Optimizationof fuselage shape for better pressurization and drag reduction

IJRET: International Journal of Research in Engineering and Technology eISSN: 2319-1163 | pISSN: 2321-7308
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Volume: 05 Issue: 08 | Aug-2016, Available @ http://ijret.esatjournals.org 37
OPTIMIZATIONOF FUSELAGE SHAPE FOR BETTER
PRESSURIZATION AND DRAG REDUCTION
Manish Kumar1, Geetesh Waghela2, Nakash Nazeer3
1
School of Aeronautical Engineering, Hindustan University, Chennai, Tamilnadu, India
2
3
Abstract
The fuselage of any aircraft is essentially to accommodate the payload. It is normally not as streamlined as the wing. Cabin
pressurization has been a major concern in the manufacturing of aircrafts. Generally, a cylindrical shape is preferred from a
pressurization point of view as it has a higher strength and weighs less too. On the other hand, a sphere is considered as the best
pressure vessel among all the shapes, but, sphere being a bluff body is not suitable for carrying payloads. On this note, a cylinder
is considered to be better than a sphere to carry the payload and mainly to achieve a streamlined flow. In this paper, the shape
chosen is a combination of the sphere and the cylinder to achieve optimum results for pressurization as well as a better
streamlined flow. Our prime aim is to convert this bluff body into something more efficient and useful, rather than only for
carrying the payload. We have focused basically on two details viz. 1) Better Pressurization and 2) to assist in minimizing the
drag, thereby increasing the overall lift of the aircraft and hence increasing the fuel efficiency. The proposed fuselage structure
was designed in CATIA V5 software and structural analyses were done in Auto-Desk Multi-Physics software. As a result, a better
structural load capacity was found. A load of 10 N/mm2 was applied on both the bodies under consideration (cylinder and
ellipse) having the same material, surface area, volume and weight. For the proposed elliptical design, 78% reduction in the
minimum stress value and 10% reduction in the maximum stress value were noticed.
Keywords: Fuselage, Lifting Fuselage, Drag Reduction, Pressurization, Hoop Stress, Multi body design, Toroidal
Shells, Multi-cylinder, Channel Propeller Configuration, Carbon Fiber, Graphite Fiber, Stabilization and
Carbonization.
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1. INTRODUCTION
The fuselage is the center body section to which other
aircraft components are joined. Especially in flight, the
fuselage experiences high bending moments and torsional
loads which it has to withstand. These forces are usually due
to the rudder movement. Therefore, the fuselage should be
structurally sound while maintaining a low weight.
Fig 1: Aircraft Parts
Transport and civil aircrafts have a similar fuselage
structure. Overall, the fuselage can be considered as a
cylindrical section with either ends tapered. These end
sections constitute the nose and tail of the aircraft
Fig 2: Parts of Fuselage
The general design used in the present day aircraft consists
of a semi-monocoque structure. This type of construction

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has been considered due its stability and light weight. It
consists of a skin that takes up all the loads supported with
stringers for stability enhancement. Perpendicular support
members are also present which keep the fuselage in shape
when flight loads are acting on the fuselage. These
perpendicular supports are called frames or bulkheads
depending on whether they are open or closed, respectively.
A uniform cylindrical structure is structurally sound, but as
the requirements of discontinuities like doors and windows
present themselves the structure of the fuselage is
compromised. The area around these cutouts must be
reinforced or else the cylinder wouldn’t be strong enough.
The fuselage is hollow in order to reduce weight and
accommodate more payloads. The shape of an aircraft’s
fuselage is dependent on the purpose of the aircraft. This
holds true for other parts too. For example, in order to
experience less drag, a fighter jet uses a streamlined and
slender fuselage for its missions. On the other hand, a
transport or civil aircraft doesn’t have to focus on speed and
hence has a wide body fuselage. These type of aircrafts have
to carry heavy payloads that constitute mostly of cargo and
passengers. The forward tapered section of the fuselage is
called the nose where the cockpit is located. The rear end is
referred to as the tail used to carry payloads. The fuel for the
mission is typically stored in compartments present in the
wing sections.
Fig 3: Cross sectional View
The configuration is different in case of a fighter jet. The
pilot is seated in a small compartment present on top of the
fuselage. The engines are usually at the tail section where
the fuel is also stored. The wings carry weapons and
ammunition.
The aircraft weight distributed all along the body of an
aircraft. Weight plays a major role in flights. The cargo and
passengers are the main load constituting members in a civil
aircraft. This load has to be monitored before every flight. In
flight, the aircraft rotates around the center of gravity. The
rotation is primarily caused due to the movement of control
surfaces which induces torque. Therefore those designing a
fuselage such factors should be noted so that the structure is
capable of withstanding such dynamic forces. Pressurization
of the fuselage has been a major concern in aircraft
manufacturing. A cylindrical shape is generally preferred
from pressurization point of view and this shape has high
strength and low weight when compared to other shapes.
Spheres are not preferred even though they are considered to
be the best pressure vessels. The issue lies in spheres being
bluff bodies and impractical in accommodating passengers
and payload. Cylinder is considered to be better than sphere
to carry the payload and to achieve streamlined flow.
In this paper, the shape chosen is a combination of the
sphere and the cylinder (i.e. Multi-bubble Design and Oval
Shape) to achieve optimum results for pressurization and a
better streamlined flow over the flow also structural analysis
has been done using Autodesk Multi-Physics software.
1.1 Multi Bubble Design
What is MBD?
In structure point of view it is an efficient fuselage design
with respect to balancing the pressurization loads. It is a
systematic arrangement of cylinders which provide good
pressurization. The outer contour of the MBD is an ellipse, a
shape that helps in providing a better streamlined flow.
Few details about the MBD are discussed below:
Three different membrane elements are composed in multi-
bubble design:
1) The cylinder which is a constituent of multi-cylinder.
2) The sections that close the multi-bubble, called multi-
sphere and
3) The toroidal shells that are connected into a multi-torus.
Fig 4: MBD Design

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The cylinders are dimensionally arranged in such a way that
the horizontal component of the membrane load of one
cylinder is balanced by the horizontal component of the
membrane load of the neighboring cylinder. In addition,
with different diameters can be connected to control the
geometry of the frontal area and bubbles of fuselage.
Fig 5: CAD Model
2. ANALYTICALANALYSIS OF THE
FUSELAGE SHAPES
According to Laplace’s law “larger the wall tension required
to withstand a given internal fluid pressure for given larger
the vessel radius”. Hence, A spherical vessel will have half
the wall tension of a cylindrical vessel for a given vessel
radius and internal pressure.
Fig 6: Tension for cylindrical vessel
If the upward part of the fluid pressure remains the same,
then the wall tension must remain the same at the downward
component. But for the less curvature the total tension must
be greater in order to get that same downward component of
tension. For a load hanging on cable be in equilibrium, we
can explore the effects of having a smaller angle for the
supporting cable tension.
Fig 7: Cable Tension Illustration
In the aircraft, pressurization has been a cause for concern.
The load acting on the fuselage is hoop stress. This stress
can be roughly calculated using the equation for hoop stress
in an infinitely long cylinder subjected to an internal
pressure load.
Stress = P.r/t
P = Internal Pressure
r = cylinder radius
t = cylinder wall thickness
For our model, the calculations are as follows
P = 10N/mm2 R = 300mm T = 10mm.
Hoops stress = 300N/mm2
Stress analysis carried out on a cylindrical fuselage is shown
in fig9. The stress analysis is selected because it is a best
way to denote the pressure distribution on the surface.
Minimum stress value = 123.08 N/mm2
Maximum stress value = 306.25 N/mm2
2.1 Structural Analysis of the Fuselage Shapes
The shape chosen is a combination of the sphere and the
cylinder to achieve optimum results for pressurization and a
better streamlined flow.
Fig 8: Elliptical Fuselage
Hence an elliptical fuselage (combination of sphere and
cylinder) was created having the same dimensions as the
cylinder and was analyzed for stress, and the results are as
shown in fig10.

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Fig 9: Cylindrical Shape Analysis Report
A load of 10 N/mm2 was applied on both the bodies under
consideration (cylinder and ellipse) having the same
material, volume, area and weight.
Fig 10: Elliptical Analysis Report
We found minimum stress value for elliptical Shape to be 26
N/mm2 and for cylindrical shape the maximum stress value
to be277 N/mm2.
Fig 11: Stress value
2.2 Effect of Shape
A load of 10 N/mm2 was applied on both the bodies under
consideration (cylinder and ellipse) having the same
material, volume, area and weight.
For the Elliptical design, 78% reduction in the minimum
stress value and 10% reduction in the maximumstress value
were noticed.
Fig 12: Cross section of CAD Model
2.3 CFD Analysis
In order to see the effect of Drag on the chosen shape, it is
necessary to do a CFD analysis. Steps followed starts from
Designing to Analyzing. Commercial Code ANSYs Fluent
17.0 was used to analyze.
An unstructured mesh with 1.2 million elements was chosen.
Boundary conditions were taken as follows:
 Velocity Inlet: 35 m/s inlet velocity
 Pressure Outlet: atmospheric pressure
Grid independent study was performed to select the mesh
count. Convergence criteria of 1e-06 were selected since it is
a flow analysis without any heat generation. Pressure based
solver was chosen and analysis was run.
Results obtained are as follows:
Fig 13: Velocity Contour over the cross section
Figure13 tells us the velocity distribution over the cross
section of the aircraft. There is not much fluctuations in the
flow at zero degrees.
Moving on to the pressure distribution over the cross section
of the aircraft, 0 degree does not see a major change in
pressure distribution over the surface which results in less
flow separation.

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Fig 14: Pressure Contour over cross section
However, examining drag values at 0 and 5 degrees flow
around the aircraft gives us interesting results. The body is
kept stationary and flow is moving in the analysis.
The Aerodynamic Efficiency is then calculated on finding
the CL/CD values for 0 degree and 5 degree flow.
The value of CL comes to be 0.484 and CD comes up to be
0.007. The Aerodynamic efficiency comes to approximately
65. By reducing the drag value considerably which shows a
good improvement in the design. However, there is not
much increase in the CL value.
Fig: 15 Aerodynamic Efficiency
3. CONCLUSION
This paper studied the pressurization of a new fuselage
design concept which integrates two shapes viz. a sphere
and a cylinder. The resultant shape similar to an ellipse not
only proved to provide better fuselage pressurization but
also guaranteed a streamlined flow over its surface. The
resultant effect is a drag minimizing fuselage which caters to
better pressurization and minimal drag giving an
aerodynamic efficiency of 65 at 5 degree angle of attack.
Hoop Stress analysis shows the capacity to carry more load
for elliptical shape. Reduction in minimum and maximum
stress developing on the surface decreases by a significant
amount of 88% and 10% respectively. Smooth aerodynamic
shape results in less interference with the flow resulting in
lesser drag and higher aerodynamic efficiency.
Future work is to be done to find the effect of this shape on
more factors like having a wide range of velocities and angle
of attacks.
ACKNOWLEDGEMENT
The authors would like to acknowledge the technical help
and guidance of Prof. Dr. T.S. Krishnamurthy, Mr. Nikhil
John and Mr. AravindSasikumar who have supported and
helped us in our work.
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BIOGRAPHIES
Mr. Manish Kumar is currently working
as an Assistant Professor in Priyadarshini
College of Engineering Nagpur. He
completed Master of Engineering (M.E) in
Space Engineering & Rocketry from Birla
Institute of Technology Mesra and B.E. in
Aeronautical Engineering from Hindustan
University, Chennai.
E-id:manisrob@gmail.com
Mr. GeeteshWaghela is currently working
as an Application Engineer, in ARK Info
Solution. He completed Master of
Technology (M.Tech) in Computational
Fluid Dynamics from University of
Petroleum and Energy Studies, Dehradoon
and B.E. in Aeronautical Engineering from Hindustan
E-id:geeteshwaghela1234@gmail.com
Mr. NakashNazeer is currently pursuing
Master of Science (MSc.) in Aerospace
Engineering (structures and materials) from
Nanyang Technological University,
Singapore. He completed B.E. in
Aeronautical Engineering from Hindustan
E-id: nakash1422@yahoo.com

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