Article citation information:
Kužma, L., Kužma, D., Miženková, Ž. Helicopter UAV fuselage bulkhead
modelling. Scientific Journal of Silesian
University of Technology. Series Transport. 2016, 93, 69-78. ISSN: 0209-3324. DOI: https://doi.org/10.20858/sjsutst.2016.93.8.
Ladislav KUŽMA[1], Dalibor KUŽMA[2], Žaneta MIŽENKOVÁ[3]
HELICOPTER UAV FUSELAGE
BULKHEAD MODELLING
Summary.
This article deals with the design of helicopter UAV airframe components. There
is a description of UAV airframe design modelling involving already existing
components in three-dimensional (3D) form. The modelling methodology focuses in
detail on proposed bulkheads by using “top-down-bottom-up” methodology. In conclusion,
there is a brief description of all proposed bulkheads and an outline of
possible solutions for how to design airframe stringers.
Keywords: helicopter; modelling; airframe
components design
1. INTRODUCTION
The article deals with the description of the
design for UAV bulkheads based on helicopters. Due to the large scope of the
work performed during the modelling phase, we were forced to limit the
description of the design to one of the four bulkheads used to determine the
shape of the skin, as well as serve to increase the rigidity of the structure
in resisting aerodynamic forces, which are acting on the UAV fuselage during
flight. The reason why we have chosen to describe only one structural part is
that other bulkheads were designed and digitized in a similar manner. For
designing, we used the modelling and sheet metal environments of the Siemens
PLM software NX 9.0 [3].
2. CREATING A MODEL OF THE EXISTING
PARTS
We began the whole process of designing a new
UAV design and construction by thoroughly studying the literature of helicopter
structures and new trends in the field of UAS systems, and by conducting a
dimensional analysis of already existing parts of the research device OKO2. The
current real shape of the device can be seen in Figure 1.
Fig.
1. Current shape of UAV OKO2
From the measured dimensions, we created a
virtual appearance using the tools in the modelling environment of the two
plates, which form the main element supporting the whole structure, tanks
and spacing webs, which define the distance between the plates. All the
parts we created were saved in a separate *.prt file. After that we linked up
all the parts into the “assembly”, where each defined component was positioned
relative to other components and gripped by a constraint tool. When using this
type of sequence modelling, we are talking about top-down-bottom-up methodology,
which means that, at first, we created the individual parts of a structure
and then created the whole assembly. The final assembly of the base structure
is shown in Figure 2.
Fig.
2. Basic design of the measured assembly
After completing the previous assembly, we went
to the upturned methodology, which is so-called “top-down” stage, where we
gradually created more structural parts of the UAV for the assembly. Rather
than use reverse engineering, we next created our own new designs for the
parts. This method is much more advantageous when creating completely new
construction parts without templates. This is because all parts of the assembly
are always visible and can be seen in real time, such that we can review
whether the units are compatible with each other in size and design. Both
methodologies are explained in the general procedures chart shown in Figure 3
[1][2].
Fig.
3. General creation methodologies of structural units
3. CREATING OF BULKHEAD
As
mentioned above, the purpose of the proposed construction of bulkheads in UAVs
is to determine and maintain the shape of the fuselage structure. The detailed
description of the one bulkhead is sufficiently applicable to the creation of
the other three, because they are structurally similar. The creation of the
final dam was divided into two phases. Initially, we created a solid body,
whose outer edge reference line we received and used as the local circumference
of the fuselage, as well as in the creation of fuselage skin. We conducted
after the completion of creating the skin in the second creation phase of the
final bulkhead. The reason for making a division to create two phases was
the need to make the rim face compatible with the bulkhead-shaped skin, so that
all sides lay flat on their covers to enable the bulkhead to link to the skin.
This type of reverse modelling was initially done using the metal sheet
environments in the Shape Studio, after which we created solid bodies from the
sheet surfaces [2].
4. CREATING A SOLID BODY FOR THE BULKHEAD
WITHOUT ADAPTING THE RIM
In
the first step of creating a bulkhead, we added a new part to the assembly
using “Add → Create New” in the assembly environment. Adding a new part
required a definition of the plane in which the new part was to be located
after its creation. We added a new plane using the Datum Plane tool, then
determined its distance from the reference plane by choosing the “At Distance”
drop-down dialogue box in the Datum Plane.
In the
Extrude tool dialogue box, we defined the plane on which we created the first
shape of a bulkhead. We created this plane before we clicked on the Extrude
tool in the same manner as when establishing the plane in the assembly
environment. After defining the plane, the program automatically transferred us
to the two-dimensional Sketch modelling environment. In this environment, we
set up a perimeter and an internal shape of the bulkhead profile. The exact
shape of the proposed bulkhead is shown in Figure 4
Fig.
4. Contours of the bulkhead’s final shape
Parts
of the rib profile and their meanings:
1. The
upper internal space - The largest open space is used for locating the engine,
main UAV systems and supporting systems. This can be found near to the second
and third bulkheads. The size is diminished around the first and fourth
bulkheads.
2. Tank
extension and air intake - To achieve the smallest possible size and weight of the UAV,
the frame was designed with the smallest possible width. In order to include
fuel tanks, an extension had to be created in the centre of the side wall since
our UAV power unit is an internal combustion engine. It was necessary to ensure
an adequate airflow supply for its operation and cooling. The figure shows the
shape of the extension designed to fulfil this function. The extension is used
for the second and third bulkheads. The second bulkhead in the area of
extension also includes a hole for decongestion and air supply.
3. Attachment
to the top plate of the main frame - This attachment is the main bearing
element of the bulkhead and the skin; therefore, it has a wider shape.
4. Attachment
to the bottom plate of the main frame - This attachment prevents the bulkhead
twisting and bending, thereby maintaining the shape of a frame.
5. Lower
interior space - This space is used to accommodate the attachment of the
landing gear, transmissions and optional additional equipment of the UAV
(infrared camera, scanner etc.). This space is much smaller than the upper
internal space.
After
completing the required drawing shapes, we completed the creation of the layout
using the Finish Sketch command. The software automatically redirected us to
the modelling environment, with the Extrude dialogue box remaining opened. In
this dialogue box, we set the required pull-out parameters to make the 3D
element.
From
the solid body created in the previous step, we created the shell using the
Shell tool. We defined the wall thickness to be 1 mm. By simply clicking the
tool icon, the software automatically requested us to clarify the surfaces,
which had evolved into a recess of the shell.
The
Shell tool did not remove the inner rim of the bulkhead, which was helpful
because of the need to create a small bent section along the inner edge. Such
upturned edges are used to increase the bulkhead rigidity in the transverse
direction. We also wanted to keep the bulkhead tabs attached to the lower
and upper plates. We used Extrude to reduce the height of the inner rim in
order to reduce the weight. In the Sketch environment, we drew a profile using
Extrude in order to remove excess surfaces from the rim. Our suggested new
profile had to be larger than the inner rim, but at the same time smaller than
the outside one.
We
confirmed the use of the Extrude tool by clicking “OK” and continued modelling.
Another action involved “rounding off” the outer edges of the bulkhead. For
this purpose, the Edge Blend tool was used. By clicking on this tool, we
opened up a dialogue box, which requested us to mark the edges that we had
planned to round off. We rounded off all the outer edges of the bulkhead
profile with a radius of 2 mm.
5. CREATION OF THE FINAL BULKHEAD BODY WITH A
TIGHT-FITTING RIM TO THE SKIN
This
part of the bulkhead modifications came after creating a skin, which is the
subject of the work reported in another article. In this case, we could create
a projection of the skin shape within the desired distance of the future
bulkhead rim. The spacing was determined according to the created plane at a
distance of 15 mm.
The
projection of profile curves of the skin was conducted using the Intersection
Curve tool during work on the skin. This was subsequently projected on the work
component of bulkhead. Being able to see the projection of the skin curves and
interact with it in another component of the bulkhead is an advantage of the
top-down modelling methodology. To create projections of these curves, we
first created a new working plane using the Datum Plane tool at a distance 17
mm from the plane, which determined the rear wall of the bulkhead in the
previous procedure. The difference of 2 mm was established by using the far
side of the radius, related to the formation of the skin. On this plane,
we created a separate Sketch environment, using the Project Curve tool to
project the shape curves created by the skin. These projection curves can be
seen in Figure 5, as highlighted by the red line.
The
second curve needed to create the surface of the bulkhead was created, namely,
the curve forming the vertex of the angle between the rim and the back
surface of the bulkhead. We first set up a working plane at a distance of
2 mm from the initial plane of the bulkhead part. The reason for the difference
of 2 mm is the same as for the first curve. Sliding the edge of the bulkhead by
2 mm achieves the difference between the radius of the bulkhead and the
skin.
We created
another Sketch environment pertaining to a new plane. In this environment, we
used the Show tool to observe a solid body of the bulkhead created by the
previous procedure. According to the edge of this body, we created a projection
of the corner curves’ shape. The top side of the curve was removed from
the distribution curves due to the need for at least two parts. This step was
essential for the creation of the surface of the bulkhead rim. Without this
split, the program was unable to assign directions and the beginning of the
surface creation by the curves.
Fig.
5. Projected curves’ intersection of the skin and the Datum Plane
We have
made progress towards the creation of interconnection lines between the front
and rear rim lines of the bulkhead. These connections are required for creating
sheet metal where these lines define the start and end sections, which need to
be created. These interconnection lines were created using the Line tool
without the Sketch environment. During the creation of interconnection lines,
we captured the start and end points of the segment directly in relation to the
front and back rim lines. These connections had to be define by clicking
“Point” in the dialogue box of the Line tool. By doing so, we were able to
open a new window, in which we were able to choose the end point in a list of
attachment options. This meant that we created the start/end point at the very
end of the curve, which was located where we wanted to catch the generated
line. Thus, we created a line on both sides. If the line had not exactly fit
the curve, it would have been impossible to create a surface using the
interconnection line segments.
The
last part was created in the same way the second part of the back rim line by
joining the rim and backs. This curve was created in the same way as in the
first part, using the Quick Trim difference usage tool in a new Sketch
environment and deleting all lines except the top one (see the inset in Fig.
6).
Fig.
6. Creation of the top curve
After this
step, we were able to continue creating new sheet metal to cover the bulkhead.
For this purpose, we used the tools in the sheet metal environment. The first
was the Bounded Plane tool, which fills the space between two predefined
curves. We chose it because of the formation of the dorsal surface of the
new bulkhead. First, we marked the outer curve. The program automatically
filled the entire interior space. Then it was necessary to select the second
inner curve, which was created on the surface cut out of the desired shape.
In the
next step, we created the rim surface using the Through Curve Mesh tool. After
clicking on the tool, a dialogue box automatically opened with instructions for
using this tool. As first, we marked the primary curve in the Primary Curves
input field. At least two curves had to be present. We distinguished every mark
of the curves out of the plane by clicking “Add New Set”. After determining the
primary curves, we continued marking the cross curves, which were bound
together at the beginning and during the end surface’s creation. These curves
had to be marked in the Cross Curves input field in a similar way as in the previous
case. We had to separate the individual curves by clicking “Add New Set”. The sheet
metal surface was automatically created after marking the order of the second
(final) curve. We created the second part of the bulkhead edge using the same
procedure. The usage of the Through Curve Mesh tool is shown in
Figure 7.
Fig.
7. Creating the bulkhead rim
After
creating the surface, it was necessary to define the thickness of the sheet
metal to forge it into a solid body. The easiest method of creating a solid
body from sheet metal was to use the Thicken tool. This tool can create the
desired thickness of the body by a simple click. As first, we created a solid
body from the surface of the bulkhead’s back part, where we defined a thickness
of 3 mm, followed by the surface of the bulkhead rim, where we defined a thickness
of 1 mm. A thickness of 3 mm in the case of the back part is justified by the
need to create an end radius on the edges due to the increased rigidity of the
structure.
The
intersection of two materials in the connecting part between the rim and the
back was solved using the Chamfer tool. This tool allows chamfering bodies
around the desired curve.
After
the edges were finalized, they were ready to be knitted together into one solid
body. We continued with this operation using the Unite tool. We clicked
successively on other body parts, which were automatically merged.
By merging
other body parts, we continued with the creation of soft edges around the body
of the bulkhead. The Edge Blending tool was used to create the radius, which
involved a similar process as that in the first phase of the bulkhead
creation. We also created a bended edge at the free end of the bulkhead’s back
using the Shell tool. To remove the top edge of the back, we had to turn
off the display by right-clicking on the rim and selecting “Hide” in the
shortcut menu. Then we removed the desired edge by simply clicking on the Shell
tool. After this operation, we observed the rim by clicking on the Show tool
and choosing the desired rim.
The next
task was to create the turning points of the flanges for mounting the bulkhead
to the base plate of the assembly. We created the turning points by drawing the
desired profile in a Sketch environment of the Extrude tool. Then we defined
the setup in the Extrude dialogue box in order to subtract the solid body. We
expanded our subtraction as shown in Figure 8 and accepted the changes by
clicking “OK”.
Mounting
flanges were created using the Extrude tool, with which we defined the sketch
plane. As a reference, we selected the surface on the mounting flanges.
By
clicking on the surface, we were automatically redirected to the Sketch
environment. There, we simply projected rectangular shapes of future mounting
flanges using the Project Curve tool. Then we returned to the 3D environment,
in which we defined the distance from the flange (see Fig. 9).
Fig.
8. Creating the turning points of the mounting flanges
Fig.
9. Creating the mounting flanges and holes
In Figure
9, it is also possible to see the outlines of the holes for attaching the
bulkhead to the base plate. These holes were created using the Extrude tool
with a similar procedure to that for the mounting flanges. The only difference
was in removing the volume option in the Extrude tool settings. Before
cutting holes, we used the Unite tool to connect the newly created bodies of
the flange to another body.
6. CONCLUSION
The
final version of the bulkhead spacing in the UAV structure is shown in Figure
10. Bulkhead numbering starts with number 1, located on the left side of the
image, with numbers 2, 3 and 4 towards the right.
Fig.
10. Final model of the UAV structure
Bulkhead 1
is attached to the base plate designed to form the nose cone of the model with
the possibility of sensor or camera positioning. Bulkheads 2 and 3 are
structurally the most complex, with their shape designed according to the needs
of the UAV airframe systems’ location. The tail section and transmission of the
UAV should be attached to bulkhead 4, which is the most rigid compared with the
others in terms of effectively transferring loads from the tail section to the
frame. The system of stringers will be the subject of further research. It is
assumed that two stringers along the fuselage will be located on top of the airframe
and one will be located on the bottom.
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Received 09.10.2016;
accepted in revised form 25.10.2016
Scientific Journal of Silesian University of
Technology. Series Transport is licensed under a Creative Commons Attribution
4.0 International License
[1] Faculty of Aeronautics, Technical
University of Košice, Rampová 7 Street, 041 21 Košice, Slovakia.
Email: ladislav.kuzma@student.tuke.sk.
[2] Faculty of Aeronautics, Technical
University of Košice, Rampová 7 Street, 041 21 Košice, Slovakia.
Email: dalibor.kuzma@tuke.sk.
[3] Faculty of Aeronautics, Technical
University of Košice, Rampová 7 Street, 041 21 Košice, Slovakia.
Email: zaneta.mizenkova@tuke.sk.