Integrated Landing Gear System.pdf

8/9/2019 Integrated Landing Gear System.pdf

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MSC Software 2013 Users ConferenceIrvine, CA, May 7-8, 2013 http://www.mscsoftware.com/

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Multibody Dynamics Simulation of an Integrated Landing Gear System

using MSC.ADAMS

A. A. Yazdani, J. Jin1, G. Lepage-Jutier and G. Cozzolino

1

Mecaer Aviation Group, [email protected]

ABSTRACT

This study outlines the effectiveness and reliability of MSC.ADAMS to perform themultibody dynamics simulation of the integrated landing gear systems. As perReference [1], landing gear design encompasses more engineering disciplines than anyother aspect of aircraft design.

Landing gear system retraction and extension analysis is an important part of the

certification requirement. Herein, the dynamic behavior of an electrically drivenlanding gear system during retraction/extension cycles is investigated under variousdesign solutions using MSC.ADAMS. These simulations are done with real geometryand with joints having the realistic degrees of freedom. Masses and rotational inertiaare assigned to every part of the landing gear system. So, gravity loads are also appliedto this model. Design studies are performed with ease by using the parameterizationtool available in this software. Calculated loads are also obtained by allowing thesoftware to account for flexibility during simulations. Using this software saved aconsiderable amount of effort in troubleshooting of landing gear design.

Comparing the obtained results from both simulations and testing reveals goodcorrelations. Based on the outcome of this study it can be concluded that the cost andtime can be significantly reduced and the optimization of performance of such anintegrated system can be achieved by using MSC.ADAMS.

Keywords:MSC.ADAMS, Landing Gear, Flexible, Retraction, Extension

1 INTRODUCTION

In this study, MSC.ADAMS software (Refs [2]-[3]) is used to optimize a Nose Landing Gear (see Figure 1)performance during retraction and extension cycles (Figure 2). This summarizes the simulation phasesat Mecaer Aviation Group (MAG) that consists of: prediction, correlation against test results and finallyoptimization. MAG is the landing gear supplier to several major fixed and rotary wing OEMs, includingBell Helicopter Textron, Eurocopter, Agusta-Westland, Diamond Aircraft, Eclipse Aerospace, PiperAircraft, Turkish Aerospace Industries and the Korean Aerospace Industry. The engineering capabilitiesinclude design, performance, stress and fatigue life assessments as well as reliability analyses.

The multibody dynamics simulation is done for the Nose Landing Gear shown in Figure 1. This NLG is asemi-levered suspension type shock strut incorporating a single wheel/tire installed on a wheel axlebetween the two arms of a double-sided wheel fork. This gear is a semi-levered suspension type withthe wheel trailed backwards and frees to swivel over 360o. The shock absorber is an oleo-pneumatictype, with a separator piston between oil and nitrogen chamber. The main components of this NLG areidentified in Figure 1.


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Figure 1 Nose Landing Gear (NLG)

Figure 2 NLG Retraction & Extension

Upper Drag Brace

Lower Drag Brace

Over-center SpringCartridge

Main Fitting

Piston

Toque Link

Trailing Arm

Turning Support


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2 RETRACTION/EXTENSION SIMULATION

The goals of this study are: To investigate the performance of retraction/extension mechanism; To provide the required actuator load and major attachment loads.

MSC.ADAMS software is used for this simulation. This model is done by including joint definition,friction, over-center spring preload and stiffness, mass, inertia, drag brace over-center stops andretraction up position stop. Simulation is initially performed by using rigid bodies then the impact offlexibility of the major components of landing gear is investigated. Finally, the obtained results arecompared against test results.

Schematic of NLG retraction is presented in Figure 2. Herein, an electrically driven landing gear systemduring retraction/extension cycles is investigated. An electromechanical actuator (similar to Figure 3) isresponsible for retraction and extension cycles. The actuator stroke versus time profile used in thissimulation is presented in Figure 4. It is worth mentioning that the actuator speed ramp has asignificant impact on the actuator load particularly at endpoints (down and up positions shown inFigure 5).

Figure 3 Electromechanical Actuator

Figure 4 Actuator Stroke versus Time


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Figure 5 Fully Extended and Retracted Configurations

ElectromechanicalActuator

ElectromechanicalActuator

Bellcrank

Link

Bellcrank


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3 SIMULATION RESULTS

3.1 Baseline Design

The NLG retraction and extension performances under two distinguishing mechanical characteristicsare investigated. Obtained results are graphically presented and the motion of the NLG is animated.

The initial design consists of an over-center spring with stiffness of 19 lbf/in and preload of 44 lbf.Using this configuration of NLG, some retraction/extension tests were made by the helicoptermanufacturer. Obtained results are graphically presented in Figure 6. The correlation seems to beconvenient, bearing in mind that real test conditions are unknown, the actuator stroke shown in Figure4 is an assumption).

In Figure 6, the peak and valley points are identified on extension and retraction curves obtained byrigid bodies MSC.ADAMS simulation. These loads are used for fatigue life assessments of neighbouringparts (e.g., bellcrank and link shown in Figure 5).

800

600

400

200

0

200

400

600

0 2 4 6 8 10 12

Load

(lbf)

Time

(s)

Actuator

Load

Spring:

Stiffness=19

lbf/inch,

Preload=44

lbf

TestData

Simulation Data

ExtensionCycle RetractionCycle

1e

2e

3e

4e

5e

6e

1r

2r

3r

4r

5r

5r

Figure 6 Extension & Retraction Curves (Baseline Model)

FEM based fatigue life assessments are performed on bellcrank. MSC Patran is used for pre/post-processing steps and this FEM is solved by MSC.Nastran. The main purpose of this analysis is todetermine the stress distribution in NLG Bell Crank due to the above simulated design load casesduring extension/retraction cycles. In this FEM, bellcrank and interface pin to the main fitting lugs areboth modeled. 10-node tetrahedral elements with aluminum properties and 8-node hexahedralelements with steel properties are associated to bellcrank and pin, respectively. Actuator and link loadsare applied to this model at correct interface points through RBE3 MPCs as shown in Figure 7. Theobtained results for all peak and valley points (shown in Figure 6) are presented in Appendix A. Basedon this assessment, limited fatigue life is predicted for the most critical fatigue spot of bellcrank. Toimprove the fatigue life of this part, actuator loads during extension and retraction cycles must bereduced.

Using rigid and flexible bodies for baseline design the extension and retraction curves are obtained by

simulation. These curves are presented in Figure 8. For the sake of simplicity, only three majorcomponents that are closer to the actuator are introduced as flexible bodies (e.g., main fitting and bothdrag braces). Both simulations predict conservative loads for extension and retraction cycles.MSC.ADAMS/Flex simulation is in better agreement with test results at the beginning of extension andretraction cycles.

6r


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For the third simulation shown in Figure 8, the stiffness matrices for the Nose Landing Gear at theFuselage/Main Fitting attachments and Actuator attachment are also introduced into MSC.ADAMSsimulation. These stiffness matrices are shown below:

Tx Ty Tz

Tx Ty Tz

Tx Ty Tz

Tx 10,000

Ty 30,000

Tz 30,000

Tx 10,000

Ty 30,000

Tz 30,000

Tx 10,000

Ty 20,000

Tz 20,000

RHSMain

Fitting

Attach

Joint

LHSMain

Fitting

Attach

Joint

Actuator

Attach

Joint

Diagonal Stiffness Matrix for the Nose Landing Gear at the Fuselage/Gear Attachments (lbs/in)

DOF's RHSMainFittingAttachJoint LHSMainFittingAttachJoint ActuatorAttachJoint

The diagonal terms in the above matrices are assumed by MAG and the accuracy of this assumption isnot confirmed by fuselage manufacturer. Consequently, discrepancies observed between the obtainedcurves with this scenario and test results can be explained by the lack of confidence on the assumedstiffness at attachment points. However, it must be mentioned that the predicted actuator loads byMSC.ADAMS under all scenarios are generally conservative.

Figure 7 Bellcrank Finite Element Model

Total Num ber of Elem ents & Nodes

CHEXA = 3,381CTETEA = 312,509GRID = 490,746

Actuator

Link

Interface Pin toMain Fitting Lugs

Spot 1

Spot 2


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350

250

150

50

50

150

250

350

450

550

0 1 2 3 4 5 6

Load

(lbf)

Time(s)

TestData

Simulation Data(RigidBodies)

Simulation Data(FlexBodies)

Simulation Data(FlexBodies&Attach)

ExtensionCycle

350

250

150

50

50

150

6 7 8 9 10 11

Load

(lbf)

Time

(s)

TestData

Simulation Data(RigidBodies)

Simulation Data(FlexBodies)

Simulation Data(FlexBodies&Attach)

RetractionCycle

Figure 8 Retraction Curve for Baseline Design (Test versus Simulation)


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3.2 Redesign Solution

To improve fatigue life of bellcrank, the length of the over-center spring is reduced and the actuatorloads for retraction and extension cycles are rechecked.

So, the redesign solution consists of an over-center spring with stiffness of 23 lbf/in and preload of 27lbf. Using this configuration of NLG, some retraction/extension tests were also made by the helicoptermanufacturer. Simulated and test results are graphically presented in Figure 9 and Figure 10,

respectively. It can be noticed that the redesign solution reduce significantly the actuator loads forboth simulation and test curves.

The extension and retraction curves are obtained by simulation, using rigid and flexible bodies forredesign scenario. These curves are presented in Figure 11.

800

600

400

200

0

200

400

600

0 2 4 6 8 10 12

Load

(lbf)

Time(s)

Spring: Stiffness=19lbf/in,Preload=44lbf(Baseline)

Spring: Stiffness=23lbf/in,Preload=27lbf


Figure 9 Extension & Retraction Curves (Simulation Data)

800

600

400

200

0

200

400

600

0 2 4 6 8 10 12

Load

(lbf)

Time(s)

TestData(Baseline) TestData(Redesigned Spring)


Figure 10 Extension & Retraction Curves (Test Data)


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300

200

100

0

100

200

300

400

0 1 2 3 4 5 6

Load

(lbf)

Time(s)

TestData(2)

SimulationData(Rigid)

SimulationData(FlexBodies)

SimulationData(FlexBodies&Attach)

ExtensionCycle

300

250

200

150

100

50

0

50

100

150

6 7 8 9 10 11

Load

(lbf)

Time(s)

TestData(2)

SimulationData(Rigid)

SimulationData(FlexBodies)

SimulationData(FlexBodies&Attach)

RetractionCycle

Figure 11 Extension and Retraction Curves for Redesign (Test versus Simulation)


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4 CONCLUDING REMARKS

This paper presented a real case study in which the multibody dynamics simulation of an integratedlanding gear system is performed by MSC.ADAMS. Conclusions drawn from the above investigationsare shown below:

With MSC.ADAMS, virtual prototypes of a complete landing gear system can be built efficiently

(reducing engineering time, cost and risk); MSC.ADAMS models for retraction and extension cycles can be used to improve design and toinvestigate quickly new ideas with ease;

Simulation results demonstrated good agreements with the test data for both scenarios(baseline & redesign);

MSC.ADAMS/Flex models had better agreements with test results at the beginning of extensionand retraction cycles;

In general, both (rigid & flex) simulations predict conservative loads for extension andretraction cycles.

T r adema r k Acknow l edgem en t s

NASTRAN is a registered trademark of NASA and MSC.NASTRANis an enhanced, proprietary

version developed and maintained by the MacNeal Schwendler Corporation. MSC.PATRANMSC.FATIGUE and MSC.ADAMSare registered trademarks of the MacNeal

Schwendler Corporation.

REFERENCES

[1] Aircraft Landing Gear Design: Principles and Practices, Currey N. 1989, AIAAEducation Series.

[2] "MSC Software, ADAMS/Solver Help",http://simcompanion.mscsoftware.com/infocenter/index?page=content&id=DOC9391

[3] "MSC Software, ADAMS/Flex Help",http://simcompanion.mscsoftware.com/infocenter/index?page=content&id=DOC10098


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Appendix A - Bellcrank FEA Results

In this Appendix the FEA results for bellcrank mesh shown in Figure 7 are presented. These results areobtained by MSC.Nastran and post-processed by MSC.Patran are presented. As shown in Figure 6, sixpoints are identified on extension/retraction curves. Since, visualization of the stress distribution at

contact regions (e.g. sockets, lugs) is not in our interest, for the sake of simplicity, interface bushingsare neglected and glued contact is used between the interface pin and bellcrank. The obtained resultsare presented in Figure 12 to Figure 15.

By performing fatigue life assessments, limited life is predicted for the most critical fatigue spot. Inorder to meet the expected life, the magnitude of actuator loads during extension and retraction cyclesmust be reduced. For this purpose, a redesign is required. This approach is discussed in Section 3.2.

Tension

Compression

Figure 12 Bellcrank von Mises Stress Distribution for Max. Tension & Max. Compression


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Point 1r Point 2r Point 3r Point 4r

Point 5r Point 6r Point 1e Point 2e

Point 3e Point 4e Point 5e Point 6e

Figure 13 Bellcrank Displacement Distribution at Deformed Shapes


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Point 1r Point 2r Point 3r Point 4r

Point 5r Point 6r Point 1e Point 2e

Point 3e Point 4e Point 5e Point 6e

Figure 14Bellcrank von Mises Stress Distribution


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Point1r Point2r Point3r Point4r

Point5r Point6r Point1e Point2e

Point3e Point4e Point5e Point6e

Figure 15Bellcrank Max. Principal Stress Distribution

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Integrated Landing Gear System.pdf