Patent Publication Number: US-8525090-B1

Title: Pneumatically actuated control surface for airframe body

Description:
STATEMENT OF GOVERNMENT INTEREST 
     The inventions described herein may be manufactured, used and licensed by or for the U.S. Government for U.S. Government purposes. 
    
    
     BACKGROUND OF THE INVENTION 
     The invention relates in general to airframe bodies and in particular to the guidance and control of airborne projectiles. 
     Numerous devices are known for the control and/or guidance of airframe bodies, such as projectiles. Steering devices for projectiles, for example, movable wings, flaps, and spoilers, may provide a disturbance to the airstream fluid flow path. By disturbing and redirecting the fluid flow path, a reactive moment is generated and imposed on the airframe body. The reactive moment may alter the angle of attack of the body, thereby changing the original flight trajectory. 
     Mechanical and electrical devices, such as hydraulic and electromagnetic systems, may actuate control surfaces on an airframe and direct the control surfaces into the airstream to provide a fluid flow disruption. Many guidance and control systems are expensive, complex, and may be difficult to package within the constraints of smaller projectiles. Hydraulic systems may not be feasible for smaller airframes due to space limitations, complexity, and cost. 
     Electromagnetic systems, particularly those using electromagnetic solenoids, may only be able to operate effectively at a lower frequency rate in the 1-15 Hz range. Such an electromagnetic system may drastically lose performance capability at frequency rates above approximately 25 Hz. Electromagnetic solenoids may require high power batteries to operate efficiently. Also, electromagnetic solenoids may only be able to actuate in one direction and may rely on a spring or other such device to return the solenoid to its home position. 
     A need exists for a control surface and actuator for an airframe body that may be simpler and less expensive than known control surfaces and actuators. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to provide a pneumatically actuated control surface for an airframe body. 
     In one aspect of the invention, a projectile may include a body having an external surface, a stagnation port on the external surface, and a cavity. A spoiler may be translatable in the cavity between a retracted position wherein the spoiler is substantially completely disposed in the cavity and an extended position wherein the spoiler projects from the external surface of the body. 
     A pair of ports may be formed in walls of the cavity. The pair of ports may be selectively fluidly communicable with the stagnation port. The spoiler may be translatable by pressurizing one of the pair of ports with compressed air and venting the other of the pair of ports. 
     The projectile may include fins formed on a rear portion of the projectile. The spoiler may be located forward of the fins. 
     A separation member may divide the cavity into an extend cavity and a retract cavity. The separation member may include stops that protrude into the extend cavity and the retract cavity. One of the pair of ports may be in fluid communication with the extend cavity and another of the pair of ports may be in fluid communication with the retract cavity. 
     In one embodiment, the spoiler may include an extend piston surface, a retract piston surface, and an opening between the extend piston surface and the retract piston surface. Pressure applied to the extend piston surface may cause the spoiler to extend out of the cavity and pressure applied to the retract piston surface may cause the spoiler to retract into the cavity. 
     In another embodiment, the cavity may include a spoiler guideway and a vane guideway, and the projectile may include a rotary vane disposed in the vane guideway. The rotary vane may include an eccentric cam and the spoiler may include a cam guide. The eccentric cam may be disposed in the cam guide. 
     In another aspect of the invention, a method may include providing and launching a projectile. The airstream around the projectile may be disturbed to thereby induce a guidance maneuver for the projectile. The airstream may be disturbed by translating a spoiler from a retracted position to an extended position. 
     The invention will be better understood, and further objects, features, and advantages thereof will become more apparent from the following description of the preferred embodiments, taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the drawings, which are not necessarily to scale, like or corresponding parts are denoted by like or corresponding reference numerals. 
         FIG. 1  is a perspective view of one embodiment of a projectile having a pneumatic guidance and control system. 
         FIG. 2  is a perspective view, partially cut away, of the projectile of  FIG. 1 . 
         FIG. 3  is a perspective view, partially cut away, showing the spoiler of  FIG. 2  in a retracted position. 
         FIG. 4  is a perspective view, partially cut away, showing the spoiler of  FIG. 2  in an extended position. 
         FIG. 5  is an exploded, perspective view of another embodiment of a projectile having a pneumatic guidance and control system. 
         FIG. 6  is a perspective view, partially cut away, showing the spoiler of  FIG. 5  in a retracted position. 
         FIG. 7  is a perspective view, partially cut away, showing the spoiler of  FIG. 5  midway between a retracted position and an extended position. 
         FIG. 8  is a perspective view, partially cut away, showing the spoiler of  FIG. 5  in an extended position. 
         FIG. 9  is a schematic drawing of one embodiment of a pneumatic guidance and control system. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A pneumatic actuation system may include a low-current electronic valve that may be used to activate a pneumatic actuator, such as a cylinder or rotary vane. The electromagnetic pneumatic valve that is used to actuate the pneumatic device may have low electric power consumption. Thus, the electromagnetic pneumatic valve may effectively reduce total overall electrical power requirement to a fraction of that required for a solenoid actuated system. A benefit of a pneumatic/electronic system may be a fast response time due to the electronically actuated valve. Another benefit may be a high force advantage due to pneumatic pressure acting on a piston/vane area. Electronic/pneumatic actuation may provide a compact, high speed, high powered system. 
     An airframe may operate through a transonic speed range and may be exposed to very high speed airstream velocities. The airframe or projectile may include a port that is exposed to the airstream. The exposed port may develop a stagnation pressure. The stagnation pressure is directly related to the fluid mechanics of the airstream and may be plumbed to a storage chamber. The storage chamber may function as a pressure source for a pneumatic actuator. Or, the stagnation pressure may be plumbed directly to a control valve for a pneumatic actuator. Air pressure may also be supplied by an onboard compressed air supply or gas generator. 
     When using airstream stagnation pressure for a pneumatic supply on an airframe, the supply may have a zero or near zero pressure prior to flight of the airframe. The pneumatic supply may become pressurized when the airframe is in flight and at a sufficient velocity. 
       FIG. 1  is a perspective view of an embodiment of projectile  10  having a pneumatic guidance and control system. Projectile  10  may be in an airstream flow A. Spoilers  12  (shown in a retracted position in  FIG. 1 ) may be disposed toward the rear of the projectile main body  14 . Spoilers  12  may be proximal to the rear fins  16  to thereby provide a close relationship between the spoilers  12  and the fins  16 . Air pressure may be supplied via one or more stagnation ports  36  on body  14 . 
     When one or more spoilers  12  are deployed, the resulting disturbance of the air flow A may affect the air flow across the portion of projectile body  14  to the rear of the spoiler  12  (towards the fins  16 ). The air flow disturbance may impart a moment to the projectile  10 . 
       FIG. 2  is a perspective view, partially cut away, of the projectile  10  of  FIG. 1 . The main body  14  of the projectile may function as a housing to contain and seal the spoiler  12 . In  FIG. 2 , the spoiler  12  is shown removed from the body  14  of the projectile  10 . Body  14  may include a cavity having an extend cavity  22  and a retract cavity  24 . The wall of the extend cavity  22  may include an extend port  18 . The wall of the retract cavity  24  may include a retract port  20 . Ports  18 ,  20  may allow pressurized air to alternately enter the respective cavities  22 ,  24 . 
     Cavities  22 ,  24  may be separated from each other by a separation member  26 . Separation member  26  may include stops  34  that extend into both the extend and retract cavities  22 ,  24 . The portion of body  14  that is cut away in  FIG. 2  may form the front wall of cavities  22 ,  24 . 
     Spoiler  12  may function as both a piston and as a control device. Spoiler  12  may include a retract piston surface  28  and an extend piston surface  30 . The retract piston surface  28  and the extend piston surface  30  may be separated by an opening  32 . Spoiler  12  may be disposed in cavities  22 ,  24  such that the retract piston surface  28  is in retract cavity  24  and the extend piston surface  30  is in extend cavity  22 . 
       FIG. 3  is a perspective view, partially cut away, showing the spoiler  12  of  FIG. 2  in a retracted position. The extend cavity  22  ( FIG. 4 ) may be pressurized by air supplied by extend port  18 . Retract cavity  24  may be depressurized by venting through retract port  20  ( FIG. 3 ). The pressurized air in cavity  22  acts on extend piston surface  30  of spoiler  12  to thereby translate spoiler  12  outward from the retracted position of  FIG. 3  to an extended position shown in  FIG. 4 . Spoiler  12  may continue to move outward until retract piston surface  28  contacts stops  34  in retract cavity  24 . 
     Similarly, when the extend port  18  is vented and the retract port  20  is pressurized, the spoiler  12  translates from the extended position of  FIG. 4  to the retracted position of  FIG. 3 . The spoiler  12  may retract until the extend piston surface  30  contacts the stops  34  in the extend cavity  22 . 
       FIG. 5  is an exploded, perspective, partially cut away view of another embodiment of a projectile  50  having a pneumatic guidance and control system. Projectile  50  may include a body  52 . Body  52  may include a cavity having a spoiler guideway  54  and vane guideway  56 . A spoiler  66  may translate in the spoiler guideway  54 . A rotary vane  62  may rotate in the vane guideway  56 . The vane guideway  56  may include an extend port  58  and a retract port  60 . The extend and retract ports  58 ,  60  may be disposed on opposite sides of rotary vane  62 . 
     The rotary vane  62  may include an eccentric cam  64 . Eccentric cam  64  may be disposed in a cam guide  68  in spoiler  66 . The eccentric cam  64  and cam guide  68  may transform the rotary motion of the rotary vane  62  to a linear displacement of the spoiler  66 . Opposite sides of the rotary vane  62  may be pressurized with compressed air via the extend port  58  and the retract port  60 . When one of the ports  58  or  60  is pressurized, the opposite port  58  or  60  is vented. Thus, the rotary vane  62  may be subject to a pressure differential. 
     The pressure differential on vane  62  may cause vane  62  to rotate. The eccentric cam  64  disposed in cam guide  68  may convert the rotary motion of the vane  62  to a linear displacement of the spoiler  66 . In  FIG. 6 , the spoiler  66  is retracted. As the extend port  58  is pressurized pneumatically and the retract port  60  is vented, the rotary vane  62  sweeps across the vane guideway  56 , rotating the eccentric cam  64  which is coupled to the spoiler  66  and extending the spoiler  66  into the airstream, as shown in  FIG. 7 . The spoiler  66  is shown completely extended in  FIG. 8 . 
     From the position shown in  FIG. 8 , if the retract port  60  in the vane guideway  56  is pneumatically pressurized while the extend port  58  is vented, the rotary vane  62  may sweep back toward the retracted position. Through the interaction of the eccentric cam  64  coupled to the cam guide  68  in spoiler  66 , the spoiler  66  is also translated to the retracted position. 
       FIG. 9  is a schematic drawing of one embodiment of a pneumatic guidance and control system  100 . System  100  may include a stagnation port  36  on the body of a projectile. The stagnation port  36  may be fluidly communicable via air line  102  to a multi-position valve  104 . Valve  104  may be, for example, a four-way valve. Valve  104  may be controlled by a control unit  106 , for example, a microprocessor. Valve  104  may be fluidly communicable with extend and retract ports  108 ,  110  via air lines  112 ,  114 , respectively. A vent line  116  may lead from valve  104  to a vent port  118  on the exterior surface of a projectile. Vent port  118  may be located on the projectile at an area of pressure that is less than the stagnation pressure. If desired, an accumulator (not shown) may be disposed between stagnation port  36  and valve  104 . 
     While the invention has been described with reference to certain preferred embodiments, numerous changes, alterations and modifications to the described embodiments are possible without departing from the spirit and scope of the invention as defined in the appended claims, and equivalents thereof.