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High Flexibility Rotorcraft Driveshafts using FlexibleMatrix Composites and Active Bearing Control

Principal InvestigatorsKon-Well Wang, Ph.D.

Diefenderfer Chaired Professor in Mechanical EngineeringCharles Bakis, Ph.D.

Professor of Engineering Science and MechanicsEdward Smith, Ph.D.

Professor of Aerospace Engineering

Graduate Student supported by RCOEBryan Mayrides (M.S. student)

Other Team MembersHans DeSmidt (Ph.D. student)

Ying Shan (Ph.D. student)

PS 2.2

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Issues of Current Driveline Systems Problem Statement and Technical Barriers

Current Drivelines

Segmented shafting with significant

# of flex couplings/bearings for

misalignment compensation

Passive dampers needed for supercritical speed shafts

High Maintenance and Cost

Component (bearings, couplings, dampers) wear

Shaft balancing and alignment

Strict shaft eccentricity tolerances

Issues applicable to both helicopter and tiltrotor

Couplings Bearings

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1 8 5 5Program Goal and Ideas

To address the issues with current systems and

overcome the technical barriers for achieving a

simple, high performance, low vibration, low cost,

and low maintenance driveline of rotary-wing aircraft

Reduce number of mechanical contact components

Reduce maintenance need

Suppress vibration and ensure stability

IDEAS ?

Develop and utilize newly emerging materials and active

control technologies -- a combination of

Flexible matrix composite(FMC) materials and

Active magnetic bearings (AMB)

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1 8 5 5Ideas

Flexible matrix composite (FMC) materialswith tailored ply orientations for shafting

Soft in flexure and stiff in torsion to accommodateforlarge misalignment and effectively transmit power

Withoutmulti-segment shafting and large # ofbearings/couplings -- reduce cost and maintenanceneed

New

AMBsFMC shaft

Current

Couplings Bearings

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Ideas (cont.)

Active magnetic bearings for low maintenance and vibration control While highly flexible composite driveshaft systems have many

advantages, their vibration behavior could be issues that need to be

addressed before realizing the idea

Penn State researchers have explored the feasibility of active vibration

control of tailrotor-drivetrain structure via active magnetic bearings(AMB) by proper controller design, the AMB actuator could be a good

candidate for helicopter driveline control (size, weight, power) [DeSmidt,

Wang, and Smith, Proc of 54th AHS Forum, 1998]

Non-contact -- no frictional wear

Large frequency range -- ideal foractivevibration control in rotorcraft setting

Light backup roller bearings (only contact

with active failure) forfail-safe purpose

Stator

Airgap

Electro-

Magnetic Coil

Shaft

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1 8 5 52004 Review Comments and Actions

Assess Potential Payoffs

We have examined payoffs for supercritical driveline in previous studies;this year we expanded the study to show potential payoffs (weight andcomponent reductions) for subcritical drivelines via system design

Assess Cost Benefit

Qualitatively, reducing components/maintenance = reducing cost;

To quantify cost benefit requires development on specific drive systemwith manufacturers and users (future RITA project)

Examine Practicality of Magnetic Bearing

Have achieved another successful demonstration of AMB controller forFMC shafting with uncertainties

In the process of examining AMB design (weight, size, power) in rotorcraftsetting via NASA Glenn design code (On-going effort)

Have generated new ideas of hybrid active-passive failsafe devices asfuture basic research topics

Address Failure Modes

Thorough study beyond scope of current program Have generatedideas/ lan to examine this issue as a future basic research to ic

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1 8 5 5Research Issues and Task Objectives

Materials and Composite Issues

Structural Mechanics and

Dynamics Issues

Systems and Controls Issues

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1 8 5 5Research Issues and Task Objectives

Materials and Composite Issues Rationale:

Traditional barrier to higher strain operation of fiber compositesis matrix cracking

Flexible, low-modulus matrix can potentially avoid cracking

Technical Objectives:

Select a trial flexible matrix system (carbon/polyurethane)

Develop filament winding process

Characterize stiffness & damping behavior and validate modelsover range of temperatures, frequencies, and strains

Build lab-scale shafts for experimental validation of self-heating, structural dynamics, and to investigate fatiguebehavior

0 090

Matrix

Cracking

FMC

0 090 90

RMC

0 090 9090 90

MatrixCracking

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1 8 5 5Materials and Composite Sub-Task

Achievements 2001-2003/04

Developed wet filament winding technique for trial flexible matrix

composite shafts (carbon/polyurethane)

Developed test apparatus & method for characterizing frequency and

temperature dependent damping & stiffness of FMC laminas andlaminates

Developed & validated models for frequency and temperature

dependent damping & stiffness of FMC laminas and laminates

Developed model and test method to investigate self-heating behavior

of rotating misaligned FMC shafts

Summary of Accomplishments in 2004/05:

Refined and experimentally validated self-heating model of rotating

misaligned FMC shafts

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Input to the temperature model: frequency and temperature dependent laminaproperties of FMC material; misalignment strain; shaft speed

The misalignment strain and rotation speed can be controlled. The stand can spinFMC shafts at up to 1.25% misalignment strain, and at speed up to 2500 RPM

Internal Self-Heating Model and Experimental ValidationMethod for Misaligned Rotating FMC Shafts

Shaft Self-Heating Model

x

y

or

a

b

M

z

P

Convection into air

(T) due to rotation

r

a b

Insulated

T0Tn

T1 Ti-1 Tn-1Ti Ti+1

r/2 r/2

r

Ti,'''iq

2.5 HP DC

Motor

Bearing

IR T/C

FMC Shaft

IR Tachometer

5 ft

Misaligned Rotating Shaft Test Stand for ModelValidation and Fatigue Characterization

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Shaft Speed (RPM)

0 500 1000 1500 2000 2500 3000

Temperature

Increase,

T(oC)

0

10

20

30

40

Shaft Speed (RPM)

0 500 1000 1500 2000 2500 3000

Temperature

Increase,

T(oC)

0

10

20

30

40

0.25%, RMC0.25%, FMC

Shaft Speed (RPM)

0 500 1000 1500 2000 2500 3000

Temperature

Increase,

T(oC)

0

5

10

15

20

25

0.25%

0.50%

0.75%

0.95%

1.15%

Model Results and Experimental Validation

(45) deg. FMC

Model capable of predicting self heating behavior of FMCmaterials and providing guidance for design and control ofFMC shaft

Self-heating of FMC shaft is insignificant compared to RMC

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1 8 5 5Effect of Temperature on Shaft Properties

Laminate design affects temperature sensitivity of shaft

Tool developed can predict temperature effect on shaft

properties

provide design and control guidance

A lied Fre uenc , f Hz

0 20 40 60 80 100

LongitudinalMod

ulus,

Ex(GPa)

30

31

32

33

34

23oC

80oC

Shaft Longitudinal Modulus

[+60/-60/+25/-25]s

Applied Frequency, f (Hz)

0 20 40 60 80 100

LongitudinalMod

ulus,

Ex(GPa)

0.0

0.2

0.4

0.6

0.8

1.0

23oC

80oC

[+45/-45/+45/-45]s

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1 8 5 5Research Issues and Task Objectives

Materials and Composite Issues

Structural Mechanics and Dynamics Issues

Develop analysis tools for driveshaft dynamic loads/

deformation characterization (e.g., strain level, buckling,

stability, damping effect on temperature & property

variation)

FMC materials selection and structural

tailoring/optimization to satisfy design desires (e.g.,

maximum allowable misalignment, minimum weight, and

minimum internal damping)

Systems and Controls Issues

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Structural Mechanics andDynamics Sub-Task

Summary of Previous Work (2001-2003/04)

FE model and analysis tools have been developed to

analyze driveline static and dynamic characteristics

(deformation,stress level,natural frequency, etc.)

Utilizing the model and tools developed,

Performed study to provide information regarding

parameter effects on system (durability, stability, etc.)

System parameters were tailored to achievesatisfactory system performance forsupercriticaldriveline

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Structural Mechanics andDynamics Sub-Task

Summary of Current Work (2004/05) Examined feasibility of designing FMC driveshafts for

subcritical applications

Maintain advantages of current supercritical driveline (light

weight, fewer bearings) but without the shortcomings (highvibration, whirl instability, and external damperrequirements)

Performed optimization study where shaft parameterswere tailored to find minimum weight and/or component

driveline that meets performance requirements

Examined applications for model/analysis tool

Reducing weight in subcritical driveline (Blackhawk,Chinook)

Design a driveline for a minimum number of components

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Inputs Helicopter properties (shaft geometry, speed, power)

Applied loads (torque, misalignment, imbalance)

Design variables (ply sequence, ply angles, # bearings, outer diameter)

Inputs used to iteratively calculate temperature dependent

laminate properties and steady state temperature Accounts for self-heating (misaligned rotation) and considers atmosphericheating and rotor downwash cooling

Laminate properties (at steady state temperature) to calculateperformance indices Critical speed ratio (ensures subcritical)

Tsai Wu strength factor (measure of strength) Torsional buckling safety factor

Torsional yield safety factor

Driveline with minimum weight/components is optimum

design

Design Approach/Model Outline

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Minimum Weight DesignStudy Results - Blackhawk

Blackhawk: current driveline specifications 5 segments

4 midspan flex couplings, 4 midspan bearings

Driveline mass = 31.3 kg (69 lbs)

Blackhawk: optimum FMC driveline specifications 1 segment with [60/-60/-25/25]S layup 0 midspan couplings, 3 midspan bearings

Driveline mass = 21.6 kg (47.6 lbs)

Conventional AlloyNew - FMC

Input Torque 734

Nm

(reduction of 5 components)

(reduction of 29.5%)

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Minimum Weight DesignStudy Results - Chinook

Chinook: current driveline specifications 7 segments

6 midspan flex couplings, 6 midspan bearings

Driveline mass = 60.4 kg (133 lbs)

Chinook: optimum FMC driveline specifications 1 segment with [50/-50/-20/20]S layup

0 midspan couplings, 5 midspan bearings

Driveline mass = 44.4 kg (97.9 lbs)

Input Torque

4067 Nm

Conventional - AlloyNew - FMC

Conclusion: Designers go from subcritical to supercriticalto reduce weight, but weight savings (even component

reduction) can also be realized by using FMC drivelines

while maintaining subcritical operation

(reduction of 25.5%)

(reduction of 7 components)

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Minimum ComponentDesign Study

Model & analysis tool applied to re-design drivelinefor minimum components (reduce maintenanceneeds) instead of minimum weight

Can we still achieve weight savings when minimizing

driveline components?

One example: Blackhawk with [1/-1/-2/2]slayupCurrent Min Weight Min Comp

Lay-up - [60/-60/-25/25]S [70/-70/-10/10]S

OD (m) 0.0889 0.101 0.14

# Midspan Couplings 4 0 0

# Bearings 4 3 2

Weight (kg) 31.3 21.6 23.8

Observations:Always eliminate all midspan couplings for FMC designs

(both methods)

The number of bearing components can be further reduced

even with subcritical speed requirementWeight still saved for this case as compared to current

design

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Materials and Composite IssuesStructural Mechanics and Dynamics Issues

Systems and Controls Issues

Effective vibration and stability control methodology Vibration suppression -- Shaft imbalance with uncertain

magnitude and distribution

Stability issues for supercritical shafting -- whirl instability due

to shaft internal damping

Adaptive control to compensate for operating condition

uncertainty and shaft property variations

Actuator/system design in rotorcraft setting (size,

weight, power)

Research Issues and Task Objectives

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Systems and Controls Sub-Task-Achievement Summary

Achievements (2001- 2003/04)

Preliminary study to identify issues and feasibility of AMB

actuators/control in rotorcraft setting

Developed state equation and uncertainty functionformulation for the AMB-FMC driveshaft system

Synthesized hybrid robust feedback/adaptive feed-

forward control law for AMB driveline system and

developed robust controller design methodology

Analytically and experimentally evaluated and validated

closed-loop controller performance on AMB-driveline

testrig (on conventional segmented Alloy shaft)

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Summary of New Achievements (2004/05) Developed H/Synchronous Adaptive Feed-Forward

controller for AMB/FMC driveline system

Suppress imbalance vibration

Suppress whirl instability (if supercritical) Account for FMC shaft stiffness and damping uncertainties due to

operating temperaturevariations

Concurrent optimal design of control parameters and AMB

locations to maximize closed-loop robustness

Analytically and experimentally evaluated AMB/FMC

driveline closed-loop performance on testrig

Stability and vibration suppression performance and robustness

Multiple operating conditions (various shaft speeds, load torques,

and operating temperatures)

Systems and Controls Sub-Task

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AMB-FMC Driveline System withHybrid H/Adaptive Control

u

d

y

uFBRobustH

FeedbackController+

uAVC y

Synchronous

Adaptive Feed-

Forward Vibration

Control

TAMB-FMC

Driveline

Hybrid H/AVC Control Law

Robust H feedback - Levitatesdriveline & ensuresstability

Adaptive feed-forward - Adapts

to suppress driveline vibration

Non-Contact

Active Magnetic

Bearing

AMB-FMC Driveline SystemShaft Imbalance

AerodynamicLoads

AMB1

Load

Torque

AMB2AMB3

One-Piece FMC shaft with rigidcouplings supported by ActiveMagnetic Bearings (AMB)

Driveline subjected to shaft

imbalance, misalignment, torque &ambient temperature variations

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AMB-FMC Driveline SystemClosed-Loop Robustness & Performance

Due to FMC stiffness and dampingtemperature sensitivity, H/AVCdesigned to be robust to variationsabout nominal temperature

Closed-loop system has significant

temp. robustness [ -20F