Abstract:
A frame, panel, and fastener system for use in constructing modules that are to be installed on a ground support equipment cart. The modules have a rectangular frame that is constructed primarily by connecting together members constructed as folded sheet metal tubes substantially rectangular in cross section but, on two adjoining sides, bent perpendicularly outwards to form a first shelf perforated with fastener mounting holes, these frame members having ends that may be fastened to pairs of ends of other like frame members at perpendicular angles to form the corners of the rectangular frame and of the modules. Panels having edges bent over to form stand-offs and perforated with fastener mounting holes are sized so the stand-offs rest upon the first shelves on plural sides of the rectangular frame. Plural fasteners have first fastener parts that are attached to the shelf fastener mounting holes and second fastener parts that are attached to the panel fastener mounting holes, with the fasteners aligned to join and to detachably hold the panels upon the first shelves to form removable side panels for the modules.

Description:
[0001]    This application is a non provisional of provisional application Ser. No. 60/984,008 filed Oct. 31, 2007 (Atty. Docket No. 21588-P1) and provisional application Ser. No. 61/036,734 filed Mar. 14, 2008 (Atty. Docket No. 50-004 ITW 21588-P2). 
     
    
     CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0002]    The present patent application is one of a set of commonly owned applications filed on the same day as the present application, sharing some inventors in common, and relating to airplane ground support equipment and carts. The other applications in this set, listed here, are hereby incorporated by reference into the present application: “A Multi-Voltage Power Supply for a Universal Airplane Ground Support Equipment Cart,” James W. Mann, III and David Wayne Leadingham (Ser. No. ______, Atty. Doc. No. 50-002 ITW 21608U); “An Adjustable Cooling System for Airplane Electronics,” Jeffrey E. Montminy and Steven E. Bivens (Ser. No. ______, Atty. Doc. No. 50-003 ITW 21585U); “A System of Fasteners for Attaching Panels onto Modules that are to be Installed on an Airplane Ground Support Equipment Cart,” Jeffrey E. Montminy, Brian A. Teeters, and Kyta Insixiengmay (Ser. No. ______, Atty. Doc. No. 50-005 ITW 21587U); “Airplane Ground Support Equipment Cart Having Extractable Modules and a Generator Module that is Separable from Power and Air Conditioning Modules,” James W. Mann, III and Jeffrey E. Montminy (Ser. No. ______, Atty. Doc. No. 50-006 ITW 21586U); “An Adjustable Air Conditioning Control System for a Universal Airplane Ground Support Equipment Cart,” James W. Mann, III, Jeffrey E. Montminy, Benjamin E. Newell, and Ty A. Newell (Ser. No. ______, Atty. Doc. No. 50-007 ITW 21606U); “A Compact, Modularized Air Conditioning System that can be Mounted Upon an Airplane Ground Support Equipment Cart,” Jeffrey E. Montminy, Kyta Insixiengmay, James W. Mann, III, Benjamin E. Newell, and Ty A. Newell (Ser. No. ______, Atty. Doc. No. 50-008 ITW 21583U); and “Maintenance and Control System for Ground Support Equipment,” James W. Mann, III, Jeffrey E. Montminy, Steven E. Bivens, and David Wayne Leadingham (Ser. No. ______, Atty. Doc. No. 50-009 ITW 21605U). 
       BACKGROUND OF THE INVENTION 
       [0003]    1. Field of the Invention 
         [0004]    The present invention relates generally to the field of the design of sheet metal frames for covered enclosures, and more particularly to the design of frames and panels for air conditioning, power generation, and power conversion equipment modules that are to be installed on a universal airplane ground support equipment cart. 
         [0005]    2. Description of the Related Art 
         [0006]    When an airplane is on the ground with its engines shut down, the airplane is typically unable to provide power for its electrical systems and chilled air for its air conditioning systems; and some airplanes are also unable to provide liquid coolant for some critical electronic (or “avionic”) components. It is customary to connect such a grounded airplane to an airplane ground support equipment system. Such a system may have its components mounted upon a mobile equipment cart that is called an airplane ground support equipment cart and that may be parked, placed or mounted conveniently close to an airplane requiring ground support. Such a cart typically contains an air conditioner that can provide conditioned and cooled air to an airplane plus an electrical power converter that can transform power drawn from the local power grid into power of the proper voltage (AC or DC) and frequency required by the airplane. Such an airplane ground support equipment cart may also contain a diesel engine connected to an electrical generator that enables the cart to provide both air conditioning and also electrical power conversion for an airplane without any connection to the local power grid. And if an airplane requires a source of cooled liquid for its electronics, some carts may also include a source of liquid coolant. 
         [0007]    In the past, particularly with regard to military airplanes, such ground support equipment carts have been custom designed to meet the specialized needs of a single particular type or class of airplane. Hence, a cart designed to support the specific requirements and needs of a first type or class of airplane cannot be used to support the differing specific requirements and needs of other types or classes of airplanes. Different airplanes typically may require different pressures and volumes of cooled air, different amounts of electrical power, different electrical voltage levels, and different electrical frequencies (or direct current). And different airplanes typically may require differing pressures and volumes of cooled liquid for use in cooling onboard electronics. Accordingly, every airport must be supplied with as many different types of ground support equipment carts as there are different types or classes of airplanes that may land and take off at each airport or military base. Problems arise when more airplanes of a particular type arrive at a specific location than there are ground support equipment carts suitably designed to service the needs of that particular type or class of airplane. 
         [0008]    As an example of an airplane cart arrangement that provides air and electrical conditioning for an airplane, PCT patent application No. PCT/US2006/043312 (Intl. Pub. No. WO 2007/061622 A1 published on May 31, 2007) discloses an airplane ground support cart that has a modular design of its electrical conditioning components. This cart provides air conditioning and electrical power conversion as well as optional electrical power generation services to airplanes.  FIG. 5  reveals that the cart disclosed in this patent application may receive interchangeable, modular power conversion modules. Thus, a module  72 , which generates 3-phase 115 volt 400 Hz A.C. power, may be removed and replaced with a module  78 , which generates 270 volt D.C. power.  FIG. 6  illustrates that this cart may also accept a module  92 , which generates 28 volt D.C. electrical power. 
         [0009]      FIG. 2  of the above PCT patent application illustrates a typical arrangement of the mechanical components of a dual air conditioning system within an airplane ground support equipment cart  14 . The air conditioner&#39;s mechanical components are spread all across the entire length of the cart  14 . Two sets of condenser coils  34  are positioned at one end of the cart  14 ; and the thickness of the coils  34  and their housing, together with the thickness of the associated cooling fans, occupies roughly one-fifth of the cart&#39;s overall length. A filter and upstream evaporation coil  30  and a downstream evaporation coil  40  and outlet connection  42  (to which can be attached a duct leading to an airplane) are positioned at the other extreme end of the cart  14 , occupying somewhat less than one-fifth of the cart&#39;s overall length. A blower fan  32 , a discharge plenum  38 , and two compressors  36  are shown positioned in the central portions of the cart  14 . These mechanical components of the air conditioning system are not confined within a rectangular module within a portion of the volume of the cart  14 —these components are spread all across the cart  14  and thus cannot be conveniently removed from the cart for servicing or for use away from the cart  14 . Other cart components, such as a diesel engine  54  and generator  56  (shown in FIG. 4 of the PCT application) and an electrical power converter unit  72  (shown in FIG. 5 of the PCT application) are squeezed in among the air conditioning components wherever there is room. This intermixing of non-air-conditioning components with the air-conditioning components greatly complicates servicing of all the components, since they are all crowded into the same cramped space. A service man working on the air conditioner compressors or blowers may find the diesel engine  54  and the generator  56  are in the way of these components, for example. 
         [0010]    The present invention has as its goal the realization of modules of similar design, both large and small, that may be installed on such a cart, interchanged with one another, and removed for convenient servicing. Larger modules might contain air conditioning equipment or power generation equipment, while smaller modules may contain power converter equipment, such as units that can convert 3-phase 460 volt 60 Hz A.C. incoming power into 270 volts DC or 115 volts 400 Hz A.C. Other modules may contain control panels and displays and computers and other such equipment. 
         [0011]    These modules should be strong enough so that they may be lifted and moved about without damage. They should be relatively easy to disassemble so that repairs can be carried out without great difficulty, but there should be no loose parts that could be sucked up into a jet turbine engine, causing serious damage. The module design should lend itself readily to electromagnetic shielding. They should be relatively water and weather resistant, but there should be a minimum of internal enclosed channels where moisture could collect and do serious damage. The design of these modules should scale easily up or down into large or small modules as required by the nature of the ground support equipment being housed. 
       SUMMARY OF THE INVENTION 
       [0012]    An embodiment of the invention relates to a frame, panel, and fastener system for use in constructing modules that are to be installed on a ground support equipment cart. The modules have a rectangular frame that is constructed primarily by connecting together members constructed as folded sheet metal tubes substantially rectangular in cross section but, on two adjoining sides, bent perpendicularly outwards to form a first shelf perforated with fastener mounting holes, these frame members having ends that may be fastened to pairs of ends of other like frame members at perpendicular angles to form the corners of the rectangular frame and of the modules. Panels having edges bent over to form stand-offs and perforated with fastener mounting holes are sized so the stand-offs rest upon the first shelves on plural sides of the rectangular frame. Plural fasteners have first fastener parts that are attached to the shelf fastener mounting holes and second fastener parts that are attached to the panel fastener mounting holes, with the fasteners aligned to join and to detachably hold the panels upon the first shelves to form removable side panels for the modules. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  is an isometric view of an embodiment of a universal airplane ground support equipment cart. 
           [0014]      FIG. 2  is an isometric view of the cart shown in  FIG. 1  with the power generation portion of the cart separated from the rest of the cart. 
           [0015]      FIG. 3  is an isometric view of an electrical power converter module of the cart shown in  FIG. 1  to illustrate how it may be slid out of and away from the cart. 
           [0016]      FIG. 4  is a perspective view of a set of modules shown placed upon an airplane ground support equipment cart&#39;s platform, with the module side panels removed. 
           [0017]      FIG. 5  is a perspective view of the set of modules shown in  FIG. 4  with the right-most power generation module and portion of the cart moved to the right and with one of the central electrical power converter modules shown slid out to the front to illustrate the way in which the modules may be separated. 
           [0018]      FIG. 6  is an isometric view of an embodiment of the frame of a module designed in accordance with the present invention. 
           [0019]      FIG. 7  is an isometric view of a cross section of a bottom module frame illustrating its shape, the module frame being shown supporting interior equipment support frames that can support air conditioning or electrical equipment within a module. 
           [0020]      FIG. 8  is an isometric view of a cross section of two module frames illustrating how stair step-shaped members may strengthen the frame of a module by forming the frame into a hollow tube. 
           [0021]      FIG. 9  is an isometric view of a cross-section of the frame of a module illustrating the positioning of fasteners and electromagnetic radiation shielding mounted on the frame. 
           [0022]      FIGS. 10 and 11  present isometric views of the corner of a module, illustrating how a cover plate is fastened to each side of the module, with a cover plate removed in  FIG. 10  and screwed down into place in  FIG. 11 . 
           [0023]      FIGS. 12 ,  13 ,  14 , and  15  present various isometric views illustrating the use of an embodiment of fasteners especially designed for the present invention to attach the frame of a module to a cover plate. 
           [0024]      FIG. 16  presents a cross-sectional view, taken along the lines A-A in  FIG. 10 , illustrating in detail the nature of the fasteners for the module cover plates, including: a bolt; an insert to hold the bolt in place in a cover plate; a nut having a raised, internally-threaded shaft; and a washer that keeps the nut attached to the frame of a module. 
           [0025]      FIG. 17  presents a cross-sectional view, taken along the lines B-B in  FIG. 11 , illustrating the relative position of a frame, the frame&#39;s cover plate, and a fastener that attaches the cover plate to the frame. 
           [0026]      FIG. 18  presents a cross-sectional view, taken along the lines C-C in  FIG. 11 , illustrating the relative position of a frame and the frame&#39;s cover plate, with tin-plated, beryllium copper spring EMI shielding filling the gap between the frame and its cover plate. 
           [0027]      FIG. 19  presents a sectional side view of the frame&#39;s cover plate, including an exploded view of an alternate design for the cover plate fastener and its washers. 
           [0028]      FIG. 20  presents a perspective view of the cover plate upon which is mounted the fastener illustrated in  FIG. 19 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0029]    The detailed description which follows is broken into three sections. Section A presents an introduction to the environment of the present invention, which relates to the design of a modularized universal airplane ground support equipment cart. Section B, which is particularly relevant to the present invention as claimed, presents a detailed mechanical description of installable and removable modules having removable cover panels which are designed for use in conjunction with such a cart. Section C presents a detailed description of the fasteners that are used to removably attach panels to the sides of the modules and which include provision that prevents them from coming loose from the panels and modules. 
       A. Modular and Universal Airplane Ground Support Equipment Cart 
       [0030]    Airplane ground support equipment carts are wheeled, towable carts or fixed mounted (permanently or temporarily) devices that provide air conditioning, avionics equipment liquid cooling, and electrical power conversion and generation services to airplanes whose engines are shut down. These carts preferably should be conveyed by military and other airplanes to airports and military bases all over the world, so it would be convenient and an advantage to have this equipment be no larger than a standard military equipment conveyance palette. However, many such carts today do not fit one standard palette, and this reduces the numbers of ground support equipment that is available in the field. Traditionally, such ground support equipment carts are custom-designed—they provide such services to only one type or class of airplane. Hence, different carts must be provided for each different type of airplane. Also traditionally, the air conditioning components mounted on such carts are so bulky that they occupy the entire area of the cart, making it necessary to sandwich electrical power conversion and other components wherever there is room and thereby making it extremely awkward to service or replace such cart-mounted components. 
         [0031]    The present invention is embodied in a universal airplane ground support equipment cart—universal in the sense that it is designed to service the varied needs of a variety of types and classes of airplanes, rather than just one type or class. This ground support equipment cart is also modular—its components are rectangular modules that may be easily separated or removed from the cart for service or exchange. The modules may also be used independently of the cart, and modules not needed for a particular type of airplane may be readily removed and used elsewhere, standing by themselves, in a highly flexible manner. Such a cart  10  and several of its modules—an electrical power generation module  14 , an electrical power conversion module  20 , and a dual air conditioning module  400  (which also provides PAO liquid cooling)—are illustrated in simplified form in  FIGS. 1-3 . (Much more detailed drawings of these components are included in this application and also in the related applications cited above). 
         [0032]    In use, the cart  10  is mounted near or drawn up to an airplane (not shown) by a suitable tractor or truck (not shown). An operator connects an air conditioning plenum or air duct  26  from the dual air conditioning module  400  to a cooled air input port (not shown) on the airplane. And if the airplane has avionics or other electronic components that require a supply of liquid coolant, then the operator also connects a pair of PAO liquid coolant conduits  28  from the air conditioning module  400  to a pair of PAO ports on the airplane. The operator then uses a suitable electrical power cable (not shown) to connect an electrical power output port or receptacle (not shown in  FIGS. 1-3 ) on the electrical power conversion module  20  to a matching port or cable on the airplane. To supply the varying needs of different types of airplanes, there may be as many as two electrical power conversion modules  20  the cart  10 , a first module  20  having both a 115 volt, 400 Hz AC power output port and also a separate 270 volt DC power output port, and a second module  1208  ( FIG. 5 ) having a 28 volt DC power output port (one or the other of these modules  20  or  1208  may be removed from the cart  10 ). 
         [0033]    Next, the operator depresses a “Start” pushbutton (not shown) on the front panel of a control module  22  having a display screen  24  that then displays a main menu (not shown). If the airplane is a T-50 Golden Eagle, the operator depresses a pushbutton adjacent the label “T-50 Golden Eagle” on this menu, and then the operator depresses a pushbutton adjacent the word “Start” on a “T-50” menu that then appears. In response, all of the modules automatically reconfigure themselves as needed to service this specific type of airplane with air conditioning of the proper pressure and volume of air, with electrical power of the proper type, voltage, and frequency, and with liquid coolant (if needed). If the operator selects the wrong type of airplane, pressure and air flow measurements can detect this and shut down the system, illuminating a colored status light (not shown) to signal an error and displaying an appropriate error message on the control panel  24  to the operator. The system is halted when the operator depresses a “Stop” pushbutton on the front of the control  22 . 
         [0034]    A universal airplane ground support equipment cart is designed to provide flexible support for the needs of many different types and classes of airplanes having widely varying air conditioning and liquid cooling and electrical power support needs. The present invention can provide different pressures and volumes of cooled air and cooled liquid to different airplanes, and it can provide different types and quantities of electrical power to different airplanes. It also provides a simplified, integrated control panel where airplane service personnel can simply select the type of airplane that is to be serviced and have the various appliances on the cart automatically configured to optimize the support for that particular type of airplane. 
         [0035]    A modular airplane ground support equipment cart is one where the different support systems provided by the cart are each confined to rugged, compact, optionally EMI shielded, rectangular modules that may be easily removed, serviced, replaced, and used stand-alone separate from the cart and its other modular components. 
         [0036]    In the cart  10 , for example, a two-stage air conditioning module  400  contains all of the air conditioning components of the cart  10 , including a liquid PAO cooling system. An electrical power converter module  20  contains the power conversion components of the cart  10 , including a 270 volt D.C. supply and a 115 volt 400 Hz A.C. supply; and the module  20  may be replaced or supplemented with the other module  1208  ( FIG. 5 ) that includes a 28 volt D.C. supply, providing up to three different types of electrical power conversion in accordance with the specialized needs of different types and classes of airplanes. 
         [0037]    A power supply module  14  contains a diesel engine and a generator for producing 60 cycle, three-phase, 460 volt electrical power when the cart cannot be conveniently hooked up to a 360 to 500 volt, 50 or 60 cycle A.C., three phase supply provided by the local power grid. The power supply module  14  is confined to one end of the cart  10  and may be detached from the cart  10 , as is illustrated in  FIG. 2 . 
         [0038]    Any or all of these modules  14 ,  20 ,  400 , and  1208  may optionally be equipped with an internal transformer (not shown) that transforms the incoming high voltage electrical power down to 120 volts or 240 volts at 50- or 60-Hz and feeds this low voltage to standard, weather protected outlets (not shown) which can be used to provide power to hand tools and to portable lighting equipment and the like, with ground fault protection also provided to these appliances. 
         [0039]    As is illustrated in  FIG. 1 , the control module  22  is mounted on the cart  10  above the power converter module  20 . The control module  22  has on its front panel a pair of start and stop pushbuttons, colored status lights, and the display screen  24 . The display screen  24  has sets of four pushbuttons positioned adjacent the display screen  24 &#39;s left and right sides (these pushbuttons and lights are not shown in this application). When turned on, the display screen  24  presents a main menu display (not shown) which permits airplane maintenance personnel to select the type of plane that is to be serviced by depressing one of the adjacent pushbuttons. A maintenance menu display (not shown) permits service personnel to view and (in some cases) to alter the state of the air conditioning and PAO module  400 , the electrical power converter modules  20  and  1208 , and the power supply module  14 . The modules  14 ,  20 ,  22 ,  400 , and  1208  are automatically networked together by a network (not shown) when they are installed upon the cart  10 . In addition, each of the modules  14 ,  20 ,  22 ,  400 , and  1208  is equipped with a network jack (not shown) that can be connected to an external portable computer (not shown) which can then serve as the control module and display for all of the modules, with mouse clicks on menus replacing depressions of pushbuttons. 
         [0040]    The cart  10  is optionally mounted upon two wheel and axle truck assemblies  18  and  19 . In the space on the cart  10  between the power generation module  14  and the two-stage air conditioning module  400 , one or both of the electrical power converter modules  20  and  1208  may be slid into place and attached to the cart  10 , as is illustrated in  FIGS. 2 and 3 . (If both are installed, they may be on opposite sides of the cart, as shown, or they may be installed one above the other.) 
         [0041]    If the power generation module  14  is not required for a particular airplane support task, the module  14  and the wheel and axle truck assembly  19  beneath the module  14  may be completely detached from the rest of the cart  10 , as is illustrated in  FIG. 2 , and removed to be used entirely separately elsewhere, wherever a portable source of 60 Hz, 460 volt, three-phase power is required. As illustrated in  FIGS. 2 and 3 , the electrical power converter modules  20  and  1208  may be slid out on tracks and locked in position to give service personnel convenient access for the servicing of these modules  20  and  1208  and their internal electrical and electronic components. They may also be removed for repair or for use elsewhere as stand-alone power converters, or they may be replaced with different power converter modules that generate different voltages and frequencies as needed for servicing different airplanes. 
       B. Frame and Panel System for Constructing Modules 
       [0042]    Referring now to  FIG. 6 , a rectangular frame  40  for a representative module  20  is shown in greater detail. The frame  40  is formed by welding together frame members  41  at their corners to form a unitary structure with considerable strength that constitutes the frame  40  of the module  20 . The frame members  41  are formed from sheet metal by applying a series of 90 degree bends to the sheet metal to give the frame members  41  strength and to enable them to resist bending. 
         [0043]    Viewed in cross section (See  FIGS. 7 ,  8 , and  9 ), the 90 degree bends in the frame members  41  can be seen. With reference particularly to the left side of  FIG. 8 , which presents an isometric cross-sectional view of the frame member  41 , the frame member  41  can be seen to have been formed from sheet metal bent to form two adjoining outer surfaces  48  and  50 , two inner surfaces  46  and  52 , two shelves  44  and  54 , and two interior mounting brackets  42  and  56  that are joined to each other by 90-degree bends at seven corners  58 ,  60 ,  62 ,  64 ,  66 ,  68 , and  70  of the cross section. The three corners  62 ,  64 , and  66 , the four adjoining outer and inner surfaces  46 ,  48 ,  50 , and  52 , and a dotted line missing portion  72  ( FIG. 8  only), taken together, form a rectangle. This indicates that the central portion of the frame member  41  (formed by the four surfaces  46 ,  48 ,  50 , and  52 ) has a generally rectangular cross section, but with the dotted line missing portion  72  missing from what would otherwise be a closed, rectangular frame member. 
         [0044]    The two inner surfaces  46  and  52  can be seen to be only about half as wide as the two outer surfaces  48  and  50 . The two outer surfaces  48  and  50  and the corner  64  which joins the two outer surfaces  48  and  50  together form the outer, visible edges of the frame  40  and of the module  20 . The remaining inner surfaces  46  and  52 , the shelves  44  and  54 , and the interior mounting brackets  42  and  56  and their respective corners  58 ,  60 ,  68 , and  70  are hidden inside of the module  20  when cover plates  76  (shown in  FIGS. 10 and 11 ) are installed. 
         [0045]    The shelves  44  and  54  respectively join the two inner surfaces  46  and  52  at the two corners  60  and  68 , as shown, and project outwards from the inner surfaces  46  and  52  parallel to the respective outer surfaces  48  and  50  to form depressed (with respect to the respective outer surfaces  48  and  50  and corners  64  of the frame  40  and module  20 ) shelves that are perforated with spaced-apart holes  72  to which fasteners  78  ( FIGS. 9 ,  10 , and  11 - 16 ) and tin-plated, beryllium copper springs  74  serving as EMI shielding ( FIGS. 9 and 18 ) may be attached.  FIG. 9 , for example, illustrates fasteners  78  that are attached to the shelves  44  and  54 . (The details relating to the design of the fasteners  78  is presented below in the section which follows). 
         [0046]    In one embodiment, tin plated, beryllium copper springs  74  ( FIG. 9 ) are fastened into the holes  72  to provide good grounding of the panels  76  ( FIGS. 2 ,  10 , and  11 ). These tin plated, beryllium copper springs  74  are part number 81-02-11832 Springline beryllium copper gaskets supplied by Chomerics. 
         [0047]    Note again that the shelves  44  and  54  which support the fasteners  78  are parallel to, but depressed inwards from, the respective outer surfaces  48  and  50 . This provides room such that bent-over edges  80  of removable module side cover panels  76  ( FIG. 10 ) may rest upon and against the shelves  44  and  54  or upon and against any tin-plated, beryllium copper springs  74  serving as EMI shielding that may be installed to prevent RF and EMI signals generated by computer or power switching components or by motors and solenoids or relays from leaking out, and also to keep out RF and EMI interference originating from external sources. The edges  80  may be assigned a depth such that the outer surfaces of the panels  76  lie in the same plane as the outer surfaces  48  and  50  of the frame members  41 , thus giving the module  20  completely flat surfaces, as is illustrated in  FIGS. 17 and 18  (which are drawn true to scale). 
         [0048]    With reference again to  FIG. 8 , stair-step members  82  (which also can have just one 90 degree bend instead of three as shown or which can take on other shapes) may be strapped across the frame members  41  to connect the two surfaces  42  and  56  together, as shown in  FIG. 8 , to cause the frame members  41  to have a closed cross section over portions of their length, thereby giving frames  40  constructed from these reinforced frame members  41  considerably more strength and rigidity where needed. At other locations, the frame members  41  may be left with an open cross section to facilitate drainage of water from the frame and to facilitate its maintenance. 
         [0049]    As shown in  FIG. 7 , additional holes  84  are provided in the two interior mounting brackets  42  and  56  for the mounting of internal brackets  86  having an L cross section as shown to which internal supports  88 ,  90  having a C cross section as shown may be attached that can then be used to support and suspend equipment  30 ,  32 , and  34  ( FIGS. 4 and 5 ) within each module  20 . The stair-step members  82  also may be attached using the holes  84 . The holes in these universal C cross section supports  88 ,  90  will always line up with holes in the frame, and this present a large number of equipment mounting options to the designer and to the modifier of a module  20 . 
       C. Details of Fasteners Used to Attach Removable Panels to the Sides of Modules 
       [0050]    With reference to  FIGS. 12-17 , the detailed design of the fasteners  78  is presented. As explained above, the fasteners  78  mount in the holes  72  of the shelves  44  and  54  (see  FIG. 7 ) and also in the holes  82  in the removable cover panels  76  (see  FIG. 13 ). 
         [0051]    Each fastener  78  comprises four components: two components  96  and  98  mounted in the holes  72  on the shelves  44  and  54 , and two components  92  and  94  mounted in the holes  82  on the removable cover panels  76 . 
         [0052]    The four components of a fastener  78  can best be seen in  FIGS. 13 and 15  which present an exploded view of the fastener  78 , and also in  FIGS. 16 and 17  which present cross-sectional views of the fasteners  78 .  FIGS. 12 and 14  also present exploded views but with the module frame  40  and the cover plate  76  rendered transparent and shown with dotted lines to reveal the details of the fastener  78 . In the cross-sectional view presented by  FIG. 16  (the cross section taken along the lines A-A in  FIG. 10 ), an installed fastener  78  is shown mounted in a cover plate  76  and in a frame member  41 , the cover plate  76  and the frame member  41  being slightly separated but in position to be fastened together. In the cross-sectional view presented in  FIG. 17  (the cross section taken along the lines B-B in  FIG. 11 ), the view is similar to that in  FIG. 16  but the cover plate  76  and frame member  41  are shown fastened tightly together, with the edge  80  of the cover plate  76  shown resting on the nylon washer  96  (described below). 
         [0053]    With reference to all of the  FIGS. 13 through 16 , the fastener  78  comprises a hexagonal nut  98  having mounted on its upper surface a hollow, internally threaded shaft  99 ; a nut retaining polyethylene (nylon) washer  96 ; an insertable hole liner  94 ; and a bolt  92  having a shaft  93 - 95  that is partly a threaded shaft  95  away from the head of the bolt and partly an unthreaded shaft  93  between the bolt head and the threaded shaft  95 , as shown. 
         [0054]    The nut  98  is a female, blind-threaded standoff, part number BSOS-832-16 manufactured by Penn Engineering. The insertable hole liner  94  and bolt  92  are called captive fasteners, part number F5-832-P8 manufactured by Southco. 
         [0055]    As shown in the figures, the nut  98  has its shaft  99  press-fitted into one of the larger holes  72  in one of the shelves  44  or  54  with the hexagonal base positioned inside of the module  20  and with the shaft  99  pointing outwards towards the removable panel  76  as shown in the figures. The nylon washer  96  has been designed such that the inside diameter of the nylon washer  96  is somewhat less than the outside diameter of the shaft  99  such that when the nylon washer  96  is pressed downwards against the outward-facing surface of one of the shelves  44  or  54 , the nylon washer  96  becomes captive. The major function of the nylon washer  96  is to provide a compression stop for the panel  76  to the shelves  44  and  54  of the frame members  41 . This compression stop prevents the tin-plated, beryllium copper springs  74  serving as an EMI gasket from deforming beyond its elastic limit, which would otherwise permanently flatten such a gasket and render it less effective as an EMI shield. 
         [0056]    The insertable hole liner  94  is a cup-shaped hollow washer having a hole  91  (see  FIG. 91 ) in the bottom of the hole liner through which the bolt  92  may pass. This liner  94  is press-fitted downwards into a hole  82  that passes all the way through the panel  76 . The insertable hole liner  94  is thus sunk into the upper surface of the panel  76 . 
         [0057]    The hole  82  that passes all the way through the panel  76  is large enough to accept the hole liner&#39;s core  77 . The unthreaded portion  93  of the bolt  92  is smaller in diameter than the threaded portion  95 . The hole  91  in the bottom of the insertable hole liner  94  is slightly smaller in diameter than the threaded shaft  95  portion of the bolt  92  and slightly larger in diameter than the unthreaded portion  93  of the bolt  92 . 
         [0058]    Accordingly, after the insertable hole liner  94  has been press-fitted into the hole  77 , the bolt  92  may be screwed through the hole  91  in the hole liner  94 . The bolt  92  will then be free to move up and down, with its non-threaded shaft  93  portion free to slide back and forth within the insertable hole liner  94 . However, the bolt  92  cannot fall off of the panel  76  because the threaded shaft  93  cannot fit back out of the hole  91 . Likewise, the nut  98  is retained in position and kept from falling out of the frame member  41  by the nylon washer  96  which fits tightly about the internally-threaded shaft  99  and holds the nut  98  in place. Yet the two parts  92  and  98  of the fastener  78  are held in position so that when the panel  76  is placed over one side of the frame  40 , a screwdriver may be used to tighten the bolt  92  into the nut  98  and to thereby fasten the panel  76  on to the frame  40  of a module  20 . 
         [0059]    It is essential that the bolt  92  and the nut  98  not be permitted to come free and accidentally become sucked into a turbojet engine, where such components can easily cause many thousands of dollars of damage. The present invention provides protection against such an accident at minimal cost without in any way making it more difficult to fasten and unfasten the fasteners  78 . 
         [0060]      FIG. 17  shows the bolt  93  screwed firmly into the nut  72  such that the panel  76  is pressed tightly against the nylon washer  96  adjacent the nut  73 . Elsewhere, the panel  76  makes contact with and depresses the tin-plated, beryllium copper springs  74 , as shown in  FIG. 18 , thereby blocking radio frequency waves, particularly EMI, from leaking either into or out of the module  20 . 
         [0061]      FIGS. 19 and 20  present an alternative arrangement that may be used instead of the captive fastener formed from the elements  93  and  94  shown in  FIGS. 12 through 16 . With reference to  FIG. 19 , a flat head screw  102  (Accurate Screw Machine Corporation part number 114132) having a hexagonal socket may be inserted through a finishing washer  104  (Accurate Screw Machine Corporation part number 16007) that is almost 0.6 inches in diameter and that is shaped to conform to the outside shape of the screw  102 , as is shown in  FIG. 20 . These are passed through the hole  77  in the panel  76 . A plastic washer  108  (McMaster-Carr part number 95647A121) having a 7/16″ outside diameter is placed over the shaft of the screw  102  along with a smaller washer (Accurate Machine Corporation part number W114050) on the other side of the panel  76  to keep the screw  102  from falling loose, as is shown and as has been described above. This arrangement allows the hole  77  to be enlarged so that a good deal of misalignment can be tolerated, but not large enough to permit the plastic washer  108  to pass through the hole  77 . 
         [0062]    While an embodiment of the invention has been disclosed, those skilled in the art will recognize that numerous modifications and changes may be made without departing from the true spirit and scope of the claims as defined by the claims annexed to and forming a par of this specification.