Abstract:
A fastening system for airplane cowls that uses a countersunk bushing that has a countersunk hole for the installation of a #10 screw that can be used with a nut plate attached to the substructure of the cowling.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     Not Applicable 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT 
     Not Applicable 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to cowl fastener systems for small aircraft and particularly to cowl fastener systems utilizing a single countersunk bushing. 
     2. Description of the Prior Art 
     Airplane fastener systems in use today use a three-part fastener that has a screw, a spring-loaded screw body and a receptacle can that is attached to the underside of a cowling or other airplane surface.  FIGS. 1-7  illustrate this prior art fastening system.  FIG. 1  is a perspective view of a lower retainer  100  can for a spring-loaded fastener system as prior art. This can has a lower body  101 , a top flange  102  an internal wall  103  that accepts the screw body, and a threaded center hole  104  that accepts the screw. 
       FIG. 2  is a perspective view of a prior art spring-loaded fastener body  105  that shows a screw  106  installed in it.  FIG. 3  is a detail view of a prior art fastener system, partially assembled. Here, the screw body  105  and screw  106  are positioned above the lower retainer can  100 .  FIG. 4  is a cross-sectional view of the spring-loaded fastener body view, as prior art. Here, the screw body  105  is shown having a spring  107  installed in it. The screw  106  is shown within the spring.  FIG. 5  is a cross-sectional view of the prior art assembled fastener system as prior art. In this view, the lower retainer can  100  is shown riveted to a piece of structure  110  using rivets  111  through the top flange  102 . The screw body  105  is shown seated in the internal wall  103  of the retainer can  100  with the bottom of the screw  106  engaging the threads in the threaded center hole  104 . 
     In this design the spring is used to keep tension on the screw so that the screw body remains seated, yet, when the screw is backed off, the screw body pops up from the structure for easy removal, as shown in  FIG. 5 , where the screw body is above the structure.  FIG. 6  is a top detail view of the prior art cowling fastener installed, as prior art.  FIG. 7  is perspective detail view of the prior art cowling fastener installed, as prior art. These figures show the device as fully installed, with the screw and screw body flush with the upper surface of the structure 
     Although this system works, is has limitation in strength because of how it is made and how it is designed to work. 
     BRIEF DESCRIPTION OF THE INVENTION 
     The instant invention overcomes these difficulties. It is a fastening system that is it designed to outlast the original equipment fasteners by a factor of greater than 50 for a fraction of the cost. The system simplifies the installation by using a countersunk bushing that has a countersunk hole for the installation of a #10 screw that can be used with a nut plate attached to the substructure of the cowling. In this way, the system eliminates the spring and ensures a stronger, longer lasting installation. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a lower retainer can for a spring-loaded fastener system as prior art. 
         FIG. 2  is a perspective view of a spring-loaded fastener body, as prior art. 
         FIG. 3  is a detail view of a prior art fastener system, partially assembled, as prior art. 
         FIG. 4  is a cross-sectional view of the spring-loaded fastener body view, as prior art. 
         FIG. 5  is a cross-sectional view of the prior art assembled fastener system as prior art. 
         FIG. 6  is a top detail view of the prior art cowling fastener installed, as prior art. 
         FIG. 7  is perspective detail view of the prior art cowling fastener installed, as prior art. 
         FIG. 8  is a perspective view of a screw and bushing installed in the nut plate without the cowling in place. 
         FIG. 9  is a top plan view of the nut plate used in the instant invention. 
         FIG. 10  is a bottom perspective view of the nut plate used in the instant invention. 
         FIG. 11  is a bottom perspective view of the bushing used in the instant invention. 
         FIG. 12  is a cross-sectional view of the bushing used in the instant invention, taken along the line  12 - 12  of  FIG. 13 . 
         FIG. 13  is a top view of the bushing used in the instant invention. 
         FIG. 14  is a side view of the screw. 
         FIG. 15  is a top plan view of the invention installed in a cowling. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to  FIG. 8  is a perspective view of a screw and bushing installed in the nut plate without the cowling in place. Here, the three elements of the invention are shown. The first is a nut plate  10  and the second is a tapered bushing  11 . Note, as discussed below, the inside of the busing is countersunk to accommodate a screw. The final component of the invention is a screw  12 . All of these components are discussed in detail below. Note that in use, the nut plate is normally attached to the inside of a cowling, and the bushing and screw are outside. The illustration here shows no cowling for clarity. 
       FIG. 9  is a top plan view of the nut plate  10  used in the instant invention. The top plate  10   a  is shown being generally flat. It is shown here with rounded front edges  14  that have a radius r. Two small holes  15  that are used to rivet the type MS21059L3 self-locking floating nutplate to the top plate are spaced along an axis having an angle α with respect to the corner as shown. In the center of the top plate  10   a  is a larger hole  16  that is used to receive the screw  12 . 
       FIG. 10  is a bottom perspective view of the nut plate  10  used in the instant invention. Here, the top plate  10   a  is shown as before. The holes  15  are visible. In the center of the top plate is the type MS21059L3 self-locking floating nutplate  17  that is formed as shown. The nutplate  17  has a center threaded receptacle  18  that extends downward from the top plate when in its normal configuration, see  FIG. 8 . The type MS21059L3 self-locking floating nutplate is a commercially available fitting, well known in the art. 
       FIG. 11  is a bottom perspective view of the bushing used in the instant invention. Here, the bushing  11  is shown. It has a flat bottom  11   a  a cylindrical spacer portion  11   b  and a flared top  11   c . It also has an open center  11   d  to receive the screw  12 . 
       FIG. 12  is a cross-sectional view of the bushing used in the instant invention, taken along the lines  12 - 12  of  FIG. 13 . Here, the bushing is shown with the flat bottom  11   a , the cylindrical spacer portion  11   b , the flared top  11   c , and the open center  11   d . Also shown is the countersunk portion  11   e . In the preferred embodiment, the bushing is made of 17-4 PH Steel (H900/H925). Also in the preferred embodiment, the bushing has a minimum tensile strength of 160,000 psi, and therefore, a shear allowable of approximately 0.60 times that amount or 95,000 psi. The bushing is a minimum of 0.373 inch in diameter with an approximate 0.198 hole for the #10 screw. The cross sectional area is therefore, 0.0258 in and the minimum shear capability is 2,450 lb. 
       FIG. 13  is a top view of the bushing used in the instant invention. Here the countersunk portion  11   e  as well as the open center  11   d  are shown. 
       FIG. 14  is a side view of the screw  12 . In the preferred embodiment, the screw is #10 in size (0.190 inch diameter). Assuming the full diameter is capable of carrying the shear and a shear force Fsu of 75 ksi (0.60×125 ksi min per MS24694 specification) the maximum shear capability of the fastener is approximately 2,100 lb. 
       FIG. 15  is a top plan view of the invention installed in a cowling. Note that the nut plate  10  is shown in dashed lines under the cowling  110 . The bushing  11  and screw  12  are shown above the cowling. 
     The fastener system is critical at the screw in shear. The actual allowable force is less than that described above due to the screw threads reducing the cross-section of the shaft at the connection. 
     By observation the 0.050 inch thick plate with attached MS21059L3 nut plate is deemed to be structurally to the prior art FX10-1502 receptacle. The nut plate fully engages the threads of the installed screw. The floating action of the nut plate allows the screw to bear into the top plate  10   a , which is structurally more significant than the FX10-1502 receptacle of the prior art installation. 
     The present disclosure should not be construed in any limited sense other than that limited by the scope of the claims having regard to the teachings herein and the prior art being apparent with the preferred form of the invention disclosed herein and which reveals details of structure of a preferred form necessary for a better understanding of the invention and may be subject to change by skilled persons within the scope of the invention without departing from the concept thereof.