Impact Analysis of Mini UAV during Belly Landing
Akhilesh Kumar Jha
S. Sathyamoorthy
Bharath Kumar
Laxminarayan.k
Scientist
ADE,DRDO
New Thipsandra , C.V
Ramannagr Bangalore
Bangalore – 560 075
Scientist
ADE,DRDO
New Thipsandra , C.V
Ramannagr Bangalore
Bangalore – 560 075
Scientist
ADE,DRDO
New Thipsandra , C.V
Ramannagr Bangalore
Bangalore – 560 075
Senior Manager
Design Tech Sys Ltd
Bangalore
Abstract
The purpose of this study is to analyze the impact loads on the composite sub-structures of a mini UAV due
to the belly landing. “Emperial Eagle” Mini UAV is designed and Developed by Aeronautical Development
Establishment (DRDO). This study is limited to the calculation of stresses and deformation that is caused by
the low velocity impact forces encountered during belly landing. Belly landing analyses of the mini UAV are
done using Radioss Block (HyperWorks), which is an explicit finite element solver. Model building and post
processing are done via HyperView and HyperMesh.
Keywords: Unmanned aerial vehicle, low velocity impact, belly landing, composite structure
Introduction
The role of Unmanned Air Vehicles (UAVs) is steadily expanding in military and civil aviation as well as
scientific research particularly for intelligence, surveillance, and reconnaissance missions due to their ease
of production, flexibility of maintenance, lighter in weight, elimination of landing gear system and simplicity of
use. In addition, the whole airframe of vehicle is fabricated using composite materials to reduce its weight
and enhance strength. They are usually built to meet “hand launching” and “belly landing” criteria in order to
have easy flight and easy landing features. The aircraft has to be launched from the hand, climb up to 300
m above the launch point and do the required maneuvers like turning with minimum radius. Finally, the
aircraft has to be recovered with belly landing by gliding or deep stall maneuver.
In an operation, belly landing mini UAV’s may encounter tough landing areas like gravel, concrete or hard
soil. Such landing areas may create landing loads which are impulsive in character. The effect of the landing
loads on the airframe of the mini UAV must be completely understood and the mini UAV be designed
accordingly in order not to damage it during belly landing. Typical impact speeds during belly landing is
relatively low (in the range of 5-10 m/s) and in general, belly landing phenomenon can be treated as low
velocity impact [1].
Impact is a transient physical excitation and causes a force to be applied for a very short period of time.
When two bodies come into contact together with some velocity, a certain amount of impulse arises at the
contact zone in both bodies. For the impact of particles, impulse is normal to the particles’ contact plane.
However, for more complex bodies, there is a region of contact through which the impact loads are induced
on the impactor and the target material, and deformation on both bodies occur due to the impact [2].
Impulse forces on this deformed surface are associated so that there is no interpenetration of the bodies.
Process Methodology
The purpose of this paper is to present a general overview of impact analysis specifically by the low velocity
impact forces encountered during belly landing. The subject of impact attracts the interest of scientists and
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engineers to predict the behaviour of colliding objects. Our focus in this paper, however, will be mainly on
impact modeling as it relates to rigid target to elastic aircraft structures. The purpose of this study is to
analyze the impact loads on the mini UAV structures which is made up of carbon and Kevlar fabric and
estimate stresses, strains and displacements in critical location that is caused by low velocity during the
belly landing.
Figure 1: Impact classification on based of impact velocity [7]
Low level impacts may result in internal damage on the composite that may not be visible by naked eyes. If
the impact velocity is between 10-2m/s and 10m/s, then the force equilibrium is assumed to be quasistatic[3]. (ΣF≈ 0) Internal damage caused by low velocity impact can be examined in two categories:
interlaminar damage, which is called “delamination”; and intralaminar damage, which is transverse ply
cracking. Depending on impact characteristics (velocity, materials), the assumptions made and the results
sought, one aspect will become more predominant than the others. Thus, it leads to a solution approach for
impact analysis. These four aspects are Contact mechanics, Plastic deformation, Classical mechanics and
Elastic stress wave propagation. Below is an overview of contact mechanics approach, which has been
used in this paper.The contact stresses resulting from the impact of two bodies are another area of interest
in the study of impact[4]. Conventional contact mechanics is mainly concerned with static contact, although,
it has been extended to approximate solutions when impact is involved.
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Figure 2: Belly landing Approach in MINI UAVs
In the simple analytical solution of the low velocity impact response of plate like structures, the magnitude
and distribution of pressure distribution in the target can be obtained by combining the dynamic solution to
the problem of impact of solids with the static solution for the pressure between two bodies in contact. Thus,
in this method, by applying the Hertz Contact Law [5], this dynamic problem can be converted into a static
problem. Hertz Law states that the magnitude and the application area of the force caused by the impact
can be estimated by an analytical approach.
FEM approach
Finite element modelling is done using HyperMesh. 2D elements are modeled for the entire MUAV in
HyperMesh. Quality of the 2D elements is corrected in HyperMesh before proceeding for analysis.
Orientation of plies is checked in HyperMesh after creating meshed model. MATERIAL MODEL 25 is used
in Radioss for creating composite materials along with Tsai- wu criteria. Also, composite modeling is done
ply based using P11_SH_SANDW, in which we have used different materials for different plies.
MATERIAL MODEL 1 is used for defining structural material model. For defining boundary conditions, we
used load collectors in Radioss. INVEL_COLLECTOR is used for defining velocity magnitude and
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direction.GRAV_COLLECTOR is used for defining body force for the entire component. 9810 mm/sec
gravity is applied for the entire component. Wall is modeled using INFINTE PLANE RIGID WALL, in
Radioss, since, we did not want to consider time step parameter for the rigid wall. Rigid wall by default is
kinematically constrained in all the degrees of freedom. Also, for contact definition, by default, rigid wall is
considered as master and all the parts of MUAV are considered as slave.
Type 7 contacts is used for defining self contact for MUAV, since this contact will identify contacts
automatically whenever there is a contact between internal parts. OUTPUT BLOCK in Radioss is used for
requesting output for all the parts of MUAV for getting Strain, velocity, displacement and stresses for each
PLY.
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Figure 3: Inclined landing impact velocity Vs time
Figure 4: Wing tip displacement respect to time in inclined drop
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Figure 5: strain respect to time in inclined drop
Figure 6: cortical strain plot to time in inclined drop in boom
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Figure 7: Maximum stress plot Vs time in inclined drop
Conclusions
In this study, belly landing analysis of a mini UAV is conducted for inclined and vertical drop approach. The
key question to be answered was how the stress, strain, approach of landing and target properties affect the
design of composite structures and its durability life. To have a consistent answer to above mentioned
findings, further series of experimental verification is required.
References
[1]
W.J.Stronge, “Impact Mechanics”, Cambridge University Press, 2000 York, 1999
[2]
Serhan yüksel serhan “Low velocity impact analysis of a composite mini unmanned air vehicle during belly landing” thesis
submitted to the graduate school of natural and applied sciences of middle east technical university.
[3]
Choi, I.H., “Low-velocity impact analysis of composite laminates under initial in-plane load”, 2008
[4]
Johnson K. L., Contact Mechanics, Cambridge University Press, 1985.
[5]
1. 12. Choi, I.H., “Low-velocity impact analysis of composite laminates under initial in-plane load”, 2008
[6]
Jones, R.M., “Mechanics of Composite Materials”, Hemisphere Publishing Coorporation,
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