multibody dynamics simulation of an integrated landing...

MSC Software 2013 Users Conference Irvine, 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

1Mecaer Aviation Group, [email protected]

ABSTRACT This study outlines the effectiveness and reliability of MSC.ADAMS to perform the multibody dynamics simulation of the integrated landing gear systems. As per Reference [1], landing gear design encompasses more engineering disciplines than any other 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 driven landing gear system during retraction/extension cycles is investigated under various design solutions using MSC.ADAMS. These simulations are done with real geometry and with joints having the realistic degrees of freedom. Masses and rotational inertia are assigned to every part of the landing gear system. So, gravity loads are also applied to this model. Design studies are performed with ease by using the parameterization tool available in this software. Calculated loads are also obtained by allowing the software to account for flexibility during simulations. Using this software saved a considerable amount of effort in troubleshooting of landing gear design. Comparing the obtained results from both simulations and testing reveals good correlations. Based on the outcome of this study it can be concluded that the cost and time can be significantly reduced and the optimization of performance of such an integrated 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 phases at Mecaer Aviation Group (MAG) that consists of: prediction, correlation against test results and finally optimization. MAG is the landing gear supplier to several major fixed and rotary wing OEMs, including Bell Helicopter Textron, Eurocopter, Agusta-Westland, Diamond Aircraft, Eclipse Aerospace, Piper Aircraft, Turkish Aerospace Industries and the Korean Aerospace Industry. The engineering capabilities include 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 a semi-levered suspension type shock strut incorporating a single wheel/tire installed on a wheel axle between the two arms of a double-sided wheel fork. This gear is a semi-levered suspension type with the wheel trailed backwards and frees to swivel over 360o. The shock absorber is an oleo-pneumatic type, with a separator piston between oil and nitrogen chamber. The main components of this NLG are identified 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 Spring Cartridge

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 and retraction up position stop. Simulation is initially performed by using rigid bodies then the impact of flexibility of the major components of landing gear is investigated. Finally, the obtained results are compared against test results.

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

Figure 3 Electromechanical Actuator

Figure 4 Actuator Stroke versus Time


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Figure 5 Fully Extended and Retracted Configurations

Electromechanical Actuator

Electromechanical Actuator

Bellcrank

Link

Bellcrank


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3 SIMULATION RESULTS

3.1 Baseline Design The NLG retraction and extension performances under two distinguishing mechanical characteristics are 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 helicopter manufacturer. Obtained results are graphically presented in Figure 6. The correlation seems to be convenient, bearing in mind that real test conditions are unknown, the actuator stroke shown in Figure 4 is an assumption). In Figure 6, the peak and valley points are identified on extension and retraction curves obtained by rigid bodies MSC.ADAMS simulation. These loads are used for fatigue life assessments of neighbouring parts (e.g., bellcrank and link shown in Figure 5).

800

600

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200

0

200

400

600

0 2 4 6 8 10 12

Load

(lbf)

Time(s)

ActuatorLoadSpring:Stiffness=19lbf/inch,Preload=44lbf

TestData

SimulationData

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 to determine the stress distribution in NLG Bell Crank due to the above simulated design load cases during extension/retraction cycles. In this FEM, bellcrank and interface pin to the main fitting lugs are both modeled. 10-node tetrahedral elements with aluminum properties and 8-node hexahedral elements with steel properties are associated to bellcrank and pin, respectively. Actuator and link loads are applied to this model at correct interface points through RBE3 MPCs as shown in Figure 7. The obtained results for all peak and valley points (shown in Figure 6) are presented in Appendix A. Based on this assessment, limited fatigue life is predicted for the most critical fatigue spot of bellcrank. To improve the fatigue life of this part, actuator loads during extension and retraction cycles must be reduced. 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 major components that are closer to the actuator are introduced as flexible bodies (e.g., main fitting and both drag 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 and retraction cycles.

6r


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

Tx Ty Tz Tx Ty Tz Tx Ty TzTx 10,000Ty 30,000Tz 30,000Tx 10,000Ty 30,000Tz 30,000Tx 10,000Ty 20,000Tz 20,000

RH

S M

ain

Fitti

ng

Atta

ch

Join

t

LHS

Mai

n Fi

tting

At

tach

Jo

int

Actu

ator

At

tach

Jo

int

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 is not confirmed by fuselage manufacturer. Consequently, discrepancies observed between the obtained curves with this scenario and test results can be explained by the lack of confidence on the assumed stiffness at attachment points. However, it must be mentioned that the predicted actuator loads by MSC.ADAMS under all scenarios are generally conservative.

Figure 7 Bellcrank Finite Element Model

Total Number of Elements & Nodes CHEXA = 3,381 CTETEA = 312,509 GRID = 490,746

Actuator

Link

Interface Pin to Main Fitting Lugs

Spot 1

Spot 2


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350

450

550

0 1 2 3 4 5 6

Load

(lbf)

Time(s)

TestData

SimulationData(RigidBodies)

SimulationData(FlexBodies)

SimulationData(FlexBodies&Attach)

ExtensionCycle

350

250

150

50

50

150

6 7 8 9 10 11

Load

(lbf)

Time(s)

TestData

SimulationData(RigidBodies)



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 actuator loads 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 27 lbf. Using this configuration of NLG, some retraction/extension tests were also made by the helicopter manufacturer. 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 for both simulation and test curves. The extension and retraction curves are obtained by simulation, using rigid and flexible bodies for redesign scenario. These curves are presented in Figure 11.

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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)

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Load

(lbf)

Time(s)

TestData(Baseline) TestData(RedesignedSpring)


Figure 10 Extension & Retraction Curves (Test Data)


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Load

(lbf)

Time(s)

TestData(2)

SimulationData(Rigid)



ExtensionCycle

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50

0

50

100

150

6 7 8 9 10 11

Load

(lbf)

Time(s)

TestData(2)

SimulationData(Rigid)



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 integrated landing gear system is performed by MSC.ADAMS. Conclusions drawn from the above investigations are 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 to investigate 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 extension and retraction cycles;

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

Trademark Acknowledgements

NASTRANis a registered trademark of NASA and MSC.NASTRANis an enhanced, proprietary version developed and maintained by the MacNeal Schwendler Corporation.

MSC.PATRAN MSC.FATIGUE and MSC.ADAMSare registered trademarks of the MacNeal Schwendler Corporation.

REFERENCES

[1] Aircraft Landing Gear Design: Principles and Practices, Currey N. 1989, AIAA Education 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 are obtained by MSC.Nastran and post-processed by MSC.Patran are presented. As shown in Figure 6, six points 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 bushings are neglected and glued contact is used between the interface pin and bellcrank. The obtained results are presented in Figure 12 to Figure 15. By performing fatigue life assessments, limited life is predicted for the most critical fatigue spot. In order to meet the expected life, the magnitude of actuator loads during extension and retraction cycles must 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 14 Bellcrank von Mises Stress Distribution


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Point1r Point2r Point3r Point4r

Point5r Point6r Point1e Point2e

Point3e Point4e Point5e Point6e

Figure 15 Bellcrank Max. Principal Stress Distribution

multibody dynamics simulation of an integrated landing...

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