Strut structure for suspending loads under aircraft

This strut structure for suspending loads under aircraft comprises essentially a hollow beam comprising at least one element of compound material consisting mainly of mineral fibres embedded in a binder forming setting resin such as expoxide resin, this element extending throughout the length of the beam, and metal members joined to the compound material element or elements for rigidly connecting the beam to the aircraft and to the means from which the load is suspended under the aircraft.

BACKGROUND OF THE INVENTION 
This invention relates in general to strut structures of the type intended 
for suspending loads from aircraft. 
It is known that compound materials consisting of mineral fibres such as 
glass fibres, boron fibres and more particularly carbon fibres embedded in 
a resin binder, notably epoxide resin, may attain a high degree of 
mechanical strength and more particularly a high rigidity whereby 
structures having specific strength and rigidity values comparing with 
those of metal structures while having a considerably reduced weight can 
be obtained. 
SUMMARY OF THE INVENTION 
It is the primary object of this invention to provide a structure for 
beams, struts, poles or masts of the type designed for carrying or 
suspending loads under aircraft, which takes advantage of the specific 
properties of the above-mentioned compound materials. In the following 
disclosure, the term "compound material" will therefore refer, as in the 
preceding paragraph, to a material consisting essentially of high-strength 
fibres embedded in a setting resin binder such as epoxide resin. 
The structure according to the present invention consists essentially of a 
hollow beam comprising at least one element of compound material extending 
throughout the beam length and metal elements joined to said compound 
material elements and interconnecting on the one hand said beam and the 
aircraft structure, and on the other hand the beam and the load to be 
carried under the aircraft. 
Preferably, the beam configuration is generally simple, for example of 
parallelipipedic shape, the elements of compound material being cemented 
or bonded to the metal elements along flat surfaces parallel to the beam 
axis. 
According to a complementary feature characterizing this invention, the 
beam constituting the structure for supporting a load under aircraft is so 
designed that stresses are transmitted from the load to the aircraft and 
vice versa through the medium of metal members reinforced by elements made 
of compound material which partake in the general strength of the 
assembly, and more particularly in its torsional strength and rigidity. 
Still more particularly, the beam composition is such that the loads are 
retained along two different paths, whereby the resistance to stress 
exerted in case of failure of one path is maintained according to the 
so-called "fail-safe" safety principle; in this case, the stress will be 
directed for example on the one hand through the metal elements and on the 
other hand through the compound material elements, and the various 
component elements will be assembled by using a suitable bonding 
procedure. The component elements of this hyperstatic structure are 
calculated as a function of the various forces, of both aerodynamic and 
inertia types, applied to the load carried under the aircraft.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring first to FIG. 1, the reference numeral 1 therein designates the 
core of a structure for supporting loads under aircraft. This core 1 is a 
parallelipipedic beam having a box-shaped cross section, made of compound 
material such as carbon-fibre reinforced epoxide resin. This core 1 is 
encompassed by the metal member 2 interconnecting the load and the 
aircraft, which comprises a tapered top projecting plug 3 of which the 
details are well-known in the art and therefore not shown or described 
herein. The device actually intended for suspending or supporting the load 
under aircraft (not shown) is adapted to engage the gap left between pairs 
of metal straps 4, 5 straddling the core 1 on either side of plug 3 and 
formed with holes 6 for releasably coupling same to the load suspension or 
carrier device. The particularly simple shape of the core 1 of compound 
material greatly simplifies its manufacture, and the shrink-on or clamping 
metal members 2, 4 and 5 tend to reinforce the holding of said beam 
without impairing its strength, the various elements being assembled by 
bonding or cementing. Full advantage of the properties of the compound 
material constituting the core of the structure illustrated is taken, 
notably in the matter of strength in relation to weight. The simplified 
design of the assembly is such that its optimal dimensions can easily be 
calculated. 
The parallelipipedic box-sectioned core 1 of compound material may comprise 
for instance an assembly of two U-sectioned elements 7 and 8 (FIG. 2) 
having their bases opposed to each other; these elements 7, 8 are 
assembled by bonding. Alternatively, this core 1 may consist of a single 
square-sectioned tubular element (FIG. 3) which, though structurally 
simpler, requires a considerably more complicated equipment for its 
manufacture. 
In FIG. 4 the reference numeral 11 designates a hollow longitudinal metal 
member supporting the top plug 13 for coupling same to the aircraft, and 
reference numerals 14, 15 designate a pair of opposite in-turned lower 
lips for assembling this longitudinal member with metal strap 16, the 
latter for fixing the carrier device (not shown) through the medium of a 
longitudinal I-sectional coupling member 17 of which the central web is 
positioned in the slot formed between said lips 14 and 15 and also between 
similar in-turned lips of strap 16. A relatively shallow longidudinal 
U-sectioned member 18 of compound material has a central through-hole 
formed therein for receiving the tapered top plug 13, and another 
U-sectioned longitudinal member 19 of compound material is disposed 
astride said metal strap 16; finally, an omega-sectioned longitudinal 
member 20 also of compound material encloses the hollow metal member 11. 
Side plates 21, 22 of compound material enclose stiffening elements 23, 24 
lining the side arms of the omega-sectioned member 20, and other 
stiffening elements 25, 26 line the side arms of the U-sectioned 
longitudinal member 19 of compound material. Preferably, these stiffening 
elements consist of panels having a suitable texture, for example a 
honeycomb texture as shown in FIG. 5 or a sine wave or corrugated texture 
as shown in FIG. 6 in order to obtain a high degree of rigidity 
notwithstanding a substantial weight reduction. 
It is clear that the structure illustrated in FIG. 4 makes full use of the 
so-called "fail safe" technique, for the efforts are transmitted between 
the load carrying device secured by means of the pairs of aligned holes 6 
and the means interconnecting the structure and the aircraft; namely the 
tapered top plug 23, by means of the metal chain comprising the members 
16, 17 and 11, on the one hand, and by means of the chain of compound 
material (fibres plus epoxide resin) comprising the member 19, 20, 18 and 
side plates 21, 22, all bonded to one another, on the other hand. 
FIG. 7 illustrates a modified structure based on the same principles but 
simplified by reducing the number of component elements, for example when 
this simplification is permitted by a reduction in the weight of the load 
to be suspended under the aircraft. The reference numeral 31 designates a 
metal hollow longitudinal member similar to element 11 of the preceding 
form of embodiment, which comprises an integral tapered top plug 13 and is 
covered by a U-sectioned longitudinal member 32 of compound material, 
through which said top plug 13 protrudes as shown. Another U-sectioned 
longitudinal member 33 also of compound material constitutes a strap for 
receiving the load carrying device (not shown). The inner faces of the 
side arms of this member 33 are lined with metal reinforcing plates 34, 35 
through which pairs of holes 36, 37 for fixing the load carrier device and 
other pairs of holes 38, 39 for assembling said plates 34 and 35 to the 
compound material member 33, are provided. Side plates 40, 41 similar to 
those 21 and 22 of FIG. 4, are bonded to the lateral faces of members 32, 
33 for constituting a compact, unitary structure. 
In this exemplary structure the efforts applied to the load are transmitted 
through the carrier or suspension device to the structure at the level of 
fixing holes 36 and 37 via metal members 34 and 35 and compound material 
members 33, 40 and 41. These various component elements are safely 
assembled on the one hand by bonding or cementing and on the other hand as 
a consequence of the expansion of the compound material constituting 
element 33 into the holes 38 and 39 formed for this purpose in metal 
members 34 and 35. Thus, the stress path may be followed on the one hand 
along the side plates 40,41 and through the compound material member 32 
receiving the tapered top plug 13 therethrough, and on the other hand 
through the compound material member 33 and the metal member 31 assembled 
by bonding. 
In all the cases described hereinabove, the substantial reduction in the 
volume of steel parts, as a consequence of the use of lighter yet 
extremely strong compound material, is attended by considerable reduction 
in the weight of the assembly. 
It will be readily understood by those conversant with the art that the 
specific forms of embodiment disclosed herein with reference to the 
attached drawing should not be construed as limiting the scope of the 
invention, since various modifications and changes may be brought thereto 
without departing from the basic principles of the invention set forth in 
the appended claims. Thus, the structure of this invention is applicable 
to devices intended for carrying several separate loads, though the above 
description refers for the sake of clarity and simplification to the 
fixing of a single carrier device.