Abstract:
A propulsion-assisted projectile has a body, a cowl forming a combustion section and a nozzle section. The body has a fuel reservoir within a central portion of the body, and a fuel activation system located along the central axis of the body and having a portion of the fuel activation system within the fuel reservoir. The fuel activation system has a fuel release piston with a forward sealing member where the fuel release piston is adapted to be moved when the forward sealing member is impacted with an air flow, and an air-flow channel adapted to conduct ambient air during flight to the fuel release piston.

Description:
[0001] The United States Government has rights in this invention pursuant to Contract No. W-7405-ENG-48 between the United States Department of Energy and the University of California for Management of the Lawrence Livermore National Laboratory. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates to the field of high-speed gun or artillery launched projectiles. Particularly the present invention relates to air-breathing propulsion assisted projectiles, and more particularly to air propulsion assisted projectiles that accelerate after launch. Even more particularly the present invention relates to fuel release systems used in air breathing propulsion systems that accelerate after launch.  
           [0004]    2. Description of the Prior Art  
           [0005]    The ramjet and supersonic ramjet propulsion cycles for supersonic and hypersonic engines are well known within the art of aerospace propulsion. In ramjet propulsion high velocity air is compressed through a series of forebody and inlet shocks and through a subsonic diffuser all of which decelerate the air to a subsonic velocity near the fuel flame speed. Fuel is injected into a combustor and conventional subsonic combustion increases the temperature and pressure of the fuel-air mix. The high-pressure gas is then expanded through a nozzle increasing the velocity and momentum of the flow to produce thrust. Ramjet can be efficiently used to a velocity of approximately Mach 5. Above Mach 5 the temperatures and pressure associated with decelerating the flow to subsonic speeds for combustion are severe and begin eroding the engine cycle and the engine structure. It is at this point when supersonic combustion ramjet, called scramjet, is the preferred form of propulsion.  
           [0006]    For Mach numbers above 5, a principal advantage of scramjet propulsion is that supersonic velocities within the combustion chamber are accompanied by lower static temperatures, pressures, and reduced total pressure losses. By reducing combustion product dissociation, reduced temperatures increase combustion efficiency, reduced pressures decrease loads on engine structure, and reduced total pressure losses increase the flow energy available for thrust production.  
           [0007]    Research in supersonic air breathing propulsion systems for aircraft and missiles has been in progress since the 1940&#39;s. As empirical knowledge grew on the subject in the 1950&#39;s, researchers investigated propulsion for hypersonic aircraft and missiles, using scramjet engines. Research into scramjet propulsion continued during the 1970&#39;s at the Nasa Langley Research Center and John Hopkins Applied Physics laboratory, and in the 1980&#39;s and 1990&#39;s work continued under the auspices of the National Aerospace Plane Program.  
           [0008]    Starting in 1993 the Super High Altitude Research Project (SHARP) launched hypersonic air breathing vehicles for the purpose of data development on SCRAM propulsion. SCRAM propulsion has been discussed for several decades and is the cornerstone of many advanced vehicle concepts. The projectiles were launched using the SHARP hypervelocity launcher, which is a two-stage light gas gun. Because the flight duration was short, high specific impulse was required from the engine in order to produce a measurable deviation from pure ballistic flight. This lead to the selection of gaseous hydrogen as the fuel. One drawback of hydrogen is its low energy density. This, coupled with the low fuel volume available on the projectile, means that hydrogen must be stored at high pressure, e.g. 6000-10000 psi, and must not be prematurely released, i.e. before the projectile exits the launch tube. Using the SHARP light gas gun, velocities of up to MACH 9 have been recorded. The greatest advantage of the light gas gun launch is that high Mach number and high Reynolds numbers can be achieved simultaneously in invitiated air (clean). This guarantees that the flow field around a properly scaled model will match that of a full-scale hypersonic vehicle at operational speed and altitude. The primary disadvantage of the gun is that in gun launch there is a high axial acceleration load. In the SHARP test this can exceed 20,000 “g”. For this reason it is necessary that a robust mechanical design be implemented for launching the device.  
           [0009]    Several devices have been created for use as projectiles for launch from a light gas gun. These devices take advantage of the characteristics inherent in scramjet and ramjet technology, and select hydrogen for its projectile fuel source. Hydrogen is selected as a gas source because, in order to achieve a measurable deviation from ballistic flight, an engine must produce high specific impulse, which is attainable using hydrogen.  
           [0010]    U.S. Pat. No. 5,485,787 (1996, Bowcutt et al.) discloses a gas gun launched propulsion assisted scramjet projectile adapted to be fired from a gun preferably at velocities greater then MACH 5. The projectile includes a body with an internal combustion section, i.e. combustor, an external compression section, a nozzle section, and means for channeling fuel to the combustor to produce thrust greater than drag when the projectile travels at velocities greater then Mach 5. The projectile further includes a plurality of circumferentially spaced stabilization fins located at the nozzle end of the body. In addition the device includes a pusher for launching the device and protecting it from propulsive forces of the launch. One disadvantage of this device is that it is prone to fuel leakage and premature activation of the fuel system. A properly functioning fuel source is extremely important because of the low energy density of hydrogen gas. In addition, the projectile does not have provisions for repetitive cycling of the mechanism and testing before launch.  
           [0011]    U.S. Pat. No. 5,513,571 (1996, Grantz et al.) discloses an air breathing propulsion assisted projectile designed to be rocket or gun launched and capable of accelerating to hypersonic velocities. This design includes a body having an encompassing cowl, an air compression section, an engine assembly located adjacent the air compression section, and a nozzle section located adjacent the engine assembly. The engine assembly includes apparatus for fuel storage and delivery to a combustion region. The rear end portion of the cowl is configured to direct the exiting combusted air and fuel mixture over the nozzle section of the body.  
           [0012]    A scramjet system launched from a light gas gun for scramjet propulsion testing and experiments in a closed test chamber was documented in 1968 by H. H. King and O. P. Prachar in the Air Force Aero Propulsion Laboratory Technical Report AFAPL-TR-68-9. This study represents an early attempt to launch a scramjet-shaped projectile from a gun barrel, and the projectile was too small to contain a fuel source. The experiments were conducted only to assess the flight characteristics of scramjet models. Fuel sources were tested but only in conical shaped forms that did not constitute the principles of scramjet or ramjet technology.  
           [0013]    All of these current projectile designs face the significant problem of utilizing their fuel source efficiently. The efficient use of hydrogen is significant because of its low energy density and the low fuel volume available on the projectile. Thus, it is critical that the fuel source is activated at the correct time and that all fuel is combusted. Inefficient fuel use leads to decreased projectile performance.  
           [0014]    Therefore, what is needed is a scramjet projectile that incorporates a fuel release mechanism where the projectile design is able to withstand the high acceleration loads of a gun launch. What is further needed is a projectile powered by scramjet propulsion with a fuel activation source that is activated at a correct and consistent time after the projectile has left the gun muzzle. What is still further needed is a projectile that activates the fuel source without leaking or wasting uncombusted fuel.  
         SUMMARY OF THE INVENTION  
         [0015]    It is an object of the present invention to provide an air breathing propulsion assisted projectile capable of travel at hypersonic velocities that will overcome some of the deficiencies and drawbacks of currently known air breathing propulsion assisted projectiles. It is another object of the present invention to provide a novel air breathing propulsion assisted projectile that is capable of acceleration by scramjet combustion operation at hypersonic velocities. It is yet another object of the present invention to provide a fuel injection mechanism that will activate only after the projectile has left the launcher muzzle and will not activate prematurely. It is a further objective of the present invention to provide a fuel activation mechanism that does not leak fuel from the projectile body.  
           [0016]    The present invention achieves these and other objectives by providing a hypersonic projectile assembly having a main body, a cowl surrounding the main body, a nozzle formed by the rear end surfaces of the cowl and body, a forebody, and a nosecone. The main body contains a fuel cavity and a fuel activation system that is triggered by air stagnation pressure. The projectile assembly also includes a pusher that engages the aft end of the projectile. The pusher forms a seal between the projectile and the high pressure gas that propels it down the launch tube, and safely transfers the gun acceleration force to the projectile mechanical structure. To optimize specific impulse in scramjet propulsion, the above components must be designed with the following parameters considered: forebody and inlet contraction ratios, inlet efficiency, the fuel mixing efficiency, the combustor efficiency, and the nozzle efficiency.  
           [0017]    The nosecone and forebody of the present invention contain an air intake port and channel, which is part of the fuel activation system, leading to a fuel injection activation mechanism. This feature distinguishes the present invention from all known projectiles of similar type. The channel created by the intake is referred to as the “pitot” tube.  
           [0018]    Attached to the forebody is the main body of the projectile that houses the fuel cavity, the fuel activation mechanism, and a plurality of fuel distribution channels and fuel injection orifices that lead to the combustor region. Inside the body of the projectile, which is constructed of a metal such as aluminum, is the fuel cavity. The fuel activation mechanism retains the fuel within the fuel cavity. The fuel activation mechanism includes a fuel release piston and a fuel activation pin stop. The fuel activation pin stop is the rearward most portion of the fuel release piston. The fuel release piston, which is positioned within the fuel cavity, seals the fuel cavity to ensure that the fuel does not leak from the fuel cavity and releases fuel into the fuel distribution chamber when activated. To perform these functions, the fuel release piston includes at least two communicably attached sealing members, a forward fuel sealing member and a rear piston member. The forward fuel sealing member seals the fuel within the fuel cavity and prevents the fuel from entering into the fuel distribution chamber until required, i.e. until the projectile leaves the muzzle of the gun. The rear piston member, on the other hand, seals the capillary fueling channel once the fuel release piston is activated during launch. The rear piston member is attached to the channel sealing member, which may or may not be an integral part of the fuel release piston. The rear channel sealing member contains a capillary fixedly attached to the base for fueling the projectile. A taper in the fuel activation mechanism ensures that the piston seats forward during fuel charging. A third sealing member may also be employed for sealing the pitot tube to ensure that the air from the pitot tube and fuel do not mix before the fuel reaches the combustor region of the projectile.  
           [0019]    In it&#39;s most basic form, the fuel release piston must have a fuel sealing member with a forward surface that acts as the surface on which the air pressure supplied by the pitot tube is applied to activate the fuel system. This may be the pitot tube sealing member if employed or the forward fuel sealing member.  
           [0020]    Pressure on the channel sealing member ensures that the forward fuel sealing member of the fuel release piston does not displace prematurely, thus compromising fuel release. The rear piston member is communicably attached to the channel sealing member, which is positioned within a channel that extends into the fuel cavity from the rearward end of the projectile body. The channel sealing member transmits pressure to the fuel release piston, which is communicably attached to the forward fuel sealing member, restricting any movement by the fuel release piston. The channel sealing member rests against the pusher or sabot, which is fitted to the rearward end of the projectile body.  
           [0021]    The pusher is fitted to the body only during the in-bore phase of projectile launch. When the projectile and pusher exit the muzzle, drag separates the pusher from the projectile, freeing the channel sealing member, which in turn frees the fuel release piston, thereby allowing stagnation pressure to activate the fuel supply.  
           [0022]    The effectiveness of the fuel activation system is very important due to limited fuel storage available on scramjet projectiles. The thrust required for projectile flight at speeds of approximately Mach 9 dictates that the fuel source be hydrogen or like gasses. Gasses such as hydrogen and the like have a low energy density. The low energy densities and minimal storage inherent in high velocity projectile flight dictate that fuel activation be achieved with little waste of fuel. The fuel activation system must initiate fuel delivery at a consistent and correct time. The correct time to initiate fuel activation is the moment the projectile exits the gun muzzle. Activation of the fuel source must also be achieved without leaking fuel from the fuel cavity. After activation the fuel is then routed through the fuel distribution plenum from the fuel cavity to the combustor region of the projectile in which the fuel is mixed with air and ignited.  
           [0023]    In free flight, the fuel release piston is subject to primarily four forces. The pressure load (easily calculated from the piston differential cross sectional area and the fuel fill pressure), the o-ring static friction load and the inertial load (estimated from the aerodynamic drag and piston mass), all act forward. The projectile nose is in “clean” air so that the pitot or stagnation pressure, which acts aft, is found from the Rayleigh formula or, alternatively, from the normal shock tables. Once the forces are known, it is a straightforward matter to calculate piston acceleration and the time required to initiate fuel flow past the forward fuel sealing member, through the injectors and into the combustor region. Computational fluid dynamics modeling is not required to predict performance. Though, in the present case, some modeling was performed to ensure that the small normal area presented by the pitot tube inlet would not affect inlet capture or significantly increase projectile drag. This mechanism is made possible by the non-linear scaling of pitot pressure with Mach number and would be less appropriate for more conventional projectile velocities. But at hypersonic velocities, a small opening, which presents minimal cross sectional area to the external air flow, can provide sufficient force to mechanically actuate fuel flow.  
           [0024]    The use of pitot pressure at hypersonic velocities is not limited to activation of gaseous fuel flow. Pitot pressure may serve to drive a piston or a diaphragm for the purpose of injecting a liquid fuel. Pitot pressure may also be used to drive other mechanical processes such as the post-launch deployment of control surfaces, e.g. fins and wings. The pitot tube, in conjunction with a transducer and telemetry unit, can concurrently be used to measure projectile velocity.  
           [0025]    The channel sealing member in conjunction with the fuel release piston and the pitot tube solve the problems of current projectile designs with respect to eliminating premature fuel release and fuel leakage. The fuel release piston slides into the fuel cavity sealing the fueling capillary channel and releasing the fuel into the combustor when activated by the air flow pressure from the pitot tube. Pressure on the channel sealing member ensures that the fuel release piston is not displaced prematurely. The materials selected allow a high strength weld for making a leak-proof attachment of the fueling capillary to the channel sealing member.  
           [0026]    In the embodiment described above the use of only two sealing surfaces allows for some mixing of air and fuel within the fuel distribution lines at the end of the pitot tube. To stop this from occurring, the second embodiment includes a pitot tube sealing member communicably attached to the fuel release piston. The pitot tube sealing member is positioned in between the aforementioned forward fuel sealing member and the air intake pitot tube. In this embodiment the pitot pressure is placed on the face of the pitot tube sealing member and the force is then communicated to the fuel sealing member, which consistent with the first embodiment seals the fuel within the fuel cavity. The pitot tube sealing member seals the pitot tube in front of the fuel distribution lines, and as a result ensures that the air in the pitot tube does not mix with the fuel in the fuel distribution chamber. This is the preferred solution for hydrogen fuel. Without the pitot tube sealing member, the hydrogen fuel, which is at much higher pressure than the pitot stagnation pressure, will spill out of the pitot tube. This produces pressure thrust aft, in the wrong direction. Further, the hydrogen spilling from the nose auto-ignites, which disrupts the flow to the scram inlet. In certain situations, however, such as where solid fuels are used, pre-mixing of fuel and air to partially burn a solid fuel “gas generator” to inject fuel-rich partially combusted gases into the scramjet combustor may be the preferred method.  
           [0027]    A third embodiment of the present invention includes a removable nosecone for repetitive cycling tests of the mechanism before launch. To simulate pitot pressure, the nosecone is unscrewed and replaced with a fitting that allows the charged projectile to be connected to a gas cylinder. This allows non-destructive testing of the fuel release mechanism under expected flight stagnation pressure conditions. In practice, fuel flow could be initiated in this manner at pressures within a few percent of design predictions.  
           [0028]    Additional advantages and embodiments of the present invention will be set forth in part in the detailed description that follows and in part will be apparent from the description or may be learned by practice of the invention. It is understood that the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0029]    [0029]FIG. 1 illustrates an embodiment of the present invention showing the fuel release mechanism with the pitot sealing member.  
         [0030]    [0030]FIG. 2 illustrates an embodiment of the present invention showing the fuel release mechanism without the pitot sealing member.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0031]    The preferred embodiment of the present invention is illustrated in FIGS.  1 - 2 . The projectile  10  according to the present invention includes a projectile body  20  and a pusher assembly  100 . The projectile is preferably constructed to an overall length of approximately 21″. The pusher system  100  is coupled to the projectile body  20  to seal high pressure gas behind the projectile, to safely transfer loads to the projectile structure during launch and to stop premature activation of fuel release before the combined assembly leaves the gun barrel.  
         [0032]    The projectile body  20  includes a nosecone  30 , a forebody portion  40 , a main body  50 , a cowl  70  surrounding main body  50 , and a nozzle portion  90 . The nosecone  30  is approximately 4.9 inches long including a threaded portion  32  and is connected to the forebody  40  through a cooperating threaded fitting  41 . In this embodiment, the exposed portion of forebody  40  is 5.1 inches long. It is 7.2 inches long including a threaded section  43  and a fuel distribution chamber  35 . In addition to connecting the nosecone  30  to forebody  40  the threaded region  41  allows one to remove nosecone  30  and attach an air-pressure fitting for repetitive static testing and repetitive cycling before launch. By removing the nosecone  30  and connecting the projectile  10  to a gas cylinder, it is possible to simulate pitot pressures.  
         [0033]    Nosecone  30  and forebody  40  include an external compression surface  42  extending from the tip of nosecone  30  rearwardly over the forebody  40  into the main body  50  of projectile  10 . External surface  42  is configured to compress the fluid through which projectile  10  passes as it travels along its trajectory. Forebody  40  and nosecone  30  also incorporate a channel  33  which extends axially starting from an air intake port  31  of nosecone  30  through forebody  40  to the fuel distribution chamber  35  within forebody  40  of projectile  10 . Channel  33  is about a ⅛″ diameter tube and from this point will be referred to as a pitot tube  33 . The main body  50  is threadably secured to the forebody  40  via threads  43 . O-rings are provided on axial sides of the plenum  74  for sealing the connection between main body  50  and forebody  40  as well as plenum  74 .  
         [0034]    The main body  50  is approximately 8.5″ long and houses a fuel activation system  60 . Fuel activation system  60  includes a fuel cavity  51  a fuel release piston  61  and a channel sealing member  81 . Fuel cavity  51  contains the fuel material in a gaseous state such as hydrogen. The fuel material is installed under high pressure and, in the present design, the pressure is on the order of 7000 psi. Fuel release piston  61  contains the pressurized fuel within fuel cavity  51 . Fuel release piston  61  includes a pitot sealing member  62 , a forward fuel sealing member  63  and a rear piston member  64 . Pitot sealing member  62  includes an O-ring  62   a  that seals the fuel distribution chamber  35  from the air in the pitot tube  33 . Rear piston member  64  serves as a piston stop to limit the travel of the fuel release piston  61 . Forward fuel sealing member  63  includes an O-ring  63   a  that seals fuel cavity  51  until activation. Channel sealing member  81  abuts the pusher  100  and extends into the main body portion  50  of projectile  10  through a channel  80  located at the rearward end of the main body  50 . Channel sealing member  81  prevents fuel release piston  61  from moving. In addition to gaseous fuel, other fuel mediums can be utilized using the current invention.  
         [0035]    Main body  50  of the projectile  10  is surrounded by the cowl  70  in such a manner as to create an engine internal flowpath defined by an inlet  72 , an isolator  73 , a combustion region  75 , and an internal nozzle  90 . The cowl leading edge  71  and the main body  50  create the inlet  72  to combustion region  75  of projectile  10 . Inlet  72  must have a small enough area of contraction to permit the inlet  72  to start airflow. Leading edge  71  of cowl  70  has a radius of approximately 12.5 mils, which is sized to survive aerothermodynamic heating. Leading edge  71  is built up from electro-deposited copper, which is then skim cut to final dimension leaving a leading edge  71  of copper and copper plating on the exterior surface of cowl leading edge. Copper is chosen because copper has the longest “time-to-melt” of commonly available materials. Cowl  70  is connected to main body  50  by eight splitters (not shown) that are spaced circumferentially about main body  50 . The splitters serve to segregate adjacent internal flowpaths, which are individually fueled by a plurality of fuel injection channels  86  terminating in the combustion region  75 . While not shown here, fuel injectors may also be located in the splitters and or on the cowl  70 . The scramjet projectile of the present invention is capable of high “g” accelerations. Although the cowl splitters may be provided with widths that thicken as a function of axial station, in the present invention, the splitters are a robust and constant ¼″ thick. This was done to make flowpath analysis easier, to make it easier to do electric discharge machining of the internal flowpaths (the cowl and body are formed from a single piece of aluminum), and to accommodate the crush force on the cowl due to in-bore side loads. It is to be understood that ablative materials or heat sink metals may be used to protect the cowl  70  and splitter structures from high-localized aerodynamic heat loads. Once the fuel is ignited in the combustor region it is expelled through the nozzle section  90 .  
         [0036]    The nozzle  90  of projectile  10  is defined by the trailing edge  79  of the cowl  70  and a rear external expansion surface  78  of main body portion  50 . Rear external expansion surface  78  tapers away from a matching taper on the trailing edge  79  creating an increasing distance between the external expansion surface  78  and the cowl  70  towards the rearward end of projectile  10 .  
         [0037]    Fuel activation is achieved by a fuel activation system  60  that incorporates the pitot tube  33  and the fuel release piston  61 . The pitot tube  33  is connected to the air intake port  31  that is positioned at the tip of nosecone  30  and extends through the forebody  40  to the fuel distribution chamber  35 . The fuel release piston  61  is positioned at the end of the pitot tube  33  and acts to seal fuel within the fuel cavity  51  and to prevent fuel release until activated. Fuel release piston  61  extends into fuel cavity  51  and includes three sealing members, pitot sealing member  62 , forward fuel sealing member  63 , and rear piston member  64 . Fuel sealing member  63  contains the fuel within the cavity  51  until fuel activation. Pitot tube sealing member  62  is positioned to receive the air pressure through pitot tube  33  during flight, and is communicably attached to the forward fuel sealing member  63 . The pitot tube sealing member  62  is the surface on which the force of the air pressure acts in triggering fuel activation. It also seals the pitot tube  33  from the fuel cavity  51  and the fuel distribution chamber  35 . By sealing the pitot tube  33 , pitot sealing member  62  ensures that the fuel is not contaminated with the air used to trigger fuel flow. The rear piston member  64  of fuel release piston  61  is communicably connected to the forward fuel sealing member  63  and pitot tube sealing member  62 . The primary function of rear piston member  64  is to limit the stroke of the fuel activation system  60 , thereby maintaining the integrity of the pitot tube seal and preventing air from mixing with fuel in fuel distribution chamber  35 . Rear piston member  64  also functions to seal off the capillary channel  82  during fuel activation to prevent fuel leakage when channel sealing member  81  is disengaged from pusher  100  after projectile  10  leaves the gun barrel during launch. Pin channel  80  is sealed by O-ring sealing member  85  at all times.  
         [0038]    Contacting the rear piston member  64  of the fuel release piston  61  is a channel sealing member  81  which extends through the rearward end of the fuel cavity  51  to the aftmost end of the nozzle portion  90  of the projectile. The channel  80  is preferably disposed centrally along the longitudinal axis of the projectile  10  and has a ½″ diameter. Channel sealing member  81  applies pressure from the pusher  100 , which is temporarily connected to the main body  50  of the projectile  10 , to the rear piston member  64  of the fuel release piston  61  restricting the movement of the fuel release piston  61 . Channel sealing member  81  insures that the seal will remain for as long as the pusher  100  and the projectile  10  are connected, i.e. while in the gun launch tube. This ensures that the fuel activation system  60  will only be triggered after the projectile  10  and pusher  100  have left the muzzle of the gun. Once the pusher  100  and projectile  10  leave the muzzle, the aerodynamic drag on pusher  100  will cause it to separate from the projectile body  10 . As the pusher  100  separates, channel sealing member  81  is allowed to slide in response to the air pressure provided by pitot tube  33  to pitot sealing member  62 . As the forward sealing member  63  releases the fuel into the fuel distribution chamber  35 , the rear piston member  64  of the fuel release piston  61  closes capillary channel  82 . This ensures that there is no leakage of uncombusted fuel through capillary channel  82  and that all of the fuel in the fuel cavity  51  is directed through the forward end of the fuel cavity  51  into fuel distribution chamber  35  and a plurality of fuel distribution channels  86  to the combustion region  75 .  
         [0039]    The process of directing the released fuel to the combustion region  75  of the projectile  10  begins at the fuel distribution chamber  35  when the fuel release mechanism  61  is activated. Fuel distribution chamber  35  extends from the fuel cavity  51  forwardly to a plurality of fuel distribution channels  87  that are disposed at a predetermined radial orientation to the longitudinal axis of projectile body  20 . The outer radial extent of each fuel distribution channel  87  is coupled to a toroidal fuel plenum  74  opposite cowl  70  and downstream of inlet  72 . Fuel plenum  74  communicates with the injection channels  86  for distributed delivery of the fuel material to the internal engine flowpaths at a location between the isolator  73  and the combustion region  75 .  
         [0040]    A second embodiment illustrated in FIG. 2 includes a fuel activation system  260  where the fuel release piston  261  has only two sealing members, air pressure/forward fuel sealing member  263  and rear piston member  264 . Rear piston member  264  is identical to the rear piston member  64  in FIG. 1 and serves the same function. Air pressure/forward fuel sealing member  263  performs the combined function of the pitot tube sealing member  62  and the forward fuel sealing member  63  in FIG. 1. A disadvantage of this second embodiment is that without the pitot tube sealing member  62  the air introduced through pitot tube  33  can mix with the fuel as it is distributed through fuel distribution channels  86  to combustion region  75 . In addition, the hydrogen fuel, which is at much higher pressure than the pitot stagnation pressure, will spill out of the pitot tube. This produces pressure thrust aft, in the wrong direction. Further, the hydrogen spilling from the nose auto-ignites, which disrupts the flow to the scram inlet. In certain situations, however, such as where solid fuels are used, pre-mixing of fuel and air to partially burn a solid fuel “gas generator” to inject fuel-rich partially combusted gases into the scramjet combustor may be the preferred method.  
         [0041]    The present invention functions in the following manner. The projectile is rammed and then charged through a capillary  82  welded to the base of the channel sealing member  81  of the fuel activation mechanism  60 . A taper in the mechanism ensures that the piston seats forward during charging. The taper is not a true taper in the sense of a gradual change in diameter. It is the seal  63  to seal  85  size differential, i.e. seal  63  is slightly larger than seal  85 , 0.500″ versus 0.492″ diameter respectively. The gun is fired, the capillary is severed, and the fuel release piston  61  is held forward against its inertial load by pressure transmitted through the channel sealing member  81  from the pusher  100  as it travels down the launch tube. After projectile  10  leaves the muzzle, the high drag pusher  100  rapidly disengages under the high dynamic pressure load on the forward face of the pusher  100 . In free flight, the fuel release piston  61  is subject to the four forces previously described and is mechanically activated by the stagnation pressure in the pitot tube  33 . Fuel is then allowed to enter the fuel chamber  35  and flows out through the fuel injection channels  86  into the combustion region  75 . While in the launch tube of the gun, pusher  100  seals the high pressure gas behind the projectile  10  and provides a mechanism for transferring the load to the base of projectile  10 . The internal fuel system for projectile  10  may also be fitted with a regulator to keep the flow rate in the injectors constant.  
         [0042]    Once the projectile  10  and pusher  100  separate the stability of the projectile in flight may be increased by providing a plurality of stabilization fins integrated within selected splitters or at the outside back end of cowl  70 . Although not shown, the span of these fins and hence their area could be increased beyond the barrel diameter using control surfaces internal to the projectile that deploy after the projectile clears the muzzle. As previously mentioned, pitot tube pressure may also be used to deploy these fins.  
         [0043]    Many modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.