Abstract:
According to one embodiment, a modular aircraft includes a propulsion module dedicated to flight, combining avionic equipment—wing structures assembly, flight deck, engines, tail unit—and a module dedicated to the carriage of passengers and/or goods. These modules include external cells extending longitudinally along a main axis and having tubular end parts of the same outline in the region of two disconnectable-coupling structures, one axial-coupling structure for keeping an end face of the propulsion module against an end face of the carriage module, and one radial-coupling structure for keeping an end face of the propulsion module against an end face of the carriage module. The wing structures assembly of the propulsion module includes two wing structures having opposite sweeps which are connected at the end and by a longitudinal connecting spar.

Description:
TECHNICAL FIELD 
       [0001]    The invention relates to a method of separably coupling a propulsion module dedicated to flight and a module dedicated to carriage, the coupling of these modules forming an aircraft. The invention also relates to a modular aircraft able to implement such a method. 
         [0002]    The invention applies to the aeronautical field. Conventionally, aircraft comprise propulsion structures dedicated to flight—flight deck, engines, wings and tail unit—and structures dedicated to the carriage of passengers and/or goods—fuselage and hold. The invention relates to the connection between these structures. 
       PRIOR ART 
       [0003]    An aircraft is conventionally a single cell structured simultaneously to provide propulsion/lift and to carry passengers and/or goods. 
         [0004]    All the operating cycles: flight, maintenance, overhaul, embarkation/loading, disembarkation/unloading, etc. have an impact on the aircraft as a whole. 
         [0005]    The main problem is that the entire aircraft is tied up throughout all of the phases of operation of an aircraft cycle on the ground and, as a result, most of the phases are sequential and cannot be performed in parallel. Thus, the cycle remains incompressible, despite every effort made at optimizing the time spent on each of these phases. 
         [0006]    The concept of separating the flying part and the carriage part is known. The approach was developed notably by Lockheed and described for example in pioneering patents U.S. Pat. No. 2,388,380, U.S. Pat. No. 2,577,287 or U.S. Pat. No. 2,683,005, or even in alternative forms described in patents U.S. Pat. No. 3,361,396 or U.S. Pat. No. 4,379,533. This approach involves providing an assembly between the two modules—propulsion and carriage—that makes it possible to reconstruct an overall structure similar to that of a conventional aircraft structure, with a carriage module situated under or on the module dedicated to flight. 
         [0007]    These solutions do not allow the creation of a simple, dependable and quick disconnectable coupling between the modules. In addition, aerodynamic constraints are not met because of the discontinuities between the aerodynamic envelopes of the modules: turbulence is thus created in flight and this has the result of creating significant drag. Fuel consumption is thereby appreciably increased. 
       SUMMARY 
       [0008]    The invention seeks to get around these disadvantages by proposing two connections, an axial connection and a radial connection, between the two modules to form a central cell of continuous form. This configuration is then consistent with the aerodynamic constraints having a drag which is similar to, or even better than, that of a conventional present-day aircraft. 
         [0009]    More specifically, one subject of the present invention is a method of separably coupling a propulsion module dedicated to flight, incorporating avionic equipment—wing structures assembly, flight deck, flight controls, drive, tail unit—and a module dedicated to the carriage of passengers and/or goods, the coupling of these modules forming a modular aircraft. This method consists in creating the modules around an external form with overall continuous curvature extending longitudinally along a main axis and having complementary tubular coupling end parts. It then consists in axially coupling the coupling ends of the modules aligned along a longitudinal axis coinciding with the main axes using disconnectable mechanical connections. A longitudinal connection is formed axially and a connection is formed radially so that continuity of external form occurs at these connections, the propulsion module being positioned behind the carriage module in the conventional direction of travel of the aircraft. The wing structure of the propulsion module comprises two opposite sweeps which are connected at the end and between the disconnectable mechanical connections. 
         [0010]    Advantageously, the avionic equipment of the propulsion module—flight deck, flight controls, wing structure assembly, drive, tail unit—is positioned according to the requirements for balancing in order to observe the laws of mechanics of flight of the modular aircraft once it has been assembled. 
         [0011]    This modular nature allows the use of several carriage modules for one and the same propulsion module. It is thus possible to get around the need of making the same aircraft up using the same modules each time, thus improving the flight cycle: the carriage module can be prepared in advance of the phase of use, allowing a significant time saving. In addition, the maintenance cycles involving the carriage module are also optimized because they can be performed as a parallel task, and the propulsion module operating time is optimized for reduced operating costs. In particular, the time spent parked on the ground is reduced to a minimum. In addition, the times spent pressurizing and depressurizing the carriage module can be evened out over time. 
         [0012]    Preferably, the carriage module is disconnected as soon as the aircraft lands and is transported to a disembarkation station of the airport, thus allowing a new module to be reconnected to the same propulsion module immediately, ready for a new flight. 
         [0013]    According to advantageous embodiments: 
         [0014]    the distance between the wing structure sweeps is set to minimize the flow of load between the wing structure and the propulsion module; that being so, the flow of load absorbed is substantially less than the load absorbed in the current design in which the wings are embedded in the fuselage of an aircraft—by the first rib of the central section—because the lever arm, which passes on the fixed-end bending moment between the wing structure and the fuselage of a conventional aircraft, is thereby appreciably lengthened; 
         [0015]    the carriage module has an oblong external fuselage of a shape and length that are suited to the type of carriage—passengers and/or goods—and to the type of flight—long-haul or medium-haul—the shape of the fuselage making it possible to define substantially the same center of gravity while at the same time varying the capacity to carry goods and/or passengers, the axial and radial connections making it possible to achieve an interchangeable coupling between one propulsion module and various carriage modules; 
         [0016]    the external shape of the fuselage is dimensioned so that it too, in addition to the wing structure of the propulsion module, contributes to creating the lift of the modular aircraft and thus improving the overall balance; 
         [0017]    the external shape of the fuselage of the carriage module is that of an ogive in order to improve drag during flight. 
         [0018]    The invention also relates to a modular aircraft able to implement such a method. This modular aircraft comprises a propulsion module dedicated to flight, combining avionic equipment—wing structures assembly, flight deck, flight controls, engines, tail unit—and a module dedicated to the carriage of passengers and/or goods, these modules being coupled to one another by disconnectable mechanical means. The modules comprise external cells extending longitudinally along a main axis and having tubular end parts of the same outline in the region of two disconnectable-coupling means—one axial-coupling means which extends axially to keep an end face of the propulsion module against an end face of the carriage module, these complementary faces extending radially, and one radial-coupling means which extends radially to keep an end face of the propulsion module against an end face of the carriage module, these complementary faces extending longitudinally—so as to form a continuous continuation of external form at the coupling means, the propulsion module being positioned behind the carriage module in the conventional direction of travel of the aircraft. The wing structures assembly of the propulsion module comprises two wing structures having opposite sweeps which are connected at the end and by a longitudinal connecting spar extending between the disconnectable-coupling means. 
         [0019]    According to certain preferred embodiments: 
         [0020]    said end faces are substantially planar; 
         [0021]    the wing structures assembly is made up of an upper wing structure, positioned forward of a lower wing structure which supports the engine and comprises two symmetric wings which are embedded in the propulsion module under the flight deck, and the upper wing structure extends above the carriage module and comprises a central portion which is extended longitudinally by the connecting spar and is embedded in a complementary portion of the carriage module, these portions having the complementary faces on which the radial-coupling means are mounted; 
         [0022]    said complementary faces of said portions are planar, the longitudinal complementary face of the carriage module forming a flat on the carriage module; 
         [0023]    a retractable front landing gear is mounted on the carriage module and a retractable rear landing gear is mounted on the propulsion module; 
         [0024]    at least one additional catching element is mounted in a rear position of the carriage module and can be coupled disconnectably to a catching element mounted on a vehicle that drives the carriage module along on the ground, the catching elements forming a disconnectable-coupling means; 
         [0025]    each of the axial-coupling means and radial-coupling means consists of at least one disconnectable element, particularly a spigot, combined with a retractable locking means arranged in a housing. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0026]    Further details, features and advantages of the present invention will become apparent from a study of the non-limited description which follows, with reference to the attached figures which respectively depict: 
           [0027]      FIGS. 1   a  and  1   b:  perspective overall views of two examples of a modular aircraft according to the invention comprising a module intended for the carriage of passengers and of goods respectively; 
           [0028]      FIGS. 2   a  and  2   b : perspective views of the passenger-carriage and goods-carriage modules corresponding to  FIGS. 1   a  and  1   b  respectively; 
           [0029]      FIG. 3 : a side view of the two modules of one example of modular aircraft according to the invention, these being positioned along one and the same axis so that they can be coupled; 
           [0030]      FIG. 3   a : a view in cross section of the means of disconnectable attachment of the passenger carriage module according to  FIG. 3  to a vehicle that drives it along on the ground; 
           [0031]      FIG. 3   b:  a view in cross section of one example of a mounting of a spigot of the axial-coupling means of the carriage module according to  FIG. 3 ; 
           [0032]      FIG. 4 : a half view from the front of the propulsion module according to  FIG. 3 ; and 
           [0033]      FIGS. 5   a  and  5   b , a side view and a view from above of the modular aircraft of  FIG. 3  after the modules have been coupled. 
       
    
    
     DETAILED DESCRIPTION 
       [0034]    In this text, the qualifiers “front”, “rear”, “upper” and “lower” or their equivalents, relate to elements which are positioned in relation to an aircraft in conventional movement. The qualifiers “transverse”, “longitudinal”, “radial” denote positionings in relation to the main dimension of an aircraft extending along an axis X′X. 
         [0035]    With reference to the overall views of  FIGS. 1   a  and  1   b,  two examples of a modular aircraft la and lb according to the invention have been illustrated. These aircrafts have one and the same propulsion module  2  coupled to the rear of a module  3   a  for the carriage of passengers and their luggage ( FIG. 1   a ) or of a module  3   b  for the carriage of goods ( FIG. 1   b ), along a main axis X′X. The aircraft and its constituent modules exhibit symmetry with respect to a central plane Ps which, when the aircraft or the modules are on the ground, is vertical. The modules  2 ,  3   a  and  3   b  have central external forms  20 ,  30   a,    30   b  of overall continuous curvature. The interchangeable nature of the modules means that the operating cycles for operating a fleet of aircraft can be optimized. 
         [0036]    The propulsion module  2  incorporates the avionic equipment dedicated to flight and flight control around the central tubular cell  20 : a double wing structure  4 , engines  5   a,    5   b,  a flight deck  6 , flight controls (built into the electronic cabinets in the hold and not visible in the figures), and a steering tail unit  7  arranged at the rear of the tubular cell  20 . 
         [0037]    The double wing structure  4  is made up of an upper wing structure  4   a  and of a lower wing structure  4   b  which extend transversely to the central cell  20  and are jointed together at their ends  40 . The length of the connections between the wing structures  4   a,    4   b  is reduced because of the sweeps formed by these wing structures. The structural bracing of these sweeps stiffens the reaction to the cantilever effect between the built-in end where the lower wing structure  4   b  is embedded in the central cell  20  and the coupling of the top wing structure  4   a  to the carriage module  3   a  or  3   b.  In addition, vertical winglets  4   c  are provided at the tips of the wings to contribute to weakening the wing tip vortex effect and reduce the drag of the aircraft. 
         [0038]    The upper wing structure  4   a,  arranged forward of the lower wing structure  4   b,  comprises two wings  40   a  which form a sweep bending toward the front “Av” of the aircraft and are connected by a central portion  41 . This central portion  41  is extended longitudinally by a connecting spar  42  between the upper wing structure  4   a  and a radial end face  22  of the central tubular cell  20  of the propulsion module  2 . This spar provides reinforcement and balances structural loading. In addition, the length of this spar is determined so that the distance between the wing structure sweeps minimizes the absorption of the flow of load between the wing structure and the propulsion module. 
         [0039]    The lower wing structure  4   b  supports the engines  5   a,    5   b  and that makes it possible to reduce the noise impact on the ground during take off or landing phases. This lower wing structure  4   b  is made up of two symmetric wings  40   b  which form a sweep bending toward the rear “Ar” of the aircraft. The length of the connections between the wing structures  4   a,    4   b  is reduced because of the sweeps. The wings  40   b  of the lower wing structure  4   b  are embedded laterally in the central cell  20  under the flight deck  6 . A calculator of a center of gravity (not depicted) assists with balancing the propulsion module by managing the mass of fuel contained in the upper wing structure  4   a  compared with that contained in the lower wing structure  4   b.    
         [0040]    The carriage module  3   a  or  3   b  extends longitudinally along the same axis X′X as the propulsion module  2  and to the front of this same module  2 . The front  31  of the carriage modules  3   a,    3   b  advantageously has the shape of an ogive providing aerodynamic optimization for best penetration through the air and to limit the angle of drag in flight. The module  3   a  is in the form of a substantially cylindrical fuselage of circular base  30   a,  making it possible to simplify its production line and its maintenance. Access doors  9  are incorporated into the fuselage. 
         [0041]    Because the carriage module is not designed to obey only flight control constraints, these being dedicated to the propulsion module, there is even more freedom in the form it can adopt. However, this carriage module is self-contained in terms of energy supply as it houses an auxiliary power unit (APU). An APU in fact supplies the energy necessary for starting the engines, for the air conditioning and for pressurizing the module. 
         [0042]    The form of the carriage module can be adapted homothetically to suit the type of goods and/or the type of flight, for example from a transversely widened form like that illustrated in  FIG. 1   b.  This module in particular has an external fuselage of oblong shape of ovoid type  30   b,  of a length suited to the type of goods and to the type of flight—long-haul or medium-haul—this ovoid shape of the fuselage allowing more or less the same center of gravity to be defined while at the same time varying the capacity to carry goods or passengers. 
         [0043]      FIGS. 2   a  and  2   b  respectively show the passenger-carriage module  3   a  and goods-carriage module  3   b.  More specifically, the coupling faces  32  and  33  for coupling with the propulsion module are visible in these figures. These faces are planar and orthogonal. The face  32  is radial and extends perpendicular to the main axis X′X. The longitudinal other face  33  extends parallel to the axis X′X as far as, on the one hand, an edge  100  in common with the radial face  32  and, on the other hand, a radial cutout  101  of an upper cylindrical section  102 . 
         [0044]    Spigots  50  and  51  are respectively incorporated into the radial face  32  and longitudinal face  33  in order to perform the mechanical couplings with the propulsion module, as will be described in greater detail hereinafter. As an alternative, these spigots may be incorporated into the corresponding coupling faces of the propulsion module. These spigots are situated substantially in the central plane of symmetry Ps of the modules  3   a  and  3   b  and are off-centered respectively toward the edge  100  and toward the cutout  101  in order to maximize the push-together fit of the modules and the relative immobilization thereof once coupled. Effective and safe locking of the “fail safe” type (see below) is thus obtained. 
         [0045]    The mechanical couplings to be achieved between a carriage module  3   a  and a propulsion module  2  are now described with reference to the side view of  FIG. 3  which illustrates these modules aligned along the axis X′X so that they can be coupled. The modules have, facing one another, tubular end parts  31   a  and  21  of the same outline, so as to ensure complementary shape continuity, after coupling, with the same external form. 
         [0046]    The carriage module  3   a  comprises, arranged under the generally cylindrical fuselage  30   a  of this module: cameras  70  which assist with running, a retractable front landing gear  34 , coupling spigots  50  and  51  and an additional spigot  55  for coupling to a vehicle  5  that tows it along the ground. 
         [0047]    In one embodiment, the view in cross section of  FIG. 3   a  illustrates the spigot for attachment of the carriage module  3   a  to a towing vehicle  5 . This additional spigot  55  enters a housing  62  of the vehicle  5  via a bushing  52  mounted on a bearing  53 . 
         [0048]    Prior to coupling to the propulsion module, the passengers and luggage and/or the goods are loaded as a parallel operation then, as soon as the carriage module  3   a  is ready to depart, it can already be pressurized, making it possible to even out the cabin pressurizing/depressurizing curves, for better passenger comfort. 
         [0049]    In addition to the equipment already described with reference to  FIGS. 1   a  and  1   b,  the propulsion module  2  comprises, with reference to  FIG. 3 , the orthogonal coupling faces—the radial face  22  (to be coupled to the face  32 ) and the longitudinal face  23  (to be coupled to the face  33 )—a retractable landing gear  24 , a stabilizing stand leg  25 —to facilitate coupling/uncoupling phases and to stabilize the module while it is being filled with fuel—and retractable locking shutters  60  and  61  (shown as hidden detail through the wing structure  4   a ). These locking means are mounted in housings  62 ,  63  which receive the spigots  50  and  51  of the carriage module  3   a.  In the phase in which the propulsion module  2  approaches and runs along the axis of the carriage module  3   a,  the pilots are assisted by cameras  71 ,  72  installed on the central portion  41  of the upper wing structure  4   a  of the module: there is no longer a direct view of the runway because the spar  42  and the upper wing structure  41  do not allow a complete view but instead allow an appreciation to be gained via viewing means capable of supplying additional data, for example regarding the condition of the runway. 
         [0050]    The coupling (arrows Fc) of the two modules by bringing them axially closer together along the axis X′X is automated by laser with load transfer compensation—in the same way as known guidance systems of “Belouga” type—in order to avoid any risk of damage. The spigots  50  and  51  simultaneously and respectively marry with the housings  62  and  63 . When the flanges  40   c  and  41   c  of the spigots  50  and  51  have penetrated sufficiently far into the housings  62  and  63 , the blocking shutters  60 ,  61  are actuated under pressure to block the spigots and lock them in these housings. The axial housing  50  of the radial face  32  is a cylindrical recess  62 . The housing of the radial spigot  51  of the longitudinal face  33  is a longitudinal slot  63  made in the central portion  41 . 
         [0051]    The coupling between the modules has built-in safety (or is what is known as “fail safe”), guaranteeing an equivalent of two points of connection to each coupling point thanks to their positioning in interfaces  22 / 32  and  23 / 33  which are orthogonal. This coupling makes it possible to prevent any risk of the modules becoming detached. 
         [0052]    The center-of-gravity computer mentioned earlier is also used for balancing according to the type of carriage module connected to the propulsion module, and in flight to balance the aircraft to make it stable and flyable, in conjunction with the flight controls. 
         [0053]    When the propulsion  2  and carriage  3   a  or  3   b  modules are being separated following landing, the propulsion module goes to the end of the runway and the pressure on the shutters is removed: the spigots  50  and  51  are released by the withdrawal of the shutters  60  and  61  freed of their pressurizing. A drive vehicle comes to collect the carriage module to bring the passengers or goods to the terminal provided for disembarkation. The carriage module remains self-contained in terms of energy by starting its APU. During the transfer time, a new module, which has already been filled, is coupled to the propulsion module so that the aircraft thus reconstructed can run out to the end of the runway and take off immediately. 
         [0054]    The view in cross section in  FIG. 3   b  shows one example of the mounting of the spigot  50  on the rear coupling face  32  of the carriage module  3   a.  The spigot  50  is mounted on a domed sealed end  15  held by a structural stiffening web  16 . The domed end  15  is fixed at the end of the fuselage skin  30   a  by orbital rivets  17 . A fairing  18  extends the fuselage skin to form the coupling face  32 . 
         [0055]    With reference to the front half view of the propulsion module  2  illustrated in  FIG. 4 , it is apparent that the upper wing  40   a  and the lower wing  40   b  of the wing structures are far enough apart that the upper wing  40   a  does not disturb the engine  5   a.  This figure also partially shows the coupling face  22  for coupling with the radial face  32  of the carriage module  3   a  (see  FIG. 2   a ), the flight deck  6  and the tail unit  7 . 
         [0056]    When the two, propulsion  2  and carriage  3   a,  modules are coupled by the blocking of the spigots  50  and  51  in the appropriate housings  62  and  63  by the shutters  60  and  61  ( FIG. 3 ), the modular aircraft  1  is as illustrated in the side and top views of  FIGS. 5   a  and  5   b . The carriage module  3   a  in this instance is a module of the “ferry flight module” type created using a very short fuselage in the overall shape of an ogive and dimensioned to ballast the aircraft and give it an aerodynamic shape. The external forms of the modules  2  and  3   a  are in continuous continuation once the modules have been coupled which means that the aircraft la appears to be made up as a single piece. Advantageously, the forms may be slightly conical in order to improve their centering and flush fitting and the aerodynamic connection between them. 
         [0057]    The invention is not restricted to the embodiments described and depicted. Thus, there may be multiple spigots on each coupling face, these for example being organized in a line, a circle or an array. These spigots may be mounted on the coupling faces of the carriage module or of the propulsion module. Further, the pressure means applying pressure to the spigots may be actuating cylinders, springs or elastic leaves.