Hollow structural element

A hollow structural element has a hollow member having a circumferential wall and a side wall which closes one of the axial ends of the circumferential wall, a cover member arranged to close the other end of the circumferential wall of the hollow member and connecting elements for connecting the structural element with other structural elements. The connecting elements include an undercut projection provided in the cover member and arranged for inserting into an undercut groove of another structural element, and an undercut lateral slot provided in the side wall of the hollow member and arranged for engaging with an undercut projection of a further structural element. The lateral slot has a first enlarged portion through which the projection of the further structural element can pass, and a second reduced portion extending from the first portion toward the axis of the circumferential wall and dimensioned so that the projection of the further structural element engages in the reduced portion.

BACKGROUND OF THE INVENTION 
The present invention relates to a hollow structural element, and more 
particularly to such a hollow structural element which is closed by a 
collar member and provided on its side walls with connecting means. 
Hollow structural elements of this known type are provided with connecting 
means for connecting the same with other structural elements. Inasmuch as 
such elements do not provide for sufficiently strong connection, they are 
of little use for constructing stable and bend-resistant fuselage of 
flying models or the like. Hollow structural elements have been further 
proposed which have a square or rectangular cross-section and are provided 
with undercut connecting elements wherein undercut grooves formed in a 
circumferential wall of the hollow structural element cuts out both side 
walls limiting the circumferential wall. When fuselages of flying models 
and the like are assembled, the remained cutouts of the outer face of the 
circumferential wall considerably deteriorate the appearance of the 
structural element. 
SUMMARY OF THE INVENTION 
Accordingly, it is an object of the present invention to provide a hollow 
structural element which avoids the disadvantages of the prior art. 
More particularly, it is an object of the present invention to provide a 
hollow structural element which forms a strong connection for assembling, 
for example, fuselages of flying models wherein the visible outer surfaces 
are not undesirably affected by connecting means. 
In keeping with these objects, and with others which will become apparent 
hereinafter, one feature of the present invention resides, briefly stated, 
in a hollow structural element which has a hollow member having a 
circumferential wall and a side wall closing one of the ends of the 
circumferential wall, a cover member arranged to close the other end of 
the circumferential wall of the cover member, and means for connecting the 
hollow structural element with other structural elements, wherein the 
connecting means includes an undercut projection provided in the cover 
member and arranged for inserting into an undercut groove of another 
structural element, and an undercut lateral slot provided in the side wall 
of the hollow member and aranged for interacting with an undercut 
projection of a further structural element. The undercut lateral slot has 
a first enlarged portion located adjacent to the circumferential wall and 
dimensioned so that the projection of the further structural element 
passes through the enlarged portion, and a second reduced portion which 
extends from the first portion toward the axis and is dimensioned so that 
the projection of the further structural element engages in the reduced 
portion. 
In order to assemble two hollow structural elements with one another they 
are so displaced relative to one another that the undercut projection of 
one of the elements is inserted into the first enlarged portion of lateral 
slot of the other structural element. Then, both structural elements are 
so displaced relative to one another that their outer surfaces of the 
circumferential walls are in alignment with one another by means of 
displacement of the undercut projection in the undercut groove. The 
high-strength connection is attained so that the assembling of stable and 
bend-resistant fuselages for flying models becomes possible. Since the 
connecting means is not visible on the outer face of the structural 
element the thus assembled fuselage remains smooth so that especially 
original appearance can be attained by impressing on the fuselage a row of 
windows, symbols, signs and the like. 
The circumferential wall of the hollow member and the side walls thereof 
provided with the lateral slot can be manufactured by an injection molding 
process. After this, the cover member provided with connecting projection 
and manufactured by a separate injection molding process is inserted 
through an open end of the cap-shaped hollow member and connected thereto 
by means of glueing or ultrasonic welding. 
The projection of the cover member may be formed as an assembling pin. The 
hollow member may be cup-shaped and the circumferential wall thereof may 
be cylindrical. The second portion of the lateral slot of the side wall of 
the hollow member may extend outwardly beyond the axis so as to permit 
relative displacement of the hollow connecting elements to be connected 
with one another. 
Another feature of the present invention is that the second reduced portion 
of the lateral slot of the side wall extends outwardly beyond the axis of 
the hollow member by a distance which is substantially equal to half of a 
transverse dimension of the projection of the cover member. The thus 
dimensionally limited second portion of the lateral slot forms an abutment 
for the projection of the cover member so that when the projection of the 
cover member engages in the second portion of the lateral slot, the outer 
faces of the circumferential walls of two hollow structural elements 
connected with one another are in alignment with each other. In such a 
construction the fuselage portions can be exactly adjusted relative to one 
another in a simple manner, that is conventionally especially difficult 
for small children as a result of different sliding friction and static 
friction. 
In accordance with still another feature of the present invention, the 
cover member has a sleeve-shaped extension portion having an elongated 
inner hole into which the projection or the assembling pin is pressed. On 
the grounds of wear, the projection and the structural element are 
manufactured of differing materials. In order to obtain a firm pressure 
connection for the connecting projection, the connecting projection is 
received in a portion of the cover which is formed as the above-mentioned 
sleeve-shaped extension in view of the material economy considerations. 
The cylindrical elongated portion of the connecting projection is provided 
with ribs which serve for roughening the same. 
In accordance with a further feature of the present invention, two 
elongated slots are provided in the circumferential wall of the hollow 
member and located opposite to one another. The elongated slots extend 
from the open end of the hollow member which is closed by the cover 
member. This makes possible to fix additional elements on the 
circumferential wall of the structural element, for example, wings of the 
flying model. Since the elongated slots are open at the end of the hollow 
member, the above-mentioned elements, such as wings, must be inserted into 
these slots prior to connecting further structural elements to the hollow 
member. 
In accordance with a still further feature of the present invention, the 
elongated slots provided in the circumferential wall of the hollow member 
have end sections which are open at the end of the circumferential wall 
and have an enlarged cross-section. This facilitates the insertion of the 
structural elements such as wings into the elongated slots. 
In accordance with an additional feature of the present invention the 
portion of the circumferential wall which is provided with the elongated 
slot is flat. In such a construction a flat improved abutment of the 
structural elements, such as wings, against the outer surface of the 
circumferential wall is provided. 
In accordance with a still additional feature of the present invention the 
cover member is provided with two such undercut projections, and the side 
wall of the hollow member is provided with two such undercut slots. The 
distance between the undercut projections as well as the distance between 
the undercut slots is twice as much as the distance between the outer 
surface of the circumferential wall and the adjacent one of the undercut 
projection or the undercut slot, respectively. Due to this arrangement of 
the connecting means in pairs, the structural elements connected with one 
another are completely secured against relative rotation. Moreover, this 
gives a possibility to connect the structural elements in an offset 
position relative to one another so as to form substantially flat models, 
for example, floating bodies. 
In order to improve the carrying capacity of such floating bodies, it is 
possible, in accordance with yet another feature of the present invention, 
to provide a plate-like coating element which has undercut projections 
engaging in the undercut slots of the structural elements. 
The novel features which are considered as characteristic for the invention 
are set forth in particular in the appended claims. The invention itself, 
however, both as to its construction and its method of operation, together 
with additional objects and advantages thereof, would be best understood 
from the following description of specific embodiments when read in 
connection with the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
A hollow structural element in accordance with the present invention has a 
hollow member which is identified by reference numeral 1. The hollow 
member 1 is cup-shaped and has a cylindrical circumferential wall 1'. A 
side wall 2 forming a bottom of the hollow member 1 is provided at one end 
of the latter. The side wall 2 has a lateral slot. This slot includes an 
undercut portion 3 and a portion 6. The portion 6 of the slot is located 
adjacent to the circumferential wall 1' of the hollow member and has a 
greater cross-section, whereas the undercut portion 3 of the lateral slot 
extends from the portion 6 toward the axis of the circumferential wall and 
has a smaller cross-section. 
A cover member 4 with an assembling pin 5 is provided. The assembling pin 
has a head section 5', and a portion 6 of the lateral slot of the hollow 
member 1 has a transverse dimension substantially corresponding to that of 
the head section 5' of the pin 5. The portion 3 of the lateral slot of the 
hollow member 1 extends from portion 6 thereof outwardly beyond the axis 
of the hollow member 1. It extends beyond this axis by a distance which is 
substantially equal to half of the transverse dimension of the pin 5. A 
limiting edge 7 of the lateral slot forms an abutment face for a neck 
portion 8 of the pin 5 so that when the pin 5 of one of the structural 
elements is engaged with the portion 3 of the lateral slot of another 
structural element, the outer surfaces of the circumferential walls 1 
thereof are in alignment with one another. 
The cover 4 which carries the assembling pin 5 seals the hollow member 1. 
The cover 4 has an outer sleeve-shaped portion 9 which extends from a side 
flange 10. When the cover member 4 closes an open end of the hollow member 
1 the outer sleeve-shaped portion 9 abuts inwardly against the inner 
surface of the hollow member 1. More particularly, the flange 10 closes 
the open end of the hollow member 1. The fixation of the cover member 4 
can be performed by glueing or ultrasonic welding. 
In order to improve the holding capacity of the assembling pin, the cover 
member 4 has an inner sleeve-shaped portion 9' which extends from the 
flange 10 and has an inner hole 12. The pin 5 has a section 11 which is 
provided with ribs 12 and pressed into the inner hole 12 of the elongated 
sleeve-shaped portion 9' of the cover member 4. 
In order to attach additional structural elements to the circumferential 
wall 1' of the hollow member, for instance for assembling flying models, 
the circumferential wall 1' has two elongated slots extending from an open 
end of the circumferential wall 1', which end is closed by the cover 
member 4. Each of the elongated slots of the circumferential wall 1' has 
an undercut portion 13. A further structural element 14 is attached to the 
circumferential wall 1' by insertion of the former through the open end of 
the elongated slot before closing the open end by the cover member 4. In 
order to facilitate the insertion of the element 14 into the elongated 
slot, each of the elongated slots has a portion 15 located adjacent the 
open end of the circumferential wall 1' and having an increased 
cross-section. In order to improve the connection of the element 14 to the 
circumferential wall 1', the latter has a flat portion 16 in the region of 
the elongated slot. Thus, the element 14 abuts against the circumferential 
wall 1' with a flat surface contact. 
It is to be understood that the interior space of the hollow member 1 is so 
dimensioned as to accommodate battery cells, electric motors or the like, 
for instance for assembling motor-driven flying models. Further, the 
hollow member 1 can be so manufactured that the interior space thereof can 
accommodate required wiring for the models. 
The hollow member 1 which is shown in FIGS. 3 and 4 have two lateral slots 
provided in the side wall 2. Each of the lateral slots has an undercut 
portion 3 of a smaller cross-section and a portion 6 of a greater 
cross-section, similarly to the lateral slot shown in FIGS. 1 and 2. The 
portion 3 extends from the portion 6 outwardly beyond the axis of the 
hollow member 1 by a distance substantially corresponding to half of the 
outer dimension of the neck section 8 of the assembling pin 5. The 
limiting edge 7 of the lateral slot forms an abutment surface for the neck 
8 of the assembling pin 6 so that when the structural elements are 
connected with one another their outer surfaces of the circumferential 
walls 1' are in alignment with one another. The cover member 4 has two 
undercut assembling pins 5. The fixation of the cover member 4 which 
carries the pins 5 can be performed by glueing or ultrasonic welding. 
The distance a between the connecting members, that is between the lateral 
slots or between the pins 5 is twice as much as the distance b between the 
outer surface of the circumferential wall 1' and an adjacent one of the 
lateral slots or projections, respectively. With such a construction, the 
structural elements may be offset relative to and connected with one 
another so as to form a model with a flat surface, for instance, a 
floating body. In order to improve the carrying capacity of the 
thus-formed floating body, the lateral slots of the structural elements 
which remain open after assembling of the structural elements with one 
another, are water-tightly closed by a plate-like element 20. The 
plate-like element 20 has undercut connecting projections 21 which engage 
in the undercut lateral flats of the structural element 1. 
It will be understood that each of the elements described above, or two or 
more together, may also find a useful application in other types of 
constructions differing from the types described above. 
While the invention has been illustrated and described as embodied in a 
hollow structural element it is not intended to be limited to the details 
shown, since various modifications and structural changes may be made 
without departing in any way from the spirit of the present invention. 
Without further analysis, the foregoing will so fully reveal the gist of 
the present invention that others can, by applying current knowledge, 
readily adapt it for various applications without omitting features that, 
from the standpoint of prior art, fairly constitute essential 
characteristics of the generic or specific aspects of this invention.