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Helicopter Blade Lag Damping Using Embedded Inertial Dampers

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Aeromechanical Instabilities (Ground Resonance and Air Resonance) ... Spar (10 lbs) Damper (1 lb) Hub. Rotorcraft Center of Excellence. Lord Corp. Helical Tuning Port ... – PowerPoint PPT presentation

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Title: Helicopter Blade Lag Damping Using Embedded Inertial Dampers


1
Helicopter Blade Lag Damping Using Embedded
Inertial Dampers
Jason S. Petrie MS jpetrie_at_psu.edu
Dr. Edward C. Smith Professor of Aerospace
Engineering ecs5_at_psu.edu
Dr. George A. Lesieutre Professor of Aerospace
Engineering g-lesieutre_at_psu.edu
  • 2004 National Rotorcraft Technology Center Review
  • May 3, 2005

2
Presentation Outline
  • Background
  • Embedded Damper Concept
  • Objectives
  • Technical Approach
  • Accomplishments
  • Embedded Fluidlastic Damper Design
  • Experiment Hardware and Resuts
  • Conclusions

3
Aeromechanical Instabilities
Major design considerations in the development of
both Articulated and Hingeless Rotor Systems
are Aeromechanical Instabilities (Ground
Resonance and Air Resonance) An effective method
to avoid these instabilities is the addition of
Blade Lag Damping
Lag Damper
4
State-of-the-Art Lag Dampers
  • Extremely High Maintenance
  • Many Critical Flight Conditions / Loads
  • Limited Life / High Cost of Replacement
  • Stroke Limits for Elastomeric Dampers
  • No Breakthrough Advances in Passive Rotor Blade
    Lag Damper Technology in the Last 20 Years

5
Embedded Inertial Dampers
Simplified Hub Design Fewer Parts Less
Constraints
Chordwise Motion of the Mass Out of Phase with
Rotor Blade Lag Motion
Large Moment Arm
Blade Cavity
Mass
?
Ma
Elastomeric Spring
Restoring Inertial Moment about the Lag Hinge
Embedded Damper System
Hebert, Lesieutre Zapfe (1996 1998)
6
Embedded Inertial Dampers
Embedded Dampers
Viscous Root End Dampers
7
Embedded Dampers vs Root End Dampers
Root End Damper
Embedded Inertial Damper
Difficulties with the Geometry of the Blade or Hub
Yes (Especially with Bearingless Rotors)
Yes (Small Blade Cavity)
Moderate - Large
Amount of Lag Damping
Small - Moderate
Possibly Reduce MLag (Stiff In-Plane?)
Hub Loads
Increases MLag
Small Increase (Utilized Leading Edge Mass)
Rotor Weight
Moderate Increase
Does Not Affect Hub
Complexity of Rotor Hub
Increases
Does Not Affect Hub
Rotor Hub Drag
Increases
Small
Size
Moderate to Large
High Centrifugal Force Loading
Yes
No
8
Embedded Devices
Embedded mechanical devices have been
successfully integrated into full scale rotor
blades. An embedded inertial damper will be
subject to similar loads and geometric
constraints as existing embedded devices.
Reference DARPA - Smart Rotor Program - 2004
9
Objectives
Initial research shows that embedded inertial
dampers may be promising for lag damping of rotor
blades. In addition, embedded inertial dampers
may utilize part of the leading edge weight of
the blade and simplify the rotor hub
considerably.
Current Research Objectives
  • Theoretical and experimental investigation of the
    feasibility of blade lag damping using embedded
    inertial dampers
  • Develop a physical understanding of blade lag
    damping with embedded inertial dampers (modal
    properties, stability, and response)
  • Establish design guidelines for rotor blade lag
    damping with embedded inertial dampers

10
Technical Approach
  • Theoretical Investigation of Blade Lag Damping
    Using Embedded Inertial Dampers
  • Develop Aeromechanical Stability Analysis for the
    Rotor-Fuselage-Damper System
  • Aeroelastic and Aeromechanical Stability Analysis
    of Rotor System with Embedded Damper
  • Parametric Study
  • Analysis Validation and Experimental
    Investigation of Blade Lag Damping Using Embedded
    Inertial Dampers
  • Isolated Blade Lag Damping
  • Aeromechanical Stability of Rotor System
  • Embedded Inertial Damper Device Design and Test

11
2004 RCOE Review
  • External Interactions
  • Lord Corporation
  • US Army
  • Sikorsky
  • Bell Helicopter

12
2001 - 2002 Accomplishments
  • Isolated Blade Lag Damping Experiment
  • Validated the Analytical Model and Concept
  • Revealed the Excessive Static Displacement of the
    Damper Mass
  • Identified the Technical Barriers
  • Developed an Understanding of the Design Issues
    Related to Embedded Chordwise Inertial Dampers
  • Modified Design Analysis to Capture Realistic
    Physics
  • Non-Linear Effects of the Static Lag Angle on
    Damper Response
  • Investigated Additional Conceptual Design
    Parameters
  • Angular and Radial Damper Response
  • Conducted an Initial Investigation of Blade Lag
    Damping Using Embedded Fluid Elastic Dampers
  • Developed a pure lag blade-embedded damper model
  • Conducted a parametric study

13
2003 Accomplishments
  • Conducted Initial Simulation of Rotor Blade Loads
    and Hub Vibration in Forward Flight
  • Refined Fluid Elastic Damper Model to Include All
    Necessary Fluid Motion Dynamics and Attributes
  • Conducted a Study of Blade Lag Damping Using
    Embedded Fluid Elastic Dampers
  • Conducted a parametric study to determine the
    effects of the fluid elastic element on rotor
    blade lag damping and the damper response
  • Compared the use of fluid elastic inertial
    dampers with elastomeric dampers previously
    investigated
  • Conducted feasibility study of embedded fluid
    elastic inertial dampers
  • Completed Initial Design of Fluid Elastic Damper
    with the Lord Corporation for Full Scale and
    Model Rotors

14
2004-05 Accomplishments
Development of a New test facility to evaluate
Lag Damper Technologies Completed Detailed
Design of Fluid Elastic Damper with the Lord
Corporation for Full Scale and Model
Rotors Fabrication of Second Generation (Fluid
Elastic) Embedded Inertial Damper Benchtop and
initial rotor testing completed Published AIAA
and AHS Conference Papers, MS Thesis, and AIAA
Journal of Aircraft paper
15
Presentation Outline
  • Background
  • Embedded Fluidlastic Damper Design
  • Experiment Hardware and Resuts
  • Conclusions

16
Elastomeric Damper Design
Damper Equation of Motion
Damper Response
17
Elastomeric Damper Design Issues
  • The static displacement of the embedded inertial
    damper may be excessive
  • A low damper tuning frequency is required to
    produce a suitable damping band for
    aeromechanical stability of system
  • An ideal embedded chordwise inertial damper for
    helicopter blade lag damping would have both a
    high static stiffness and a low dynamic stiffness

18
Fluid Elastic Damper
  • High Static Stiffness
  • Low Dynamic Stiffness
  • As a result of blade lag motion, the damper mass
    oscillates in the lag direction and the fluid in
    the tuning port is pumped through the inner
    chamber.
  • Fluid motion creates a force which reduces the
    effective stiffness of the damper. The fluid
    force increases as the frequency of the system
    increases.
  • References
  • Halwes (Bell Helicopter) 1980
  • McGuire (Lord Corp.) 1994
  • Kang (PSU) 2001

19
Fluid Elastic Damper Model
Mass-Spring Equivalent of a Fluid-Elastomer Damper
ap
at (G-1)ap
mp
at
apo
mt
ka
ato
b
a
Reference Halwes (Bell Helicopter) 1980
mp Damper Primary Mass mt Tuning Mass Fluid
Mass AL? A Tuning Port Cross Sectional Area L
Length of Tuning Port ? Density of Fluid G
b/a Outer Cylinder-Tuning Port Area Ratio
Parameters
20
Fluid Elastic Damper Design
Fluid Mass
Tuning Frequency
Stiffness
Tuning Port Area Ratio
Step 1
  • Establish an appropriate tuning frequency in
    order to maintain the aeromechanical stability of
    the rotor system

21
Fluid Elastic Damper Design
Fluid Mass
Tuning Frequency
Stiffness
Tuning Port Area Ratio
Step 2
  • Establish the amount of mass that can be used
    within the blade cavity for the damper device
  • Embedded inertial dampers are intended to utilize
    part of the leading edge mass or part the tip
    mass of a rotor blade

22
Fluid Elastic Damper Design
Fluid Mass
Tuning Frequency
Stiffness
Tuning Port Area Ratio
Step 3
  • Set the stiffness of the elastomer such that the
    device will be able to resist the centrifugal
    force at rotor speeds that correspond to the
    tuning frequency of the device

23
Fluid Elastic Damper Design
Fluid Mass
Tuning Frequency
Stiffness
Tuning Port Area Ratio
Step 4
  • The fluid mass and the tuning port area ratio are
    then determined based on the equation for the
    elastomer stiffness

24
Fluid Elastic Damper Design
Fluid Mass
Tuning Frequency
Stiffness
Tuning Port Area Ratio
  • The fluid mass and the tuning port area ratio
    will affect the overall size of the embedded
    fluid elastic damper

The device must be able to fit within the blade
25
Fluid Elastic Damper Design
Conceptual Device
Practical Device
26
Fluid Elastic Embedded Damper
Spar (10 lbs)

Hub
Damper (1 lb)
27
Lord Corp. Helical Tuning Port
Enables very high Tuning port ratios (G
50) Suited for compact embedded designs
Elastomeric Element The average stiffness was 
2058 lbs/in at - .010" and 5 Hz.  Loss factor
.042
28
Benchtop Damper Test
- Clear tuning frequency at 7.5 Hz - This shows
fluid amplification effect
29
Fluid Elastic Damper Experiment
Phase 2 Bench Top Test
Phase 1 Spin Test
Full Scale Embedded Fluid Elastic Inertial Damper
for Commercial Rotor Blade System
Scale Model Embedded Fluid Elastic Inertial
Damper for New PSU Lag Test Stand
Measure Static and Dynamic Stiffness of Device
Measure Blade Lag Damping and Frequency
  • Examine the Stiffness Characteristics of the
    Damper
  • Validate Analytical Model and Damper Design

30
Fluid Elastic Damper Experiment
Blade
Flexure
Actuator
Hub
Rotor
Slip Ring
Support Structure
Hydraulic Motor
31
Fluid Elastic Damper Experiment
  • Steel Flexures
  • Dictates Lag Frequency
  • Interchangeable
  • Adds Strength

32
Fluid Elastic Damper Experiment
  • Embedded Actuator
  • Excites Blade
  • Tunable
  • Adds Versatility

33
Lag Damping Test Rig
34
Fluid Elastic Design - Full Scale
Simulated Annealing Algorithm (derived from
RCOE Mount Task) Comanche-like rotor
properties (R 20ft, Lag freq 3.5 Hz) 3
critical damping Absorber tuning Freq 4.9 Hz
(based on 220 RPM crossing) Damper limit of
10 blade mass, 1chord dynamic stroke
35
Fluid Elastic Design - Full Scale
Target Damping Level Achieved within realistic
constraints Other variations possible based
on modified objectives
36
Fluid Elastic Damper- Model Test Predictions
Prototype damper fabricated at Lord Corp
37
Fluid Elastic Damper- Model Test Predictions
Very low static displacement (no
instability)
Proper tuning freq and low dynamic stroke
38
Presentation Outline
  • Background
  • Rotor Loads and Vibration Simulation
  • Embedded Damper Design
  • Elastomeric Damper vs. Fluid Elastic Damper
  • Fluid Elastic Damper Design and Experiment
  • Conclusions

39
Conclusions
  • An embedded fluid elastic inertial damper is
    capable of producing rotor blade lag damping
    within a desirable frequency band for
    aeromechanical stability of the system.
  • The static stiffness of a fluid elastic inertial
    damper is large enough to maintain a reasonable
    static amplitude.
  • aStatic / ao lt 5 of the Chord
  • Static Instability Problem Resolved!

40
Conclusions
  • A new lag damping test rig was successfully
    designed and brought online
  • Detailed Design and Fabrication of a Compact
    Second Generation (Fluid Elastic) Embedded
    Inertial Damper was completed
  • Benchtop testing of the new device confirmed the
    dynamic characteristics predicted by design
    analysis

41
Publications and Presentations
  • AIAA SDM Conference (April 2002)
  • Lord Corporporation (May 2002)
  • Sikorsky (June 2002)
  • ARO Aeroelasticity Workshop (November 2003)
  • Lord Corporation (February 2004)
  • AIAA Journal of Aircraft Paper (Accepted March
    2004)
  • AIAA SDM Conference (April 2004)
  • Jason Petrie MS Thesis (August 2004)
  • Boeing, Mesa (January 2005)
  • Lord Corporation RD Center (March 2005)
  • AHS Forum (June 2005)

42
2005 Plans
  • Complete spin testing of embedded damper devices
  • Complete additional analysis of vibratory hub
    loads
  • and chordwise blade loads in forward flight
  • (Dr. Zhang)
  • Explore opportunities for industry team for
    further
  • development of full scale prototype
    (including
  • designs effective for both articulated and BMR)

43
Schedule and Milestones
2004
2005
2001
2002
2003
Tasks
STAGE ONE Fundamental Study System
Modeling Stability Analysis Blade Lag Damping Test
STAGE TWO Model Refined Parametric Study Concept
Design of Absorber Fluid Elastic Damper Test
STAGE THREE Design of Absorber Rotor Loads
Vibration Report, Guideline of Design
Long Term
Completed
Short Term
44
Helicopter Blade Lag Damping Using Embedded Fluid
Elastic Inertial Dampers
Questions?
  • This project is co-funded by the Lord Corporation
    (Project Technical Monitors John Heilman,
  • Denny McGuire)

45
Previous Accomplishments
  • Basic Study of Blade Lag Damping Using Embedded
    Inertial Dampers (Kang, Smith Lesieutre 1999
    2001)

Rigid Blade/Embedded Damper Model
Parametric Study
  • Developed an analytical model of a rotor system
    with an embedded damper
  • Demonstrated that an elastomeric device could
    produce blade lag damping

46
Previous Accomplishments
  • Aeromechanical Stability Analysis for Rotor
    Fuselage Embedded Inertial Damper (Kang, Smith
    Lesieutre 2001 - 2002)

Damper Mass 0.1 (Ma/Mb) Location 1.0R Tuned
Frequency 13.95 Hz (0.84W0) Loss Factor 0.5
Consider a Hingeless Rotor System with Embedded
Inertial Damper (AFDD Rotor)
  • Indicated that embedded chordwise dampers had the
    potential to maintain the aeromechanical
    stability of helicopters

47
Previous Accomplishments
  • Isolated Blade Lag Damping Tests

  • (Kang, Smith Lesieutre 2001 2002)

48
Previous Accomplishments
RESULTS
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