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Stress Analysis on Composite Strut Landing Gear during Rough Landing
Article · January 2016
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Transactions on Innovations in Science & Technology
Volume.2, Issue.1, 2016, pp.46-51
www.transistonline.com
Stress Analysis on Composite Strut Landing Gear during Rough
Landing
Sujith Stephen, Nithin S Nair, J. V. Muruga Lal Jeyan, Akhila Rupesh
Department of Aeronautical Engineering, Rajadhani Institute of Engineering and Technology, Attingal – 695102, India.
*Corresponding author email: sujithstephen007@gmail.com, Tel.: +91 8129140660
ABSTRACT
Landing gear is the undercarriage of an aircraft and is typically designed to support the vehicle only at post-flight. A strut
is a structural component designed to resist longitudinal compression. Struts provide outwards-facing support in their
lengthwise direction, which can be used to keep two other components separate, performing the opposite function of a
tie. The need for lightweight, high performance flying machine has today shifted the emphasis from the use of
conventional advanced metallic materials to that of composites.
At critical situations for both civil and military aircraft, they are needed to be landed on rough landing surfaces which
may cause structural damage to the landing strut. For that specified reason, the landing strut made to be very strong, the
main parameter that here to be considered is a strength to weight ratio, the strength of the strut should be very high at the
same time the weight should be reduced. For that here we have introduced the strut which is made of composite material
which satisfies our requirements. The composite material that we have selected here for our fabrication of strut is glass
fiber and carbon fabric of alternate layers and also the structural analysis of landing strut is carried out in ANSYS for
various impacting conditions with respect to aircraft weight.
Keywords – Composite Materials, Landing Gear Design, Rough Landing.
1. INTRODUCTION landing gear design tends to have several interferences
with the aircraft structural design. In this report, the
The main landing gear is one of the most critical structural design aspects of the landing gear are not
components of an aircraft, capable of reaching the addressed; but, those design parameters which strongly
largest local loads on the airplane. It is a primary source impact the aircraft configuration design and aircraft
of shock attenuation at landing. It controls the rate of aerodynamics will be discussed. In addition, some
compression extension and prevents damage to the aspects of landing gear such shock absorber, retraction
vehicle by controlling load application rates and peak mechanism and brakes are assumed as non-aeronautical
values. issues and may be determined by a mechanical
engineer. Thus, those pure mechanical parameters will
The landing gear is the structure that supports an
not be considered in this chapter either. In general, the
aircraft and allows it to move across the ground or
followings are the landing gear parameters which are to
water. For this report the type of landing gear to be
be determined in this chapter:
analyzed is the tricycle gear, this simply means that the
gear is arranged in a tricycle fashion. The tricycle 1. Type (e.g. nose gear (tricycle), tail gear, and bicycle)
arrangement has one gear strut in front, called the nose
wheel, and two or more main gear struts slightly aft the 2. Fixed (faired, or un-faired), or retractable, partially
center of gravity. The advantage of the tricycle gear is retractable
that it is nearly impossible to make the plane “nose
over”. The tricycle gear also allows for a level cabin 3. Height
area making the loading and unloading of the aircraft
4. Wheelbase
much easier than that of an inclined plane.
5. Wheel track
Aircraft’s major component that is needed to be
designed is landing gear (undercarriage). The landing 6. The distance between main gear and aircraft CG
gear is the structure that supports an aircraft on the
ground and allows it to taxi, take-off, and land. In fact, 7. Strut diameter 8. Tire sizing (diameter, width)
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Transactions on Innovations in Science & Technology, 2017, 2 (1), 46-51
9. Landing gear compartment if retracted aircraft category, this can range from 3 to 7% of the
aircraft total mass.
In the case of a vertical take-off and landing aircraft
such as a helicopter, wheels may be replaced with skids. The main functions of the landing gear are as follows:
Figure 9.1 illustrates landing gear primary parameters.
The descriptions of primary parameters are as follows. 1. Energy absorption at landing;
Landing gear height is the distance between the lowest
2. Braking;
point of the landing gear (i.e. bottom of the tire) and the
attachment point to the aircraft. Since landing gear may 3. Taxi control.
be attached to the fuselage or to the wing; the term
height has a different meaning. Furthermore, the 2.1 Extraction and retraction:
landing gear height is a function of the shock absorber
and the landing gear deflection. The height is usually A retractable landing gear is installed whenever a drag
measured when the aircraft is on the ground; it has improvement is worthy. This means in all aircraft with
maximum take-off weight, and landing gear has the exception of agricultural and small general aviation
maximum deflection (i.e. lowest height). airplanes, where the installation of a movable landing
gear would increase the costs beyond the requirements
Assembly modeling is the process of creating designs of the aircraft category.
that consist of two or more components assembled
together at their respective work positions. The Landing gear extraction is a primary operation and
components are brought together and assembled in the always its actuation has high redundancy. There are
Assembly Design environment by applying suitable different solutions for the mechanism to obtain suitable
parametric assembly constraints to them. The assembly landing gear movement. Some are schematically shown
constraints allow restricting the degrees of freedom of in fig. Many solutions are based on the four-bar linkage
the components at their respective work positions. (cases A to C), where one bar is represented by the
aircraft frame. In other solutions (case D) one bar end
2. METHODOLOGY can slide along a slot. More complex kinematics
includes three-dimensional motion and the deflection of
In our model, the system includes the following parts. the bogie that for the main landing gear of large
We have optimized many things which include weight airplanes is made of double tandem wheels.
reduction, high strength to weight ratio, material life
etc. The landing gear system includes
➢ Strut
➢ Shock absorber
➢ Extraction/retraction mechanism
➢ Wheel
➢ Tyre
➢ Electro actuator
➢ Pneumatic actuator
The shock absorber and extraction/retraction
mechanism may not be present in small airplanes.
The landing gear is the interface of the airplane to the
ground so that all the ground loads are transmitted by it
Fig 2.1.1 Landing Gear Illustration
to the aircraft structure. There is then a high influence
of the landing gear on the local structure, which must be 2.2 Installed actuators at various positions
taken into account since the initial design stage. (existing)
The landing loads can reach factors of 2.5 for transport Actuators, normally of the hydraulic type, control the
aircraft, 4.5 for small general aviation vehicles and extraction/retraction operation. In general, the
higher for combat aircraft. The system must then have mechanism should be designed in such a way that
considerable mechanical resistance, which means in gravity and aerodynamic drag favor extraction; if the
general that its mass is significant. Depending on conditions of gravity and drag are satisfied, the
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Transactions on Innovations in Science & Technology, 2017, 2 (1), 46-51
extraction is possible with no power from the hydraulic make a good decision. In aeronautical applications,
system; a diagram reporting piston load vs. stroke, with strength allied to lightness is most important in material
a constant sign: this means that retraction is obtained by selection, when the material is stable in environment
applying a force to contrast drag and movable conditions. In the majority of situations, trials and errors
equipment weight, while extraction can initiate by could be very expensive and a good project and design
gravity and be completed by drag. The area under the are necessary. For the reasons mentioned above, the
load line represents the necessary work. If this is materials properties must be considered for structural
divided by the area of the rectangle defined by the max application as:
load and stroke, one obtains the efficiency of the
kinematic mechanism, which commonly is in the range • Ultimate stress
70 – 80 %. • Yield stress
• Stiffness (modulus of elasticity)
In both extracted and retracted configurations, the • Temperature limits
mechanism must be blocked (downlock and uplock • Corrosion resistance
respectively). A kinematic lock at extraction can be • Fatigue resistance
obtained by making the four-bar linkage to reach its
• Fracture toughness
dead center at full extraction. In any case, a downlock
• Fragility at low temperatures
based on a hydraulic or electric device is activated to
• Crack growth resistance
prevent any movement of the strut when the aircraft is
• Ductility
taxiing. An uplock is also activated when the landing
• Maintainability
gear is fully retracted, to prevent non-intentional
extraction during flight, which also could be a • Reliability
dangerous operation at high velocity. Uplocks and • Fabricability
downlocks are normally provided for the landing gear
3.1 Carbon fiber:
doors too.
Carbon fiber is a material consisting of fibers about 5–
10 μm in diameter and composed mostly of carbon
atoms.
The properties of carbon fibers, such as high stiffness,
high tensile strength, low weight, high chemical
resistance, high-temperature tolerance and low thermal
expansion, make them very popular in aerospace, civil
engineering, military, and motorsports, along with other
Fig 2.2.1 Piston stroke diagram competition sports.
3. MATERIAL SELECTION Carbon fibers are usually combined with other materials
to form a composite. When combined with a plastic
Material selection must be based on mechanical resin and wound or molded it forms a carbon-fibre-
properties (stiffness, strength, hardness, etc.), corrosion reinforced polymer, which has a very high strength-to-
behavior, physical properties (density, etc.), weight ratio, and is extremely rigid although somewhat
manufacturability, availability and other properties. brittle.
Some important factors have been considered during 3.2 Glass fiber:
the selection of a material for the aeronautical
application. This material is submitted a various Glass fiber is a material consisting of numerous
environments conditions like humidity, temperature and extremely fine fibers of glass.
submitted under different types of mechanical
Glass fiber has roughly comparable mechanical
solicitations like tension, compression, bending,
properties to other fibers such as polymers and carbon
cyclical forces, creep and torsion. Nowadays, a lot of
fiber. Although not as strong or as rigid as carbon fiber,
materials are available and it’s difficult to choose the
it is much cheaper and significantly less brittle when
better solution because there are too many variables
used in composites. Glass fibers are therefore used as a
involved, and the cost is also an important factor to
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Transactions on Innovations in Science & Technology, 2017, 2 (1), 46-51
reinforcing agent for many polymer products; to form a A Pneumatic actuator mainly consists of a piston, a
very strong and relatively lightweight fiber-reinforced cylinder, and valves or ports. The piston is covered by a
polymer (FRP) composite material called glass- diaphragm, or seal, which keeps the air in the upper
reinforced plastic (GRP), also popularly known as portion of the cylinder, allowing air pressure to force
"fiberglass". This structural material product contains the diaphragm downward, moving the piston
little air, is denser than glass wool, and is an especially underneath, which in turn moves the valve stem, which
good thermal insulator. is linked to the internal parts of the actuator. Pneumatic
actuators may only have one spot for a signal input, top
3.3 Epoxy resin: or bottom, depending on action required. Valves require
little pressure to operate and usually double or triple the
Epoxy is the cured end product of epoxy resins, as well
input force.
as a colloquial name for the epoxide functional group.
Epoxy is also a common name for a type of strong 4.1 Servo Motor:
adhesive used for sticking things together and covering
surfaces, typically two resins that need to be mixed A servomotor is a rotary actuator that allows for precise
together before use. It can also be used as a solver due control of angular position, velocity, and acceleration. It
to its high melting and boiling points consists of a suitable motor coupled to a sensor for
position feedback. Servomotors are not a specific class
Epoxy resins, also known as polyepoxides are a class of of motor although the term servomotor is often used to
reactive prepolymers and polymers which contain refer to a motor suitable for use in a closed-loop control
epoxide groups.The reaction of polyepoxides with them system.
or with polyfunctional hardeners forms a thermosetting
polymer, often with strong mechanical properties as 5. RESULT ANALYSIS
well as high temperature and chemical resistance.
Epoxy has a wide range of industrial applications, Table 5.1 Material Properties
including metal coatings, use in electronic and electrical
components, high tension electrical insulators, fibre- Sl. No. Layer no. Orientation Material GSM
reinforced plastic materials, and structural adhesives
1 Layer1 0 ° Glass fibre 6 0 0
commonly used in boat building.
2 Layer2 9 0 ° Carbon fibre 5 5 0
4. PNEUMATIC ACTUATOR:
3 Layer3 1 8 0 ° Glass fibre 6 0 0
A pneumatic actuator converts energy (typically in the
form of compressed air) into mechanical motion. The 4 Layer4 2 7 0 ° Carbon fibre 5 5 0
motion can be rotary or linear, depending on the type of
actuator. Some types of pneumatic actuators include: 5 Layer5 3 6 0 ° Glass fibre 6 0 0
6 Layer6 0 ° Carbon fibre 5 5 0
7 Layer7 9 0 ° Glass fibre 6 0 0
8 Layer8 1 8 0 ° Carbon fibre 5 5 0
9 Layer9 2 7 0 ° Glass fibre 6 0 0
Fig. 4.1 Pneumatic Actuator 10 Layer10 3 6 0 ° Carbon fibre 5 5 0
➢ Tie rod cylinders
➢ Rotary actuators
➢ Grippers
➢ Rodless actuators with magnetic linkage or
rotary cylinders
➢ Rodless actuators with mechanical linkage
➢ Pneumatic artificial muscles
➢ Vacuum generators
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Transactions on Innovations in Science & Technology, 2017, 2 (1), 46-51
Test nature – bending test
Fig 5.1
Fig 5.1.2
6. CONCLUSION AND FUTURE SCOPE OF
WORK
Conclusions:
Fig 5.2 Several technology programs were carried out
successfully by collaboration between industries,
research establishments, and universities.
The programs demonstrated that RTM can be used as a
fabrication method for making complex shaped damage
tolerant landing gear components with a high level of
part integration. By using composites instead of steel
large weight saving can be obtained. For large series
also cost savings are feasible.
Fig 5.3
Based on the results of the technology programs, the
composite landing gear components are feasible cost-
effective alternatives for steel landing gear components.
Composite landing gear components, therefore, are
opportunities to be taken for application in the next
generation civil and military aircraft.
Future Scope:
1. Carbon composite landing gear brake materials have
Fig 5.4 become a mature technology like the radial tires and
will be widely used in future landing gears.
5.1 RESULT
2. Use of composite material may reduce weight &
Test nature – tensile test strength can be improved.
3. Low-density foam filled Ke49/PEEK tubes for the
skids and IM7/8552 cross member tapered beams are
recommended for investigation
4. New materials such as Duocel Al foam43, which can
exhibit as high as 10% elastoplastic strain, could be
very useful in energy reduction mechanism for the
entire rotorcraft.
Fig 5.1.1 5. For filament wound composites, Hashin’s 3-D
damage initiation criteria are recommended. Thus, all
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Transactions on Innovations in Science & Technology, 2017, 2 (1), 46-51
the modeling in ABAQUS would have to be with 3-D [12]. Essam Albahkali & Mohammed Alqahtani”Design
C3D8R 104 solid elements. of Light Landing strut”, 2011.
6. Experimental testing of the designed skid landing
gear will be required to ascertain all computationally
predicted results.
7. With testing supplementing and guiding the
computational analysis, it could be worthwhile to
further explore the area of light crashworthy composite
skid landing gears.
References
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[4]. Derek Morrison, Gregory Neff and Mohammed
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[5]. James N. Daniels, “A Method for Landing strut
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[10]. Oraig Gellimore “Constrained layer damping
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[11]. Jerzy Malachowski “Dyanamical analysis of
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