ME 548 Aero Structures Final Project

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ME 548 Aerostructures Final Project ANSYS Analysis Landing Gear

By: Dave Briscoe

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AbstractFor this final project an analysis of a STOL CH 701s (Figure 1). Landing Gear will be obtained using the ANSYS software. Initial hand calculations of the body forces acting on the landing gear will be made, a free body diagram for the gear will be needed for this. Graphic construction of the landing gear will be made using the ANSYS software, Analysis of the forces acting on the landing gear will be derived also using finite element analysis method with the ANSYS software.

Figure 1: Stohl CH 701

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Table of ContentsAbstract................................................................................................................................2 Introduction..........................................................................................................................4 Design Objectives................................................................................................................5 Theory ................................................................................................................................. 6 Procedures........................................................................................................................... 7 Calculations......................................................................................................................... 8 Static................................................................................................................................ 9 Dynamic.........................................................................................................................12 ANSYS Results................................................................................................................. 15 Geometry:...................................................................................................................... 16 Lines Connecting Kps:............................................................................................. 16 Fillet Creation for arcs:.............................................................................................. 16 Boundary Conditions..................................................................................................... 18 Mesh Generation:...........................................................................................................19 Von Mises Stress............................................................................................................20 Yield Strength Criteria............................................................................................... 20 Maximum Strut Displacement:...................................................................................... 21 Conclusion......................................................................................................................... 22 Appendix............................................................................................................................ 24

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IntroductionThe landing gear is the structure that supports an aircraft and allows it to move across the ground or water. For this report the type of landing gear to be analyzed is the tricycle gear, this simply means that the gear is arranged in a tricycle fashion. The tricycle arrangement has one gear strut in front, called the nose wheel, and two or more main gear struts slightly aft the center of gravity. The advantage of the tricycle gear is that it is nearly impossible to make the plane nose over. The tricycle gear also allows for a level cabin area making the loading and unloading of the aircraft much easier than that of an inclined plane.

The main gear (Figure 2) comprises of a simple single piece aluminum spring leaf which is bolted to the bottom of the fuselage. This main gear provides a double cantilever deflection. The main gear is fitted with large treaded tundra tires, with independent hydraulic disk brakes.

Figure 2: Single carry-through main gear

In other to analyze this landing gears static forces, the forces acting on the gear are to be analyzed and interpreted into ANSYS command file. After construction of the landing

5 gear graphically, statistical analysis will be made with real life forces having been taking account of.

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Design Objectives Using the ANSYS software, graphically design the STOHL CH 701 landing gear. Study the relationship of deflection of the landing gear strut and the design load factor. Perform hand calculations on the strut. Determine the forces which will be applied on the strut Through hand calculation predict the results that should be expected from ANSYS. Perform structural analysis on the strut using ANSYS Perform similar analysis on PRO E software, and use results to compare and contrast with ANSYS. Interpret results received from ANSYS.

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TheoryTo understand the application of forces on the landing gear, an understanding of the theory behind the forces acting on it must be explained. Statics is the branch of physics concerned with the analysis of loads, such as force, moment, torque, etc.

Static equilibrium refers to a state where the relative positions of subsystems do not vary over time, or where components and structures are at rest under the action of external forces of equilibrium.

By Newtons Second law, static equilibrium dictates that the net force and net moment on every body in the system is zero. In other words for every force there is an equal but opposite force acting on it. For the dynamic case Kinetic energy is the work needed to accelerate a body from rest to its current to velocity. The work done accelerating or in our case decelerating a body during an infinitesimal time interval dt is given by the equation of:-

Now expressing the Force (F) as change of pressure with respect to time we derive:Now rewriting pressure as mass multiplied by volume, the final formula for the force is derived. To convert to kinetic energy, we must integrate the force with respect to

an axis, in this case x.

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Procedures The dimensions of the landing gear must be obtained in other to properly design the gear on ANSYS, After acquiring the dimensions for the gear, the graphical interpretation was then started. Using commands the landing gear was then fabricated on ANSYS. Hand calculations were then started for the forces that act upon the landing gear at the moment of landing. Using Newtons laws, static and simplified dynamic forces were calculated for the landing gear. The fabricated ANSYS model of the landing gear was then meshed, material properties of the landing gear specified, and the model was prepped for structural analysis. Forces found through hand calculations were then applied to the fabricated model. A replica model of the landing gear was then constructed on the software Pro Engineer, static analysis were also studied and the results obtained will be used for analytical comparison with that of the ANSYS software. After both software analyses had been solved, the results obtained were compared for accuracy.

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Calculations

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ANSYS ResultsGeometry:Key points 1 2 3 4 5 6 7 8 9 10 11 12 13 X 0 -0.61 -0.827481 -0.822165 -0.800219 -0.804976 -0.598790 0 -0.862165 -0.862165 -0.822165 -0.4830 -0.5084 Y 0 0 -0.29936 -0.40096 -0.40096 -0.305789 -0.02200 -0.0220 -0.40096 -0.37556 -0.37556 0 0 Z 0 0 0 0 0 0 0 0 0 0 0 0 0

Lines Connecting Kps:Line L1 L2 L3 L4 L5 L6 L7 L8 L9 L10 L11 L12 L13 KP1 1 13 13 2 3 11 10 9 4 5 6 7 8 KP2 12 12 2 3 11 10 9 4 5 6 7 8 1

Fillet Creation for arcs:

13 lfillt,3,4,0.050 !upper outer arc lfillt,4,5,0.050 !lower outer arc lfillt,5,6,0.015 !stress reliever arc lfillt,10,11,0.048 !lower inner arc lfillt,11,12,0.048 !upper inner arc

Figure 3:3D ANSYS Model

Figures: 2a, 2b, 2c, 2d: The above figures show the sequence that was used to model the landing strut in the ANSYS software. Starting from the left top picture, here we can see that a set of key points were created representing the geometry of the strut. Moving to the left, we can see how the shape of the strut is created by using ANSYS commands to create and connect KPs with each other, thus given the strut its shape. The following picture at the left bottom corner, we can see how the strut is now a full 2d model by creating an area bounded by the lines created in figure 2b. Now at the last figure, we see that the strut is now a full 3d model ready for analysis, this one was created by extruding the area created in the last figure in the negative z-direction.

Boundary Conditions: 3D ANSYS MODEL

Fig.3: The above figure (Figure 3), shows how the boundary conditions where selected. Boundary Condition 1, at the top surface of the strut is represented by the line which bounds the area occupy by the bracket design to hold the landing gear in place with the fuselage of the plain. This boundary condition is constrain in all direction, ux, uy, uz, meaning that it doesnt have any degree of freedom in any direction. Boundary condition 2 represented by the arc at the far right tip of the strut, for this boundary condition instead of constraining only a line we constraint the entire area in the ux & uz directions but we left it free in the uy direction. This means that this B.C is allow to move up and down in the uy direction. The forces were applied in the extended arm created to simulate the shaft that hold the tires connected to the landing strut. The vertical force Fy, was applied in the bottom surface of the extended arm, while the horizontal force was applied at the key points bounding this area of this arm.

Mesh Generation:3D ANSYS MODEL

Figure: 4 Here we could see the strut ANSYS model fully meshed. The mesh is very critical of F.E.A since it is what determines the accuracy of your results. The mesh size used to run the analysis of our strut design was of element size of 15mm. This mesh element size was determined to give us good results and save us computing time.

Deformed Mesh Model: 3D ANSYS MODEL

Figure: 5 The figure above shows the meshed model of the strut elastically deform after running the analysis with the chosen boundary conditions and the applied forces used to simulate the forces on the landing.

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Von Mises Stress: 3D ANSYS MODELYield Strength Criteria

Figure: 6 The figure above shows the Von Mises Stress on the strut. The landing Strut exhibits a maximum yield stress of 339Mpa & a minimum stress of 1.15Mpa.

Maximum Strut Displacement: 3D ANSYS MODEL

Figure: 7A

Figure: 7B The above figures show the quantified displacements of different portions of the strut. It shows the magnitude of the displacement based on the color of each portion of the strut; the colors are ranked from lowest (blue) to maximum displacement (red). The maximum strut displacement has a magnitude of 0.055657m (2.19in).

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ConclusionWith the determination of the maximum von misses stress and the maximum deflection determined for the ANSYS software, to provide proof of consistency with theses results, comparisons must be made using another software. The software used is Solid-Works.

Figure 4: deflection diagram using solid works

(2)

(3)

Figure 5: von mises stress using solid works

Table 1: Results from both ANSYS and Solid Works software Max Von mises stress Max Deflection ANSYS software 339 Mpa 2.19 in Solid Works software 358 Mpa 1.52 in % difference 5.31% 47.60%

From Table 1 it is evident that there are differences in the results gotten from solid works from those gotten from ANSYS. These differences can be a result of the meshing differences between the two programs, also the constraints applied to the strut is slightly different for both software, due to the opportunities of variable constraints found the two software. When compared to the hand calculation result of 2.64in the difference with the struts result is 17%, this is reasonable, since hand calculations are always less accurate than the results gotten from software.

AppendixCommand file for ANSYS/title, Landing Gear Group: IV /prep7 FY=5533 !Vertical Force (N) Fx=765 !Horizontal force (N) E=73.5e9 pss=0.35 A1=0.0035591551 A2=0.002260346 A3=0.0058195011 k,1,0,0,0 k,2,-0.61,0,0 k,3,-0.827481,-0.29936,0 k,4,-0.822165,-0.40096,0 k,5,-0.800219,-0.40096,0 k,6,-0.804976,-0.305789,0 k,7,-0.598790,-0.02200,0 k,8,-0,-0.0220,0 K,9,-0.862165,-0.40096,0 K,10,-0.862165,-0.37556,0 K,11,-0.822165,-0.37556,0 !second suport cinstraint line k,12,-0.4830,0,0 k,13,-0.5084,0,0 !!!!! l,1,12 l,13,12 l,13,2 l,2,3 l,3,11 l,11,10 l, 10,9 l,9,4 l,4,5 l,5,6 l,6,7 l,7,8 l,8,1 !creating arcs/cuvatures ! ! lfillt,3,4,0.050 !upper outer arc lfillt,4,5,0.050 !lower outer arc lfillt,5,6,0.015 !stress releiver arc lfillt,10,11,0.048 !lower inner arc lfillt,11,12,0.048 !upper inner arc !creating area bounded by lines and arcs al,all !volume voffst,1,0.08899 !EXTRUDED DEDTH 3.503543 IN et,1,solid187 !element type solid187 mp,ex,1,E !Youngs Modulus MP,prxy,1,pss !possoins ratio mp,dens,1,2810 !dENSITY !CONSTRAINTS AREA AT THE END OF THE SYMMETRICAL PLANE DA,20,UX,0 DA,20,UZ,0 !FULLY CONSTRAINT AREA INCONTACT WITH PLANE BRACKET !DA,4,UY,0 !DA,4,UZ,0 !DA,4,UX,0 ! !line ontop constraint !dl, 38,20,uy,0 !dl,38,20,uz,0 dl,38,20,uy,0 dl,38,20,uz,0 dl,38,20,ux,0 ET, 1,SOLID187 !ELEMENT TYPE SOLID187 ESIZE,0.015,0, !lenght of elements 15 mm MSHKEY,0 !MAPPED meshing MSHAPE,0,3d !tetrahedral-shaped 3D mesh vmesh,all !aaplied forcess on the strut !Force:Fy !fk,33,fy,5200 !fk,10,fy,5200 !fk,34,fy,5533 !fk, 9,fy,5533 SFA,13,1,PRES,5533/A1 SFA,14,1,PRES,5533/A2 !FORCE:Fx fk, 33,fx,765 fk,10,fx,765 fk,34,fX,765 fk,9,fX,765 FINISH /SOLU ANTYPE,0 SOLVE FINISH /TRIAD,OFF /POST1