Abstract:
An aircraft door includes an outer skin configured as a panel structure; and a rear body structure configured as an integral cast structure and operatively connected to the panel structure so as to provide rigidity.

Description:
Priority is claimed to German Application No. DE 10 2009 019 434.7, filed Apr. 29, 2009 and U.S. Provisional Application No. 61/173,610, filed Apr. 29, 2009, the entire disclosure of both applications is incorporated by reference herein. 
    
    
     BACKGROUND 
     An aircraft door consists essentially of an outer skin, which in the closed state of the aircraft door is matched to the surface contour of the fuselage, and also a rear body structure, which is connected with the outer skin and gives the latter the necessary rigidity. This structure is also provided for doors designed as hatches, which are arranged without hinge units in a frame fitted to the fuselage, and are closed in normal operation of the aircraft, so that for reasons of simplification the term aircraft door or door also includes hatches of this type, in particular emergency evacuation hatches and access hatches, which enable an emergency evacuation or provide access for maintenance tasks. 
     Emergency evacuation hatches are inserted into the frame from the interior and are locked by means of a locking mechanism. In an emergency situation the hatch can be unlocked and lifted out of the frame into the interior of the aircraft; it is then thrown sideways out of the aircraft through the opening created so as to clear an emergency route, onto the wing, for example. A window ensures that the operator can detect any risks outside the aircraft fuselage, such as fire, obstacles, and similar, and if necessary leaves the hatch closed. 
     At the present time it is usual to manufacture aircraft doors of this type in a differential form of construction by means of a riveting and/or adhesive technique with a multiplicity of differing production steps. One production step includes the manufacture of the rear body structure, wherein beam and frame elements are joined together by means of overlaps and ancillary brackets to create a framework. In a method of known art the outer skin, designed as a skin panel, is subsequently connected with the rear body structure, in particular by means of riveting. Here the production resource requirement is significant, since for the manufacture of the rear body structure a large number of individual components and connecting elements is required. Also it is disadvantageous that overlaps and ancillary brackets are necessary for the joining of the individual components in the connecting regions. In addition to high assembly costs this requires an increased structural weight overall. 
     In addition to the differential form of construction it is furthermore of known art, to manufacture aircraft doors in a single piece, integral form of construction by means of a casting and/or milling technique. From DE 100 46 004 A1 an aircraft door is of known art in which the rear body structure and outer skin are designed in one piece using a sand casting method. This solution has, however, the disadvantage that the moulding tools required have a complex structure and the outer skin can only be cast with a high minimum thickness, so that the door of this type either has a high structural weight or by virtue of the finish machining of the skin field using milling technology is extremely resource intensive in production engineering terms. 
     SUMMARY OF THE INVENTION 
     In contrast an aspect of the present invention is to create a high-strength aircraft door that has a reduced structural weight and can be manufactured with minimal production engineering resource. 
     The aircraft door according to the invention is provided with an outer skin designed as a panel structure, to which is assigned a rear body structure for purposes of rigidity. In accordance with the invention the rear body structure is designed as an integral cast structure. Compared with DE 100 46 004 A1 the moulding tools required according to the invention are less complex and the thickness of the outer skin can be freely selected, essentially in accordance with the structural loading. By virtue of the modular design of the rear body structure as an integral cast structure, an aircraft door is achieved which, compared with the prior art, is optimised overall to the loading, which satisfies the high demands on strength in aviation, and compared with conventional structures has a lower structural weight with the same or higher rigidity. In particular when the door is designed as an emergency evacuation hatch a lower structural weight enables easier manipulation of the hatch in the event of an emergency. 
     In accordance with the invention it has been identified that the aerodynamic contour of the aircraft door can advantageously be achieved by means of a pre-shaped skin panel, which in production engineering terms can be manufactured simply and cost effectively by means of rolling and/or pressing processes. The outer skin is then connected with the rear body structure that has been cast to shape. The rear body structure can advantageously be manufactured with small production tolerances using a sand, precision or pressure casting technique from high-strength light metals and light metal alloys that are suitable for casting, such as, for example, aluminium, magnesium and/or titanium alloys. In the case of aircraft doors with a window frame the latter is advantageously cast into the rear body structure, so that in this regard further production stages can be eliminated. 
     In accordance with a particularly preferred example of embodiment of the invention the rear body structure has integrally designed beams and/or frames. The stiffening elements of the rear body structure are preferably arranged and dimensioned as a function of the structural loading, so that overall a light structure is achieved with a high rigidity. 
     It has been found to be advantageous, if at least two central frames are provided, which are continuously formed and extend over the whole length of the door. As used herein, the at least two central frames extending over the whole length of the door means the at least two central frames essentially extending over the whole length of the door. By this means a homogenous force distribution is achieved with a reduced structural weight for the aircraft door. 
     In a preferred example of embodiment of the invention the two frames have a web extending at right-angles to the outer skin, with flanges running at right-angles to the web, so that overall a light structure is achieved with a high rigidity. As used herein, extending at right-angles means extending at approximately right angles, and running at right-angles means running at approximately right-angles. The flanges facing away from the outer skin are designed as T-flanges, at least in sections, and are provided for the purpose of connecting a door inner cladding. 
     In an example of embodiment according to the invention the two central frames are designed in accordance with the structural loading to be curved in an arced shape relative to the longitudinal axis of the door. Here it has been found to be advantageous if the frames are designed to be curved such that these are spaced apart matched to the geometry of the window opening. By this means a homogenous force distribution is achieved in the region of the window opening. 
     In a preferred example of embodiment of the aircraft door according to the invention the side of the frames facing away from the outer skin is designed to be curved in an arced shape, at least in sections, in particular in accordance with the structural loading. By this means a further optimisation of the weight of the rear body structure is achieved. 
     In a concrete example of embodiment of an aircraft door at least one beam has a structural height that reduces from the centre of the door to its edge regions, so that a homogeneous force distribution is made possible. The beams extend essentially parallel to one another and run at right-angles to the frames, so that the beams, together with the frames, form a high-strength box structure. 
     The side of at least one beam facing away from the outer skin is designed to be curved in a convex arced shape relative to the outer skin, preferably in accordance with the structural loading. The beams advantageously form an integral framework structure with cut-outs and/or stiffening webs. By this means a further optimisation of the weight of the rear body structure is made possible with a homogeneous force distribution. 
     In the region of the door frame the aircraft door can be provided with a peripheral edge beam, which has a web extending approximately at right-angles to the outer skin, and a flange running approximately at right-angles to the web. The edge beam of peripheral design forms a further component of the light structure and increases the rigidity of the door in the subsequent region of contact with the door frame of the aircraft fuselage. 
     In a method for the manufacture of an aircraft door according to the invention the rear body structure is designed in a first step using a casting technique. The panel structure is then provided as an outer skin and connected with the rear body structure. 
     In production engineering terms it has here been found to be particularly advantageous if the outer skin is connected with the rear body structure by means of a riveting technique. Alternatively or additionally the outer skin can be attached with adhesive to the rear body structure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In what follows a preferred example of embodiment of the invention is elucidated in more detail with the aid of schematic drawings. In the figures, 
         FIG. 1  shows a half section of an aircraft door according to the invention designed as an emergency evacuation hatch, 
         FIG. 2  shows a sectional representation of the emergency evacuation hatch from  FIG. 1  along the line A-A, 
         FIG. 3  shows a sectional representation of the emergency evacuation hatch in the region of the upper beam, 
         FIG. 4  shows a sectional representation of the emergency evacuation hatch in the region of the beam provided in the window region, 
         FIG. 5  shows a sectional representation of the emergency evacuation hatch in the region of the beam arranged under the window, 
         FIG. 6  shows a sectional representation of the emergency evacuation hatch in the region of the lower beam. 
     
    
    
     DETAILED DESCRIPTION 
     In the figures the same design elements have the same reference symbols. 
       FIG. 1  shows an aircraft door designed as an emergency evacuation hatch  1 , which enables persons to evacuate an aircraft in an emergency. The emergency evacuation hatch  1  is essentially formed from an outer skin  2  designed as a panel structure, which is provided with a rear body structure  4  for rigidity. In accordance with the invention the rear body structure  4  is designed as an integral cast structure, thereby achieving a hatch that is optimised for loading, which has a low structural weight with a high rigidity. The outer skin  2  is connected by means of rivets with the rear body structure  4  such that the inner side of the outer skin  2  is located against the rear body structure  4 . A window  6  ensures that the operator of the emergency evacuation hatch  1  can detect hazards outside the aircraft, such as fire, obstacles, and similar, and if necessary leaves the hatch  1  closed. A closure mechanism and other additional equipment, not represented, are arranged in the region of the rear body structure  4 . 
     For the manufacture of the hatch  1  the rear body structure  4  has been cast with small production tolerances in a sand casting technique from a high-strength aluminium alloy and then connected with the outer skin  2  provided as a pre-shaped panel structure. In production engineering terms it has been found to be particularly advantageous if the outer skin  2  is connected with connecting sections  8  of the rear body structure  4  by means of rivets. The rear body structure  4  is formed essentially from integrally cast frames  10 ,  12  and beams  14 ,  16 ,  18 ,  20 ,  22 , wherein according to the example of embodiment of the invention represented two frames  10 ,  12 , four beams  14 ,  16 ,  18 ,  20  and also a peripheral edge beam  22  are provided. In the region of the door frame the hatch  1  is provided with a peripheral edge beam  22 , which increases the rigidity of the hatch  1  in the subsequent region of contact with the door frame of the aircraft fuselage. The beams  14 ,  16 ,  18 ,  20  extend in the fuselage longitudinal direction X and in the radial direction Y are spaced apart, parallel to one another. The beams  14 ,  16 ,  18 ,  20  are arranged over the whole width of the hatch  1  and at their end sections, i.e. in the edge region of the hatch, are connected with the peripheral edge beam  22 . The two frames  10 ,  12  extend essentially in the radial direction Y of the fuselage and are spaced apart from one another in the fuselage longitudinal direction X. The end sections of the frames  10 ,  12  are likewise connected with the edge beam  22 . 
     The two frames respectively formers  10 ,  12  are in each case continuously formed and extend essentially over the whole length of the hatch  1 . The frames  10 ,  12  have, in each case a web,  24  and  26  respectively, extending approximately at right-angles to the outer skin  2 , with flanges running approximately at right-angles to the webs. The flanges  28  facing away from the outer skin  2  are designed in sections as T-flanges and are provided for the purpose of connecting a door inner cladding, not represented. The frames  10 ,  12  are connected with the four beams  14 ,  16 ,  18 ,  20  running transverse to the frames. The integrally designed beams  14 ,  16 ,  18 ,  20 ,  22  and frames  10 ,  12  are arranged and dimensioned as a function of the structural loading such that overall a light emergency evacuation hatch is achieved with a high rigidity. It has been found to be particularly advantageous if the two central frames  10 ,  12 , as represented in  FIG. 1 , are designed in accordance with the loading to be curved in an arced shape relative to a longitudinal axis  30  of the hatch  1 , wherein the frames  10 ,  12  are designed to be curved such that these are spaced apart, matched to the geometry of the window opening. By this means a homogeneous force distribution is achieved in the region of the window opening  6 . 
     As can be seen from  FIG. 2 , which shows a sectional representation of the emergency evacuation hatch  1  from  FIG. 1  along the line A-A, the emergency evacuation hatch is curved in a convex manner corresponding to the radius of curvature of the aircraft fuselage. The sides of the frames  10 ,  12  facing away from the outer skin  2  are designed in sections in accordance with the structural loading curved in a multiply-arced shape, wherein between the beams  14 ,  16 ,  18 ,  20 ,  22 , stiffening ribs  23   a - h  are in each case designed on the frames  10 ,  12 , which extend between the outer side and inner side of the rear body structure. By this means a further optimisation of the weight of the rear body structure  4  is achieved with a high rigidity. In the example of embodiment of the invention represented the frames  10 ,  12  are provided with a reduced web height in the region of the window opening  6  and in a region underneath the window opening  6 . In what follows this is elucidated in more detail with the aid of  FIGS. 3 to 6 , which in each case show sectional representations of the emergency evacuation hatch  1  in the region of the beams  14 ,  16 ,  18 ,  20 . 
     According to  FIG. 3 , which shows a sectional representation of the emergency evacuation hatch  1  in the region of the upper beam  14 , the latter has a central web region with an approximately rectangular cross-section, which is bounded on both sides by the frames  10 ,  12 . The frames  10 ,  12  are provided in this region with flanges  28   a - d  arranged displaced relative to one another, wherein the flanges  28   a - d  in the connecting region of the outer skin  2  are directed inwards with reference to the longitudinal axis  30  (see  FIG. 1 ), and in the connecting region of the inner cladding are directed outwards. The beam  14  has a structural height that in each case starting from the frames  10 ,  12  reduces towards the peripheral edge beam  22 , so that a homogeneous force distribution is made possible. In the region between the frames  10 ,  12  and the peripheral edge beam  22  the beam  14  is provided with an integral framework structure of stiffening webs  34   a ,  34   b  and cut-outs  36   a - d , wherein in each case a stiffening web  34   a ,  34   b  is provided that extends approximately at right-angles to the fuselage inner side of the beam  14 . The edge beam  22  has a web  37  extending approximately at right-angles to the outer skin  2 , and a flange  38  running approximately at right-angles to the web. On the side of the edge beam  22  a contact profile  39  is integrated into the cast structure, which via a bearing surface  40  extending approximately parallel to the outer skin surface can be brought into contact with the door frame and has a seating  42  for the door seal. 
       FIG. 4  shows a sectional representation of the emergency evacuation hatch  1  in the region of the beam  16  provided in the window region, according to which a window frame  44  of the window  6  is already integrated into the rear body structure  4 , i.e. has been cast into the latter, so that in this regard further production stages can be eliminated. The frames  10 ,  12  are designed as T-beams with a relatively small web height, since in this region the window frame  44  is provided as an additional load-bearing structure. 
     As can be seen from  FIG. 5 , which shows a sectional representation of the emergency evacuation hatch  1  in the region of the beam  18  arranged under the window frame  44  (see  FIG. 1 ), the beam  18  has a structural height that starting from the centre of the hatch reduces towards its edge regions. The side of the beam  18  facing away from the outer skin  2  is designed to be curved in a convex arced shape relative to the outer skin, in accordance with the structural loading. The beam  18  is provided with an integral framework structure of stiffening webs  46   a - d , and cut-outs  48   a - g , wherein in a central region  54  between the frames  10 ,  12  two diagonally running stiffening webs  46   b ,  46   c  are provided such that a triangular framework structure is formed. The stiffening webs  46   b ,  46   c  extend from a skin-side central region of the structure  4  to the interior-side end sections of the frames  10 ,  12 . By this means a further optimisation of the weight of the rear body structure  4  is achieved with a high rigidity. 
       FIG. 6  shows a sectional representation of the emergency evacuation hatch in the region of the lower beam  20 . The side of the beam  20  facing away from the outer skin  2  is designed to be curved in a convex arced shape relative to the outer skin  2 , in accordance with the structural loading, wherein the maximum web height of the beam  20  is reduced compared with the beam  18  represented in  FIG. 5 . The beam  20  is provided with an integral framework structure of stiffening webs  50   a ,  50   b , and cut-outs  52   a - e , wherein in a central region  56  between the frames  10 ,  12  two diagonally running stiffening webs  50   a ,  50   b , are provided such that a homogeneous force distribution is made possible with a high rigidity. The stiffening webs  50   a ,  50   b  extend from a skin-side central region of the structure  4  to the interior-side end sections of the frames  10 ,  12 . 
     The aircraft door according to the invention is not limited to the emergency evacuation hatch  1  as described, rather the aircraft door according to the invention can be designed in the form of an alternative, not represented, example of embodiment as a freight door, an access hatch, or similar, with an outer skin  2 , which is connected with a rear body structure  4  designed as an integral cast structure. 
     Disclosed is an aircraft door  1  with an outer skin  2  designed as a panel structure, to which is assigned a rear body structure for purposes of rigidity, wherein according to the invention the rear body structure  4  is designed as an integral cast structure; also disclosed is a method for the manufacture of an aircraft door of this type. 
     REFERENCE SYMBOL LIST 
     
         
           1  Emergency evacuation hatch 
           2  Outer skin 
           4  Rear body structure 
           6  Window 
           8  Connecting sections 
           10  Frame/Former 
           12  Frame/Former 
           14  Beam 
           16  Beam 
           18  Beam 
           20  Beam 
           22  Edge beam 
           23  Stiffening rib 
           24  Web 
           26  Web 
           28  Flange 
           30  Longitudinal axis 
           32  Web region 
           34  Stiffening web 
           36  Cut-out 
           37  Web 
           38  Flange 
           39  Contact profile 
           40  Bearing surface 
           42  Seating 
           44  Window frame 
           46  Stiffening webs 
           48  Cut-out 
           50  Stiffening webs 
           52  Cut-out 
           54  Central region 
           56  Central region