Abstract:
A baseball cap including features for stabilizing the cap in a moving stream of air. The cap includes a modified bill having a downforce generator configured to create a relatively stagnate recirculation zone between the downforce generator and the head covering. This recirculation zone tends to negate the lifting effect found in prior art bills. The invention preferably includes a vent through the bill. The vent is located behind the downforce generator, to connect the underside of the bill to the recirculation zone formed in the wake of the downforce generator. The vent is selectively closed by a flexible flap. The flap remains closed to prevent rain from passing through the vent. However, if pressure beneath the bill significantly exceeds pressure above the bill, the vent opens to equalize the pressure. This action prevents the creation of a net lifting force which might lift the cap off the wearer&#39;s head.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
       [0001]    This application is a continuation in part of U.S. patent application Ser. No. 12/154,562, which was filed on May 23, 2008. The parent application listed the same inventor. 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    Not Applicable. 
       MICROFICHE APPENDIX 
       [0003]    Not Applicable 
       BACKGROUND OF THE INVENTION 
       [0004]    1. Field of the Invention 
         [0005]    This invention relates to the field of headwear. More specifically, the invention comprises a baseball cap having a modified bill configured to produce downforce when the cap is placed in a moving airstream. 
         [0006]    2. Description of the Related Art 
         [0007]    The “baseball cap” is one of the world&#39;s best known hats.  FIG. 1  shows a typical example. Baseball cap  10  is comprised of head covering  12  and bill  14 . Head covering  12  is a generally circular assembly of flexible material sized to fit fairly closely over the human head. Bill  14  has leading edge  52  and trailing edge  54 . The trailing edge is attached to the forward portion of the head covering. As the hat is normally worn, the bill extends forward from the wearer&#39;s face. The bill provides shade and weather protection for the user&#39;s face. 
         [0008]    Those familiar with the art will know that such hats are made using a variety of technique. The example of  FIG. 1  is constructed using a sewn assembly of wedge-shaped pieces. These are curved inward and join at the top, where a button is usually affixed. Such hats must typically include size-adjusting features. The rear of the hat may have a break spanned by an adjustable strap. The strap is used to adjust the circumference of the hat at its largest section. Alternatively, the head covering may include elastic material which eliminates the need for other adjustment features. 
         [0009]      FIG. 2  shows an elevation view of a person actually wearing a prior art baseball cap. Such caps are often worn while traveling in an open vehicle—such as a fishing boat. Air flow directed toward the wearer&#39;s face has a tendency to lift the baseball cap off the wearer&#39;s head. As for most situations involving subsonic compressible flow, the phenomenon is explained by the application of Bernoulli&#39;s equation, which can be written as: 
         [0000]    
       
         
           
             
               
                 
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                   2 
                 
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                   v 
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                 gh 
                 1 
               
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                   P 
                   1 
                 
                 
                   ρ 
                   1 
                 
               
             
             = 
             
               
                 
                   1 
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                   v 
                   2 
                   2 
                 
               
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                 gh 
                 2 
               
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                   P 
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         [0010]    In this expression, v stands for the flow velocity at a given point, g stands for gravitational acceleration, h stands for the height above a reference plane, P stands for the pressure of the air at a given point, and ρ stands for the density of the air at a given point. 
         [0011]    From this equation one may easily discern the fact that when a compressible fluid is flowing past an object at subsonic speeds, the faster the flow is sin a particular region the lower the pressure will be in that region. When looking at  FIG. 2 , the reader will observe how the flow must split to flow over the top and bottom of bill  14 . The flow over the top passes smoothly over the head covering and is not decelerated very much. This is denoted in the view as high velocity region  18 . 
         [0012]    The flow passing under the bill, however, impacts the wearer&#39;s face  16 . This produces a recirculation area denoted as stagnation region  20 . The flow in this area is relatively slow. Thus, from Bernoulli&#39;s equation, one may accurately predict that the air pressure in the area beneath the bill will be greater than the air pressure in the area above the bill. The result is the creation of lift  24 , which tends to lift the cap free of the wearer&#39;s head. 
         [0013]    Prior hat designers have accounted for this phenomenon by angling the bill downward as shown. The downward angle has the effect of an airfoil having a negative angle of attack. The flow over the top therefore creates downforce  22 . If the magnitude of downforce  22  exceeds that of lift  24 , then the hat will stay on. Of course, the motion of the wearer&#39;s head alters the bill&#39;s angle of attack. If the user inclines her head slightly, downforce  22  will be greatly reduced. This will likely be the instant when the moving airstream lifts the cap free of the wearer&#39;s head and carries it away. 
         [0014]    The loss of such a cap is a significant inconvenience. This is particularly true in a boating situation, where the hat is likely to blow overboard and be lost. Prior art designers have attempted to remedy this known problem in a variety of ways. For example, some caps have incorporated a bill having a hinged vent flap. The vent flap pivots upward if the pressure difference between the region beneath the bill and above the bill becomes large enough. Other designs have incorporated one or more fixed vents through the bill. Still other designs have incorporated a bill with a severe downward angle, so that the bill&#39;s angle of attack remains negative throughout the range of motion of the user&#39;s head. 
         [0015]    While these prior art designs have in part remedied the problem, no prior art design has produced a good solution while still maintaining the conventional benefits of the traditional baseball cap. The present invention seeks to remedy these shortcomings. 
       BRIEF SUMMARY OF THE PRESENT INVENTION 
       [0016]    The present invention is a baseball cap including features for stabilizing the cap in a moving stream of air. The cap includes a modified bill having a downforce generator configured to create a relatively stagnate recirculation zone between the downforce generator and the head covering. This recirculation zone tends to negate the lifting effect found in prior art bills. 
         [0017]    The invention preferably also includes a vent through the bill. The vent is located behind the downforce generator, so as to connect the underside of the bill to the recirculation zone formed in the wake of the downforce generator. The vent is selectively closed by a flexible flap. The flap remains closed to prevent rain from passing through the vent. However, if pressure beneath the bill significantly exceeds pressure above the bill, the vent opens to equalize the pressure. This action prevents the creation of a net lifting force which might lift the cap off the wearer&#39;s head. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0018]      FIG. 1  is a perspective view, showing a prior art baseball cap. 
           [0019]      FIG. 2  is a side elevation view, showing the flow of air over a prior art baseball cap. 
           [0020]      FIG. 3  is a perspective view, showing the present invention. 
           [0021]      FIG. 4  is an exploded perspective view, showing the various components of the present invention. 
           [0022]      FIG. 5  is a detail view, showing the operation of the downforce generator and the vent. 
           [0023]      FIG. 6  is a detail view, showing the operation of the downforce generator and the vent. 
           [0024]      FIG. 7  is a perspective view, showing the present invention with the downforce generator removed. 
           [0025]      FIG. 8  is a side elevation view, showing an alternate embodiment. 
       
    
    
       [0026]      
         [0000]    
       
         
               
             
               
               
               
               
               
             
           
               
                   
               
               
                 REFERENCE NUMERALS IN THE DRAWINGS 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 10 
                 baseball cap 
                 12 
                 head covering 
               
               
                   
                 14 
                 bill 
                 16 
                 face 
               
               
                   
                 18 
                 high velocity region 
                 20 
                 stagnation region 
               
               
                   
                 22 
                 downforce 
                 24 
                 lift 
               
               
                   
                 26 
                 stay-on cap 
                 28 
                 modified bill 
               
               
                   
                 30 
                 downforce generator 
                 32 
                 splitter 
               
               
                   
                 34 
                 vent 
                 36 
                 flap 
               
               
                   
                 38 
                 drain 
                 40 
                 upper pressure 
               
               
                   
                 42 
                 lower pressure 
                 44 
                 flap attachment 
               
               
                   
                 46 
                 free end 
                 48 
                 secondary downforce 
               
               
                   
                 50 
                 forward region 
                 52 
                 leading edge 
               
               
                   
                 54 
                 trailing edge 
                 56 
                 gap 
               
               
                   
                 58 
                 cavity 
                 60 
                 first lateral extreme 
               
               
                   
                 62 
                 second lateral extreme 
                 64 
                 trailing portion 
               
               
                   
                 66 
                 closing pressure 
                 68 
                 throat 
               
               
                   
                 70 
                 exit 
               
               
                   
                   
               
             
          
         
       
     
       DETAILED DESCRIPTION OF THE INVENTION 
       [0027]    The central concept of the present invention is to provide a system that prevents moving air from forcing a cap off a wearer&#39;s head by providing an uplifting force on the cap&#39;s bill. At the same time, the system should retain the normal sun shading and moisture channeling capabilities of a conventional cap. In order to achieve these objectives, the invention features a vent through the bill which is selectively opened and closed by a moveable flap. 
         [0028]    The flap operates in conjunction with a downforce generator located on top of the bill. The geometry of the vent, the flap, the cap, and the downforce generator combine to selectively create (1) a first state in which the flap opens to allow flow through the bill when needed to keep the hat in place; and (2) a second state in which the flap is forced closed in order to restore the normal functions of the bill. The automatic transfer between these two states is referred to as “active load relief,” meaning that the cap automatically changes its configuration in order to hold the cap in position on the wearer&#39;s head. 
         [0029]      FIG. 3  shows the present invention in an assembled state. Stay-on cap  26  has modified bill  28 . Downforce generator  30  is preferably attached to modified bill  28 . The reader will observe how the downforce generator preferably assumes a form reminiscent of a snow plow blade. Splitter  32  preferably lies near the middle of the downforce generator. Air flow impacting the downforce generator strikes the splitter and is thereafter divided into a first portion directed toward a first lateral extreme  60  and a second portion directed toward a second lateral extreme  62 . 
         [0030]      FIG. 4  shows the same assembly in an exploded state. Modified bill  28  has vent  34  passing through it from top to bottom. This vent is preferably covered by flap  36 . Downforce generator  30  then lies above the location of the forward portion of the flap. The invention can be made in a variety of sizes. The absolute dimensions are not as important as the ratios between certain dimensions, as will be explained subsequently. However, it may be helpful or the reader to understand some typical dimensions based on a typical cap size. 
         [0031]    The width of bill  14  is preferably between about 15 cm and 25 cm. The length of the bill is preferably between about 6 cm (a “short bill”) and about 14 cm (a “fishing bill”). The width and length of vent  34  is obviously less than that of the bill. The width of vent  34  is between about 12 cm and about 21 cm. The slot is preferably between 1.5 cm and 3 cm across. Flap  36  preferably covers the entire slot. Thus, flap  36  is preferably between about 13 cm and about 22 cm wide. It is preferably between 1.6 cm and 4 cm across. 
         [0032]      FIG. 5  shows a section elevation view through modified bill  28  in the region of vent  34  (with the vent in a closed state). The reader will observe that downforce generator  30  is a thin-walled structure rising upward and rearward from the leading edge of modified bill  28 . Cavity  58  is formed by downforce generator  30  and modified bill  28 . The reader will observe that the downforce generator extends only part of the way from the leading edge of modified bill  28  to forward region  50  of head covering  12 . Thus, gap  56  is formed between the trailing edge of the downforce generator and forward region  50 . The shape of the downforce generator is significant. The upward curvature of the downforce generator increases to a maximum in trailing region  64 . The significance of this feature will be explained subsequently. 
         [0033]    The presence of gap  56  creates a recirculation zone behind the trailing edge of the downforce generator. The airstream impacting the upwardly inclined forward surface of the downforce generator creates downforce  22  (through stagnation pressure of the air impacting the device). Downforce  22  obviously tends to hold the hat down on the user&#39;s head. The creation of the recirculation zone in gap  56  tends to create relatively high pressure in this region, which places secondary downforce  48  on the upper surface of flap  36  and tends to retain the flap in the closed position when the air is passing over the bill in the fashion shown in  FIG. 5 . 
         [0034]    Flap  36  is made of a flexible material. It is preferably attached to the bill by flap attachment  44  (which can be a sewn joint, an adhesive joint, etc.). The effect of this construction is that the leading edge of flap  36  remains in a fixed position with respect to the bill, but free end  46  can lift upward, thereby opening vent  34  and allowing flow to occur from below the bill to above the bill. 
         [0035]    In the configuration shown in  FIG. 5 , upper pressure  40  (the air pressure above the bill) is equal to or exceeds lower pressure  42  (the air pressure below the bill). Thus, secondary downforce  48  exceeds lift  24  and flap  36  remains closed. This represents the normal configuration. In this configuration, the hat functions as a normal baseball cap in that it does not allow sun or rain to reach the wearer&#39;s face. Free end  46  is preferably designed to rest flat against forward region  50  or the bill itself, so that rain falling down the vertical portions of the cap will not leak through vent  34 .  FIG. 7  shows a view of flap  36  in the closed position (with the downforce generator removed for visual clarity). 
         [0036]    In  FIG. 6 , the relative flow velocity or flow direction has changed so that the pressure below the vent exceeds the pressure above it. An example of a situation creating such a change is a person riding in an open boat. If the person keeps his or her head pointed straight ahead, a conventional cap will stay on. However, if the person momentarily forgets about the hat and tilts his or her head upward, the relative wind will increase the pressure underneath the bill and lift the cap off the person&#39;s head. The reader will note that in  FIG. 6  the wearer&#39;s head is tilted back somewhat. 
         [0037]    In the scenario of  FIG. 6  the pressure underneath the bill exceeds the pressure above the bill. In such a case flap  36  is forced open as shown. Air then flows from beneath the bill and into gap  56 , where it joins the stream passing over the top of the cap. This results in a significant reduction in lifting force. Meanwhile, the air flowing over the downforce generator continues to produce downforce  22 . Those skilled in the art will therefore realize that by appropriately sizing and shaping the elements disclosed, it is possible for downforce  22  to exceed the lifting force in nearly all configurations. Thus, the cap has a much greater tendency to stay on the wearer&#39;s head. 
         [0038]    The relative scaling of the geometry of the vent, the downforce generator, and the cap is important to the operation of the device. Returning briefly to  FIG. 5 , the reader will recall that flap  36  is attached to bill  14  along flap attachment  44 . Flap attachment  44  is preferably a secured seam, where the two pieces of material—one from the flap and one from the bill—are overlapped for some distance and joined together. Such a seam tends to help hold the flap closed, as the flap material itself must bend in order to open vent  34 . 
         [0039]    This phenomenon is shown in  FIG. 6 , where the reader will observe that flap  36  has to bend in order to open vent  34 . This naturally produces a curved shape to the opening. The result is a crude form of venturi. Flexible flap  36  bends until its trailing edge is approximately parallel to (within ten degrees of parallel) the adjacent portion of forward region  50 . The air enters through vent  34 , passes through throat  68 , and passes out through exit  70 . A recirculation zone is created on the back side of flap  36 , as indicated by the circular arrow. The phantom line shows the approximate boundary of the expanding air as it moves through throat  68  toward exit  70 . The opposite boundary of the expanding air is of course formed by forward region  50  of the cap itself. 
         [0040]    The flow through the venturi is governed by Bernoulli&#39;s Equation, which is restated below: 
         [0000]    
       
         
           
             
               
                 
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         [0041]    The left side of the equation represents a first position in the moving flow and the right side represents a second position in the moving flow. From the equation, one may easily perceive that as flow velocity increases, the pressure of the moving air decreases. The flow velocity is greatest in the region of throat  68  (as for any venturi) and as a result this is the region of lowest pressure. The flow velocity in the recirculating region behind flap  36  is nearly zero, and the pressure in that region is much higher. The differential pressure results in the creation of closing pressure  66 , which tends to force the flap closed again. 
         [0042]    The differential pressure created by the venturi effect causes the flap to close significantly faster than gravity alone. The result is that less pressure (under the bill) is required to open the flap than is required to hold it open. A quick up-lifting pressure is generally what blows the cap off the wearer&#39;s head. The present venturi design rapidly opens. However—unless a sustained flow is passing through the vent—it will rapidly close again. This means that the venturi design provides the desired rapid pressure relief while also quickly returning to the closed state in order to provide sun shade and rain exclusion. 
         [0043]    In order to create the desired effect, the geometry of the flap and exit must be appropriately sized. In the embodiment of  FIG. 6 , the vent and flap are sized to produce a throat  68  opening that is about 1.8 cm across. Trailing portion  64  is separated from forward region  50  enough to make exit about 3.6 cm across. Those skilled in the art will know that the significant geometry is the area of the throat compared to the area of the exit (an “area ratio”). Since the components all have about the same width (across the front of the cap), the area ratio turns into a function based on the distance across the throat compared to the distance across the exit. 
         [0044]    The throat area is W t ·L t , while the area of the exit is W e ·L e , where W is width, L is length, t stands for throat, and e stands for exit. If the length of the throat is the same as the length of the exit (which is roughly true), then the area ratio may be simplified to the distance across the exit divided by the distance across the throat. This ratio is preferably maintained between 2 to 1 and 4 to 1. Thus, in the embodiment of  FIG. 6 , the throat is configured to be 1.8 cm across while the exit is configured to be 3.6 cm across (a ration of 2 to 1). 
         [0045]    Returning now to  FIG. 5 , some addition features of the invention will be discussed. The reader will observe that downforce generator  30  is preferably a thin walled structure. It is preferably attached near the bill&#39;s leading edge. This fact creates cavity  58  between the bill and the downforce generator. Depending on the configuration of the bill, this cavity may trap rainwater. Thus, in some embodiments a drain is desirable. Turning now to  FIG. 3 , the reader will note the inclusion of three drains  38  through the downforce generator. These allow rain flowing off the head covering and bill to escape cavity  58 . 
         [0046]      FIG. 8  shows an alternate location for the drain. In this embodiment, drain  38  passes through the bill. The drain can be placed in any convenient location, so long as it allows water collecting in cavity  58  to exit. 
         [0047]    Although the preceding description contains significant detail, it should not be construed as limiting the scope of the invention but rather as providing illustrations of the preferred embodiments of the invention. As an example, although the invention has been illustrated with a thin walled downforce generator, a solid or thick-walled design made of lightweight foam material could be substituted. Many other variations will be apparent to those skilled in the art. Thus, the scope of the invention should be fixed by the following claims rather than any specific examples provided.