design and analysis of composite landing strut for a

© 2020 JETIR August 2020, Volume 7, Issue 8 www.jetir.org (ISSN-2349-5162)

JETIR2008317 Journal of Emerging Technologies and Innovative Research (JETIR) www.jetir.org 99

DESIGN AND ANALYSIS OF COMPOSITE

LANDING STRUT FOR A VERTICAL

TAKEOFF AND LANDING UNMANNED

AERIAL VEHICLE 1M Upesh Kumar Rao, 2Dr. R.J.V Anil Kumar,

1PG Student, 2Assistant Professor, 1Department of Mechanical Engineering, Anantapuramu, India, 2Department of Mechanical Engineering, Anantapuramu, India.

Abstract: Landing strut is the critical component of Unmanned Aerial Vehicle (UAV), which plays a crucial role in landing the

UAV safely and gives support to the UAV structure in the rest position. In this paper, landing strut designed according to

requirements of the UAV. The landing strut can be sepatared into two parts one is bridge cradle, and the other is a skid. The skid

can be designed with two different cross-sections, one is rectangular skid, and the other is a circular skid. The landing strut model

is designed in CATIA V5. The modelling and analysis for both the model carried out by Hyperworks software and compared with

the theoretical values. The objective of this study was to compare the results of CFRP and GFRP materials by static, dynamic and

buckling analysis using the computational tool.

Keywords: Landing strut, skid, dynamic and buckling analysis, Catia V5, Hyperworks.

I. INTRODUCTION:

UAV has a unique structural design of a landing strut and supports to land on the ground surface safely while taxiing,

takeoff, landing, and protect the UAV from colliding to ground. The landing struts can be designed with wheels or skids; the wheels

have more weight compared to skids, so most of the helicopters designed with skids. Skid landing strut is fundamental and lighter

weight, so it is the best choice for little UAVs as weight is reliably an idea. Moreover, skid landing strut needs practically no help,

yet the drawback is that ground dealing with is dynamically problematic. In small UAVs ground dealing with wheels can be annexed

to the slides and the helicopter moved around by one person. The structural design depends on the required characteristics of a

UAV. The landing struts are less expensive and can design with innovative ideas. The landing strut consists of two different parts,

one is bridge cradle connected to the UAV’s fuselage and another, is skid, attached to cradle end, and fixed. In this paper, the

structure of the landing strut designed with two different skids, applying composite material properties for analysis to determine the

structural characteristics of landing strut.

II. LITERATURE SURVEY:

The project presents a static, dynamic and buckling analysis of impact loading landing strut in Hypermesh software. The

improvement of the landing strut requires several references and is developed from the Hypermesh Software.

Rasees Fifa Swati1, Dr. Abid Ali Khan2 et al [1] have investigated on optimizing procedure of designed landing strut model and

carried out the static analysis with impact analysis. Finally, they concluded that the model weight was optimized from the original

model weight.

R. Arravind1, M. Saravanan2, R. Mohamed rijuvan3 et al. [ 2 ] performed on the analysis of landing strut cast-off composite

material to optimize the weight design by taking the iterations as thickness to minimize the weight of the landing strut. They

concluded that the optimized model is safe for fabrication.

Xinyu Zhu1, Junwen Lu2 et al. [3] had created a FEM model by assigning composite materials on the landing gear for estimating

the static analysis and buckling analysis. They showed the damaging locations in the landing gear model.

S. Naresh1, J. Abdul Shukur2, K. Sriker3, A. Lavanya4 et al. [4] studied on landing gear skid and analysed by assigning different

composite alloy properties to evaluate the deformations in landing gear skud. Lastly concluded that material which can to resist

maximum stress, it has high strength.

Mandeep Chetry1, Han Dong2 et al. [5] conducted the static analysis on helicopter skid landing gear on both the composite

materials and aluminium alloy. They compare the results of materials from the stress and displacements to reduce the deformation

in the skid landing gear.

S. A. Mikhailov1, L. V. Korotkov2, S. A. Alimov3 et al. [6] have modelled on the landing of a helicopter with skid under-carriage

in regards for the second landing impact. They presented a comparison between the analysis results and the experimental data.

Benazir Zia1, Hafiz Sana Ullah Butt2 et al. [7] was analysed the dynamic response of a composite strut of landing gear by using

ANSYS LS-DYNA software. They concluded on the effect of impact velocity on the landing gear and finalized the results having

higher the impact velocity and impact reactions on the strut.

G Krishnaveni1, E.S Elumalai2, S.Mayakkannan3 et al. [8] performed on buckling analysis of landing gear under static condition.

They calculated the model and verified using the software. The landing gear will not buckle for any load below limit load under

static static conditions.

Jerzy Józwik1, Jaroslaw Pytka2, Arkadiusz Tofil3 et al. [9] analysed on dynamic analysis of aircraft landing gear wheel. They

performed the test with the use of one aircraft on two different surfaces. The results considered the time course of displacement,

velocity and acceleration of one selected point on the sidewall of the tire during a drop from a kilometre ramp.

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III. MODELING:

The modelling of the landing strut is designed according to the design requirements of the UAV. The landing struts consist

of a horizontal cradle connected to the fuselage bottom of the UAV to sustain the impact load while taxiing, takeoff, and landing.

The skid connected to another end of the bridge cradle that gives safe landing from the damage of the UAV body, and has less stress

distribution from skid to strut vice versa. Here landing strut designed with two different skid models one is rectangular skid, and

the other is circular skid landing strut.

Fig 1: Rectangular Skid Landing Gear Fig 2: Circular Skid Landing Gear

IV. MATERIAL PROPERTIES:

Most of the UAVs and Light Helicopter (LH), where the aerial body and landing strut are fabricated with the composite

material, which has advantage strength to weight ratio and strength to volume ratio. Fibre-reinforced polymer (FRP) mostly used

for fabrication because of high rigidity, corrosion resistance, electric conductivity, fatigue resistance, and excellent tensile strength

but brittle. CFRP and GFRP materials are using in this project for the analysis of the landing strut. CFRP materials and GFRP

materials commonly used in military, automotive, submarines, ships, etc. Materials properties of CFRP and GFRP are taken the

NAIR AGATE website https://www.niar.wichita.edu/agate/. The values are considered in report on Carbon Plain Weave Fabric

3K70P/NB321 and E-Glass Fabric 7781/NB321.

Table 1: Mechanical Properties of CFRP

Property Tensile

Strength

Mpa

Young’s

Modulus

Mpa

Compressive

Strength

Mpa

Density

Kg/m3

Poisson

Ratio

Tensile 620.183 66327.45 - 1500 0.058

Compression - 4247.47 114.97 1490 0.058

Table 2: Mechanical Properties of GFRP

Property Tensile

Strength

Mpa

Young’s

Modulus

Mpa

Compressive

Strength

Mpa

Density

Kg/m3

Poisson

Ratio

Tensile 438.27 28957.93 - 1740 0.138

Compression - 4198.9 131.73 1860 0.138

V. PROCEDURE:

1. Firstly, define the geometry and dimensions of the landing strut; design the 3D model with the acquired geometry by using

CATIA software. After that model should export into IGES or STP file for further steps.

2. Import the model in the Hypermesh workbench by setting the profile as bulk data in Radioss solver, meshing to be done

to model by giving the element size and mesh type.

3. Next, the preprocessing setup carried out by creating materials, properties, loads, and boundary conditions.

4. Solve the analysis in Radioss solver, view the results, and contour in Hyperview.

VI. Model Meshing:

Meshing plays a crucial role in finite element analysis that gives a direct output of the process. Meshing was created by

setting up the mesh type to quad that creates the QUAD4 elements through the nodes and to restrict the size of the element; the

element size value is given here as 5. With the help of element size, nodes, and elements are created according to the given element

size value. After creating the mesh, the preprocessing arrangement to be assigned to the meshed component.




Fig 3: Mesh Model of Rectangular Skid Landing Gear Fig 4: Mesh Model of Circular Skid Landing Gear

VII. LANDING LOADS:

The landing loads that include gravity and body weight. These loads were considered for landing strut to examine structural

strength. After the meshing of components, the next step is assigning boundary conditions and applying forces to the components.

Table 1 shows the landing loads applied to land strut. The landing load is applied on the landing strut bridge cradle (the connection

between fuselage and strut), which was applied in the downward z-direction, and skids are constrained in all directions. By applying

these loads, the strut deforms in a negative z-direction.

Table3: Landing Loads

Load Type Value

Landing load 130 N

Fig 5: Landing Loads of Fig 6: Landing Loads of

Rectangular Skid Landing Circular Skid Landing Gear

VIII. STRUCTURAL STATIC ANALYSIS:

The landing strut model was imported from CATIA, which consists of fuselage, strut, and skid. This imported model

meshed and applied a landing load of UAV weight as 130 N to analyse the structural deformation. Before analysis, the structure

assigned to boundary conditions in all directions. In this study, landing loads have applied on the bridge cradle which can be seen

in fig (5, 6), i.e. connected to the bottom of the fuselage and the skids were constrained in all degrees of freedom. The static analysis

shows the results of vonmises stresses and displacements under applied static loads. The deformation contour of the structure

visually seen in hyperview software. The results of the stress and displacement shown in table 4 and 5.

8.1 Displacement:

a. CFRP:

Fig 7.a: Displacement Contour of Tension Properties for Rectangular Skid Landing Strut




Fig 7.b: Displacement Contour of Tension Properties for Circular Skid Landing Strut

Fig 8.a: Displacement Contour of Compression Properties for Rectangular Skid Landing Strut

Fig 8.b: Displacement Contour of Compression Properties for Circular Skid Landing Strut

b. GFRP:

Fig 9.a: Displacement Contour of Tension Properties for Rectangular Skid Landing Strut

Fig 9.b: Displacement Contour of Tension Properties for Circular Skid Landing Strut




Fig 10.a: Displacement Contour of Compression Properties for Rectangular Skid Landing Strut

Fig 10.b: Displacement Contour of Compression Properties for Circular Skid Landing Strut

8.2 Stress:

a. CFRP Material:

Fig 11.a: Vonmises Stress Contour of Tension Properties for Rectangular Skid Landing Strut

Fig 11.b: Vonmises Stress Contour of Tension Properties for Circular Skid Landing Strut

Fig 12.a: Vonmises Stress Contour of Compression Properties for Rectangular Skid Landing Strut




Fig 12.b: Vonmises Stress Contour of Compression Properties for Circular Skid Landing Strut

b. GFRP Material:

Fig 13.a: Vonmises Stress Contour of Tension Properties for Rectangular Skid Landing Strut

Fig 13.b: Vonmises Stress Contour of Tension Properties for Circular Skid Landing Strut

Fig 14.a: Vonmises Stress Contour of Compression Properties for Rectangular Skid Landing Strut

Fig 14.b: Vonmises Stress Contour of Compression Properties for Circular Skid Landing Strut

Table 4: Results of Tensile Properties in Static Analysis

Materials

Rectangular Skid Circular Skid

Displacement

Mm

Stress

Mpa

Displacement

Mm

Stress

Mpa

CFRP 8.52 98.16 8.42 101.1

GFRP 19.46 95.43 19.31 98.02




Table 5: Results of Compressive Properties in Static Analysis

Materials


Displacement

Mm

Stress

Mpa

Displacement

Mm

Stress

Mpa

CFRP 133.0 98.16 131.6 101.1

GFRP 134.2 95.43 133.1 98.02

IX. DYANAMIC ANALYSIS:

FEM model used in Hypermesh consist of, 2D (Quad-shell and Tria shell elements) elements, considering the boundary

conditions at one end of a skid as fixed and free at the other end of landing strut and fuselage. Normal mode analysis is carried out

for both landing strut models using Radioss as the solver, where the mode shapes and frequency are obtained.

9.1 Mode Shape 1:

a. CFRP Material:

Fig 15.a: Fuselage Nose Pitching Mode for Rectangular Skid Landing Strut

Fig 15.b: Fuselage Nose Pitching Mode for Circular Skid Landing Strut

b. GFRP Material:

Fig 16.a: Fuselage Nose Pitching Mode for Rectangular Skid Landing Strut

Fig 16.b: Fuselage Nose Pitching Mode for Circular Skid Landing Strut




9.2 Mode Shape 2:

a. CFRP Material:

Fig 17.a: Bending of Landing Strut for Rectangular Skid Landing Strut

Fig 17.b: Bending of Landing Strut for Circular Skid Landing Strut

b. GFRP Material:

Fig 18.a: Bending of Landing Strut for Rectangular Skid Landing Strut

Fig 18.b: Bending of Landing Strut for Circular Skid Landing Strut

9.3 Mode Shape 3:

a. CFRP Material:

Fig 19.a: Rear Fuselage Pitching Mode for Rectangular Skid Landing Strut




Fig 19.b: Rear Fuselage Pitching Mode for Circular Skid Landing Strut

b. GFRP Material:

Fig 20.a: Rear Fuselage Pitching Mode for Rectangular Skid Landing Strut

Fig 20.b: Rear Fuselage Pitching Mode for Circular Skid Landing Strut

Table 6: Dynamic Analysis using Tensile properties

Materials

Frequency (Hz)


1 2 3 1 2 3

CFRP 6.397 11.943 12.620 6.441 12.539 12.782

GFRP 3.903 7.694 7.845 3.775 7.442 7.588

Table 7: Dynamic Analysis using Compressive properties

Materials

Frequency (Hz)


1 2 3 1 2 3

CFRP 1.624 3.032 3.204 1.635 3.184 3.204

GFRP 1.427 2.699 2.853 1.438 2.834 2.853

X. BUCKLING ANALYSIS:

Buckling was characterised by failure of the structure due to compression loading, where the load is taken as 130 N. The

load was applied at the connection between the bridge cradle and base of the fuselage. At the bottom, the landing strut was

constrained in all degree of freedom. Finally, Critical loads were determined to the skid landing gear models by conducting iterations

on loads until we get mode frequency 1.




a. CFRP Material:

Fig 21.a: Buckling Contour of Tension Properties for Rectangular Skid Landing Strut

Fig 21.b: Buckling Contour of Tension Properties for Circular Skid Landing Strut

Fig 22.a: Buckling Contour of Compression Properties for Rectangular Skid Landing Strut

Fig 22.b: Buckling Contour of Compression Properties for Circular Skid Landing Strut

b. GFRP Material:

Fig 23.a: Buckling Contour of Tension Properties for Rectangular Skid Landing Strut




Fig 23.b: Buckling Contour of Tension Properties for Circular Skid Landing Strut

Fig 24.a: Buckling Contour of Compression Properties for Rectangular Skid Landing Strut

Fig 24.b: Buckling Contour of Compression Properties for Circular Skid Landing Strut

Table 8: Buckling Analysis using Tensile properties

Materials Mode Frequency Critical Load (N)

Rectangular skid Circular Skid Rectangular skid Circular Skid

CFRP 9.114 9.15 1286.72 19888.84

GFRP 3.981 3.998 645.15 19256.68

Table 9: Buckling Analysis using Compressive properties

Materials Mode Frequency Critical Load (N)

Rectangular skid Circular Skid Rectangular skid Circular Skid

CFRP 0.587 0.585 204.74 207.32

GFRP 0.579 0.575 202.48 200.12

XI. Factor of safety: The factor of safety is a significant concern in structure and landing strut. It is determined after a point by point assessment

of stresses along with the structure for loading conditions. Here the factor of safety is calculated by dividing with the tensile and

compression strength of CFRP and GFRP material with the Vonmises stresses generated in rectangular and circular skid landing

strut.

The factor of safety for UAV’s landing struts is considered as 1.2.

Table 10: Results of Factor of safety Material


Tensile Compression Tensile Compression

CFRP 6.32 1.17 6.13 1.13

GFRP 4.59 1.38 4.47 1.34

XII. CONCLUSION: This paper concludes the landing strut of CAD model designed in CATIA software, discretized in finite element analysis

by Hypermesh software and landing loads were applied in Radioss solver to estimate the structural deformations by performing the

static, dynamic and buckling analysis.

1. Comparing the results of stresses and displacements, the landing strut of CFRP material is better than GFRP material.

2. In every analysis, there is a slight deviation in results on both rectangular skid landing strut and circular skid landing strut.




3. The tensile properties and compressive properties are applied to observe the behaviour of landing strut while loading within the

constrained conditions.

4. The circular skid has less stress distribution with less deformations in the landing strut in both the tensile properties and

compression properties.

5. From the results of dynamic analysis, the frequency of the landing strut is 6.441 Hz in tensile properties and 1.635 Hz in

compression properties.

6. In buckling analysis, buckling critical loads are estimated for the models of CFRP and GFRP materials. It can be concluded that

for tensile properties and 1.03 times safer than GFRP material in a circular skid while considering the compression properties,

CFRP material is 1.01 times safer than GFRP material in rectangular skid landing strut and 1.04 times safer than GFRP material in

circular skid landing strut.

7. A load of 130 N on the landing strut has a lesser chance of failure in tensile properties, whereas landing strut is weak in

compressive properties due to factor of safety is not close to 1.2.

It can be concluded that the design methodology for landing strut through FEM considers that the compressive properties for

the design are crucial to finalise the design of the landing strut due to the compressive behaviour. The buckling studies show that

CFRP based circular skid-landing strut can be fabricated.

XIII. ACKNOWLEDGMENT:

I am thankful to my guide Mr. D. Dwarakanathan, Principal Scientist, STTD, and my mentor Dr. S. Raja, Head, STTD,

for guiding me in my project work. I also would like to thank Director of NAL for providing the opportunity to do my dissertation

work at CSIR-NAL, Bengaluru.

References: [1] Rasees Fifa Swati1, Dr. Abid Ali Khan2, Design And Structural Analysis Of The Weight Optimized Main Landing Gears For

UAV Under Impact Loading, Journal of space technology, vol-4, no-1, July-2014.

[2] R. Arravind1, M. Saravanan2, R. Mohamed rijuvan3, Structural analysis of landing strut made up of carbon fiber composite

material, International Journal of Mechanical and Production Engineering, ISSN: 2320-2092, Volume-1, Issue-1, July-2013.

[3] Xinyu Zhu1, Junwen Lu2, Stress and Buckling Analysis of a Certain Type of All-Composite Landing Gear, Advanced Materials

Research Vol 663 (2013) pp 692-697 © (2013) Trans Tech Publications, Switzerland.

doi:10.4028/www.scientific.net/AMR.663.692,

[4] S. Naresh1, J. Abdul Shukur2, K. Sriker3, A. Lavanya4, Design and Structural Analysis of Skid Landing Gear, International

Journal of Current Engineering and Technology E-ISSN 2277 – 4106, P-ISSN 2347 - 5161 ©2014 INPRESSCO®, DOI:

http://dx.doi.org/10.14741/ijcet/spl.2.2014.121 635 | International Conference on Advances in Mechanical Sciences 2014.

[5] Mandeep Chetry1, Han Dong2, Static Analysis of Helicopter Skid Landing Gear made of Composite Materials, International

Journal of Scientific and Research Publications, Volume 9, Issue 9, September 2019, ISSN 2250-3153, DOI:

10.29322/IJSRP.9.09.2019.p9378, http://dx.doi.org/10.29322/IJSRP.9.09.2019.p9378.

[6] S. A. Mikhailov1, L. V. Korotkov2, S. A. Alimov3, D. V. Nedel’ko4, Modeling of Landing of a Helicopter with Skid

Undercarriage with Regard for the Second Landing Impact, ISSN 1068-7998, Russian Aeronautics (Iz.VUZ), 2011, Vol. 54, No.

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[7] Benazir Zia1, Hafiz Sana Ullah Butt2, Dynamic Response of a Composite Strut of Landing Gear of an Aircraft against Impact

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[8] G Krishnaveni1, E.S Elumalai2, S.Mayakkannan3, Buckling Analysis Of Nose Landing Gear Under Static Condition,

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[9] Jerzy Józwik1, Jaroslaw Pytka2, Arkadiusz Tofil3, Dynamic Analysis of Aircraft Landing Gear Wheel, 978-1-5386-2474-

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design and analysis of composite landing strut for a

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