pump tube  310 . The test projectile may have a full bore structure. Therefore, some means of preventing the light gas from passing through the flow passages  200  of projectile  100  is preferably used. For example, a pusher plate  325  can be used behind projectile structure  100  between projectile structure  100  and the light gas. Alternatively, some means of protecting the rear and/or sides of projectile structure  100  (and possibly gun barrel  330 ) can be used. An example of such protection is a sabot  328 , shown in FIG. 6. Sabots also provide a means to distribute the launch load onto a larger area of projectile structure  100 . The pusher plate  325  or the sabot  328 , whichever is used, separates from the projectile structure  100  at some point after the projectile structure exits the gun barrel  330 . FIG. 7 shows piston  320  at its rightmost position and projectile structure  100  moving toward the right in gun barrel  330 . Projectile  100  is preferably accelerated to takeover velocity in gun barrel  330 . Projectile  100  then exits gun barrel  330  and proceeds through blast tank  340  and down range tank  350 . FIG. 8 shows projectile structure  100  piercing membrane  360  after exiting gun barrel  330 .  
         [0029]    Instrumentation  370  is provided to detect and record the position of projectile  100  versus time during its flight through blast tank  340  and range tank  350 . The instrumentation  370  can include x-ray stations to determine not only position vs. time, but also the structural integrity of the projectile. The instrumentation can also include photo stations for taking laser-illuminated digital photographs of the projectile; infrared stations to take infrared images of the exhausts of the engines, to determine engine efficiency; stations for ultraviolet imaging and shadowgraphs; and high speed video cameras, such as those produced under the trademark HYCAM. Projectile structure  100  may also be provided with instrumentation. The instrumentation included with projectile structure  100  can include RF transmitting/receiving capability in order to provide from the test projectile information concerning pressure, temperature, acceleration, etc. Both the instrumentation  370  and the instrumentation of the projectile structure record information about the performance of the projectile and its engines. The flight of projectile structure  100  is concluded as it impacts endwall  354  of range tank  350 .  
         [0030]    Although the method of testing according to the present invention has been described in connection with a gas gun employing a light gas, it is understood that the method is applicable to other guns, such as large military guns.  
         [0031]    As mentioned above, the relative thickness of pylons  120  in preferred embodiments of the invention provide space that can be used to store, for example, fuel, munitions, instrumentation, booster engines or other appropriate material. As discussed above, ramjet and scramjet engines must reach a takeover velocity (usually Mach 2 or greater) before they will operate. In certain embodiments of the invention, pylons  120  can be made hollow in order to allow placement of a booster, for example a solid or other rocket booster, that can be used to accelerate the ramjet or scramjet engine up to the takeover velocity. A booster can be provided in each pylon or only in selected pylons. For example, if the projectile structure  100  has eight pylons, any number from one to eight boosters may be used. However, it is preferable to space the boosters symmetrically so as to more easily create symmetrical thrust. FIG. 9 shows a rear view of a projectile structure using a rocket booster  400  in each of eight pylons.  
         [0032]    While the invention has been described with reference to particular embodiments and examples, those skilled in the art will appreciate that various modifications may be made thereto without significantly departing from the spirit and scope of the invention.