Research Proposal

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Research Proposal
Rotorcraft Blade Loads Control via Active-Passive
Devices
Edward C. SmithProfessor of Aerospace
EngineeringK. W. WangDiefenderfer Chaired
Professorin Mechanical Engineering
Research Proposal March 2005
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Background

• A low weight rotor system is an important goal
• For helicopters and tilt-rotors
• For a cost-effective large transport rotorcraft
• Primary operating cost drivers are weight
• Rotor system weight blade, hub and controls
• Power low disk loading and low aircraft drag
• Reduced weight and lower disk loading lead to
• Larger and lighter rotors with novel hub and
  control concepts
• Radically altered dynamic characteristics

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Motivation

• Need to resolve the problem of a large and light
  weight rotor
• Dynamic and aerodynamic problem due to weight
  reduction
• Reduced blade loads and hub loads could result in
  lighter blade and hub
• Active loads control is available via multiple
  trailing-edge flaps
• Pith link loads could also be reduced
• Need to augment the control authority during
  shipboard operation
• Ship-based rotorcraft operate in unique and
  dangerous environments
• Ship airwake is considered a crucial factor in
  limiting shipboard operations
• Active flaps as a secondary control

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Related Researches

• Active loads control using trailing edge flaps
• Vibration and blade loads reduction using a large
  1/rev control input (McCloud III, 1975)
• Dynamically straightened blade can yield lower
  blade loads as well as lower vibration (Kim,
  Smith and Wang, 2003)
• Active trailing edge flaps could be act served as
  either primary or secondary control to reduce the
  pitch link loads (Shen and Chopra, 2004)
• Helicopter on operation in a ship
• Optimization of helicopter stability augmentation
  system (Lee and Horn, 20032005)
• Stochastic ship airwake modeling (SORBET model,
  NASA Ames)
• Transient aeroelastic response of rotors during
  shipboard engagement and disengagement operations
  (Keller and Smith, 20002001)

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Future Trends Challenges

• Simultaneous reduction of flapwise bending
  moment, pitch link load, and vibratory hub loads
• Advantage
• Allows to use a larger and light weight rotor
  system
• Challenges
• Active flap actions within available actuator
  authority
• Conflicts between blade loads and vibration
• Active trailing edge flaps as a secondary control
  for operation in a ship airwake
• Advantages
• Utilize multiple trailing edge flaps to provide a
  secondary control authority
• Challenges
• Need to develop the active control law of active
  flaps during shipboard engagement and
  disengagement
• Increase helicopter stability (stability
  augmentation system SAS)
• Reduce the transient response

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Frequency Spectrum for Helicopter Analysis
Flight mechanics
Ground Resonance
Acoustics
Vibration
Frequency
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Objective and Approaches

• Objective
• Address critical issues and advance
  state-of-the-art of blade loads reduction,
  vibration suppression, and damage identification
  in flight for a larger and light weight rotor
• Control mechanism to simultaneously reduce blade
  loads and vibration
• Shipboard gust rejection using active flaps
• Approaches
• Explore active rotor systems with multiple
  trailing edge flaps
• Design the flap size and location, and determine
  the flap control input
• Blade loads control via various means
• Flapwise load and torsional moment control using
  dual active flaps
• Chordwise load using inertial forces due to the
  embedded mass
• Pitch link load reduction via composite tailoring
  or shock isolator
• Active flaps as a secondary control to reject the
  shipboard gust
• Analysis for shipboard engagement and
  disengagement operations
• Incorporate an accurate ship airwake model
• Design a controller based on helicopter SAS to
  reject shipboard gust

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Multiple Trailing Edge Flaps

• Comprehensive rotor analysis
• Composite rotor model with multiple trailing edge
  flaps
• Aerodynamic model
• Free-wake model for main rotor inflow (Tauzsig
  and Gandhi, 1998)
• Compressible unsteady aerodynamic model for
  trailing edge flaps (Hariharan and Leishman,
  1995)
• Active control algorithm

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Flapwise Load Torsional Moment Control
1. Deformed blade w/o control
2. Opposite action of dual flap
lift due to outboard flap
Opposite lift due to inboard flap
3. Straightened blade

• Dual trailing edge flap concept
• Generate additional moments
• Results in reducing blade loads
• Reduce blade stresses and increase blade life
• Effect to trim by dual flap could be minimized
  (net lift is nearly zero)
• Control inputs include 1/rev and higher harmonic
  components

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Chordwise Load Control

• Mechanical vibrator to reduce the chordwise blade
  load control
• Inertial dampers were initially developed for the
  increase of a blade lag damping (Kang et. al,
  2001)
• Inertia forces due to a tunable small mass can be
  used for the reduction of a blade chordwise load

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Pitch Link Load Reduction

• Composite tailoring to reduce a high pitch link
  load
• Composite tailoring can help to reduce the pitch
  link load induced by the dynamic stall (Floros
  and Smith, 2000)
• Alleviation of a dynamic stall pitch link load
  reduction
• Shock isolator for the pitch link load

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Shipboard Operations Airwake Disturbances

• Ship-based rotorcraft operate in unique and
  dangerous environments
• Ship airwake is considered a crucial factor in
  limiting shipboard operations
• Automatic flight control system is desirable to
  compensate airwake disturbances
• There are limits on roll control gain due to
  stability margin limits from rotor-body coupling

Active trailing edge flaps could be used to
increase the stability margin and to provide the
more control authority
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Shipboard Operations Engagement and
Disengagement

• Transient aeroelastic responses during shipboard
  engagement and disengagement operations
• Rotational speed is varying during shipboard
  engagement and disengagement
• To control the transient response, active flaps
  can be used
• An accurate ship airwake should be incorporated

Rotational speed variations for engagement and
disengagement
Illustration of an H-46 tunnel strike
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• Sample Results

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Sample Results Active Loads Control using
Active Flaps
Active control with 1/rev control input
Flapwise moment harmonics along the radial station
4/rev vibratory hub loads
R, radial station

• Simultaneous reduction of blade loads and
  vibration
• Flapwise bending moments 32
• Vibratory hub loads 57
• Inboard and outboard flap deflections are 6 and 4
  degrees

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Sample Results - dual flap w/ 1PFlapwsie bending
moment and Flapping motion
Through straightening the blade, which mimics
the behavior of the rigid blade, both the
vibration and bending moments can be
significantly reduced.
Baseline
Active Control
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• Appendix

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Global and Local Fault Detection

• Active rotor technology for global and local
  fault detection
• Global fault detection
• Using active interrogation using active trailing
  edge flaps
• Piezoelectric transducer circuit for damage
  detection
• Local fault detection
• Ultra-transonic transducer based damage detection
• High performance shear tube actuator
• Related researches
• Analytical and experimental studies of a
  modal-based damage detection of rotor blade mass
  and stiffness faults (Kiddy and Pines, 19971999)
• Active interrogation of helicopter main rotor
  faults using trailing edge flaps using strain
  measurement (Stevens and Smith, 2001)
• An improved damage identification method using
  tunable piezoelectric transducer circuitry
  (Jiang, Tang and Wang, 2004)

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Global Fault Detection- using active flaps

• Active interrogation using trailing edge flaps
• Excitation bandwidth of 10-50 Hz with 2.5 degrees
• Damage detection
• Residual force vector approach using frequency
  response function
• Damage extent quantification a frequency domain
  adaptation of the modal based Asymmetric Minimum
  Rank Perturbation theory

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Global Fault Detection- using piezoelectric
transducer

• Model update methods for damage identification
• Find changes to the healthy system finite element
  model that best capture the measured response of
  the damaged system
• Damage models
• Distributed stiffness Fault, blade crack and
  control system stiffness
• Piezoelectric transducer circuit with tunable
  inductance
• Increase the sensitivity of frequency shift
• Distributed piezoelectric transducer can also be
  served as the sensor

Piezoelectric transducer for damage detection
Finite element model of cracked beam
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Local Fault Detection

• Ultrasonic wave to detect the local fault
• Embedded small piezoelectric tube actuator can
  generate the ultrasonic shear wave
• Dead leading edge mass can be substituted by
  piezoelectric shear tube actuator

Dead Leading Edge Mass (10 20 Weight of the
Blade)
a
a
Substitute with Shear Piezoelectric Tube

• Segments poled along longitudinal direction, P2
• Electric field applied in the width direction, E1