Ground effect vehicle structure

Air cushion vehicle structure comprises a platform with a grid frame formed of longitudinal girders crossing crosspieces, and an upstanding caisson or compartment formed of transverse frames connected by continuous systems of sheets. The lower segment of each caisson transverse frame is constituted by a portion of the upper beam of a crosspiece of the platform, and the lower longitudinal edges of the caisson are integrated with the upper beams of two girders. The crosspieces and some girders are lattice girders, but the others are ladder girders. Upper and lower beams of the girders and the crosspieces are connected by normal tubes welded to their feet, the oblique tubes of the lattices also being welded to the feet. The structure is especially appropriate for medium tonnage ACV.

FIELD OF THE INVENTION 
The present invention relates to hovering structures expecially intended 
for transportation of rolling loads, such as ground effect vehicles of 
average tonnage, capable of transporting land vehicles including heavy 
vehicles, as in the case of conventional transshipment craft. 
BACKGROUND AND SUMMARY 
The structure of a ground effect or air cushion (ACV) vehicle identifies 
the metallic assembly which on the one hand supports the superstructures, 
motor elements and payload and which on the other hand is supported at 
least in flight by the air cushion/cushions. In average tonnage ACV's of 
the type mentioned above, the said structure generally comprises an 
essentially rectangular platform supporting one or more longitudinal 
caissons or compartments, often symmetrical with reference to the long 
axis of the apparatus, inside which caissons it may be convenient to seat 
the heavy vehicles being transported. The platform is constituted for 
example by a rectangular reticulated grid formed of a plurality of 
longitudinal beams or girders which cross a plurality of transverse beams 
or cross girders supporting the floors. A certain volume of the said 
reticulated grid, generally at the periphery in order not to interfere 
with the air supply ducts for the cushion/cushions, is designed to ensure 
to buoyancy of the vehicle. The caissons are made of stiffened sheets 
assembled along four longitudinal ribs, and they bear on a plurality of 
transverse frames. 
In the case of a single longitudinal caisson on the axis of the apparatus, 
such a structure is analogous to that of an airplane, the caisson 
resembling the fuselage, and the platform being analogous to wings running 
all along the fuselage. In longitudinal flexion the general stresses are 
accepted to major part by the central caisson. In transverse flexion they 
are accepted essentially by the platform, and in torsion, caisson and 
platform in varying degrees contribute to the total strength. On the other 
hand, local stresses on the floors due to the rolling loads that are 
transported are considerable. Consequently a structure of this kind 
presents two problems, one relating to connection of the caisson and 
platform, the other concerning the frame system of the platform. 
So far as the connection of the caisson and the platform are concerned, two 
extreme solutions can first be imagined. The first consists in providing a 
central caisson that rises over the whole height of the structure. The 
modulus of inertia of longitudinal flexion is good, but the platform is 
actually split into two semi-platforms, the transverse stresses causing 
the connections of each half platform and the caisson to work 
independently, which makes it necessary to reinforce these connections and 
complicate them. Moreover, a floor that is sufficiently stong to receive 
the heavy vehicles must be provided horizontally in the caisson, which 
increases the weight of the structure. The second solution consists in 
having the caisson rest on the platform. The platform remains integral and 
without any break in continuity, which is favorable insofar as propagation 
of transverse and diagonal stresses is concerned. The lower part of the 
caisson can serve directly as support framing or armor for the heavy 
vehicle floor. However, the modulus of inertia of the caisson is clearly 
less good, the reduction of the value of the modulus has to be compensated 
by a reinforcement of the caisson, which substantially adds to the weight 
of the structure. 
An object of the present convention consists in provision of a structure 
wherein the caisson and the platform are coupled so as to present the 
advantage of the two above solutions without their drawbacks, which allows 
production of an overall structure that is lighter. 
As far as the frame system of the platform is concerned, what must be 
provided essentially is an arrangement of contiguous squares, to get a 
relatively undeformable platform, both for its production and servicing, 
and for hoisting. 
An object of the present invention consists specifically in providing a 
relatively light platform while ensuring a certain indeformability. 
According to a characteristic of the present invention, a ground effect 
vehicle structure is provided comprising a caisson and a platform, in 
which the caisson has its two lower longitudinal edges rigidly connected 
respectively to two principal or main girders in a grid of the platform, 
the crosswise portions between the two said main girders and slightly to 
either side thereof being reinforced. 
According to another characteristic of the invention, certain girders of 
the platform, including the main girders, are lattice girders, while the 
others are ladder-structure girders, including the girder or girders 
between the two principal girders, the distribution of lattice girders and 
ladder girders being symmetrical with reference to the long axis of the 
vehicle. 
Other characteristics of the present invention will become clear upon 
perusal of the following description of an example of embodiment, said 
description being presented with reference to the attached drawings.

DESCRIPTION OF PREFERRED EMBODIMENT(S) 
The ground effect vehicle of FIG. 1 comprises a platform 1 associated with 
a longitudinal caisson 2. Platform 1, generally rectangular in form, is 
constituted by a rectangular reticulated grid comprising crosspieces 3 and 
girders such as 4 and 5, girders 4 being reinforced in a lattice, whereas 
girders 5 are not reinforced and have a ladder structure. Crosspieces 3 
are all lattice-reinforced. On either side of platform 1, beyond girders 
4, there are buoyancy caissons intended to ensure flotation of the ACV 
when the lift fans are not operating, i.e., when the air cushions are not 
inflated. These float caissons are constituted by solid surfaces of 
stiffened sheet, represented by shaded areas in FIG. 1, bearing on a 
framework with a base of transverse frames. Girders 7 which are vertically 
aligned with the sides of caisson 2 are of the same type as 4, whereas the 
median girder 8, in the plane of symmetry of the ACV, is of the same type 
as 5. The ACV is supplemented by a covering frame 6 mounted on arcuate 
members joined to platform 1 and caisson 2, an upper bridge floor 9, a 
lower bridge floor 10 intended to receive light vehicles, and a floor 11 
intended to support heavy vehicles seated inside caisson 2. 
The section of FIG. 2 illustrates a known connection of caisson 2 and the 
platform, where caisson 2 rises over the whole height of the ACV from base 
12. Thus, semi-platforms 1a and 1b are not directly interconnected and 
work independently of each other, which require reinforcement and 
complication of their connections with caisson 2. Moreover, floor 11 
nonetheless has to be reinforced to be able to bear the load of the heavy 
vehicles. 
The section of FIG. 3 shows another known connection of caisson and 
platform, where caisson 2 rests on platform 1 in a continuous arrangement. 
The lesser height of caisson 2 involves a modulus of inertia in 
longitudinal flexion that is clearly less good, and the caisson has to be 
reinforced, which increases its weight. 
The section of FIG. 4 shows how the ACV of the invention has its platform 
connected to the caisson. Girders 7, disposed perpendicularly aligned with 
reference to the side walls of caisson 2, each comprise relatively heavy 
lower beams 13. Similarly, central girder 8 has a relatively heavy lower 
beam 14. Thus, by these beams, girders 7 and 8 contribute substantially to 
a raising of the modulus of inertia of longitudinal flexion of the ACV. On 
the other hand, if we consider crosspieces 3, these have beams with webs 
that are deeper under caisson 2, floor 1 being mounted on this part of the 
crosspieces, with intermediate frames between two crosspieces to reduce 
the bearing of the floor. Thus crosspieces 3 are not interrupted in their 
passage below caisson 2, which allows better propagation of transverse and 
diagonal stresses in platform 1. 
FIG. 5 schematically shows a reinforced girder 4 comprising a lower beam 
15, an upper beam 16, uprights 17 and oblique tubes 18. Beams 15, of 
straight I or T section, is interrupted at the loci of the transverse 
elements. Selection of the straight I or T section is a function of the 
probability of warping of the beam web according to the calculated 
stresses to which it may be subjected. Uprights 17 are made as tubes. Each 
upright 17 is common to a girder 4 and a crosspiece 3, the tubular 
structure allowing simple connection with the beams of the girder and the 
crosspiece as shown with reference to FIG. 8. Beam 16 has a straight T 
section, the foot of the T being at the bottom. It is interrupted at each 
crossing, while the upper edge of the web supports floor 10. The 
connections between tubes 17, 18 and the beams will be described in more 
detail with reference to FIG. 8. 
FIG. 6 schematically shows a non-reinforced girder 5 comprising a lower 
beam 19, analogous to 15, an upper beam 20, analogous to 16, and uprights 
17. It is noted that to a certain degree beam 19 can undergo longitudinal 
shifts with reference to beam 20 whereas in 4, tubes 18 prevent any 
relative motion of this kind between 15 and 16. It is to be observed that 
in FIG. 5, tubes 18 are all parallel although they may have their slants 
alternated. 
FIG. 7 shows the section midships in an ACV with the structure of the 
invention, whereof the plane of longitudinal symmetry is shown at 21. More 
especially, FIG. 7 shows half of a crosspiece formed of a lattice girder 
comprising an upper T beam 22 whose web is continuous from one edge to the 
other of the ACV between the float caissons, a lower I beam 23, also 
uninterrupted, vertical uprights 17, likewise common to the girders, and 
oblique tubes 24. At the crossing with girder 7 (FIG. 1), upright 25 is 
slightly shorter than 17. 
Central caisson 2 is constituted by an assembly of stiffened sheets 26, 
stuctured longitudinally by a T beam 27, under the roof, and a horizontal 
flanged stringer 28, as well as transversely by T beams 29 and 30. 
FIG. 7 also shows the structure of the lateral buoyancy caissons which are 
constituted by sealed stiffened sheets 31, 32 and 33, and floor 10 (FIG. 
1). They are transversely structured by girder ring 34 that extends beams 
22 and 23. 
FIG. 7 also shows arcuate members 35 of frame 6, which are constituted by 
ribs. The base of each arcuate member has a segment 36 that is wider and 
that is connected at its base to a beam 22 (as extended by ring girder 
34). The top of each arcuate member is connected to an end of a beam 30. 
The lower part of frame 6 can be made of sheet that covers the arcuate 
members. The top part, above floor 9, for example, may be plastic. 
Beams support floor 9, defining the upper deck. They comprise a lower beam 
37 and an upper beam 38. Floor 9 is mounted on beams 38 in a conventional 
way. The connection between the beams of floor 9 and arcuate members 35 on 
the one hand and beams 29 on the other may comprise parts that are 
slightly movable so that transverse flexions of platform 1, entraining 
arcuate members 35, via 36, will not cause excessive deformation of the 
said arcuate members, the beams of floor 9 and/or uprights 29. 
Of course, the structure is reinforced by conventional stiffening devices 
such as 40 between beams 29, or 41 between beams 22. 
FIG. 8 shows node a of FIG. 7. Shown in perspective, we find there beam 22 
of crosspiece 3, upright 29 of caisson 2, reinforced web 42 of 22, and 
tubular upright 25. It is to be noted in the rest of the description that 
unless otherwise indicated the beam web will have the same numerical 
reference as the beam, while its foot will be indicated by a different 
numerical reference. Beam 22 crosses upper beam 16 of girder 7. At the 
crossing, web 42 and foot 43 of 22 are continuous, longitudinal beam 16 
consequently being interrupted on either side of 22. The webs of 22 and 16 
are of the same height, and their feet are in the same plane. The sheets 
of floor 11 are welded onto the upper edges of webs 42 and 16. Above floor 
11, sheet system 26 of the longitudinal wall of caisson 2 is 
perpendicularly aligned with web 16 while web 29 is perpendicularly 
aligned with 42. Stiffening elements 40 connect uprights 29 to each other. 
Tubes 25, 24 and 18 are directly welded onto feet 43 and 44. 
FIG. 9 is a lateral view showing how normal tube 25 and an oblique tube 
such as 24 or 18 are welded to a foot schematically shown as 45. The end 
of tube 25 is bevelled at 46 and the weld is made between the bevel and 
the foot. Similarly, the end of the tube 18 is bevelled in an irregular 
way around the ellipse of the tube bearing, better to distribute the 
stresses.