Research Proposal
Rotorcraft Blade Loads Control
via Active-Passive Devices
Edward C. Smith
Professor of Aerospace Engineering
K. W. Wang
Diefenderfer Chaired Professor
in Mechanical Engineering
Research Proposal
March 2005
The Pennsylvania State University
Rotorcraft Center of Excellence
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
The Pennsylvania State University
Rotorcraft Center of Excellence
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
The Pennsylvania State University
Rotorcraft Center of Excellence
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,
2003~2005)

Stochastic ship airwake modeling (SORBET model, NASA Ames)

Transient aeroelastic response of rotors during shipboard engagement
and disengagement operations (Keller and Smith, 2000~2001)
The Pennsylvania State University
Rotorcraft Center of Excellence
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
The Pennsylvania State University
Rotorcraft Center of Excellence
Frequency Spectrum for
Helicopter Analysis
Flight mechanics
Ground
Resonance
Vibration
Acoustics
Frequency
The Pennsylvania State University
Rotorcraft Center of Excellence
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


Blade loads control via various means




Design the flap size and location, and determine the flap control input
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
The Pennsylvania State University
Rotorcraft Center of Excellence
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
J  Z nTWz Z n  K nTWK K n   nTW  n
Z n : Vibratory hub loads,
K n : Blade loads,
 n : Control efforts
The Pennsylvania State University
Rotorcraft Center of Excellence
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
The Pennsylvania State University
Rotorcraft Center of Excellence
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
The Pennsylvania State University
Rotorcraft Center of Excellence
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
Pitch link loads
Composite Tailoring
The Pennsylvania State University
Rotorcraft Center of Excellence
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
The Pennsylvania State University
Rotorcraft Center of Excellence
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
The Pennsylvania State University
Rotorcraft Center of Excellence
Sample Results
The Pennsylvania State University
Rotorcraft Center of Excellence
Sample Results:
Active Loads Control using Active Flaps
Active control with 1/rev control input
Flapwise moment harmonics
along the radial station
x 10
4/rev vibratory hub loads
-4
2.5
2
0.005
1P Base
2P Base
1P Active
2P Active
Active control (dual flap)
0.004
Rigid blade
1.5
0.003
1
0.002
0.001
0.5
0
0
Baseline
0
0.2
0.4
0.6
R, radial station
0.8
1
Fx
Fy
Fz
 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
The Pennsylvania State University
Rotorcraft Center of Excellence
Sample Results - dual flap w/ 1P
Flapwsie bending moment and Flapping motion
Baseline
Active Control
Through straightening the blade,
which mimics the behavior of the rigid blade,
both the vibration and bending moments
can be significantly reduced.
The Pennsylvania State University
Rotorcraft Center of Excellence
Appendix
The Pennsylvania State University
Rotorcraft Center of Excellence
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, 1997~1999)
 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)
The Pennsylvania State University
Rotorcraft Center of Excellence
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
The Pennsylvania State University
Rotorcraft Center of Excellence
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
Patch
Finite element model of cracked beam
The Pennsylvania State University
Tunable
Inductance
Piezoelectric transducer for damage detection
Rotorcraft Center of Excellence
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
The Pennsylvania State University
• Segments poled along longitudinal direction, P2
• Electric field applied in the width direction, E1
Rotorcraft Center of Excellence