Structural Analysis of the Drag Strut and Dynamic analysis of Aircraft Landing Gear Manoj Susarla Student Kl University Dr No 12-3-25, Ayyevari Street Bhimavaram 534201 India S.Harshavardhan Student Kl University H-20,Cci Colony, Karankote,Tandur-501158,India Saranya Eeday Student Kl University Drno 70-2-41/D,Kisavari Street Vijayawada 520010 India Abbreviations: FEA - Finite Element Analysis Keywords: Finite element method, dynamic analysis, Drag strut, RADIOSS Abstract This paper deals with the landing gear structure, it is difficult to draw accurate stress and strain distribution through the theoretical calculation. This paper carries on modelling and force analysis to the buffer mechanism of aircraft landing gear, transforms the stress problem dynamic system in to static stress problem according to D'Alembert principle and analyzes the diagonal stay of landing gear, and at the same time, analyzes the strength of an aircraft main landing gear by using computer simulation technology and finite element analysis technology. In this paper the landing gear designed in one of the CAD package and the dynamic analysis is carried out with respect to time to calculate the displacement, velocity, acceleration, and to do the static structural analysis with various loads on the drag strut using HyperMesh RADIOSS workbench. Introduction The diagonal stay of landing gear is the essential component of strut-type main landing gear structure [1]. Its role is to control the partial stress of damper strut, restrain the rotation of strut s outer cylinder relative to fuselage and provide torque. The performance, that is good or bad, has a direct impact on the takeoff and landing of aircraft. For landing gear s strength analysis, Yu-zhen CHEN [2]et al. have studied axle s static strength simulation analysis of aircraft landing gear, Xue-hong HE [3]et al. have carried on finite element strength analysis to the four-frame of aircraft landing gear,xiao-feng WANG [4] et al. have performed static structure optimization to the stay of aircraft landing gear, but researches on dynamic stress analysis of aircraft landing gear are still scanty. This paper researches the dynamic performance simulation of landing gear, carries on the structural strength analysis to the diagonal stay of landing gear using dynamic-static method based on simulation result, which is a critical step in structure strength design and in-depth maintenance work. The main landing gear is one of the most critical components of an aircraft, capable of reacting the largest local loads on the airplane. It is a primary source of shock attenuation at landing. It controls the rate of compression extension and prevents damage to the vehicle by controlling load application rates and peak values. Thus utmost care must be taken while designing a main landing gear.d.w.young [1] discusses the technological developments in aircraft landing gears and explains some basic requirements in designing a main landing gear. Simulate to Innovate 1
Process Methodology CASE(1):- To perform structural analysis various methods are followed they are 1. Designing of drag strut using CAD package software 2. Converting the respective file in to IGES, parasolid format. 3. Importing the model in to HyperMesh 4. Applying the following material performing the static structural analysis. The mathematical model of landing gear is relatively complex. Firstly, in order to make the model simulate actual situation better, fit in with the movement characteristics of landing gear structure and easy to calculate, the origin of coordinate is set on the centre of two masses under stop condition. The assumptions made before modelling are as follows: 1) Aircraft s fuselage is a rigid body 2) All the forces of aircraft landing gear are limited in a vertical plane 3) Ignore the offset distance relative to damper s canter line 4) The canter of elastic support mass is located on the intersection of landing gear strut s centre line and trunnion s centre line of aircraft s fuselage 5) Inelastic support mass is concentrated on axle ideally Elastic support mass is the air spring support mass that includes aircraft s fuselage, wing, damper s outer cylinder, etc. Inelastic support mass includes plunger, wheel, brake gear, etc. Based on the assumptions above, a two-mass-spring system is established shown in Fig.1. Among them, m1: elastic support mass, m2: inelastic support mass, y1: the displacement of elastic support mass, y2: the displacement of inelastic support mass, Fa: the air elasticity of damper, Fh: oleo damping force, Fu: the vertical reaction force of tires. table 1: Titanium material properties Young s modulus 1.028E+005 Mpa Poisson s ratio 0.361 - density 4.510E-009 N s^2/mm^4 Yield strength 275.600 Mpa Figure 1: CAD model of drag strut Simulate to Innovate 2
Figure 2: Mesh model of drag strut table 2: Mesh properties Nodes 26547 Elements 71978 Element size 2 Type Tetramesh This paper carries on static analysis to the diagonal stay of landinggear using dynamic-static method, and the number of constraint condition is reduced substantially.the diagonal stay is mainly used to not only reduce the bending moment of strut but also retract andextend landing gear. Therefore, displacement constraints in X direction are exerted on two terminalsurfaces of the joint of diagonal stay and fuselage, which limits the revolution of diagonal stay aroundy axis or Z axis and displacement in X direction. And displacement constraints in X direction areexerted on two terminal surfaces of the joint of diagonal stay and landing gear, which limits therevolution of diagonal stay around Y axis or Z axis and displacement in X direction.as aircraft's landing is a dynamic process and the analysis at one time is static, dynamicstaticmethod of fluid kinetics is adopted. D'Alembert principle of particle system is as follow: when ever particles motion, if mass force is added to each particle, the system is in static state of equilibriumunder the action of virtual mass force, realistic active force and ideal constraint force. Within therange of linear elasticity, the stress and strain submit Hooke law. According D'Alembert principle,mass force is added to diagonal stay to make a static analysis on the basis of force analysis. That is, the stress and strain of diagonal stay is analyzed at the time when impact is maximum duringaircraft s landing. From the analysis made above, diagonal stay s force reaches the maximum at 0.18s, and themaximum is 50N tires vertical force is 30 N. At this moment, aircraft's landingacceleration is 12.5 m/ s2. Due to the use of dynamic-static method, the load is mass force and loadingdirection is in the direction opposite of actual acceleration. Material density is needed when massforce is loaded, which has been defined below. Simulate to Innovate 3
Figure 3: Deformed shape for 50N Figure 4: Deformed shape for 30N CASE(2):- To perform dynamic analysis various methods are followed they are connected with motors on side strut and the upper torsion link. Both the motors are set to 20RPM and 30RPM with respect to their axis to rotate Various types of materials are assigned to the landing gear and it is multi axle type landing gear. Figure 5: CAD model of landing gear Figure 6: Mesh model of landing gear Simulate to Innovate 4
Dynamic simulations of landing gear:- Figure 7: Simulation of landing gear at 20RPM Figure 8: Simulation of landing gear at 30RPM After completing the dynamic simulations we need to plot the graphs of displacement, velocity, acceleration with respect to time set the time period to 5sec and calculates here we represent the following graphs. Graph 1:-: Displacement vs time Simulate to Innovate 5
Graph 2:-: Velocity vs time Graph 3:-: Acceleration vs time Simulate to Innovate 6
Results & Discussions CASE(1):- From the figure we can see the maximum strength is 0.2217Mpa for 30 N force applied and 0.3684Mpa for 50N force applied. From stress nephogram we can see the stress concentration at drag strut lower end is severe and it is easy to be fractured.this illustrates that the rocker is safe in strength, but fatigue failure is still easy to occur on the parts of stress concentration after using for a long time. Although diagonal stay doesn t break, bend deformation has occurred.during aircraft landing, the stress of diagonal stay would attenuate periodically. From the analysis above we can see that, after the aircraft landed, drag strut must be replaced to ensure the safety of aircraft landing gear. CASE(2):- From the graph plotted with respect to time to calculate displacement, velocity, acceleration that had set time to 5 sec Displacement :- 10.3 cm Velocity :- 3 cm/sec Acceleration :-97 cm/ sec 2 Benefits Summary The static analysis that is carried out for the given parameters had given a good result to know behavoiur of the material and safety factor. ALTAIR HyperWorks is having complete software for analysis which can easily understand and user friendly software for both educational and industries. the multibody dynamic analysis is much benefited for all users who are using ALTAIR products. The design optimization is easier to understand and we can do the topology optimization. Challenges As this project is having more number of components it is difficult to mesh and to give constraints but as the no of components increases in particular CAD model it is a tough challenge to do mesh and perform analysis. Future Plans As the results obtained from the experiment in future we are going to do analysis for the four axle or more than that type of landing gear in aircraft using ALTAIR products. Conclusions This paper mainly achieves the finite element analysis of the diagonal stay of main landing gear. On the basis that the model of aircraft s buffer system is established and simulation result is obtained, the stress problem dynamic system is transformed into static stress problem according to D'Alembert principle. And the force situation of Drag strut is analyzed according to moment balance principle,t he conclusion that stress concentration occurs on the joint of drag strut and damper, as well as the joint of drag strut and fuselage, is drawn by using the super finite element analysis software, which provides theoretical basis for damage prediction and practical maintenance. Simulate to Innovate 7
REFERENCES [1] Science and Technology Commission of Min of Aerospace Industry: Strength Design Guide for Aircraft Landing Gears (University of Electronic Science and Technology of China Press, Chengdu1989) [2] Yuzhen CHEN and Weijian YU: Machinery. Vol. 33 (2006), p. 33 [3] Xuehong HE, Yingjie ZHANG, liyang XIE, Li HUI. FEM Numerical Analysis on Aircraft Undercarriage Four-frame Structure. in: Chinese Mechanical engineering society, eds. Proceedings of 14th Fatigue & Fracture Conference. Beijing: Aircraft Strength Research Institute of China, 2008 [4] Xiaofeng WANG and Yongjun WANG: Science Technology and Engineering. Vol. 8 (2008), p.3244 [5] James N.Daniels. A method for landing gear modeling and simulation with experimental validation.nasa Langley Research Center. Hampton, Virginia. [6] Youjin SHI and Zhengchang ZHANG: Journal of Southeast University (Natural Science Edition).Vol. 35 (2005), p. 549 [7] Lyle K H, Jackson K E, Fasanella E L. Simulation of aircraft landing gears with a nonlineardynamic finite element code[r]. AIAA- 2000-4049, 2000. [8] Yong YE, Yanhua HAO and Changhan ZHANG: Mechanical Engineering & Automation. Vol. 6(2004), p. 630826 [9] Byung-Soo Kang, Yaw-Kang Shyy: "Design of Flexible Bodies in Multibody Dynamic Systems using Equivalent Static Load Method", 49th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference, Schaumburg, IL, USA, 2008. [10] B.S. Kang, G.J. Park, J.S. Arora: "Optimization of Flexible Multibody Dynamic Systems Using the Equivalent Static Load Method", AIAA Journal, Volume 43, Issue 4, AIAA, April 2005. Simulate to Innovate 8