You are an expert at summarizing long articles. Proceed to summarize the following text:

You are an expert at summarizing long articles. Proceed to summarize the following text: 
RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Application No. 61/752,071 filed Jan. 14, 2013 and titled “Boltless Access Door,” the entire contents of which are hereby incorporated by reference. 
    
    
     FIELD OF THE INVENTION 
     This invention relates generally to access doors. 
     BACKGROUND 
     Access to particular areas or compartments of a helicopter, aircraft, vehicle or other application may be restricted by an access door. As one non-limiting example, an access door may restrict access to a vehicle&#39;s fuel tank, which can be subjected to significant pressure during a crash or other traumatic event. A properly sealed access door can help insulate the area/compartment housing the fuel tank from the rest of the vehicle and thus help contain any pressure rises or leaks within the area/compartment housing the fuel tank. The access door can also permit access to the fuel tank when required, such as during installation or maintenance of the fuel tank system. 
     Some access door assemblies include a ring that is bonded to the fuel tank and a door placed above and fixed to the ring using a plurality of fastening members, such as screws or bolts. Securing the fastening members in place axially seals the components of the access door assembly in the direction of the fastening members with the force transmitted by the fastening members. Manually securing each of the fastener members to fix the door relative to the ring is time consuming and takes approximately 10 or so minutes to complete, thus increasing installation and maintenance time. Moreover, use of a screwdriver or other suitable tool to fasten and unfasten the fastener members risks damage to the fuel tank. Further, the closing force and thus the sealing of the assembly can be diminished over the lifetime of the fuel tank as the door assembly is fixed and unfixed by screwing and unscrewing each of the fastener members. 
     In addition, whether a sufficient axial seal is created between the ring and the door depends in large part on the operator and whether the fastener members are positioned and tightened correctly. Because the fastener members maintain the closure of the door assembly and thus bear the brunt of the inner stresses (stresses from within the area/compartment of the access door assembly) and outer stresses (stresses external to the area/compartment that act on the access door assembly), the axial seal can be compromised and the resistance of the door assembly to both inner and outer stresses can be lowered if the assembly process is not performed correctly. This lowered resistance may not meet applicable resistance to crash standards required for certain uses of the access door. 
     SUMMARY 
     The terms “invention,” “the invention,” “this invention” and “the present invention” used in this patent are intended to refer broadly to all of the subject matter of this patent and the patent claims below. Statements containing these terms should be understood not to limit the subject matter described herein or to limit the meaning or scope of the patent claims below. Embodiments of the invention covered by this patent are defined by the claims below, not this summary. This summary is a high-level overview of various aspects of the invention and introduces some of the concepts that are further described in the Detailed Description section below. This summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used in isolation to determine the scope of the claimed subject matter. The subject matter should be understood by reference to appropriate portions of the entire specification of this patent, any or all drawings and each claim. 
     Disclosed in this patent are improved access door assemblies. In particular, disclosed are boltless/screwless access door assemblies that include a radial sealing mechanism. Moreover, the component of the access door assembly that absorbs inner stresses of the compartment is separate from the component of the access door assembly that absorbs outer stresses external to the compartment. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of two access door assemblies positioned with respect to two compartments. 
         FIG. 2  is a perspective view of an access door assembly according to one embodiment. 
         FIG. 3  is a cross-section of the access door assembly of  FIG. 2 . 
         FIG. 4  is a close-up view of  FIG. 3 , taken at inset B. 
         FIG. 5  is a cross-sectional view illustrating the ring relative to the door. 
         FIG. 6  is a perspective view of one embodiment of a release mechanism of the access door assembly of  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION 
     The subject matter of embodiments of the present invention is described here with specificity to meet statutory requirements, but this description is not necessarily intended to limit the scope of the claims. The claimed subject matter may be embodied in other ways, may include different elements or steps, and may be used in conjunction with other existing or future technologies. This description should not be interpreted as implying any particular order or arrangement among or between various steps or elements except when the order of individual steps or arrangement of elements is explicitly described. 
     Disclosed herein are improved access door assemblies. Such access door assemblies may be used in helicopters, aircraft, or any other desired application. In some cases, the access door assemblies may be used to restrict access to fuel tanks or other components, although use of the assemblies is not so limited. 
       FIG. 1  illustrates two access door assemblies  10  located on surfaces  13  of two compartments  11 . For simplification, the structure with which the access door assembly is used is referred to herein as a compartment, although such term should not be construed as limiting and can reference any suitable enclosure or structure. In some non-limiting embodiments, compartment  11  is a fuel tank or houses a fuel tank, but it need not be. As mentioned, access door assemblies  10  are configured to restrict access to the interior of a structure, such as compartment  11 , and to seal the interior of the compartment  11  or structure from its surroundings. 
       FIG. 2  illustrates an access door assembly  10  in isolation. As shown in  FIGS. 2-3 , access door assembly  10  includes a door  12 , a ring  14 , at least one retaining strip  16 , and a seal  20  ( FIG. 4 ). In the embodiment illustrated in  FIG. 2 , access door assembly also includes at least one release mechanism  26 , a grip  30 , and at least one stop  28 . Access door assembly  10  may have any desired shape and any suitable dimensions. For example, although door  12  and ring  14  are illustrated as oval-shaped, they are not limited to such a configuration. Door  12  and ring  14  may be made of any suitable materials or combination of materials such as, but not limited to, lightweight metal, alloy, high-performance thermoplastic polymer, composites or any suitable combination. Some non-limiting examples of materials from which door  12  and/or ring  14  may be formed include 2024 aluminum or polyphthalamide (PPA) with electrostatic discharge properties. 
     As shown in  FIGS. 3-5 , door  12  is assembled with respect to ring  14  such that door  12  is below ring  14  (i.e., toward the interior of the compartment  11  or other structure). Specifically, at least a portion of a top surface of the door  12  abuts a lower portion of the ring  14  as shown in  FIG. 4 . In embodiments where ring  14  is bonded to the interior of compartment  11  or other suitable structure, ring  14  may be assembled with door  12  by inserting door  12  through ring  14  toward the interior of the compartment  11  and then pulling door  12  toward the external surface  13  of compartment  11 . Optionally, a grip  30  (shown in  FIG. 2 ) is included to help assemble door  12  within ring  14  and hoist door  12  into position. If used, grip  30  can be fixed or removable. In other embodiments, access door assembly  10  does not include a grip at all. In one alternate embodiment, access door assembly instead includes a cavity that engages with a suitable tool for hoisting door  12  in position with respect to ring  14 . 
     As shown in  FIG. 4 , access door assembly  10  includes a seal  20 . Seal  20  is positioned within a groove  22  that extends at least partially around a circumference of the access door assembly  10 . Groove  22  may extend within either door  12  or ring  14 . Seal  20  is a radial seal that radially seals door  12  with respect to ring  14  substantially around the entire periphery of the access door assembly  10 . In some embodiments, seal  20  is made of a flexible material such as, but not limited to, rubber (e.g., nitrile (NBR), fluoroelastomer (FKM), etc.) and has a round cross section to help absorb shear resistance, although seal  20  can be made of any suitable material and have any suitable cross section. 
     As shown in  FIG. 4 , access door assembly  10  includes an abutment  24 , where a portion of the upper surface of the door  12  abuts a portion of the lower surface of the ring  14 . Abutment  24  is configured to absorb the stress/load associated with any pressure changes of the interior of compartment  11  or other suitable structure. 
     In addition, at least one retaining strip  16  is positioned within a channel of either door  12  or ring  14 . The at least one retaining strip  16  is configured to absorb any stresses/loads external to the compartment  11  (or other structure) that are acting on the access door assembly  10 . In this way, the access door assembly  10 &#39;s resistance to outer stresses and inner stress are provided by two different mechanisms, the abutment  24  and the at least one retaining strip  16 . As such, the at least one retaining strip  16  is only loaded with a fraction of the stresses applied to the access door assembly  10 . 
     The at least one retaining strip  16  is made of a harder material than the seal  20  to ensure the at least one retaining strip  16  substantially fills any gap between door  12  and ring  14  when the two are assembled. The at least one retaining strip  16  may be made of a thermoplastic polymer such as PEEK or any other suitable material. 
     In the embodiment shown in  FIG. 2 , two retaining strips  16  are used, although any suitable number of retaining strips  16  may be used. Each of retaining strips  16  extends from a release mechanism  26 . As illustrated, the release mechanism  26  is a pull ring, although release mechanism  26  can have any suitable configuration. When assembled, each of the retaining strips  16  is pushed through a channel until it abuts a stop, such as a stop  28 . For example, in the embodiment illustrated in  FIG. 2 , a first retaining strip  16 A passes through channel  34  until the retaining strip  16 A abuts stop  28 A to seal the right half of the access door assembly, while a second retaining strip  16 B passes through channel  36  until the retaining strip  16 B abuts stop  28 B to seal the left half of the access door assembly. Abutment of retaining strip  16  with the stop  28  provides an indication that the at least one retaining strip  16  has been properly positioned and the access door system  10  is in its sealed position. This indication enhances the safety of the access door assembly  10  by ensuring that the access door assembly is properly locked/sealed when so desired. When properly sealed, the access door assembly  10  is referred to as being in a sealed position. When in the sealed position, a tight (in some cases, an air and/or fuel and/or other medium tight) seal is formed between door  12  and ring  14 . 
     Removing the at least one retaining strip  16  from its channel disengages door  12  from ring  14  and moves the access door assembly  10  out of its sealed position and into an open position. Specifically, since the retaining strip  16  extends from a release mechanism  26 , releasing the release mechanism  26  from its installation position causes the associated retaining strip  16  to disengage from its channel, in turn releasing the seal between door  12  and ring  14 . In some embodiments, release mechanism  26  includes a lug or other structure  32  that cooperates with any suitable portion (such as but not limited to an aperture of the grip  30 ) of the access door assembly  10  to maintain the installation position of the release mechanism (and thus maintain the position of the retaining strip  16  within the channel) until the release mechanism is released. In this way, the retaining strip acts like a pin system. 
     The configuration of the access door assembly system described herein eliminates the need for screws, inserts or other fastener members or tools. This reduces the overall weight of the system and simplifies the manufacturing process. Moreover, the time associated with opening and closing the access door assembly is reduced, in turn reducing installation and maintenance time for maintaining any equipment (such as a fuel tank) stored within the compartment of the access door assembly. In some cases, the time required to open and close the access door assembly decreases from approximately 10 minutes to under approximately 2 minutes. 
     In addition, the configuration of the access door assembly eliminates potential operator error in closing the access door assembly to create a proper seal and thus helps ensure consistent resistance to any pressure surges or leaks experienced in the interior of the compartment or outside the compartment. In particular, externally applied force is not required to activate and maintain the seal of the access door assembly and thus the mechanical resistance of the locking system of the access door assembly is independent of operator manipulation and outside forces. This is a benefit over prior systems, where external axial forces applied by fastener members created the axial seal. 
     Further, because the structure absorbing the inner stresses (stresses acting on the door assembly from within the interior of the compartment) is separate from the structure absorbing the outer stresses (stresses acting on the door assembly external to the compartment), the structural integrity of the seal is increased and is less likely to fail. In particular, the abutment  24  absorbs the inner stresses while the at least one retaining strip  16  absorbs the outer stresses. In this way, the inner stresses are not transmitted to the at least one retaining strip  16  and the outer stresses are not transmitted to the abutment  24 . 
     Different arrangements of the components depicted in the drawings or described above, as well as components and steps not shown or described are possible. Similarly, some features and subcombinations are useful and may be employed without reference to other features and subcombinations. Embodiments of the invention have been described for illustrative and not restrictive purposes, and alternative embodiments will become apparent to readers of this patent. Accordingly, the present invention is not limited to the embodiments described above or depicted in the drawings, and various embodiments and modifications can be made without departing from the scope of the claims below.

Summary:
Systems for improved access door assemblies. In particular, disclosed are boltless/screwless access door assemblies with a radial sealing mechanism. In some embodiments, the access door assembly includes a shoulder configured to withstand interior stresses and a retaining strip configured to withstand exterior stresses. The access door assembly is also configured to be opened when the retaining strip is released.