Abstract:
A vertical take-off and landing (VTOL) aircraft includes separate axial and vertical propulsion sources. The vertical propulsion source includes pulsejet engines located in separate augmentor bays having apertured walls to equalize pulsejet thrust. The pulsejet engine structure is integrated with aircraft structure such that aircraft structural loads are partially carried by each pulsejet engine. Each pulsejet engine produces an aircraft vertical thrust component throttled or exhaust restricted to control aircraft ascent or descent separate from the axial propulsion source. One or more inlet cowls isolate the pulsejet engine bays. One or more outlet cowls at the exhaust bays assist in controlling pulsejet engine thrust. By using separate axial and vertical thrust sources and pulsejet engines for vertical thrust, aircraft speed, payload and operating range are improved and loss of one or more lift engines is mitigated compared to VTOL aircraft using a single propulsion source type for axial and vertical thrust.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to vertical take-off and landing (VTOL) aircraft and more specifically to a pulsejet vertical propulsion system for a VTOL aircraft.  
         BACKGROUND OF THE INVENTION  
         [0002]    Vertical takeoff and landing (VTOL) aircraft are known. A variety of methods have been employed to provide vertical takeoff capability. These methods include: providing ducts to redirect the discharge from the main propulsion unit of the aircraft in a downward direction to provide vertical lift; providing a tilt mechanism to permit the main engine(s) of the aircraft to tilt and provide vertical thrust; and providing separate engines for driving fan systems to lift the aircraft. In each of the known concepts, additional components and structure are added to provide vertical thrust required for vertical takeoff. The complexity of the aircraft increases greatly when the design is modified to use an existing main engine for vertical thrust. Aircraft range and payload capabilities are reduced when weight and structural changes required to incorporate vertical takeoff engines are incorporated into an aircraft.  
           [0003]    When an aircraft is optimized for horizontal flight, adding the capability of vertical takeoff and landing decreases its horizontal flight capabilities, i.e., speed, range and payload. If an aircraft is optimized for hovering and vertical lift capability, high speed horizontal flight capability or long range are usually lost. The complexity of an aircraft designed to accommodate both horizontal and VTOL capabilities also increases the maintenance requirements on the aircraft and therefore increases the overall life cycle costs to operate the aircraft.  
           [0004]    Jet engine aircraft capable of VTOL flight have a normally restricted area of operation. This restriction results from the high velocity and high temperature exhaust gases exiting from the jet engine(s) which are vectored to provide VTOL capability. The high temperature and pressure gases require that special landing areas with hardened landing surfaces be provided, i.e., a concrete landing pad or a steel plate landing surface. The special landing areas prevent damage to surrounding area, negatively impacting the surface pitch of the landing area, and minimize the chance of ingesting material into the jet engine(s). Attempting to land VTOL jet or propeller powered aircraft over non-hardened surfaces can result in a conflagration of ground or vegetation material being expelled into the atmosphere about the aircraft engines which can be entrained into the inlets of the engine causing engine damage and/or failure.  
           [0005]    A need therefore exists for a VTOL aircraft wherein a vertical lift capability is provided which is distinct from the normal horizontal flight engine(s). A need also exists for an engine design providing vertical lift capability which exhausts at both a reduced temperature and pressure and provides a significantly simplified, durable engine design which allows a multitude of vertical lift engines to be provided for redundancy, while providing engines less susceptible to damage from ingestion of ground debris.  
         SUMMARY OF THE INVENTION  
         [0006]    According to a preferred embodiment of the present invention, a vertical takeoff and landing (VTOL) aircraft provides separate axial and vertical propulsion sources including at least one pulsejet engine for vertical propulsion.  
           [0007]    According to one preferred embodiment, each pulsejet engine is provided in a separate augmentor bay. The augmentor bay includes an inner and outer wall provided to support the pulsejet engine, and a pair of apertured sidewalls. The apertures in the sidewalls provide for equalization flow between discharges of adjacent pulsejet engines. Equalizing the discharge from each of the pulsejet engines allows the thrust to be balanced across a bank of pulsejet engines. Therefore, if an individual pulsejet engine is operating above or below a desired operating condition, the resultant thrust from the individual pulsejet engine is balanced with the bank of pulsejet engines and its non-conforming condition does not jeopardize the aircraft.  
           [0008]    The structure of the pulsejet engine of the present invention is integrated into the structure of the aircraft such that the structural loads of the aircraft are partially carried by the pulsejet and ejector engine structure. This reduces the overall weight impact on the aircraft due to addition of the pulsejet engines because separate mounting structure to support each of the pulsejet engines is not required. The pulsejet engines arranged in banks of engines are throttled using a fuel injection system, or the thrust from each individual pulsejet or bank of pulsejets can be controlled using one or more deflection plates. The deflection plates can be provided as rotatable cowls which are provided on both an inlet port of each augmentor bay and a discharge port of each augmentor bay. As known in the art, each augmentor bay provides tapered walls acting as an ejector for each pulsejet engine, thereby increasing the thrust-to-weight ratio of each pulsejet engine.  
           [0009]    The inlet cowl isolates the entrance to each pulsejet engine bay therefore allowing the bay to be isolated from ambient conditions and prevent debris and undesirable materials from entering the pulsejet engines when the engines are shut down. The outlet cowl for the exhaust augmentor bays is provided to assist in controlling pulsejet engine thrust. The outlet cowl can be rotatably positioned ranging from fully opened to fully closed positions such that individual or groups of augmentor bays can be completely opened or partially isolated controlling vertical thrust of the aircraft, or completely isolated to prevent debris and undesirable material from entering the pulsejet engines when the engines are shut down.  
           [0010]    The use of banks of individual pulsejet engines for vertical lift and the main engine(s) for horizontal thrust of the aircraft provides the capability of optimizing both the main engine and the VTOL engines of the aircraft. Either subsonic or supersonic speeds for an aircraft can therefore be provided because the VTOL pulsejet engine banks are isolated after vertical flight is achieved.  
           [0011]    Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:  
         [0013]    [0013]FIG. 1 is a side elevation view of a preferred embodiment of a pulsejet engine of the present invention;  
         [0014]    [0014]FIG. 2 is a perspective view of a group of pulsejets of FIG. 1 having ejectors wherein the ejectors are formed as augmentor cells of the present invention;  
         [0015]    [0015]FIG. 3 is an elevation view of a single augmentor cell of the present invention having the pulsejet structurally mounted to the augmentor cell structure;  
         [0016]    [0016]FIG. 4 is an alternate preferred embodiment of the present invention having the pulsejet inlet diffuser and combustion chamber arranged horizontally and the discharge nozzle arranged vertically to discharge downward into an ejector of the present invention;  
         [0017]    [0017]FIG. 5 is a sectioned elevation view of a conventional pulsejet during detonation;  
         [0018]    [0018]FIG. 6 is the sectioned elevation view of FIG. 5 further showing pressure waves closing a mechanical valve and providing discharge thrust;  
         [0019]    [0019]FIG. 7 is the sectioned elevation view of FIG. 6 further showing the partial opening of the mechanical valve and inflow of a fuel/air mixture into the combustion chamber;  
         [0020]    [0020]FIG. 8 is the sectioned elevation view of FIG. 7 further showing a fully opened mechanical valve and a fuel/air mixture compression cycle;  
         [0021]    [0021]FIG. 9 is the sectioned elevation view of FIG. 8 further showing a fuel/air mixture detonation following a collision between the fuel/air mixture with reflected backpressure waves from a previous detonation;  
         [0022]    [0022]FIG. 10 is a sectioned elevation view of a preferred embodiment of a pulsejet engine of the present invention during a detonation cycle;  
         [0023]    [0023]FIG. 11 is the sectioned elevation view of FIG. 10 further showing the deflagration step following detonation wherein the air and fuel flow are choked off by compression of boundary layer injection air flow by the pressure wave generated during the detonation phase;  
         [0024]    [0024]FIG. 12 is the sectioned elevation view of FIG. 11 further showing the expansion of a fuel/air fuel mixture into the combustion chamber of a pulsejet engine of the present invention following thrust exhaust of the previously detonated air fuel mixture;  
         [0025]    [0025]FIG. 13 is the sectioned elevation view of FIG. 12 further showing the fuel/air mixture in the combustion chamber colliding with reflected pressure waves from the discharge nozzle of the pulsejet of the present invention prior to detonation of the air fuel mixture;  
         [0026]    [0026]FIG. 14 is the sectioned elevation view of FIG. 3 further showing a rotatable cowl at an inlet aperture of the pulsejet of the present invention;  
         [0027]    [0027]FIG. 15 is a perspective view of an exemplary aircraft of the present invention having both conventional main propulsion engines for horizontal flight and multiple banks of pulsejet engines providing for VTOL capability;  
         [0028]    [0028]FIG. 16 is a perspective view of an exemplary arrangement of two banks of pulsejet engines separated by typical structure of an aircraft;  
         [0029]    [0029]FIG. 17 is a perspective view of an individual bank of pulsejet engines showing the inlet and outlet cowls used to either isolate or control and trim the pulsejet engines;  
         [0030]    [0030]FIG. 18 is a plurality of elevation views of a VTOL aircraft of the present invention during the vertical lift stages to achieve flight;  
         [0031]    [0031]FIG. 19 is a plurality of elevation views similar to FIG. 18 showing a VTOL aircraft of the present invention during the various stages of a landing procedure;  
         [0032]    [0032]FIG. 20 is a perspective view of another embodiment of a VTOL aircraft of the present invention showing a side to side balanced configuration of pulsejet engine banks;  
         [0033]    [0033]FIG. 21 is a perspective view of another embodiment similar to the exemplary arrangement of FIG. 16 showing partial exemplary structure to integrate the pulsejet banks into aircraft structures;  
         [0034]    [0034]FIG. 22 is an end elevation view taken along section  22  of FIG. 21, looking forward; and  
         [0035]    [0035]FIG. 23 is a partially sectioned side elevation view of a pulsejet engine and augmentor known in the art.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0036]    The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses.  
         [0037]    Referring to FIG. 1, a pulsejet engine  10  is shown. The pulsejet engine  10  includes a body  12  having an inlet end  14  and an exhaust end  16 . Propulsion thrust from the pulsejet engine  10  discharges from the exhaust end  16  in a propulsion exhaust direction A. Air, normally at atmospheric pressure, enters the inlet end  14 . The air mixes with a fuel (discussed in reference to FIG. 11) which is detonated to produce thrust to propel a platform (not shown) in a platform travel direction B. In the exemplary preferred embodiment shown, both the air flow and the burned fuel/air mixture travel in the propulsion exhaust direction A approximately parallel with a pulsejet engine longitudinal centerline C.  
         [0038]    Referring to FIG. 2, an exemplary pulsejet bank  18  is shown. Each pulsejet bank  18  includes a plurality of pulsejets  20 . Each of the pulsejets  20  is structurally attached to a sidewall  22 . An opposed, second sidewall has been removed from the view of FIG. 2 for clarity. The sidewall  22  is curved to entrain and direct air together with the pulsejet exhaust to maximize thrust from each of the pulsejets  20  in the thrust direction D shown. A plurality of end plates  24  are connectably attached to the sidewall  22  adjacent to each of the pulsejets  20 . Each of the end plates  24  has a plurality of apertures  26  there through. The apertures  26  permit equalization of flow between each of the pulsejets  20  exhaust flows such that any of the pulsejets  20  within the pulsejet bank  18  which operate above or below a nominal operating condition are equalized with the remaining pulsejets  20  of the pulsejet bank  18 . Air enters each of the pulsejets  20  through a pulsejet inlet  28 . The exhaust gas producing thrust from each of the pulsejets  20  is discharged from a pulsejet exhaust  30  in the thrust direction D. Each adjacent pair of end plates  24  connectably joined to opposed sidewalls  22  form each of a plurality of augmentor cells  32 . Only one sidewall  22  is shown in FIG. 2 for clarity. Fuel is supplied to each of the pulsejets  20  through a fuel injection system (shown and discussed with reference to FIG. 10).  
         [0039]    Referring now to FIG. 3, an exemplary pulsejet bay  34  is detailed. Each pulsejet bay  34  includes one augmentor cell  32  and one pulsejet  20 . Each pulsejet  20  includes an inlet diffuser  36 , a tuned section as a combustion chamber  38 , and a discharge nozzle  40 . Structural members join each pulsejet  20  with one or both of the sidewalls  22  to form a unitary load bearing structure. A plurality of hollow vanes  42  surround the discharge nozzle  40 . The hollow vanes  42  serve to uniformly distribute the flow longitudinally along the augmentor cell  32  while providing structural support through the sidewalls  22  and the end plates  24 . In another preferred embodiment, a plurality of webs or intercostals (not shown) join each pulsejet  20  with one or both of the sidewalls  22 . Discharge from each of the pulsejets  20  is in the thrust direction D as shown. A portion of the discharge from the pulsejet  20  exits through each of the plurality of apertures  26  in an ejector cross flow direction E. Air enters the inlet diffuser  36  in the air inlet flow direction F. The inlet diffuser  36  is connectably joined to the combustion chamber  38  and the combustion chamber  38  is connectably joined to the discharge nozzle  40 . In still another preferred embodiment, each of the augmentor cells  32  can also be provided as an integral unit formed from a single piece of material.  
         [0040]    Referring to FIG. 4, the inlet diffuser  36  and the combustion chamber  38  are co-aligned on a horizontal axis G. A bend  44  connectably joins the combustion chamber  38  to the discharge nozzle  40 . The discharge nozzle  40  is aligned along a vertical axis H. The discharge nozzle  40  discharges in the thrust direction D into the augmentor cell  32 . The discharge nozzle  40  preferably includes an axi-symmetric/circular shape attached to the sidewalls  22  through structural webbing (not shown). This permits the inlet for the pulsejet to be aligned horizontally while the discharge is aligned vertically providing additional flexibility in the arrangement of the pulsejets. A perpendicular alignment between the inlet and the discharge of the pulsejet are shown, however, any angle can be used to suit arrangement constraints as is reasonable for proper pulsejet  20  operation.  
         [0041]    [0041]FIGS. 5 through 9 depict a complete operating cycle for a pulsejet engine known in the art. Referring to FIG. 5, a pulsejet  50  known in the art is detailed. The pulsejet  50  includes an inlet diffuser  52  which receives air in an inlet flow direction J. An exhaust nozzle  54  discharges flow from the pulsejet  50  in an exhaust flow direction K. A mechanical valve  56  is included in the inlet diffuser  52  to prevent a backflow of detonated gas from back flowing into the inlet diffuser  52 . In FIG. 5, a detonation stage of a fuel/air mixture  58  in a combustion chamber  60  is shown.  
         [0042]    Referring to FIG. 6, after the fuel/air mixture  58  of FIG. 5 detonates in the combustion chamber  60 , a plurality of reverse pressure waves  62  are generated in a deflagration stage. The reverse pressure waves  62  and the resultant combustion gas travel toward the inlet diffuser  52  and cause the mechanical valve  56  to close preventing flow of the gas through the inlet diffuser  52 . A plurality of forward pressure waves  64  is also generated during the deflagration stage. The forward pressure waves  64  and combustion gas travel in the direction of the exhaust nozzle  54  generating thrust from the pulsejet.  
         [0043]    Referring to FIG. 7, after a majority of the combustion gas exhausts through the exhaust nozzle  54 , the pressure in the combustion chamber  60  reduces and the pressure of the air supply at the inlet diffuser  52  opens the mechanical valve  56 . As the mechanical valve  56  opens, a new supply of air and fuel enters the combustion chamber  60 . A plurality of air expansion pressure waves  66  lead a fuel/air mixture  68  into the combustion chamber  60 .  
         [0044]    Referring to FIG. 8, in a compression stage compression of the fuel/air mixture  68  begins to occur in the combustion chamber  60 . The mechanical valve  56  is fully open allowing air flow through the inlet diffuser  52  in the inlet flow direction J. A plurality of high temperature discharge nozzle backpressure waves  70  reflect from the exhaust nozzle  54 . The discharge nozzle backpressure wave  70  temperature is approximately 1,500 degrees Fahrenheit (815° C.). The discharge nozzle backpressure waves  70  travel in the nozzle backpressure direction L. When the discharge nozzle backpressure waves  70  contact the fuel/air mixture  68  the fuel/air mixture  68  initially compresses in the combustion chamber  60 .  
         [0045]    Referring to FIG. 9, when the high temperature discharge nozzle backpressure waves  70  contact the fuel/air mixture  68  (shown in FIG. 8), and the fuel/air mixture  68  temperature rises to its ignition temperature, a detonation of the fuel/air mixture  68  occurs in the combustion chamber  60 . The fuel/air mixture  68  detonates at a fuel/air detonation point  72  and a new cycle for the pulsejet  50  begins. The detonation, exhaust, compression and new detonation cycle occurs rapidly in the pulsejet engine, i.e., approximately 60 to 100 cycles per second as is known in the art. Fuel is either continuously pressurized and fed by a fuel injection system (shown and discussed in reference to FIG. 10), or is pulse pressurized to enter at the optimum time of each engine operating cycle. Detonation is normally initiated and can also be controlled using a detonation device (not shown) such as a spark plug.  
         [0046]    [0046]FIGS. 10 through 13 show a single cycle of operation of a pulsejet applied in the present invention. Referring to FIG. 10, a pulsejet  100  includes an inlet diffuser  102  connected to an upstream inlet port  104  of a combustion chamber  106 . The combustion chamber  106  is enveloped by a boundary layer air plenum  108 . The boundary layer air plenum  108  provides a plurality of side injection boundary layer air ports  110 , (designated as exemplary boundary layer air ports  110 ′,  110 ″, and  110 ″′) for introduction of a boundary layer air supply (not shown) through at least one supply line  112 . The source for boundary layer air can include compressed air, oxygen generating candles, or bleed air. Boundary layer air enters the combustion chamber  106  through a plurality of apertures  114  in a body section  116  (shown in an exemplary conical shape) of the combustion chamber  106 . The apertures  114  in the body section  116  can have the same aperture size, or can increase or decrease in size, as viewed in FIG. 10, from right to left as the apertures  114  are positioned along the body section  116 . The body section  116  and the combustion chamber  106  can also be provided in other geometric shapes. One or more boundary layer air ports  110  can be used.  
         [0047]    The combustion chamber  106  tapers down and connects to a discharge nozzle  118  at a downstream exit port  120 . A fuel supply (not shown) is fed or injected into the inlet diffuser  102  upstream of the upstream inlet port  104  through one or more fuel supply lines  122 . Fuel supply lines  122  can also enter the combustion chamber  106 , or divide between both the upstream inlet port  104  and the combustion chamber  106 . A detonation stage is depicted in FIG. 10. A fuel and air mixture detonates in the combustion chamber  106  at a fuel/air detonation point  124 .  
         [0048]    Referring to FIG. 11, following the detonation stage shown in FIG. 10, a deflagration stage of the pulsejet  100  is shown. A fuel/air deflagration mixture  126  is shown. As the fuel/air mixture continues to burn and expand beyond the fuel/air deflagration mixture  126 , a plurality of reverse pressure waves  128  form. The reverse pressure waves  128  travel in the reverse pressure wave direction M toward the inlet diffuser  102  (shown in FIG. 10). A plurality of forward pressure waves  130  also form. The forward pressure waves  130  travel in the thrust direction N into the discharge nozzle  118 . The reverse pressure waves  128  contact an entering boundary layer air volume  132  and compress the boundary layer air volume  132  in the direction of the inlet diffuser  102 .  
         [0049]    A fresh air stream  134  combines with fuel supplied through the fuel supply line  122  (shown in FIG. 10) to form a fuel/air mixture  136 . The boundary layer air volume  132  contacts the fuel/air mixture  136  and a choke point  138  is formed. At the choke point  138 , the pressure of the now compressed boundary layer air volume  132  equals or exceeds the pressure of the fresh air stream  134  and further flow of the fresh air stream  134  into the combustion chamber  106  is temporarily blocked. The pressure of the boundary layer air volume  132  driven by the reverse pressure waves  128  also exceeds the pressure of the fuel injection system (not shown) at the fuel supply line  122 , or a sensor of the fuel injection system signals a fuel cut-off therefore preventing input of fuel during the deflagration stage.  
         [0050]    High pressure within the combustion chamber  106  still exists at the stage where the choke point  138  is created. The pressure in the combustion chamber  106  is relieved as thrust in the thrust direction N as the forward pressure waves  130  travel toward the discharge nozzle  118 . The high pressure of the reverse pressure waves  128  force more and more of the boundary layer air flow injected through the boundary layer air plenum  108  (shown in FIG. 10) away from the discharge nozzle facing end of the boundary layer air plenum  108  towards the inlet diffuser facing end. Boundary layer air flow is constricted to flow through an increasingly smaller injection area which causes the velocity and subsequent penetration of the boundary layer air flow into the fresh air stream  134  to increase. In effect, this creates a pneumatic throat or venturi which not only chokes the fresh air stream  134  from entering the pulsejet  100 , but also prevents combustion byproducts from exiting the engine via the inlet diffuser  102 . The choke point  138  location is determined in part by the shape of the body section  116  of the combustion chamber  106 , and by the pressure of the reverse pressure waves  128 .  
         [0051]    Referring now to FIG. 12, during an expansion stage the deflagration pressure and its effect on the boundary layer air volume  132  is reduced by thrust discharge through the discharge nozzle  118  and back reflection of the reverse pressure waves  128  from the choke point  138  (identified in FIG. 11). The reverse pressure waves  128 , traveling in the direction P, encounter the choked flow, reflect and travel in the direction of expansion direction arrows O. This reflection, together with the forward pressure waves  130  exiting the combustion chamber  106 , create a diffusion process which subsequently decreases the pressure in the combustion chamber  106 . The pressure differential between the fuel/air mixture  136  and the pressure in the combustion chamber  106  causes the fuel/air mixture  136  to flow again into the combustion chamber  106  in the direction of expansion arrows O.  
         [0052]    The reduced pressure in the combustion chamber  106  allows the boundary layer air volume  132  to redistribute itself throughout the boundary layer air plenum  108  (described in reference to FIG. 10) and the combustion chamber  106  from the boundary layer air ports  110 . As the boundary layer air flow is redistributed, it is allowed to pass through an ever increasing passage porosity (i.e., the injection area increases). With constant injection pressure and airflow, an increased area necessitates lower velocity injection due to fundamental gas laws. A lowered combustion chamber pressure and increased fresh air charge also help guide the boundary layer air flow to the outer combustor walls of the body section  116 . This serves to partially cool and isolate the hot combustor section from the inlet and also stabilizes subsequent combustion processes by focusing the combustion processes toward the fuel/air detonation point  124  (shown in FIG. 10). In this expansion stage, the forward pressure waves  130  have reached the discharge nozzle  118 . A plurality of discharge nozzle back-pressure waves  140  in the form of rarefaction waves begin to form in this stage. The discharge nozzle back-pressure waves  140  create a sub-ambient expansion which partially induces ejector airflow and combustion byproducts from the last cycle into the discharge nozzle  118 . The discharge nozzle back-pressure waves  140  also travel in the direction P.  
         [0053]    Referring now to FIG. 13, in a compression stage the fuel/air mixture  136  traveling in an fuel/air flow direction Q begins to contact the discharge nozzle back-pressure waves  140 . The fuel/air mixture  136  begins to compress in the combustion chamber  106 . A stabilizing volume of the previously expanded boundary layer air volume  132  is shown as it compresses along the perimeter of the combustion chamber  106 . The compression stage shown in FIG. 13 shows the plurality of discharge nozzle back-pressure waves  140  immediately before detonation of the fuel/air mixture  136  similar to the detonation shown in FIG. 10. Detonation begins a new cycle for the pulsejet.  
         [0054]    Referring back to FIG. 12, the combustion chamber  106  includes a taper section  142 . The taper section  142  ends at a taper distal end  144  which is the connecting point for the discharge nozzle  118 . The geometry of the taper section  142  also helps provide the constriction of the out flowing gases and the generation of the discharge nozzle back-pressure waves  140 .  
         [0055]    Referring to FIG. 14, an exemplary pulsejet bay  146  as applied in the present invention is shown. An upper aperture  148  of the pulsejet bay  146  can be partially or completely closed by a cowl  150 . In the exemplary embodiment shown, the cowl  150  is mounted to the pulsejet bay  146  by a hinge  152  or similar mechanical element. The cowl  150  rotates along an arc R about a hinge center-line S to the closed, phantom position shown. The cowl  150  is controlled by a control system (not shown). Air inlet flow to the pulsejet  100  in the pulsejet bay  146  can be controlled by the single cowl  150  shown or by two or more cowls (not shown) similar to the cowl  150 . Similar devices provided at the bottom aperture  148  of each of the pulsejet bays  146  can be used to control the thrust produced in each pulsejet bay  146 . In another preferred embodiment, the cowl  150  is provided as a flexible member which rolls out from a reel (not shown) which replaces the hinge  152 , to the closed, phantom position shown.  
         [0056]    Referring to FIG. 15, an exemplary VTOL aircraft  210  according to a preferred embodiment of the present invention is shown. The VTOL aircraft  210  structurally includes a fuselage  212  and a pair of flight wings  214 . To provide VTOL capability, a plurality of pulsejet/ejector banks are provided. A pair of pulsejet/ejector aft banks  216  and a pulsejet/ejector forward bank  220  are provided. Each of the pulsejet/ejector aft banks  216  and the pulsejet/ejector forward bank  220  include a plurality of pulsejet engines  218 .  
         [0057]    The pulsejet/ejector aft banks  216  and the pulsejet/ejector forward bank  220  provide vertical takeoff capability in the vertical lift direction T. In order to provide horizontal or axial flight capability for the VTOL aircraft  210 , a pair of main flight engines  222  are shown as known in the art. The main flight engines  222  provide for axial flight of the VTOL aircraft  210  in an axial flight direction U.  
         [0058]    The pulsejet/ejector aft banks  216  are provided in an aft compartment  224  of the VTOL aircraft  210 . The structure supporting each of the pulsejet engines  218  is integrated into the aft compartment  224  such that structural loads of the VTOL aircraft in the aft compartment  224  area are at least partially supported by the pulsejet/ejector aft banks  216 . Similarly, structure of the pulsejet/ejector forward bank  220  is integrated into the VTOL aircraft  210  in a forward compartment  226 . The vertical thrust generated by each of the pulsejet/ejector aft banks  216  and the pulsejet/ejector forward bank  220  is centered about a VTOL aircraft  210  center of gravity  228 . By centering the pulsejet banks about the center of gravity  228 , individual pulsejet engines  218  can be throttled to affect the attitude of the VTOL aircraft  210  during takeoff and landing procedures.  
         [0059]    Referring now to FIG. 16, another preferred embodiment for pulsejet/ejector banks of the present invention is shown. The pulsejet/ejector bank  230  includes a pulsejet/ejector port bank  232  and a pulsejet/ejector starboard bank  234 , respectively. One or more interior compartment bays  236  are provided between both the pulsejet/ejector port bank  232  and the pulsejet/ejector starboard bank  234 . The interior compartment bay(s)  236  can be used for a variety of aircraft purposes, including stowage, fuel stowage, acoustic isolation, and personnel spaces, (e.g., with exterior compartments used for fuel volume, or vice versa, with exterior compartments used for payload such as antennae).  
         [0060]    Each pulsejet  238  includes an inlet diffuser  240  wherein ambient air is drawn into the pulsejet  238 , and an exhaust nozzle  242  where exhaust gases generating vertical thrust by each of the pulsejets  238  discharge. Forward thrust is provided by the main flight engines  222  (shown in FIG. 15) to provide thrust to propel the VTOL aircraft  210  in the aircraft forward direction V. Ambient air enters each of the pulsejets  238  in the air inlet direction W. Exhaust gases generating vertical thrust by each of the pulsejets  238  discharges from the pulsejets  238  in the thrust direction X. In the exemplary arrangement shown by FIG. 16, both the pulsejet/ejector port bank  232  and the pulsejet/ejector starboard bank  234  are approximately equally spaced about an aircraft longitudinal centerline Y.  
         [0061]    Referring to FIG. 17, the pulsejet/ejector port bank  232  of FIG. 16 is shown in greater detail. An inlet cowl  244  is partially shown in a closed position isolating augmentor bays  245 . The inlet cowl  244  is shown as a unitary cowl capable of isolating all of the pulsejets of the pulsejet/ejector port bank  232 . The inlet cowl  244  can also be provided as individual cowls isolating each of the augmentor bays  245  individually.  
         [0062]    A pair of exhaust cowls  246  are joined to the pulsejet/ejector port bank  232  at each of a plurality of augmentor bay exhaust ports  247 . The pair of exhaust cowls  246  are rotatably attached to the structure of the pulsejet/ejector port bank  232  and operate from a fully open to a fully closed position for the augmentor bay exhaust ports  247 . By rotating one or both of the exhaust cowls  246 , or modifying the fuel supply, discharge thrust from the pulsejets in the pulsejet/ejector port bank  232  can be controlled. Similar to the inlet cowl  244 , the exhaust cowls  246  can also be completely shut to provide isolation of one or all of the augmentor bays  245 . The exhaust cowls  246  can also be provided, similar to the inlet cowl  244 , as individual cowls (not shown) isolating each of the augmentor bay exhaust ports  247 , or an intermediate number of cowls isolating 2 or more bays (not shown). Depending upon the simplicity of the design desired, either or both the inlet cowl  244  and the exhaust cowls  246  can be eliminated to reduce complexity and weight of the pulsejet bank.  
         [0063]    Referring now to FIG. 18, the individual operating stages of a VTOL aircraft of the present invention are shown. In a ready step  248 , a bank of pulsejet engines in a pulsejet ejector thrust augmentor (PETA) bank are idle. The main propulsion turbine engines are also idle. In a vertical lifting step  250 , the PETA banks power level are increased to approximately 90%. The main propulsion engine(s) power is increased to approximately 30%. Initial vertical lift of the aircraft begins at this stage as well as horizontal motion. In a forward engine initiation step  252 , PETA power is increased to full 100% power and the main propulsion engine(s) power is increased to approximately 60%. The aircraft pitches nose down and the PETA power assists in accelerating the aircraft. In a transitioning step  254 , the PETA power decreases in a range between approximately 100% to 50% power. The pulsejet engines are slowly throttled down during this step and the main propulsion engine(s) power is increased to 100% to transition to horizontal flight. As the aircraft transitions, the nose is pitched up and the wings begin to generate lift. In an acceleration step  256 , the PETA engines are reduced in power to approximately 30% and the main propulsion engine power is maintained at 100%. Aircraft acceleration continues and the pulsejet engine power is significantly reduced as the aircraft approaches its nominal flight speed. At this point, the full weight of the aircraft is supported by its wings. In a cruise step  258 , normal horizontal flight of the aircraft is achieved. The banks of PETA engines are shut down during this stage and the inlets to the PETA engines are isolated. Main propulsion turbine engines are throttled as required during this final stage where normal aircraft cruising speed has been achieved. In the exemplary arrangement shown in FIG. 18, an exemplary time of about 60 seconds elapses between the ready step  248  and the cruise step  258 .  
         [0064]    Referring now to FIG. 19, in a cruise step  260 , similar to the cruise step  258  shown in FIG. 18, the PETA engines are in their stowed and powered down conditions and the main propulsion engines of the aircraft are in their normal cruise condition. In an initiating step  262 , the PETA engines are initiated and the aircraft is maneuvered into a descent orientation. In a descent step  264 , aircraft speed is reduced by reducing the main propulsion engine power from 100% to approximately 50% while increasing the PETA engine power up to approximately 60%. In a stalling step  266 , the aircraft is positioned to stall the wings of the aircraft. The main propulsion engine power is further decreased to approximately 30% and the PETA engines are throttled up to provide just below a climbing power. In a hovering step  268 , the PETA engines are just below 100% operating power (just below climbing power) and the aircraft is in a brief hover mode. Main propulsion engine power is retained at about 30% power during this stage to provide minimum forward thrust of the aircraft. In a landing step  270 , the aircraft has landed and the PETA&#39;s engines are idled and the main propulsion engines are shut down. Any cowls on the PETA engines are isolated at this time. In the exemplary configuration shown in FIG. 19 for a landing procedure, an exemplary time of approximately 90 seconds elapses to bring the aircraft from an altitude of approximately 200 feet to a landing position.  
         [0065]    Referring now to FIG. 20, another preferred embodiment of the present invention showing an aircraft having side to side arranged pulsejet/ejector banks is shown. A VTOL aircraft  272  includes a forward port pulsejet/ejector bank  274  and an aft port pulsejet/ejector bank  276 . A plurality of augmentor bays  278  is used for each pulsejet bank. On a starboard side of the VTOL aircraft  272 , a forward starboard pulsejet/ejector bank  280  and an aft starboard pulsejet/ejector bank  282  are used. Forward propulsion for the VTOL aircraft  272  is provided by a pair of main propulsion engines  284  arranged about the aircraft longitudinal centerline Z. The forward and aft arranged pulsejet banks for the VTOL aircraft  272  are equally spaced about the aircraft longitudinal centerline Z. Aircraft attitude during vertical takeoff is controlled by one or both of throttling the pulsejet engines and using discharge cowls (detailed in FIG. 17).  
         [0066]    Referring now to FIGS. 21 and 22, an exemplary structurally integrated pulsejet/ejector bank  286  is detailed. Both a pulsejet/ejector port bank  288  and a pulsejet/ejector starboard bank  290  are structurally integrated with aircraft structure. A port inner wall  292  and a starboard inner wall  294  form the exterior walls of an interior payload bay  296 . The pulsejet/ejector port bank  288  is structurally attached to an exterior facing surface of the port inner wall  292 . Similarly, the pulsejet/ejector starboard bank  290  is structurally attached to an exterior facing surface of the starboard inner wall  294 . The pulsejet/ejector port bank  288  is connected to a port outer wall  298  and the pulsejet/ejector starboard bank  290  is connected to a starboard outer wall  300  by a plurality of apertured divider plates  302 . The apertured divider plates  302  also provide structural rigidity for the assembly. Each of the pulsejets  304  are structurally attached to either one of the inner walls or the outer walls using one of a plurality of hollow vanes  306  provided for each pulsejet  304 .  
         [0067]    By including the structure of the pulsejet/ejector bank  286  into the aircraft, separate engine support structure which is normally used to support main flight engines, such as the main flight engines  222  shown in FIG. 15, is not required. Insulation layers  308  can also be incorporated in the structure of the pulsejet/ejector bank  286  such that pulsejet acoustic levels can be attenuated. Fuel tanks  310  can be integrated. A wing structure  312  can also be incorporated into the pulsejet/ejector bank  286  allowing the pulsejet/ejector bank  286  to be totally enclosed within the fuselage of the aircraft. This reduces the aerodynamic drag of the aircraft and permits the aircraft to achieve supersonic flight (if desirable).  
         [0068]    The advantage of providing a plurality of pulsejets  304  for vertical lift capability (separate from a main flight engine) include the redundancy available from the simplified design of the pulsejet engine. Depending upon the safety factor selected, one or more of the pulsejets  304  can fail and the ability of the remaining pulsejets  304  to provide vertical lift for the aircraft provide a redundant safety feature. The simplified nature of the exemplary pulsejet/ejector bank  286  design also provides the advantage that items ingested into the inlet diffusers of each of the pulsejets do not damage the pulsejets. Foreign object damage of this nature would normally destroy a conventional turbine causing mission failure and/or loss of life. This feature is particularly advantageous if an aircraft is landing in an area where debris can be kicked up and ingested into the pulsejets.  
         [0069]    Pulsejet engines used for vertical lift capability also provide the additional advantage to operate using a wide variety of fuels. The only significant requirement of the fuel is the fuel must be capable of being atomized in order to be burned. Examples of typical types of fuel that can be used with a pulsejet engine include aircraft (JP, kerosene based) fuel, automobile grade gasoline or diesel, natural gas, alcohol, hydrogen or even a form of coal.  
         [0070]    The augmentors used for the pulsejet engine banks of the present invention entrain ambient air and decrease the temperature and velocity of the exhaust gases of the pulsejet engines. By decreasing the exhaust gas temperature and velocity, the pulsejet/ejector engine banks of the present invention can be used over a wider variety of landing areas reducing damage to the landing area. Common VTOL aircraft require a hardened landing area such as concrete or steel. This requirement for a cooled and/or hardened landing area is reduced when pulsejet engine banks of the present invention are used for vertical lift capability of an aircraft. The use of a plurality of pulsejet engines also provides the additional benefit that the individual pulsejet engines can be operated at a lower power level than if fewer numbers of engines are used. A lower operating power results in further reduced exhaust gas temperature and pressure. Reducing the discharge pressure from each pulsejet engine and increasing distributed area by increasing the number of pulsejets also advantageously reduces the chance of debris being kicked up by the exhaust gases and ingested by the pulsejets or main propulsion engine(s) of the aircraft. Although two or fewer pulsejets can be individually mounted in distinct areas of an aircraft, it is preferable that pulsejet banks of approximately 3 or greater pulsejet engines be provided in order to obtain the redundancy and lower exhaust gas temperature and pressure benefits as discussed above.  
         [0071]    Referring now to FIG. 23, an exemplary pulsejet  400  is shown attached to an exemplary ejector  402  as known in the art. The discharge from the pulsejet  400  enters the ejector  402  where the flow is constricted in the ejector bore  404 . Ambient air enters the pulsejet  400  via air flow direction path AA. Ambient air is also entrained as well as the exhaust from the pulsejet  400  in air inlet  406  in a flow direction BB. Additional ambient air can be entrained in one or more auxiliary air inlets  408 . The auxiliary air inlets  408  permit ambient air to enter directly into the ejector bore  404  area of the ejector  402 . The combined exhaust of the pulsejet  400  and the ejector  402  exits in the exhaust direction CC.  
         [0072]    A VTOL aircraft of the present invention using pulsejet engines arranged in banks offers several advantages. By using separate pulsejet/ejector engine banks which are optimized for vertical takeoff of an aircraft and using independent forward thrust engines which are optimized for forward thrust of the aircraft, both vertical takeoff and forward flight propulsion for the aircraft are optimized rather than compromised as in conventional applications. By integrating structure of the pulsejet/ejector banks with the aircraft structure, aircraft structural loads are partially borne by the pulsejet/ejector structure, therefore reducing the overall weight impact of the pulsejet/ejector engine banks. By providing a plurality of mechanically simple pulsejet engines in each pulsejet/ejector engine bank, redundancy and therefore aircraft safety is increased. Loss of one of the pulsejet engines from a pulsejet/ejector engine bank can be compensated by throttling adjacent engines, changing the attitude controls of the pulsejet cowls, or down-powering an opposite counterpart pulsejet engine. By separating the vertical takeoff capability from the horizontal flight capability, and providing the capability of isolating the inlet and exit ports of the pulsejet engine banks, unrestricted forward flight capability of the aircraft is provided (including supersonic speeds). Also, by incorporating the pulsejet engine banks into the aircraft structure, the wings of the aircraft can also be optimized for forward flight thereby reducing the structure and weight of the aircraft wings.  
         [0073]    The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.