High-capacity fuselage for aircraft

A high-capacity aircraft fuselage having two lobes placed side by side and assembled together along two longitudinal lines of junction is designed to facilitate passenger movement from one lobe to the other in accordance with aviation safety regulations. The fuselage includes a top longeron (28) for reinforcing the top line of junction, a floor (23) providing a separation between an upper internal space which can serve as a cabin (24) and a lower internal space (25) which can serve as a hold, a girder (32) for supporting the cabin floor and connecting it to the bottom portion of the fuselage, rows of seats extending from one side of the bilobed body to the other, a bottom longeron (29) for reinforcement along the bottom line of intersection, and posts (31) disposed in spaced relation in the rows of seats for connecting the top longeron (28) to structural members located in the lower region of the fuselage (32, 29).

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a bilobed fuselage for an aircraft which 
is intended to be employed for carrying passengers or freight, or both. 
The invention is more particularly concerned with a bilobed fuselage for a 
high-capacity transport aircraft. 
The invention is also directed to aircraft equipped with a fuselage of this 
type. 
2. Description of the Prior Art 
Generally speaking, the design of an aircraft fuselage has to satisfy a 
large number of criteria. These give rise to compromises between 
requirements of a functional character and requirements of a structural 
character so as to result in acceptable weight and minimum production 
cost. It is readily apparent that this design must also be adapted to 
aeronautical certification requirements and to market requirements. 
An aircraft fuselage normally has the function of carrying a payload in the 
form of passengers and baggage as well as freight. In regard to the cabin, 
this implies flexibility in the arrangement of seats and service locations 
(galleys, toilets, and so on) as well as suitable means for access and 
evacuation. The compartments provided for freight are usually loaded by 
passing into the fuselage on only one side. This makes it possible to 
reduce stopover times since access to passengers is provided on the other 
side of the fuselage. 
In order to build structures of acceptable weight, it is necessary to take 
into account the pressurization of the cabin, which ensures a comfortable 
atmosphere during high-altitude flight as well as the total load 
constituted by the resultant of the forces generated by the flight mission 
of the aircraft under given atmospheric conditions. For the greater part 
of the fuselage, the pressure within the interior of the cabin is the 
predominant load to be taken into account for dimensioning. In this 
connection, the optimum structure is constituted by a segment of 
cylindrical fuselage having a substantially circular or practically 
circular cross section. The difference in pressure prevailing on each side 
of the shell results in peripheral stress which is counterbalanced by 
longitudinal members as well as by transverse structures known as frames, 
and pressure-resistant partition walls or bulkheads. 
Production costs may be substantially reduced by making use of parts which 
already exist in other types of aircraft. Similarly, it is an advantage to 
develop aircraft having identical subassemblies or subassemblies 
comprising many common parts since initial production tooling costs may 
accordingly be amortised over a larger series. Furthermore, it may prove 
justified to make fuller use of automation owing to the additional 
reduction in costs which is thus made possible. 
In the field of aeronautics, market requirements tend to impose an increase 
in the number of passengers which can be carried by a single aircraft 
while at the same time maintaining acceptable external dimensions of the 
aircraft. The object of this tendency is to limit the congestion of 
airports and air traffic by reducing the number of flights. A further 
object is to obtain a direct operating cost (DOC) per passenger which is 
as low as possible. As a general rule, the cost just mentioned includes a 
percentage of the initial purchase price, the cost of fuel, costs of 
operating personnel (crew) and of maintenance. Under these conditions, if 
additional seats are installed at limited cost, this may appreciably 
reduce the direct operating cost per seat. Similarly, a large baggage-hold 
volume which can effectively be employed for freight or other purposes may 
significantly reduce operating costs owing to the possibilities of 
additional income which are thus offered. 
In order to increase the usable volume of the fuselage without excessively 
increasing the external dimensions of the aircraft, different cross 
sections have been studied. Vertical bilobed fuselages or in other words 
fuselages having two longitudinal lobes placed one above the other and 
juxtaposed in a horizontal plane have already been built and put into 
service. 
While being relatively compact, this form of construction is nevertheless 
subject to disadvantages in regard to volume utilization of the fuselage 
and complicates passenger access to the upper deck, taking into account 
existing airport facilities. This entails the need to install interior 
stairways, thus reducing available space as well as the structural 
efficiency of the aircraft. 
It has also been proposed to construct an airplane having a fuselage which 
is bilobed in the lateral or horizontal direction or in other words which 
has two longitudinal lobes juxtaposed substantially in a longitudinal 
vertical plane. This is the case in particular of U.S. Pat. No. 3,405,893 
(C. Flamand et al) and U.S. Pat. No. 4,674,712 (Whitener) which describe a 
bilobed-fuselage airplane, each lobe being limited by a flat longitudinal 
wall along its intersection with the other lobe. This dividing wall, which 
is thus vertical in the trim position of the airplane, constitutes a 
common vertical joint plane. Moreover, the two lobes are surrounded by an 
air-tight outer shell of oval cross-section which is formed of 
high-strength metal. In the upper portion reserved for passengers, a few 
openings of limited number are provided for passing from one lobe to the 
other. 
This bilobed-fuselage airplane constitutes a rather small improvement over 
conventional aircraft for the following reasons: 
the presence of an oval shell of high-strength metal and of a central wall 
over the greater part of the length of the aircraft result in a weight 
estimate which is not improved or which is improved only to a very slight 
extent; 
the central wall, which is almost continuous, increases the weight of the 
aircraft and constitutes a considerable obstacle to the movement of 
passengers from one side of the aircraft to the other. This is a very 
serious disadvantage from the point of view of passenger safety in the 
event of incident or of accident. As a further consequence, service on 
board the aircraft is also unfavorably affected and the same applies to 
freight loading conditions since in this case both sides of the fuselage 
have to be employed in practice for passenger access. 
The present invention relates to a different design of aircraft fuselage, 
the greater part of which has a body which is bilobed in the lateral 
direction. The object of the invention is in fact to construct a fuselage 
by means of existing components, the increase in weight of this fuselage 
being relatively small with respect to the increase in the number of seats 
of the upper deck and/or with respect to the increase in freight as well 
as increased flexibility in the distribution of seats. 
The invention is also directed to a high-capacity aircraft in which the 
movement of persons from one side of the aircraft to the other is greatly 
facilitated in order to comply with aviation safety regulations and to 
permit entry of passengers through only one side of the fuselage. 
SUMMARY OF THE INVENTION 
The present invention is thus concerned with an aircraft fuselage, the 
greater part of said fuselage being constituted by a shell which is 
bilobed in the lateral direction or in other words which has two lobes 
placed side by side so as to form two longitudinal lines of junction 
consisting respectively of a top line and a bottom line, and said fuselage 
essentially comprises: 
a top longeron means for stiffening along said top line of junction; 
a floor forming a separation between an upper internal space which may 
serve as a cabin and a lower multiple-purpose internal space for use in 
particular as a freight hold; 
means for supporting the cabin floor which are arranged between this latter 
and the lower portion of said fuselage; 
rows of seats which are arranged within the cabin space and can extend 
substantially from one side of the bilobed shell to the other; 
a bottom longeron means for stiffening along said bottom line of junction; 
spaced connecting means disposed at intervals in said rows of seats for 
connecting the top longeron means to the substructure means of the 
fuselage. 
The longeron means above referred to, which designates either a single 
member or an assembly of several members, is hereinafter in the present 
specification and claims called longeron for the sake of conciseness. 
The arrangement of the longerons along the lines of junction of the two 
lobes endows the fuselage with the necessary resistance to internal 
pressure and to dynamic stresses which makes it possible to dispense with 
the central wall at least in the greater part of the upper internal space 
and to replace it by a succession of connecting posts which almost 
entirely free the bilobed internal space and offer complete freedom of 
passenger movement within the double cabin in the transverse direction. 
In a preferred embodiment of the invention, the cross-section of the 
bilobed body comprises two secant curves each having a substantially 
circular contour having the same radius. The distance between centers of 
the two juxtaposed lobes can vary within appreciable limits, the lift 
being better as these centers are spaced at a greater distance from each 
other. However, the limit of spacing is given by the need to maintain a 
practicable passageway between the two lobes while also taking into 
account the height of the cabin floor with respect to the plane of the 
axes of the lobes. Under these conditions, it is an advantage to ensure 
that the width of a cross-section of the bilobed body is substantially 
within the range of 1.5 to 1.8 D, where D designates the diameter of each 
lobe. 
In a preferred embodiment of the invention, the fuselage comprises over at 
least part of its length: 
a top stiffening longeron placed above the top line of junction of the 
bilobed shell; 
a series of spaced posts which are disposed at intervals in the 
longitudinal mid-plane and connect the aforementioned longeron to the 
cabin floor; 
a girder which supports said cabin floor and connects it to the bottom 
stiffening longeron in the vicinity of the bottom line of junction of the 
two shell lobes. 
In another embodiment which permits free transverse movement for freight 
beneath the cabin floor, the bottom stiffening longeron is entirely placed 
beneath the bottom line of junction of the shell and beneath the 
baggage-hold floor, at least opposite to an opening for loading 
containers, and the spaced connection means such as posts are placed 
between the top longeron and the bottom longeron with intermediate 
attachment to the cabin floor. 
The two foregoing embodiments can also be associated with each other over 
the length of the fuselage. 
Preferably, the top and bottom lines of junction of the shell are covered 
by an added fairing panel which is not subjected to pressurization and 
achieves enhanced aerodynamic characteristics of the aircraft. 
As will hereinafter become apparent, the fuselage structure contemplated by 
the invention offers considerable flexibility of arrangement according to 
requirements and limits production costs while offering great ease of 
utilization.

DETAILED DESCRIPTION OF THE INVENTION 
Reference being made to FIGS. 1 and 1A of the accompanying drawings, there 
is shown a high-capacity aircraft provided with a bilobed fuselage 1 in 
accordance with the invention. Considered from front to rear, the fuselage 
consists of the nose 3, the central bilobed section 4 and a tail 6, these 
three portions being joined to each other at the level of transverse 
reinforcements or ring frames, namely a frame 7 at the forward end and a 
frame 8 at the rear. Other intermediate ring frames are shown 
diagrammatically at 5. 
The nose 3 includes in particular the cockpit enclosure and the aircraft 
control systems. The central section 4 carries a wing unit 9 which in turn 
supports propulsion engines 11. 
The tail 6 carries in particular a horizontal tailplane 12 and a vertical 
tailplane 13. 
The habitable portion of the fuselage is limited by a forward 
pressurization bulkhead 14 and an aft pressurization bulkhead 15 for 
ensuring the comfort of passengers during high-altitude flight. 
In the cross-section of FIG. 1A taken in the central section 4 which has 
been rotated to a slight extent with respect to FIG. 1 in order to show 
the internal arrangement of the bilobed fuselage 1 more clearly, there are 
shown the main structural elements constituting said fuselage. 
In particular, the section 4 comprises a bilobed shell 17 constituted by 
the junction of two lobes formed by two similar fuselage shell elements 
having substantially circular cross-sections which are placed side by side 
and meet each other along a longitudinal mid-plane of the aircraft along 
two lines of junction, namely a top junction line 18 and a bottom junction 
line 19 (see also FIGS. 2A, 2B and 3). In a preferred embodiment of the 
invention, these lines are covered by added fairings, namely a top fairing 
21 and a bottom fairing 22, which are intended to improve the aerodynamic 
properties of the aircraft and to permit uniform flow of the airstream. 
The bilobed fuselage is divided into two superposed internal spaces by a 
first floor 23 located in the vicinity of the horizontal mid-plane U--U 
which joins the axes C--C of the two lobes of the shell 17 (FIG. 2A). In 
the example of the figures mentioned above, the floor 23 is located 
beneath the plane U--U. The floor 23 forms a partition between the upper 
internal space 24 which forms a passenger cabin and a lower internal space 
25 which serves as a hold for baggage and freight. 
The internal space 25 is limited at the bottom by a second floor 26 and 
laterally by walls 27 so as to correspond to the dimensions of the 
containers 40 which are standardized in the aircraft industry. 
The internal spaces 24 and 25 will hereafter be respectively designated as 
the cabin and the hold, the floor 23 being the cabin floor and the floor 
26 being the hold floor. 
The cabin floor 23 is shown as partly broken away in FIG. 1A in order to 
show the median longitudinal structure of the bilobed fuselage more 
clearly. This structure comprises two stiffening longerons 28 and 29, 
namely a top and bottom longeron respectively, which are disposed along 
the top and bottom lines of junction of the two lobes of the shell 17. 
The longerons 28 and 29 are connected by means of a plurality of associated 
structural members which are capable of working in both compression and 
tension. Said members are disposed in the vertical mid-plane of the 
fuselage and include a succession of spaced posts 31 which extend over the 
entire length of the fuselage section 4 between the top longeron 28 and 
the floor 23. In addition, there is mounted between said floor 23 and the 
bottom longeron 29 an open-web girder 32 which supports the floor 23 in 
the longitudinal mid-plane of the aircraft. 
The girder 32 extends over the greater part of the fuselage section 4 but 
not over its entire length, as will be seen hereinafter. 
The structural members aforesaid (17, 28, 29, 31 and 32) may be constructed 
in accordance with many different designs which make use of current 
technologies in the aircraft industry. For this reason, the structures are 
not shown in detail in FIGS. 2A, 2B and 3. 
Thus the shell 17 can be constituted by a conventional structure formed by 
a longitudinal assembly of annular sections or ring frames in a honeycomb 
arrangement, a continuous metallic wall or skin surrounding these latter. 
The assembly conforms to the structure of a monolobe-fuselage aircraft but 
is cut at the level of the lines of intersection 18 and 19 provided for 
the junction of one lobe with the adjacent lobe. 
The longerons 28 and 29 are provided for joining together the edges of the 
two lobes. 
The connecting girder 32 between the floor 23 and the longeron 29 can be 
separate from said longeron and can be either attached to this latter or 
integral therewith. Said girder can in particular be constituted by an 
open-web beam as shown in FIG. 3 and having a series of upright members 
37, which are preferably (but not necessarily) located in the line of 
extension of the posts 31, and of diagonal bracing members 38. 
The girder 32 can also be constituted differently, for example by means of 
a lattice beam as will be seen hereafter. 
In all cases, the associated structural members 17, 28, 29, 31 and 32 of 
the double bilobed fuselage are so designed as to be capable of affording 
resistance to all the static and dynamic stresses to which this fuselage 
may be subjected in the various possible situations: on the ground, at 
take-off, on landing and in flight, especially at high altitude. It is in 
the high-altitude situation that the highest stresses are exerted by 
reason of the pressurization of the cabin and tend to burst the fuselage. 
The other stresses arise in particular from the load transported and from 
the weight of the structures themselves. 
The invention overcomes a prejudice by making it possible in a bilobed 
fuselage to compensate the stresses existing along the line of junction of 
the two lobes, at a discrete number of points corresponding to the posts 
31. This results in great ease of movement of passengers from one side of 
the fuselage to the other. 
Determination of the structural members which connect the lines of junction 
18 and 19 of the two lobes of the bilobed shell is carried out as a 
function of the considerations which now follow. 
In regard to stresses related to pressurization of the cabin, FIG. 29 gives 
a simplified diagram of the forces exerted in a transverse plane, at the 
upper line of junction M of two lobes of substantially circular 
cross-section. The resultant forces are two tangential forces T1, T2 which 
can be resolved on the one hand into two equal and opposite horizontal 
components H1, H2 which cancel each other and on the other hand into two 
equal and upward vertical components V1, V2 which are added to produce an 
upward resultant 2 V, and which must therefore be compensated by an equal 
downward force 2 V'. 
In order to achieve this object, the aforementioned structural members 
constituted by the top longeron 28, the bottom longeron 29 and the 
interconnection means have to perform different functions. 
The primary function of the top longeron 28 is to compensate, at each point 
of the top line of junction, the forces (V1+V2=2 V) which are represented 
schematically in FIG. 29 and generated by the pressurization. The 
compensating force 2 V' is transmitted mainly by the posts 31 which work 
in tension. Since these posts are relatively distant from each other, the 
top longeron 28 also has the function of distributing the compensation 
effort along the top line of junction. Moreover, the top longeron plays a 
contributory role in supporting the top fairing 21 as well as a service 
walkway (not shown) which may be provided and to which further reference 
will be made hereafter. 
In the region of the bottom line of junction 19 of the two lobes of the 
bilobed body 17, compensation of overpressure forces is carried out in a 
similar manner by means of the girder 32 and the bottom longeron 29. The 
girder 32 is rigidly fixed to the floor 23 and supports this latter. The 
floor 23, which includes a central longitudinal beam 35, is in turn 
attached to the posts 31. In order to carry out this compensation, the 
girder 32 works in tension. 
In accordance with another particular feature of the invention, provision 
is made to adapt the girder 32 and the bottom longeron 29 so as to permit 
the containers which have been loaded into the hold 25 through a hatchway 
or lateral opening 20, closed by hatch or a door 20a (shown in FIG. 2B) to 
be passed through the girder 32. To this end, as shown in FIGS. 2B and 3, 
the bottom longeron 29 is interrupted in the region of the girder 32 
opposite to the opening 34 through which the containers are passed from 
one lobe into the other. The hold floor plates 26 are joined to each other 
opposite to this opening by means of a horizontal-plane element 26a. To 
this end, the inner portions of the two segments of the bilobed body 17 
which are close to the bottom line of junction 19 are eliminated together 
with a portion of the bottom longeron 29, as shown in the cross-section of 
FIG. 2B. Corresponding stresses are transmitted to a longeron element 36 
forming a keel and connected in a bevel-joint at both ends 36a to the 
longeron 29 (as shown in FIG. 3). 
The assembly of longerons 29 and 36 thus formed ensures continuity in the 
transmission of forces in spite of the discontinuity produced by the 
opening 34. 
According to another aspect of the invention, provision is made to adapt 
the spacing E of the centers C of the two circular-section fuselages, the 
junction of which constitutes the bilobed shell 17 in accordance with a 
number of different criteria which can be selectively favored by the 
builder according to the specification conditions to be satisfied. 
More particularly, the diagrams of FIGS. 4 and 4A show how a bilobed 
fuselage shell in accordance with the invention can be formed from two 
cylindrical fuselage shells 41 having the same diameter D. To this end, 
each fuselage is cut at its intersection with a plane Q parallel to its 
axis, the distance d from the axis to the plane Q being the same in both 
cases. The next step consists in assembling the two lobes along their top 
and bottom lines of junction 18 and 19. 
The relatively displaced lines 18', 19' (planes Q') indicate the possible 
margins of variation of d for adaptation to the different uses which are 
contemplated, by giving preference to certain structural parameters. 
In particular, the following choices can be made as a function especially 
of the diameter D of each lobe: 
The cut-out portion should eliminate only one (G1-plane Q) or two 
(G1+G2-plane Q') seats from a row without creating any waste of space. 
It should be ensured that the cut-out portion corresponds to the 
standardized external dimensions of a container 40 or in other words that 
the vertical wall 40a of such a container is located in the plane Q (FIG. 
4) with allowance for the necessary clearances. 
With the object of using existing monolobe-aircraft shell structures, it 
should be ensured that the plane Q corresponds to the stringer 42 to which 
the return of the outer sheet 39 of a monolobe-aircraft shell is normally 
joined (as shown in FIG. 4). 
The possibility of employing partial structures of pre-existing cylindrical 
shells constitutes an essential advantage of the invention since this 
avoids the need to undertake a very large number of studies and to design 
new tool components. 
The spacing E of the centers C, which is equal to 2d, also partly governs 
the headroom H or height of passage from one lobe to the other within the 
cabin 24, together with the position of the floor 23 with respect to the 
plane C--C. This height H is equal to (h1+h2), where h1 designates 1/2 D 
sin W, where W designates the angle at the center of the opening provided 
in the shell and h2 designates the height of the floor 23 with respect to 
the plane C--C. 
In order to make the most profitable use of the invention, it is in fact 
necessary to ensure that H is at least equal to an average height of a 
man, namely between 1.80 and 2 m, h2 being usually different from zero. 
Moreover, in the case of a large transport aircraft, the diameter D of each 
cylindrical fuselage 41 can advantageously be chosen between 5 m and 6 m. 
Taking into account the value of the parameters given above, it is an 
advantage to increase the spacing E of the axes C of the two lobes in 
order to improve the lift of the fuselage. 
Preferably, the total transverse dimension of a bilobed body will be chosen 
within the range of 1.5 to 1.8 D. For example, if D=5.5 m, the bilobed 
body will preferably have a total transverse dimension within the range of 
8.25 m to 9.9 m. 
Once the two lobes have been assembled together, the fairings 21 and 22 are 
placed in position by fixing them on the shell of the bilobed fuselage, as 
will be explained hereinafter. The enclosure K (FIGS. 2A, 2B) formed 
between the shell 17 and the fairing 21 or 22 is not pressurized but only 
constitutes a confined space. 
FIGS. 5 to 10 show in greater detail the structure of the fuselage in 
accordance with the invention in the plane of symmetry, in which the two 
shells 41 are joined together so as to form the bilobed fuselage 17. 
The top longeron 28 covered by the fairing shown diagrammatically at 21 is 
mainly constituted by a ribbed beam 33 (FIG. 6) which forms a V-section 
shoe 33a at the lower end. By means of reinforcing gussets 50, the ends 46 
of the walls of each lobe are fixed on the flanges of said shoe by any 
means customarily employed in the aircraft industry (riveting, bolting, 
and so on). 
The structure of the longerons 28 and 29 varies as a function of the 
structural modifications made in the girder 32 which is constituted in 
this case by a lattice girder but has various discontinuities which 
facilitate handling operations within the hold 25. In particular, 
provision is made opposite to the hold lateral opening 20 for a large 
opening 34 through which containers can be passed from one lobe into the 
other and for an opening 44 through which members of service staff can 
pass. 
The top longeron 28 is reinforced directly above these openings. 
As shown in FIG. 7, the bottom longeron 29, which is placed beneath the 
junction line 19 of the lobes, is a ribbed beam 39 with an inverted 
V-section top shoe 39a. 
FIG. 7A shows how a continuity of level between the two lower floor plates 
26 (only one of which is shown) for the transfer of freight from one lobe 
into the other is achieved in the region of the container opening 34. 
There is shown in particular the triangulated-section structure of the 
dropped longeron member 36 provided with a keel 36b and two wings 36c 
which both serve to attach the central panels of the shell 17. The web 36d 
of the dropped longeron member 36 supports the plane element 26a which is 
located beneath the line of junction 19, thus ensuring continuity of the 
hold floors 26. 
The longeron member 36, which extends substantially beyond the opening 34, 
has the shape of an isosceles trapezoid, and its triangular ends 36a are 
connected to the bottom longeron 29 in a bevel joint. The connection is 
made so as to avoid any discontinuity or node in the distribution of 
stresses. 
FIG. 8 shows that girder 32 is a ribbed beam having a top flange that is 
integral with floor 23 and having an inverted V-section bottom flange, 
with the lobe shells 17 being clamped between the bottom flange of the 
girder 32 and the top shoe of the dropped bottom longeron member 36. 
In addition, FIG. 5 shows diagrammatically in chain-dotted lines the 
locations of the ends 8a of the ring frames of bilobed shape, said frames 
being assembled in a series which constitutes the shell 17. The ends of 
said frames have a pitch equal to that of the upright members 37. 
FIG. 9 shows how the top longeron 28 may be connected to a tubular post 31 
by means of a clevis 48a which clamps a lug or padeye 33b depending from 
said longeron and is secured to this padeye by means of a bolt 49. The 
clevis 48a is in turn connected to the upper end of the post 31 by means 
of bolts (not shown). At the lower end, the post 31 is also attached to 
the cabin floor 23 by means of a second clevis 48b which is engaged on a 
T-plate 51 and secured by means of a bolt 49b. The plate 51 is rigidly 
fixed to the floor 23 by means of bolts (not shown) which are attached to 
the top portion of the girder 32. It is apparent that a continuous 
connection is thus ensured with distribution of stresses between the 
longerons 28 and 29. 
FIG. 10 shows how the top longeron 28, the fuselage shell 17 and the top 
fairing 21 can be assembled together. 
In this example, there is provided for the shell 17, apart from its 
connection with the shoe 33a of the ribbed beam 33 (see FIGS. 6 and 10), 
an additional triangulated connection between a T-shaped top seating 52 of 
the ribbed beam 33 and that portion of the shell 17 which is close to a 
longitudinal member or stringer 53. To this end, provision is made for 
struts 55, 63 which are mounted obliquely and applied at one end against 
the seating 52 of the longeron 28 and at the other end against the shell 
17 and the stringer 53. Attachment of the strut 55 is carried out by means 
of bolts (not shown). 
The fairing 21 is preferably constituted by a series of cambered panels 
21a, 21b assembled together by means of rivets 57 in the vertical plane of 
symmetry of the aircraft. 
The fairing 21 is joined tangentially to each lobe of the shell 17, along a 
stringer 54, by means of bolts 58. Furthermore, the fairing 21 is 
supported by upright members 59 and connected thereto by means of 
attachments which are not shown in the drawings. Each upright member 59 is 
in turn attached at its lower end 56 to a strut 55 or 63. 
Triangular-section supports 61 can be fixed on the struts 55 or 63, said 
supports 61 being each provided with a platform element 62 in the line of 
extension of the seating 52 of the longeron 28. The support surface thus 
constituted can be employed in various ways and possibly in order to 
provide the necessary bearing points for the installation of a service 
walkway. 
FIGS. 11 to 14 show diagrammatically and by way of example how it is 
possible to adapt the structure of the top longeron 28 and the related 
structures in the aft transition zone close to the tail 6 (see FIG. 1) in 
which the dimensions of the fuselage decrease and in which a bilobed 
fuselage structure changes to a monolobe structure having an oval 
cross-section. 
If the fuselage structure is considered with respect to the section 8, said 
structure comprises at the forward end of the aircraft a succession of 
ring frames of bilobed shape having ends 8a and, at the tail end, a 
succession of ring frames of oval shape having ends 8b. The dimensions of 
these oval frames in a horizontal transverse direction are reduced with 
respect to those of the bilobed frames. 
At the level of the connection 8 of the ring frames of both types, a small 
dimensional discontinuity is formed as shown in FIG. 14, in which the 
double line 65 represents the limit of pressurization within the fuselage. 
The small portion of double line located at the level of 8 in FIG. 14 
virtually corresponds to a small portion of pressurization bulkhead 74a 
which is visible in FIG. 11 and is braced by enlarged portions 33a of the 
ribbed beam 33. In FIG. 12 are also shown stringers 64 which are close to 
the longeron 28 and located in the line of extension of the stringers 53. 
FIGS. 15 to 18C show how it is possible to construct a dome-shaped 
pressurization bulkhead 67 which is intended to be mounted within a 
fuselage in accordance with the invention, for example at the tail end, in 
order to constitute the bulkhead 15 of FIG. 1. 
The domical bulkhead 67 is constituted by an overlapping assembly of 
several panels 68 such as the panels 68a, 68b, . . . 68k. The panels 68 
are attached to each other by means of a curved longitudinal member 72 
(FIG. 18A) and to curved stiffeners 73 (FIG. 18). 
The bulkhead 67 is attached to a reinforcement (FIG. 15) composed of a 
peripheral frame 76 of oval shape and upright members 77. 
This pressurization bulkhead structure has very high strength and can have 
any contour according to requirements in order to be adapted to the 
fuselage. It is thus possible to equip the forward bulkhead 14 and aft 
bulkhead 15 of FIG. 1. 
In the fuselage according to the invention, arrangements are made to ensure 
that the central portion of the wing structure 9, which passes through the 
bilobed fuselage and forms a central wing box within the lower internal 
space of said fuselage, constitutes the limit of a cellular fuel tank 80 
which will thus have an increased capacity. As shown in detail in FIG. 19, 
a structure of this type comprises a series of transverse lattice girders 
81 applied on bracing struts 83 which are integrated in the structure of 
the central section 4 of the bilobed fuselage 1 and, more precisely, form 
part of the bilobed ring frames 8 defined earlier. 
Through the cutaway portion of the top wall of the wing unit 9, there can 
also be seen the main beam 85 of the wing unit 9 which passes through the 
reservoir 80 in the central portion of this latter. 
The top wall of the wing unit 9 supports spacer members 82 on which the 
cabin floor (not shown in FIG. 19) can be fixed. 
By reason of the increased width of the inserted central portion of the 
wing unit 9, there is obtained a fuel tank of very large capacity which 
represents, according to the value of E, 1.5 to 1.9 times the volume of 
the corresponding tank of a monolobe aircraft having a diameter D. This 
considerably increases the radius of action of the bilobed-fuselage 
aircraft in accordance with the invention. 
Furthermore, it is thus possible to increase the efficiency of movements of 
fuel between two tanks of the aircraft, these movements being intended to 
modify the position of the center of gravity of the aircraft during a 
flight with a view to reducing drag and achieving a saving of fuel. 
One of the main advantages offered by a bilobed fuselage in accordance with 
the invention with respect to a known bilobed fuselage of the prior art 
having a central partition-wall is to permit considerably easier movement 
of passengers from one side of the aircraft to the other during flight as 
well as at the time of boarding the aircraft and debarkation. Moreover, 
this offers possibilities of evacuation under certain critical situations 
in which evacuation of the aircraft can take place only on one side. 
According to another aspect of the invention, the considerations which now 
follow have been put to profitable use. 
The possibility of moving transversely within a bilobed fuselage provided 
with connecting posts 31 in the longitudinal mid-plane depends primarily 
on the following parameters: 
density of the posts or in other words pitch J of the posts, measured for 
example with respect to the pitch of the bilobed ring frames which form 
part of the transverse structure of the fuselage; 
pitch P of the rows of seats, this pitch being primarily dependent on the 
category of seats (economy class, business class, first class), the pitch 
P being different from the pitch J as a general rule. 
It is readily apparent that the diameter of the posts also has to be taken 
into account but is subject to only slight variation and can be considered 
as a constant. A diameter of the order of 5 centimeters can be indicated 
as an order of magnitude. 
The ease with which passengers can move in the transverse direction within 
the bilobed fuselage may be appreciated by defining a fraction L 
representing the mean obstruction percentage, that is to say the mean 
percentage of transverse passageway lost with respect to the passageway 
which would be available if the posts did not exist. L is a linear 
function of the pitch J of the posts and of the pitch P of the rows of 
seats. 
The diagram of FIG. 20 has been plotted in a system of coordinates in which 
the values of k1 J+k2 J are shown in abscissae and the values of L are 
shown in ordinates (k1 and k2 are numerical constants). 
The diagram comprises several families of curves: 
parallel dashed straight lines corresponding to constant values of the mean 
obstruction coefficient L, ranging from L=0.20 to L=0.65; 
parallel straight lines J1, J2, J3, J4 which are slightly inclined with 
respect to the preceding and correspond to constant values of the pitch J 
of the posts, with: 
EQU J1=1 .times. pitch of bilobed ring frames 
EQU J2=2 .times. J1 
EQU J3=3 .times. J1 
EQU J4=4 .times. J1; 
curves P1, P2, P3, P4 corresponding to constant values of the pitch P of 
the rows of seats, with: 
______________________________________ 
P1 = 28 ins., 
or 71 cms 
P2 = 32 ins., 
or 81 cms (pitch of economy class) 
P3 = 36 ins., 
or 91 cms (pitch of business class) 
P4 = 40 ins., 
or 101 cms (pitch of first class). 
______________________________________ 
This diagram shows that: 
the mean obstruction percentage depends fairly little on the categories of 
seats (P1 to P4) since the straight lines L and J are nearly parallel; 
as soon as the pitch J of the posts attains twice the pitch of the bilobed 
ring frames (straight line J2), the obstruction coefficient is then only 
1/3, or in other words that 2/3 of the maximum space for transverse 
passenger movement remain free. 
The invention is directed in particular to an arrangement of connecting 
posts and their position location with respect to the rows of seats, said 
posts being organized so as to ensure that, for transverse passenger 
movements, the loss of transverse passageway is less than one-half of the 
transverse passageway which would be available if the posts did not exist. 
In FIG. 20, this would correspond to the zone of the diagram located 
beneath the dashed straight line L=0.50. 
However, the obstruction coefficients drawn from the diagram considered 
above give only an indication which is valid in the general case but does 
not apply to certain specific combinations. 
For example, if we have: 
pitch of the rows of seats, P=101 cms (which corresponds to curve P4); 
pitch of the bilobed ring frames=50.5 cms; 
pitch of the posts, J=2 .times. pitch of the ring frames (which corresponds 
to the straight line J2); 
The result is: J=101 cms=P. 
In other words, if one adopts a suitable starting point, that is to say in 
transverse alignment with the seatbacks, the posts can be placed in such a 
manner as to ensure that there is never any obstruction. 
But an exceptional situation of this kind is not wholly applicable within 
an aircraft which has several categories of seats and consequently several 
distinct pitches for the rows of seats. 
Thus, if the aircraft is also equipped with a category of seats having a 
pitch P3, the pitch of the posts J2 being equal to that of the seats P4 
will necessarily be different from that of the seats P3, assuming that the 
pitch of the ring frames is constant in the first place. In this case, the 
intersection S of J2 and of P3 provides the obstruction coefficient of P3 
which is within the range of 0.30 to 0.35 as can be seen from the graph of 
FIG. 20. 
By way of example, in the arrangement of FIG. 24, the posts 31a, 31b, 31c, 
31d do not cause any obstruction whereas the post 31e does cause an 
obstruction. 
In any case, the obstruction coefficient of the fuselage in accordance with 
the invention is distinctly lower than the obstruction coefficients of 
known bilobed fuselages, especially those of the fuselages of the two 
patents cited earlier: 
U.S. Pat. No. 3,405,893 (Flamand), U.S. Pat. No. 4,674,712 (Whitener) in 
which, if reference is made to FIGS. 1 and 9 of the patent to Flamand or 
to FIG. 5 of the patent to Whitener, it is apparent that the obstruction 
coefficient is approximately 0.80. 
The two fuselages just mentioned have another unfavorable characteristic, 
namely that the space available for transverse passenger movement is 
concentrated at two or three locations whereas, in the fuselage of the 
invention, the available space is distributed along the entire 
longitudinal mid-plane. 
This last-mentioned arrangement is highly advantageous, not only for the 
comfort of passengers but also and above all in certain critical 
situations of evacuation on only one side of the aircraft. In such 
situations, any limitation in the number of zones of passage is liable to 
result in movements of panic which may in turn increase the time required 
for evacuation. 
It may be added that current airworthiness regulations in regard to 
emergency evacuation of passengers, notably in the United States and in 
Europe, require in particular: 
that aircraft must offer the possibility of discharging all the passengers 
through the doors located on one of the two sides of the aircraft, despite 
the fact that doors have to be installed on both sides; 
that all the passengers must be placed, with respect to the exit doors, 
under conditions of proximity which are suited to the emergency 
situations. 
It may be considered in regard to airworthiness certification that the 
requirements mentioned above are fully met by a bilobed-fuselage aircraft 
in accordance with the invention but that they are not fulfilled by the 
prior-art aircraft mentioned in the foregoing and that their certification 
could therefore not be obtained. 
The bilobed fuselage in accordance with the invention offers various 
possibilities of seating arrangement comprising, as shown in FIGS. 21 to 
24, in the case of each transverse row, five groups of seats separated by 
four longitudinal aisles N1, N2, N3, N4. 
Three zones of seats (see FIG. 24) designated by the references 91, 92, 93 
correspond respectively to the first class, to the business class and to 
the economy class. 
The transverse arrangement provided for the first class zone is shown in 
FIG. 21. Ten seats 86 are placed abreast and distributed in five groups of 
two seats designated from left to right by the letters a, b, c, d, e 
respectively. In the central zone, the two seats 86c which are symmetrical 
with respect to the median plane are slightly spaced apart in order that a 
connecting post 31 may be passed between them if necessary. 
Within each lobe, the central portion comprises one pair of seats, 86b-86b 
or 86d-86d. 
FIG. 22 shows the arrangement of the business class zone. Twelve seats 87 
are placed abreast and distributed in five groups also designated by the 
letters a, b, c, d, e. In contrast to the first class, the central group 
has four seats 87c arranged in two pairs which are slightly separated in 
order to allow for the post 31. 
FIG. 23 shows the arrangement of the economy class. Fourteen seats 88 are 
placed abreast and distributed in five groups a, b, c, d, e. In contrast 
to the business class, the central group 88b, 88d of each lobe comprises 
three juxtaposed seats 88b or 88d instead of two juxtaposed seats 87b or 
87d. The central region 88c always has four seats. 
In FIG. 25, there is shown one mode of construction of the top longeron 28 
(see FIGS. 5 and 6) comprising a device for drainage of the water which is 
liable to collect beneath the fairing 21 within a bottom portion of the 
top region of the shell, in the vicinity of the line of junction 18 of the 
two lobes. 
The need for this drainage also arises from the fact that the space located 
between the fairing 21 and the shell 17 is not pressurized. Although it 
does not communicate directly with the exterior, infiltrations or 
condensation may take place within this space. 
Two orifices 94 are formed on each side of the longeron 28 through a 
portion of the fuselage shell 17 which is close to the median plane and 
the reinforcing gusset 50. Nipples 97 are mounted in leak-tight manner 
within the orifices 94 and are forcibly fitted within discharge pipes 101. 
The device is completed by filling and sealing material 103 which is placed 
on each side of the web 33, said material being given profiles 106 which 
are adapted to produce good evacuation of water and in particular to 
ensure that the orifices 94 are located at the bottom points. The pipes 
101 are connected to a discharge pump (not shown in the figure). 
FIG. 26 is a diagram showing how the load carried by the aircraft is 
transmitted to the wing 9. 
The central longitudinal girder 32 carries the load of the cabin floor 23 
(weight of passengers, of seats, of galleys, and so on) and of the lower 
floor 26 (weight of freight, of baggage, and so on). The girder 32 is in 
turn supported by cross-beams 111 (see FIG. 28) which transfer the load to 
the fuselage shell 17 and from this latter to the wings by means of the 
bracing struts 83 (see FIG. 19). 
The ease with which it is possible to load and unload the double hold 25 is 
clearly demonstrated in FIG. 27 which shows diagrammatically displacement 
of a container 108 within the hold of the aircraft. The container is 
introduced in the first portion of the hold through the opening 20 after 
opening the lateral door 20a of the aircraft. Said container can then be 
displaced in the forward direction (arrow K1) or towards the rear (arrow 
K2) in this first portion of the hold. It can readily be passed into the 
second portion of the hold through the opening 34 (arrow K3) since, at the 
level of this opening, the hold floor 26 is a continuous floor (as shown 
in FIG. 7A). 
The cross-beam 111 is a lattice beam which is attached to the girder 32 by 
means of intermediate members 112, 113 and bolts 114. In the vicinity of 
the external wall, the beam 111 is bolted to reinforcing ring frames 116 
which are in turn attached to the shell 17 by means of bolts. 
It is thus apparent that the bilobed double-shell fuselage in accordance 
with the invention can be constructed in an economical and reliable manner 
by making the best possible use of pre-existing monolobe shell structures. 
Furthermore, a bilobed fuselage of this type offers many outstanding 
advantages both at the time of manufacture and during use. 
Thus the large hold volume provided by the bilobed fuselage in accordance 
with the invention permits the partial use of this latter for functions 
other than freight transport. For example, provision can be made for the 
installation of toilets, galleys or kitchens and even cabins, lounges or 
bars. Access to these specialized spaces from the cabin floor can be 
provided by one or more interior stairways or even by one or a number of 
elevators. 
As will be readily apparent, the invention is not limited to the examples 
of construction which have just been described and a large number of 
modifications may accordingly be contemplated without thereby departing 
from the scope or the spirit of the invention.