Abstract:
The sealed bottoms of aircraft passenger cabin have to be fastened with heavily sized fasteners so as to withstand loads induced by the cabin pressurization. Besides, the increase in aircrafts seating capacity makes an increase in passenger cabin widths of interest. Such a width increase however makes the structure delimiting passenger cabin less resistant to efforts induced by the cabin pressurization. The present invention proposes an aircraft wherein the structure delimiting passenger cabin extends over 360 degrees around a space defined outside structure. The invention allows structure to be more resistant to loads induced by the cabin pressurization, while allowing to reduce or even to avoid the need for a sealed bottom, and while allowing to increase the space available for passengers.

Description:
TECHNICAL FIELD 
       [0001]    This invention relates to the field of aircraft and applies particularly to the configuration of a structure delimiting a passenger cabin in an aircraft. 
       BACKGROUND 
       [0002]    The cabin to be used by passengers of an aircraft defines a pressurised space that can also contain the pilot&#39;s cabin or the cockpit. 
         [0003]    The level of loads induced by pressurisation is taken into account in the design of an aircraft and has a special influence on the design of the structure delimiting the cabin that must withstand these loads. 
         [0004]    The capability of a structure to resist such loads depends particularly on the geometry of this structure. 
         [0005]    The approximately cylindrical geometry of the structure delimiting the passenger cabin in conventional aircraft is particularly favourable for resistance to pressurisation loads. 
         [0006]    However, a structure of this type has to be closed by sealed bottoms that are inherently more sensitive to pressurisation loads, at its two longitudinal ends. Consequently the means for fastening these bottoms onto the structure have to be conservatively designed. 
         [0007]    Furthermore, an approximately cylindrical geometry limits possibilities for increasing the passenger carrying capacity of aircraft. 
         [0008]    Conversely, a wide cabin geometry provides a greater carrying capacity, but does not have such a good natural capability of resisting pressurisation loads. Under pressurisation loads, such a structure tends to move back into an almost circular shape. The term “wide” geometry refers to a structure in which the dimension along the transverse direction of the aircraft is larger than its extent along the vertical direction of the aircraft. The less good capability of the structure to resist pressurisation loads then makes necessary to increase the mass of the structure and/or use stronger but usually more expensive materials. 
       SUMMARY 
       [0009]    The purpose of the invention is particularly to provide a simple, economic and efficient solution to these problems, to at least partially overcome the above-mentioned disadvantages. 
         [0010]    To achieve this, the invention discloses an aircraft comprising a structure delimiting a passenger cabin. 
         [0011]    According to the invention, when the structure is seen from above, it includes:
       at least two lateral portions respectively delimiting two lateral regions of the passenger cabin and separated from each other by a space defined outside the structure and delimited by lower and upper fairings inscribed in an aerodynamic envelope externally delimiting the aircraft;   a forward portion connecting two forward ends of the lateral portions of the structure to each other; and   an aft portion connecting two aft ends of the lateral portions of the structure to each other.       
 
         [0015]    Obviously, the passenger cabin forms a pressurised space during flight. On the other hand, since the above-mentioned space is defined outside the structure delimiting the passenger cabin, this space is not pressurised during flight. 
         [0016]    Indeed, the presence of the space defined outside the structure and surrounded by it inside the aircraft, enables better distribution of pressurisation loads applied to the structure and thus makes this structure more capable of resisting these pressurisation loads. 
         [0017]    The presence of the above-mentioned space induces a subdivision of the structure into portions arranged on each side of this space. 
         [0018]    Thus, for each of the forward and aft portions of the structure, the ratio between the extent along a longitudinal direction of the aircraft and the extent along a direction of the height is thus less than the ratio between the longitudinal extent and the extent along the height of passenger structures in conventional aircraft or flying wings. 
         [0019]    Similarly, for each of the two lateral portions, the ratio between the extent along a transverse direction of the aircraft and the extent along the height may also be less than the ratio between the transverse extent and extent along the height of structures of passenger cabins in conventional aircraft. 
         [0020]    In one preferred embodiment of the invention, when the structure is seen from above, the forward portion of the structure has an outside edge that is concave from a first end as far as a second end opposite of the forward portion, the concave face of the outside edge facing the aft of the aircraft. 
         [0021]    Preferably, the aerodynamic envelope comprises at least one access hatch for accessing the space. 
         [0022]    Preferably, the structure comprises at least one internal door for accessing the space. 
         [0023]    Preferably, the aircraft also comprises a removable container housed inside the space. 
         [0024]    Preferably, the aircraft also comprises a landing gear housed inside the space. 
         [0025]    In one preferred embodiment of the invention, each of the lateral portions of the structure comprises a plurality of circumferential stiffening frames. 
         [0026]    Each of the forward and aft portions advantageously comprises a plurality of circumferential stiffening frames. 
         [0027]    Preferably, the circumferential stiffening frames of the structure lie in corresponding planes and are arranged such that when the structure is seen from above and following the anticlockwise direction, the plane of each of the circumferential stiffening frames defines a positive or zero anticlockwise angle with the plane of the previous circumferential stiffening frame. 
         [0028]    In one preferred embodiment of the invention, the aft portion of the structure itself comprises one median portion and two lateral portions arranged on each side of the median portion so as to define two other spaces outside the structure, extending between the median portion and the lateral portions of the aft portion respectively, and each delimited by the lower and upper parts of the aerodynamic envelope. 
         [0029]    The invention also relates to a method for embarking or disembarking passengers in an aircraft of the type described above, including the passage of passengers through the access hatch of the aerodynamic envelope, through the space and through the inside door of the structure. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0030]    The invention will be better understood and other details, advantages and characteristics of it will become clear after reading the following description provided as a non-limitative example with reference to the appended drawings in which: 
           [0031]      FIG. 1  shows a diagrammatic top view of an aircraft according to a first embodiment of the invention; 
           [0032]      FIG. 1   a  is a larger scale view of the aircraft in  FIG. 1 , in a sectional view through a horizontal plane, illustrating a structure delimiting the passenger cabin; 
           [0033]      FIG. 2  is a diagrammatic perspective view of the aircraft in  FIG. 1  without part of its aerodynamic envelope; 
           [0034]      FIG. 3  is a partial diagrammatic sectional view of the aircraft in  FIG. 1 , along plane III-III in  FIGS. 1 and 1   a;    
           [0035]      FIG. 4  is a partial diagrammatic sectional view of the aircraft in  FIG. 1 , along plane IV-IV in  FIGS. 1 and 1   a;    
           [0036]      FIG. 5  is a diagrammatic longitudinal sectional view of the aircraft in  FIG. 1 , showing a first passenger embarking and disembarking method; 
           [0037]      FIG. 6  is a view similar to that in  FIG. 1   a  showing the embarking and disembarking method in  FIG. 5 ; 
           [0038]      FIG. 7  is a view similar to  FIG. 5 , showing a second passenger embarking and disembarking method and a baggage and/or freight loading and unloading method; 
           [0039]      FIG. 8  is a view similar to  FIG. 5 , showing a third passenger embarking and disembarking method; 
           [0040]      FIG. 9  is a partial diagrammatic top view of an aircraft according to a second embodiment of the invention; 
           [0041]      FIG. 10  is a partial diagrammatic sectional view of the aircraft in  FIG. 9 ; 
           [0042]      FIG. 11  is a partial diagrammatic top view of an aircraft according to a third embodiment of the invention; 
           [0043]      FIG. 12  is a partial diagrammatic top view of an aircraft according to a fourth embodiment of the invention; 
           [0044]      FIG. 13  is a partial diagrammatic top view of an aircraft according to a fifth embodiment of the invention; 
           [0045]      FIG. 14  is a partial diagrammatic sectional view of the aircraft in  FIG. 13  along plane XIV-XIV in  FIG. 13 ; 
           [0046]      FIG. 15  is a partial diagrammatic sectional view of the aircraft in  FIG. 13  along plane XV-XV in  FIG. 13 ; 
           [0047]      FIG. 16  is a partial diagrammatic cross-sectional view of an aircraft according to a sixth embodiment of the invention. 
       
    
    
       [0048]    Identical references in all these figures may denote identical or similar elements. 
       DETAILED DESCRIPTION 
       [0049]      FIGS. 1 to 4  describe an aircraft  10  according to a first embodiment of the invention. In this embodiment, the aircraft is a flying wing. Consequently, the passenger cabin is integrated into the aircraft wing  12 . 
         [0050]    Throughout the remaining description, X refers to the longitudinal direction of the aircraft  10  along the direction of advance of the aircraft, Z is the direction of the height of the aircraft corresponding approximately to the vertical direction when the aircraft  10  is on the ground, and Y is the transverse direction of the aircraft  10  that is orthogonal to the two previous directions X and Z. 
         [0051]    The aircraft  10  globally comprises the wing  12  and, for example two turbo engines  14  mounted above the wing. 
         [0052]    The aircraft  10  integrates a structure  16  delimiting a passenger cabin  18  and a pilot&#39;s cabin or cockpit  20 . This structure  16  comprises principally a skin  17  stiffened by stiffeners and frames in a manner similar to fuselages of conventional aircraft as will become clear from the following description. 
         [0053]    The space delimited by the structure  16  and forming the passenger cabin  18  and the cockpit  20  will be pressurised in flight, in a manner known in itself. Consequently, the aircraft comprises pressurisation means that may be of conventional type. 
         [0054]    The aircraft comprises an aerodynamic envelope  22  delimiting the outside of the aircraft and that can be formed of a continuous skin or made of adjacent panels that may or may not perform a structural function. 
         [0055]    This aerodynamic envelope  22  comprises a lower part  24  defined on a lower side of the aircraft, and an upper part  26  defined on a upper side of the aircraft ( FIGS. 3 and 4 ). 
         [0056]    As can be seen in  FIGS. 1 ,  1   a  and  2 , the structure  16  is generally in the form of a torus. Thus, the structure  16  surrounds a space  28  defined outside the structure  16 , around 360 degrees, the space  28  extending between the lower part  24  and the upper part  26  of the aerodynamic envelope  22 . 
         [0057]    Since the space  28  is defined outside the structure  26 , this space  28  will remain unpressurised during flight. 
         [0058]    More precisely, the structure  16  comprises a generally toroidal part  30  that prolongs forwards to form a nose cone  32  of the aircraft integrating the cockpit  20  ( FIG. 1   a ). In the example shown, the toroidal part  30  also extends in the aft direction by a projection  34  that houses various equipment for the crew and/or toilets for passengers. The toroidal part  30  preferably has an approximately circular cross-section along the radial direction defined about the axis  35  of the toroidal part as can be seen in  FIG. 3 . 
         [0059]    The structure  16  may be subdivided virtually by two dashed lines L 1  and L 2  ( FIG. 1   a ), so as to define two lateral portions  36   a  and  36   b  connected to each other through a forward portion  38  and through an aft portion  40 . The lines L 1  and L 2  extend transversely and are approximately tangent to a forward end and an aft end respectively of the space  28 . 
         [0060]    The presence of the space  28  defined outside the structure  16  and surrounded by it inside the aircraft  10 , enables a better distribution of pressurisation loads applied to the structure  16 , and thus gives this structure  16  a better ability to resist these pressurisation loads. The presence of the space  28  induces a subdivision of the structure  16  into parts arranged on each side of the space  28 . The ratio between the extent along the longitudinal direction X and the extent along the direction of the height Z for the forward portion  38  and the aft portion  40  is thus less than the ratio between the longitudinal extent and the extent along the height of passenger cabin structures in conventional aircraft or flying wings. Similarly, as regards each of the lateral portions  36   a  and  36   b,  the ratio between the extent along the transverse direction Y and the extent along the direction of the height Z is less than the ratio between the transverse extent and the extent along the height of the structures of passenger cabins in conventional aircraft. 
         [0061]    The approximately circular geometry of the section of the toroidal part  30  of the structure  16  further increases the resistance to pressurisation loads. The structure  16  is approximately equivalent to a cylindrical structure with a circular cross-section closed on itself, which can reduce or even eliminate the need for sealed bottoms. In the example shown, only the projection  34  requires a sealed bottom  42  ( FIG. 1   a ), which is nevertheless limited in extent in comparison with sealed bottoms of conventional aircraft fuselages. As will become clearer in the following, the structure  16  does not necessarily have a projection in the aft direction in other embodiments of the invention, and therefore does not need a sealed bottom. 
         [0062]    The approximately toroidal geometry of the structure  16  makes it possible for this structure to efficiently participate in stiffening the aircraft assembly  10 , particularly with regard to bending loads applied to the wing  12  in the transverse plane. Once again, the result is saving in terms of design of the overall structure of the aircraft  10 . 
         [0063]    As can be seen in  FIG. 1   a,  the passenger cabin  18  comprises passenger seats  44  that are for example arranged radially in side regions  46   a,    46   b  of the passenger cabin  18  and circumferentially in the forward  48  and aft  49  regions of this passenger cabin. These seats  44  are installed on a main floor  50  ( FIGS. 3  et  4 ) of the passenger cabin  18 . 
         [0064]    Furthermore, the structure  16  includes for example two inside doors  52  that open up into the space  28  and two outside doors  54  that open up outside the aircraft  10  ( FIGS. 1   a  and  2 ). The two inside doors  52  are for example arranged at the front and the back of the space  28  respectively, while the two outside doors  54  are for example arranged on each side of the forward portion  38  of the structure  16 . 
         [0065]    Furthermore, the lower part  24  of the aerodynamic envelope  22  preferably includes an access hatch  56  visible in  FIGS. 3 and 4  providing communication between the space  28  and the outside of the aircraft  10 . For example, the hatch  56  includes two hinged shutters that can pivot about 180 degrees between an open position and a closed position. 
         [0066]    Since the space  28  is not pressurised, the access hatch  56  is not subjected to pressurisation loads, such that the access hatch  56  and the means of locking the access hatch may be relatively light. 
         [0067]    Note that when seen from above ( FIG. 1   a ), the forward portion  38  of the structure  16  has an outside edge  58  that is concave from a first end  60   a  as far as a second opposite end  60   b  of the forward portion  38 , with its concavity oriented towards the aft of the aircraft  10 . The two ends  60   a  and  60   b  of the forward portion  38  are defined at the virtual line L 1  separating the forward portion  38  from each of the lateral portions  36   a ,  36   b  of the structure  16 . 
         [0068]    The concave shape of the outside edge  58  of the forward portion  38  of the structure  16  has the advantage that it prevents the presence of inflections, also called “double curvatures”, which optimises the strength of this forward portion  38  to resist pressurisation loads. 
         [0069]    Furthermore,  FIG. 2  shows the aircraft  10  without an aft portion of the aerodynamic envelope  22 , showing longitudinal ribs  61  (shown very diagrammatically) designed to stiffen the part of the aircraft located aft of the structure  16  delimiting the passenger cabin. Some of these ribs have a forward end connected to the structure  16 . To achieve this, the forward end advantageously has a curved shape complementary to the section of the structure  16 . 
         [0070]    Furthermore,  FIGS. 3 and 4  give a view of a secondary floor  62  arranged under the main floor  50  at the lateral portions  36   a ,  36   b  and the aft portion  40  of the structure  16 . This secondary floor  62  delimits a hold  64  for transport of luggage and/or freight. This hold is accessible through a hold door  66  integrated in the lower part  24  of the aerodynamic envelope  22  ( FIG. 4 ). The secondary floor  62  advantageously comprises an opening facing the hold door  66  to allow the passage of luggage or freight, and preferably integrates a conveying system, in a manner known in itself. 
         [0071]      FIG. 4  also gives a view of the forward landing gear compartment  67  that, in the example shown, is integrated into the forward portion  38  of the structure  16  below the floor  50 . 
         [0072]    The aircraft  10  also comprises two aft landing gear compartments that are not shown in  FIGS. 1 to 4  and that are located in the aft part of the structure  16 . 
         [0073]    In the particular example shown, the aerodynamic envelope  22  comprises a forward portion formed directly by the skin  17  of the structure  16 , and an aft portion  69  ( FIG. 1 ) composed of a skin or adjacent panels and extending particularly around part of the structure  16 . 
         [0074]      FIGS. 5 and 6  diagrammatically show a first method of embarking passengers onboard the aircraft  10  and disembarking passengers from this aircraft  10 . 
         [0075]    For application of this method, the aircraft is preferably located on a parking area  68  under which there is a room  70  for passenger transit. 
         [0076]    The floor of the parking area  68  comprises at least one and preferably two doors  72   a ,  72   b . The room  70  comprises at least one and preferably two retractable escalators  74   a ,  74   b , shown very diagrammatically. These escalators are preferably parallel to each other and adjacent. 
         [0077]    When embarking, one  72   a  of the openings in the floor of the parking area  68  is open, and the access hatch  56  of the aircraft  10  is also open. The corresponding escalator  74   a  is extended through the door  72   a  and through the access hatch  56  so as to penetrate into the space  28  until reaching one of the inside doors  52  of the structure  16  delimiting the passenger cabin  18 . Departing passengers can thus get on the aircraft using the escalator  74   a.    
         [0078]    Similarly when disembarking, the other  72   b  of the doors in the floor of the parking area  68  is open, and the access hatch  56  of the aircraft  10  is also open. The corresponding escalator  74   b  is extended through the door  72   b  and through the access hatch  56  so as to penetrate into the space  28  until reaching the other of the inside doors  52  of the structure  16  delimiting the passenger cabin  18 . Arriving passengers can thus leave the aircraft using the escalator  74   b.    
         [0079]    Embarking and disembarking can advantageously take place simultaneously as shown in  FIGS. 5 and 6 . 
         [0080]    Since the aircraft is accessed through the inside doors  52 , the outside doors  54  can be reserved for the evacuation of passengers in case of emergency. 
         [0081]      FIG. 7  shows a second method of embarking passengers onboard the aircraft  10  and disembarking passengers from this aircraft. 
         [0082]    This method is based on the use of an elevator to transfer passengers. This transfer only requires a single door  72  in the floor of the parking area  68 . As regards the elevator, only the cabin  76  thereof is shown in  FIG. 7 . The lifting mechanism of this cabin  76  may be conventional and it is not shown in  FIG. 7  for reasons of clarity. 
         [0083]    When passengers embark, they enter the elevator cabin  76  from the room  70  located under the parking area. The access hatch  56  of the aircraft  10  is open. 
         [0084]    The elevator cabin  76  is then moved upwards through the door  72  and the access hatch  56  to reach the space  28  inside the aircraft  10 . The elevator cabin is also shown in its position inside the aircraft, and is then referred to as reference  76 ′. Preferably, two doors  78  of the elevator cabin  76 ′ open facing the two inside doors  52  of the aircraft, also in the open position to enable passengers to access the aircraft cabin  18 . 
         [0085]    Once embarking is complete, the elevator cabin can be loaded with luggage or freight and then stored in the space  28  to maximise the aircraft carrying capacity. Passengers can be evacuated in case of emergency through the outside doors  54 . 
         [0086]    Disembarking takes place in a similar manner, the order of operations simply being reversed. 
         [0087]    A method of loading and unloading luggage and/or freight may be applied similarly, as is also shown in  FIG. 7 . This method uses a luggage elevator comprising a mobile platform  80 . 
         [0088]    Luggage and/or freight previously enclosed in a container  82  that is provided for this purpose can then be loaded by putting the container  82  on the mobile platform  80  and then moving this platform upwards though a door  83  provided in the floor of the parking area  68  and then through the door in the hold  66 , these two doors  83  and  66  having previously been opened, until the container  82  penetrates into the hold  64  of the aircraft. 
         [0089]    Unloading of luggage and/or freight takes place in a similar manner, the order of the operations once again being reversed. 
         [0090]      FIG. 8  shows a third method of embarking onboard the aircraft  10  and disembarking from this aircraft. 
         [0091]    This method is based on the use of a retractable spiral staircase  84 , that is preferably permanently housed in the space  28  inside the aircraft  10 . Reference  84  in the  FIG. 8  denotes the staircase shown in its retracted state in a storage position, for example suspended from the upper part  26  of the aerodynamic envelope  22 . 
         [0092]    When embarking and/or disembarking, the access hatch  56  of the aircraft and the door  72  in the floor of the parking area  68  are previously opened and the staircase is then extended downwards (reference  84 ′ in  FIG. 8 ) such that a lower end  86 ′ of this staircase extends close to a floor of the room  70  located under the parking area  68 . 
         [0093]      FIGS. 9 and 10  show an aircraft  100  according to a second embodiment of the invention also of the “flying wing” type. This aircraft is different from the aircraft in  FIGS. 1 to 8  because the structure  16  delimiting the passenger cabin  18  is elongated in shape along the longitudinal direction X of the aircraft. 
         [0094]    The structure  16  thus has a part  30  shaped like an “elongated torus” and is thus approximately in the form of a cylinder folded on itself. This part  30  once again extends forwards to form the nose cone  32  of the aircraft and in the aft direction to form the projection  34 . 
         [0095]    The space  28  surrounded by the part  30  is also elongated in shape along the longitudinal direction X. 
         [0096]    There is only one space  28  in the example shown, but as a variant several spaces can be provided one after the other along the longitudinal direction and separated from each other by partitions or by transverse portions of the passenger cabin  18 . 
         [0097]      FIG. 9  also shows a particular configuration of corridors  101  formed inside the cabin  18  for circulation of passengers and access to the inside doors  52  and outside doors  54 . 
         [0098]    As shown in  FIG. 10 , the aircraft  100  does not have a hold under the floor  50  of the passenger cabin  18 . The aircraft is thus remarkably thin, in other words its extent along the direction of the height Z is particularly reduced ( FIG. 10 ), which improves the aerodynamic properties of the aircraft. 
         [0099]      FIGS. 9 and 10  show a particular method of using the aircraft  100  in which the space  28  is advantageously used to contain luggage and/or freight. 
         [0100]    To achieve this, the luggage and/or freight  102  ( FIG. 10 ) are for example located in two containers  104   a  and  104   b  ( FIGS. 9 and 10 ) arranged one behind the other within the space  28 . For example, each of these containers has an oblong shaped section along a direction corresponding to the direction of the height Z when the container is in its loading position within the space  28  ( FIG. 10 ). In the example shown, each of the containers also has an oblong section along the longitudinal direction X ( FIG. 9 ). Each of the containers may be held in position by any appropriate means. Each of these containers preferably comprises its own pressurisation means which are advantageously designed to pressurise containers at a pressure less than the pressure in the passenger cabin during flight, but sufficient for the transport of luggage and freight. The pressurisation means in each container may for example be in the form of a pressurised air cylinder connected to the container during flight, or a simple connector for connection to a pressurisation unit on the ground. 
         [0101]    Transport of luggage and/or freight  102  within the space  28  is compatible with the loading and unloading methods described above. It is sufficient to put the containers  104   a ,  104   b  into place after passengers have finished embarking and the space  28  is released, and then to unload the containers before starting to disembark passengers. Note that in case of emergency, the passengers can access the external doors  54  at any time to evacuate the aircraft. 
         [0102]    As a variant, the external doors  54  as well as the internal doors  52  can be used to accelerate embarking or disembarking of passengers. 
         [0103]    Furthermore,  FIG. 10  very diagrammatically shows the use of the space  28  to route aircraft ancillaries  106  in the space  28 , for example on each side of containers  104   a ,  104   b.    
         [0104]      FIG. 11  shows an aircraft  200  according to a third embodiment of the invention which is much the same type as the aircraft  100  described above except that the structure  16  delimiting the passenger cabin has no aft projection. 
         [0105]    As shown particularly in  FIG. 11 , the structure  16  includes a set of stiffening frames. 
         [0106]    More precisely, a median part of each of the lateral portions  36   a ,  36   b  of the structure  16  includes a plurality of circumferential stiffening frames  202  located one after the other along the longitudinal direction X of the aircraft. Each of these circumferential frames thus lies in plane P orthogonal to the longitudinal direction X. 
         [0107]    Furthermore, the aft portion  40  of the structure  16  and an aft portion of each of the lateral portions  36   a  and  36   b  include an alternation of circumferential stiffening frames  202  and half-stiffening frames  204 . These half stiffening frames are approximately in the form of a semi-circle with two circumferential ends connected to an upper stiffening arc  206  and a lower stiffening arc respectively (not shown in the figure). The half-frames  204  are located on the external side outside the above-mentioned two stiffening arcs. 
         [0108]    The forward portion  38  of the structure  16  and a forward part of each of the lateral portions  36   a  and  36   b  for example integrate a plurality of stiffening inner half-frames  208   a ,  208   b  and external half-frames  210  similar to the half frames  204 , and beams  212   a ,  212   b ,  213   a ,  213   b , transverse stiffeners  214 ,  214   a , and a circumferential frame  216 . 
         [0109]    The inner half-frames  208   a ,  208   b  are arranged to the inside of the structure  16 , in other words on the side of the space  28 . The circumferential ends of the first inner half-frames  208   a  are connected to a corresponding upper beam  212   a ,  212   b  and a first corresponding lower beam (not shown in the figure) respectively. The circumferential ends of the second inner half-frames  208   b  are connected to an upper transverse stiffener  214   a  and a lower transverse stiffener (not shown in the figure) respectively. 
         [0110]    The outer half-frames  210  are placed to the outside of the aircraft  200 . The circumferential ends of these outer half-frames  210  are connected to beams  212   a ,  212   b ,  213   a ,  213   b  respectively. 
         [0111]    Each of the transverse stiffeners  214 ,  214   a  have two opposite ends connected to beams  213   a ,  213   b  respectively. 
         [0112]    For reasons of clarity, virtual lines separating the lateral portions of the forward and aft portions of the structure  16  cannot be seen in  FIG. 11 . 
         [0113]    In general, integration of circumferential frames into the structure  16  makes it possible to get the best advantages due to the presence of the space  28  in terms of resistance to pressurisation loads. 
         [0114]    In the example in  FIG. 11 , the aft portion  40  also benefits from the advantages resulting from the integration of circumferential frames. 
         [0115]    Furthermore, the entire structure  16  benefits from the lack of any double curvature. 
         [0116]    In particular, when the aircraft  200  is seen from above and the structure  16  is viewed along the anticlockwise direction T, plane P 2  of each of the circumferential stiffening frames  202  defines a positive or zero anticlockwise angle θ with the plane P 1  of the previous circumferential stiffening frame. Conventionally, the angle θ is the to be “zero” when planes P 1  and P 2  are parallel, as in the lateral portions  36   a  and  36   b.    
         [0117]    The configuration of stiffening frames described above may be adapted to the aircraft in  FIGS. 9 and 10 , in which case some frames and half-frames in the aft portions  40  may be split into two to form the forward opening of the projection  34 . 
         [0118]      FIG. 12  very diagrammatically shows an aircraft  300  according to a fourth embodiment of the invention that is similar to the aircraft  200  in  FIG. 11 , but for which the structure  16  delimiting the passenger cabin is simplified. 
         [0119]    The structure  16  according to this embodiment comprises circumferential frames  302  distributed along this entire structure  16  in other words in the lateral portions  36   a ,  36   b , in the forward portion  38  and in the aft portion  40 . In particular, the structure  16  does not have any half-frames as described above with reference to  FIG. 11 . 
         [0120]    It is remarkable when the aircraft  300  is seen from above and the structure  16  is viewed following the anticlockwise direction T, the plane P 2  of each of the circumferential stiffening frames  202  defines a positive or zero anticlockwise angle θ with the plane P 1  of the previous circumferential stiffening frame. Therefore this property is valid in the lateral portions  36   a ,  36   b , in the forward portion  38  and in the aft portion  40 . Once again, the angle θ is the to be “zero” when the planes P 1  and P 2  are parallel, as in the lateral portions  36   a  and  36   b.    
         [0121]    In this embodiment, the cockpit  20  is formed in a projection  304  connected to the forward portion  38  of the structure  16  through a relatively narrow corridor  306 . 
         [0122]    In this way, the shape of the structure  16  may be as close as possible to the shape of a more or less elongated torus, which optimises resistance of this structure  16  to pressurisation loads. 
         [0123]      FIGS. 13 to 15  very diagrammatically show an aircraft  400  according to a fifth embodiment of the invention in which the structure  16  delimiting the passenger cabin  18  is globally triangular in shape when it is seen from above and defines three spaces  28 ,  402   a  and  402   b  each of which is outside the structure  16  and is surrounded by this structure  16  around 360 degrees. 
         [0124]    Thus, the structure  16  comprises the forward portion  38 , particularly including the cockpit  20 , the two lateral portions  36   a  and  36   b  being arranged on each side of the pace  28 , and the aft portion  40  defined behind the space  28 . 
         [0125]    Therefore the aircraft  400  is different from the aircraft described above with reference to  FIGS. 1 to 12  in that the aft portion  40  of the structure  16  itself comprises a median portion  404  and two lateral portions  406   a  and  406   b  located on each side of the median portion  404  so as to define the other two spaces  402   a ,  402   b  outside the structure  16  ( FIG. 13 ). These other two spaces  402   a ,  402   b  extend respectively between the median portion  404  and the two lateral portions  406   a  and  406   b  of the aft portion  40  and are each delimited by the lower and upper parts  24  and  26  of the aerodynamic envelope  22 , as is the space  28 . 
         [0126]    As shown in  FIG. 13 , the aft portion  40  of the structure  16  also comprises a forward portion  408  defined forward from a transverse line L 3  tangent to a forward end of each of the spaces  402   a  and  402   b , and an aft portion  410  defined behind a transverse line L 4  tangent to an aft end of each of the spaces  402   a  and  402   b.    
         [0127]    The structure  16  is stiffened by circumferential frames, half-frames and lower and upper stiffeners. Only the main stiffeners among the stiffening elements can be seen in  FIG. 13 , for reasons of clarity. Thus, three annular upper stiffeners  412 ,  414   a  and  414   b  are shown extending along the corresponding axes of the spaces  28 ,  402   a  and  402   b  respectively, and three straight upper stiffeners  416   a ,  416   b  and  418  connecting the upper annular stiffeners  412 ,  414   a  and  414   b  together. The structure  16  also comprises three annular lower stiffeners and three straight lower stiffeners arranged in a similar manner (not shown in  FIG. 13 ). The structure  16  comprises in particular a plurality of half-frames around each of the spaces  28 ,  402   a ,  402   b  extending in the radial planes relative to the axis of the corresponding space and connected to the corresponding lower and upper annular stiffeners. 
         [0128]    In addition to the internal doors  52  opening up in the space  28 , the structure  16  preferably includes internal doors  420  opening up in spaces  402   a  and  402   b  respectively. 
         [0129]    Furthermore, the structure delimiting the passenger cabin in conventional aircraft usually comprises geometric discontinuities necessary for the integration of structural equipment and/or connections. These geometric discontinuities reduce the natural strength of the structure for resisting pressurisation loads and make it necessary to increase the mass of the structure and/or use stronger materials. A landing gear compartment is an example of a geometric discontinuity formed in the structure delimiting a passenger cabin. In the special case of aircraft, the central wing box connecting the wings to the fuselage forms an example of a structural connection forming such a geometric discontinuity. 
         [0130]    As can be seen in  FIGS. 13 to 15 , the three spaces  28 ,  402   a  and  402   b  are advantageously used to house a forward landing gear  422  and two aft landing gears  424   a  and  424   b.    
         [0131]    Thus, the landing gear compartment does not induce any geometric irregularity in the structure  16 . 
         [0132]    This characteristic is compatible with use of spaces  28 ,  402   a  and  402   b  for passengers and/or luggage or freight to pass through while embarking and disembarking, particularly because these operations are done when each landing is extended and therefore does not occupy the above mentioned spaces. Furthermore, when in the retracted position, landing gear can leave part of each of the spaces  28 ,  402   a  and  402   b  free to hold luggage and/or freight as shown by the presence of containers  426 ,  428   a  and  428   b  in  FIGS. 14 and 15 . 
         [0133]    The embodiments described above are related to flying wings. This type of aircraft has many advantages particularly in terms of aerodynamic, mass and carrying capacity properties, and due to the lack of a central wing box and therefore the absence of an associated geometric discontinuity within the pressurised structure. 
         [0134]    As explained above, the invention can take advantage of the large internal volume of a flying wing without reducing the resistance to pressurisation loads. 
         [0135]    However, as shown in  FIG. 16 , the invention is not limited to “flying wing” type aircraft but can also be used for airplanes. Thus,  FIG. 16  shows an aircraft  500  according to a sixth embodiment of the invention, in the form of airplane in which the structure  16  delimiting the passenger cabin  18  and the cockpit  20  is no longer integrated into the wing  12 , but is arranged above the wing  12 . 
         [0136]    In the particular example shown, the structure  16  is similar to the structure of the aircraft  100  in  FIGS. 9 and 10 , and the wing is in the form of a delta wing. 
         [0137]    After reading the above, those skilled in the art will understood that the transverse section of the structure  16 , although preferably being approximately circular, can be otherwise without going outside the scope of the invention. 
         [0138]    Furthermore, as shown by the diversity of the embodiments disclosed above, different global geometries of the structure  16  are possible within the framework of the invention. In particular, the structure  16  may be generally toroidal in shape or elongated along the longitudinal direction X or elongated along the transverse direction Y.