Abstract:
A projectile includes a projectile body including a flow surface; the flow surface including at least one control surface formed therein. The controls surface is formed continuous with the flow surface, and a pressure source is connected to at least one control surface. The pressure source delivers a pressure to at least one control surface to cause at least one control surface to bulge away from the flow surface.

Description:
STATEMENT OF GOVERNMENT INTEREST 
   The invention described herein may be manufactured and used by or for the Government of the United States of America for government purposes without the payment of any royalties thereof. 

   BACKGROUND OF THE INVENTION 
   The invention relates in general to devices for steering projectiles and in particular to micro-electromechanical systems (MEMS) type control surfaces for steering projectiles. 
   Conventional control systems rely on actuators to rotate fins to provide flight path control. These fins protrude far into the flow stream and require actuators that provide sufficient torque to maintain the fins in the desired orientation. MEMS have been demonstrated for flight control on delta wings. Small perturbations in the flow field created by MEMS structures can result in a net macro force with sufficient strength to steer large objects. 
   U.S. Pat. No. 6,105,904 discloses deployable flow control devices.  FIGS. 15 and 16  of that patent show two embodiments in which a sealable, flexible element acts as a flow effector.  FIG. 15  shows the sealable, flexible element in the quiescent state while  FIG. 15A  shows it in the deformed state. The sealable, flexible element secures to the housing under lip. When plenum is not pressurized the sealable, flexible element is in its quiescent state, retracted out of the fluid boundary layer on the flow surface and within the housing. When the plenum is pressurized, the sealable, flexible element changes to its deformed state expanding such that it deploys through aperture into the fluid boundary layer on the flow surface. When the plenum is depressurized, the sealable, flexible element returns to its quiescent state and retracts out of the fluid boundary layer on the flow surface.  FIGS. 16 and 16A  show the sealable, flexible element attached to the flow surface rather than the housing. 
   One problem with the device disclosed in U.S. Pat. No. 6,105,904 is that the flow effector is a separate piece that must be attached in some manner to the projectile flow surface or skin. At high velocities, such as Mach 2 to Mach 10, the temperature of the projectile flow surface increases to several hundred degrees Centigrade, which causes weakness at areas where the flow effector is attached to the flow surface. Another problem is using a polymer as the material for the flow effector. At high velocities and temperatures, the polymer is too elastic and unstable. Still another problem is that, in the embodiment of  FIG. 15 , the flow effector is not flush with the flow surface, thereby creating a flow disturbance when the flow effector is in the “inactive” position. Similarly, in the embodiment of  FIG. 16 , the flow effector projects above the flow surface even in the “inactive” position. 
   Unexpectedly, Applicant has discovered a novel structural arrangement to overcome the above limitations. 
   SUMMARY OF THE INVENTION 
   The present invention overcomes the problems of the conventional technology by providing a control surface that is formed continuous with the surrounding flow surface. Therefore, there is no separate piece that must be attached to the flow surface. Eliminating the separate piece eliminates the possibility that the separate piece may become detached or weakened at high velocities and temperatures. In addition, the control surface will be flush with the flow surface in the “inactive” position thereby eliminating unwanted flow disturbances. Furthermore, the inventive control surface is made of the same material as the surrounding flow surface so that its elasticity and high temperature stability is suitable for high velocities and temperatures. 
   An object of the invention is to guide hypersonic projectiles, without adversely affecting the projectile drag coefficient. 
   Another object of the invention is to provide a control surface that consumes minimal power and volume. 
   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. 1A  shows a projectile. 
       FIG. 1B  is an enlarged view of a portion of the projectile of  FIG. 1A . 
       FIG. 2A  shows another projectile. 
       FIG. 2B  is an enlarged view of a portion of the projectile of  FIG. 2A . 
       FIGS. 3A and 3B  are sectional views of a control surface according to the invention. 
       FIG. 4  is a schematic of one embodiment of the invention. 
       FIG. 5  is a schematic of a second embodiment of the invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   In accordance with the invention, MEMS control surfaces and, in an embodiment, the control surface is a diaphragm structure, are formed continuous with the flow surface of a projectile so as to be intergrated with the flow surface in order to alter the flow field around the projectile. By applying a pressure stimulus to a MEMS diaphragm, the changes in the flow field result in changes in drag and lift that can be used to steer the projectile. The invention is particularly useful for projectiles traveling at hypersonic velocities. At hypersonic velocities, only a very small protuberance into the flow field is needed to influence the direction of flight. Even deflections as small as 40 μm can have a significant effect on the flow field. 
   The MEMS control surfaces may be located directly on the projectile, or on the fins of the projectile. The pressure may be supplied to the control surfaces via an actuator, or harnessed from the flow field. The MEMS control surfaces have, in essence, no moving parts. As result, the system will share benefits enjoyed by other solid-state systems, such as elimination of friction and wear and greater repeatability. In addition, MEMS batch fabrication processes generally result in dramatically reduced cost. The invention reduces volume and power requirements. The low profile structures have less drag than conventional systems, which results in a longer projectile range and reduced heating. 
     FIG. 1A  shows a projectile  10  having a nose  12 , a tail end  14  and a flow surface  15 . Flow surface  15  comprises the outer skin of projectile  10 .  FIG. 1B  is an enlarged view of the tail end portion  14  of the projectile  10  of  FIG. 1A . Two arrays of control surfaces or diaphragms  16  are shown. Each array includes a plurality of diaphragms  16 .  FIG. 2A  shows another projectile  18  having a nose  12 , a tail end  14  and fins  20 . The flow surface  19  comprises the outer skin of projectile  18  and fins  20 .  FIG. 2B  is an enlarged view of a fin  20  of the projectile  18  of  FIG. 2A . Fin  20  includes a plurality of control surfaces or diaphragms  16 . 
     FIGS. 3A and 3B  are sectional views of a control surface and, in an embodiment; the control surface is a diaphragm structure,  16 . According to the invention.  FIG. 3A  shows the flow surface  22  of a projectile. Flow surface  22  may be the outer skin or fin of a projectile. Arrow  24  represents airflow over the flow surface  22 . A control surface, for example, a diaphragm,  16  is continuously formed with the flow surface  22  so as to be integrated with the flow surface  22 . In  FIG. 3A , the control surface  16  (sometimes referred to herein as “diaphragm”) is in an inactive state wherein the external surface of diaphragm  16  is flush with the external surface of flow surface  22 . In  FIG. 3B , pressure, represented by arrow  26 , has been applied to diaphragm  16 , which is a flexible, moveable structure, to cause it to bulge outward from flow surface  22 , thereby influencing the flight path of the projectile. The deflection of the diaphragm  16  is in a range of 40 microns-1,000 microns. 
   A thickness of flow surface  22  is, for example, in a range of about 0.5 to about 7 millimeters. A thickness of the diaphragm  16  is, for example, in a range of about 10 microns to about 100 microns. The amount of deflection of diaphragm  16  from its rest state in  FIG. 3A  to its deflected state in  FIG. 3B  is, for example, in a range of about 20 microns to about one millimeter. The shape of diaphragm  16  in the plane of the flow surface  22  may vary. Generally, but without limitation, the shapes are circles or squares with a principal dimension in a range of about 1 millimeter to about five millimeters, which, in part, facilitate cycling of the control surfaces  16   
   Diaphragm  16  is formed of the same piece of material as flow surface  22 . One way of forming diaphragm  16  is by thinning out the underside of the flow surface  22  by etching with, for example, an acid. The remaining portions of the underside of flow surface  22  would be masked to prevent any unwanted thinning. Flow surface  22  and diaphragm  16  are made of a material that can withstand the extremely high temperatures associated with high velocity (Mach 2-Mach 10) flow. Generally, the materials are metals, including titanium and stainless steel. Nonetheless, in an embodiment, a ceramic material, for example, silicon carbide may also be used. 
     FIG. 5  shows another way of controlling control surfaces  16 .  FIG. 5  shows the underside (or in the case of a fin, the inside) of flow surface  22  having a diaphragm  16  formed therein. An electronic valve  36  is connected to diaphragm  16  and supplies pressurized air to diaphragm  16 . The pressurized air is fed to valve  36  via a pressure line  38 , which extracts pressurized air from the external air flowing over projectile. Valve  36  is controlled by the guidance system  30  of the projectile. Each diaphragm  16  may have its own valve  36 , or a plurality of diaphragms  16  may be served by a single valve  36  via a plenum arrangement. Valve  36  may also include a relief mechanism for relieving the pressure on diaphragms  16 . Alternatively, a relief mechanism could be located in the fluid connection between the valve  36  and the diaphragm  16  with control established directly from the guidance system  30  or indirectly from the valve  36 . 
   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. 
   Finally, any numerical parameters set forth in the specification and attached claims are approximations (for example, by using the term “about”) that may vary depending upon the desired properties sought to be obtained by the present invention. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of significant digits and by applying ordinary rounding.