PS 1.2a
Hybrid Active-Passive Rotor Systems
for Vibration and Performance
Principal Investigators
Kon-Well Wang
Diefenderfer Chaired Professor
Mechanical Engineering
Tel : (814) 865-2183
Edward Smith
Professor
Aerospace Engineering
Tel : (814) 863-0966
Graduate Student
Jun-Sik Kim
2005 RCOE Program Review
May 2, 2005
Rotorcraft Center of Excellence
Task Review, 2005
Background
• The rotorcraft industry is aggressively
pursuing successful and cost effective active
control systems to reduce vibration.
• Blade loads are design constraints for primary
control and life cycle.
• Actuator authority present major technical
barrier.
Rotorcraft Center of Excellence
Task Review, 2005
Problem Statement and Task Objective
How do we design effective active vibration/blade loads
control systems for future rotorcraft ?
Vibration
UMd, PSU, et al.
g’s w/ control
w/Control
improved actuators
V
Blade loads
hybrid design approach
f’s
Penn State (1996 - )
w/ control
w/Control
V
Objective:
To address
the
critical system
issues and advance the state Design high
authority
actuator
of-the-art
of rotor
and blade
 Large stroke
and force
andvibration
low electricsuppression
power
loads reduction through combining the two approaches
 Design active controller together with passive parameters
 High authority PZT actuators
 Re-configuration of passive structure (m, GJ, EI, etc)
 Effective hybrid vibration/blade loads control system
Rotorcraft Center of Excellence
Task Review, 2005
Piezoelectric Actuator Scaling
600
7
500
Haero*
Haero*
400
300
T*
1
1
200
5
3
Small scale
blade chord
100
Performance
as
Blade Size
T*
Haero* ~ c2R
T* ~ c3
0
0
3
5
10
MD900
blade chord
15
20
25
Chord (in)
 Aerodynamic Moment and Block Torque nondimensionalized with small scale values
Rotorcraft Center of Excellence
Task Review, 2005
Boeing 2xFrame Actuator
2003 Full Scale Whirl Test Results
(SPIE 2004, Straub et. al)
Flap deflection vs. rotor
speed multiple
 Modified MD 900 bearingless rotor
 3~3.5 degrees in hover (450V)
Rotorcraft Center of Excellence
Large rotor test stand (LRTS)
Task Review, 2005
Technical Barriers and Solution Idea
1) High active authority and low electric power of
actuator for actuator/flap coupled systems
•
Resonant Actuation System (RAS)
2) Multiple trailing edge flap configuration to utilize
the resonance actuation system
•
Vibration and blade loads reductions
Resonance Actuation System(RAS)
Rotorcraft Center of Excellence
Multiple Trailing Edge Flaps
Task Review, 2005
Nature’s Flight Actuators
Technical
Evolution
Rotorcraft Center of Excellence
Task Review, 2005
Summary of 2001 - 2003 Accomplishments
Active authority enhancement of PZT actuator
 Circuit with negative capacitor and active inductor/blocking filters was
explored to reduce electric power (2001)
 New concept to enhance the active authority of PZT actuators was
developed and evaluated on PZT benders, stacks, and tubes (2002)
 Full-Scale PZT tube / R-L-C circuit system was experimentally
realized and evaluated (2003)
Blade loads and vibration control via TEF
 Aeroelastic flap/torsion model for composite rotor blade was
developed (code validation, 2001)
 Refine control algorithm of hybrid design was developed to achieve
both blade loads and vibration reductions with minimum control
efforts (2002)
 Multiple trailing edge flap configurations with RAS was explored to
reduce the vibration (2003)
Rotorcraft Center of Excellence
Task Review, 2005
2004 Review Team Comments


The task made good progress and made good responses to the
last year suggestions.
The task deals with vibration only and it is suggested to check
noise aspect of the concepts.
- Other Research is focused on trailing edge flaps for noise reduction. (e.g. Prof.
Friedmann at Univ. of Michigan has 2005 AIAA and AHS papers on this subject).
- Researchers in industry (e.g. Straub et al) have also examined this idea.
- A thorough investigation of noise reduction was considered beyond the scope of the
present investigation.

The review team is curious about drag penalty of TEF?
- This is an important question.
- Increments in section drag are modeled in the airload calculation
- Primary penalties are for flap deflections near transonic Mach number (adv side)
and negative deflections at high angles of attack (retreating side)
- Proper control law design can mitigate these penalties (Zhang, Smith, Wang, 2000)
Rotorcraft Center of Excellence
Task Review, 2005
Performance Enhancement
Retrofit Design at 0.15
Retrofit Design at 0.30
8
Active Flap Deflections (deg.)
Active Flap Deflections (deg.)
6
4
2
0
-2
-4
-6
Flap Up
90
180
Azimuth (deg.)
270
4
2
0
-2
-4
-6
-8
-8
0
Flap Down
6
360
0
90
180
270
360
Azimuth (deg.)
• Large flap deflections may occur around 90° and 270° azimuths,
which can cause aerodynamic penalties - stall and separation
Rotorcraft Center of Excellence
Task Review, 2005
Performance Enhancement
• Modified objective function and control algorithm
J = Z nT Wz Z n + δ nT Wδ δ n + w sδ 2 (ψ )
δ (ψ )
ws
: The active flap deflections at certain time history
: Weighting factor
δ (ψ ) = δ n P (ψ )T
δ n = [δ 3c δ 4c δ 5c δ 3 s δ 4 s δ 5 s ]
P (ψ ) = [cos 3ψ cos 4ψ cos 5ψ sin 3ψ sin 4ψ sin 5ψ ]
J = Z nT Wz Z n + δ nT Wδ δ n + w s δ nT P T (ψ )P (ψ )δ n
= Z nT Wz Z n + δ nT [Wδ + w s P T (ψ )P (ψ )]δ n
J = Z nT Wz Z n + δ nT [Wδ + WP (ψ )]δ n
Rotorcraft Center of Excellence
Task Review, 2005
Performance Enhancement
Retrofit design at advance ratio of 0.30
4
Vibration Reduction
0
-2
-4
20%
15%
10%
5%
Retrofit with
constraints
2
25%
Retrofit
Percentage of the Baseline
Vibration Level
Active Flap Deflections (deg.)
6
0%
Retrofit
Retrofit with constraints
-6
-8
0
90
180
270
360
Azimuth (deg.)
• Active Flap deflections around 270° azimuth are reduced
to within 2 degrees
Rotorcraft Center of Excellence
Task Review, 2005
Performance Enhancement
Hybrid design at advance ratio of 0.15
Retrofit
Hybrid
Hybrid with constraints
8
6
0
-2
-4
40%
30%
20%
10%
Hybrid with
constraints
2
50%
Hybrid
4
Percentage of the Baseline
Vibration Level
Active Flap Deflection
Vibration Reduction
0%
-6
-8
0
90
180
270
360
Azimuth (deg.)
• Active flap deflections around 90° azimuth are reduced
from more than 6 degrees to about 2 degrees
Rotorcraft Center of Excellence
Task Review, 2005
Summary of Accomplishments in 04/05
Analysis and Experiment of Piezoelectric Resonant Actuation Systems
 Analysis is performed to explore the feasibility of a
resonant actuation system (RAS)


Dynamic characteristics of a RAS is examined via perturbation
method (forward flight)
Power consumption of a RAS is explored
 Experiment of a RAS with adaptive feed-forward
controllers – Bench Top Test



A voltage signal function is derived from the analytical model and
implemented using Matlab/dSPACE
A phase controller, so called ‘phaser’, is implemented to track the
phase variation near a resonant frequency
Actuator amplification mechanism of a RAS is modified to improve
the dynamic performance – 6.0 degrees are achieved
Rotorcraft Center of Excellence
Task Review, 2005
IDEA – Actuator authority enhancement
Resonance Actuation System
1.
2.
Resonance can be utilized to improve the actuator authority
Electric network can help to broaden and flatten the resonant driver effect
Single nominal actuator (baseline)
3,4,5/rev
Typical
Edge Flap
Deflections via
Tune
to Trailing
Operating
Frequency
Mechanical Tuning
Required authority
3/rev 4/rev 5/rev
Actuator stroke
 Baseline - Small active authority
over operating range
 Increase authority via mechanical
tuning and electrical tailoring
 May not cover the entire range of
operating frequencies
frequency
 Single flap  Three
small flaps
Rotorcraft Center of Excellence
Broaden and Flatten via
Circuit design
Frequency, Hz
Three Small Actuators
3/rev 4/rev 5/rev
Task Review, 2005
Multiple TEF w/ RAS
Resonance Actuation
System Application
RAS
Resonance Actuation System
1) PZT Actuator
2) Trailing Edge Flap (Aerodynamics)
3) Electric Circuit
Mechanical Tuning
• Amplification mechanism
• Mass moment of inertia of TEF
Electric Network
• Inductor: tune to operating
frequency (e.g., 3,4,5/rev)
• Resistor: flatten the resonant peak
• Negative capacitor: broaden the
resonant driver effect
Rotorcraft Center of Excellence
Task Review, 2005
Mechanical Tuning
Tube actuator: Kp,Mp
Hover
Kf
Tuning mass: Mtune


llever

Kf
loffset
Amplification mechanism,  = Am , Am=llever / loffset
(e.g. Am=5 will provide 5:1 amplification)
FlapFlight
hinge
Forward
Aerodynamic loads: Kf
Tuning mass: Mtune
Trailing-Edge
 Flap: Mf
{M p  (M f  M tune ) Am2 }  ( K P  K f Am2 )  0
K
 Hover: stiffnessM
is constant
2=K / M
K f ( )

Resonant
frequency
:

 Forward flight: stiffness is varying along the azimuth
 Tuned to the operating frequency (e.g. 3, 4, 5/rev)
 Periodic coefficient due to 1/rev aerodynamic forces
 Tuning parameter: Tuning mass, Amplification ratio
 Time-varying characteristics of actuation system will be discussed further
Rotorcraft Center of Excellence
Task Review, 2005
Electrical Tailoring
Actuator stroke
Broaden and Flatten via
Circuit design
Resonant frequency
frequency
Actuator authority enhancement
at tuned
frequency
(Resistor,
Inductor) via
Mechanical tuning
Problem: It is hard to control
Operating frequency: 3,4,5/rev
• Bruneau et al.(1999)
• Tang and Wang (2001)
• Behrens et al. (2001).
 Active authority: The circuit can broaden and flatten the resonant
 Phase variation near resonant freq.
effect of the tuned system and still maintain high authority
 Need to design controller to
 Inductor: tune to operating frequency
(e.g.,
3/rev,
4/rev, 5/rev)
track
phase
variation
 Negative capacitor: broaden theresonant
driver
effect
Developed
and
tested in this
Phase plot
 Resistor: flatten the frequency response
year’saround
effort the resonant peak
Rotorcraft Center of Excellence
Task Review, 2005
Perturbation Method in Forward Flight
 Time-varying characteristics of actuation system
 Equations of motion of a coupled system w/o circuitry
Mqt  K E (t )qt  F (t )
: Theodorsen’s theory for trailing edge flap
 Normalized equations for the purpose of perturbation
qt   2   2 2 sin   2 sin 2   qt   cos( ),   fn(  )
 Perturbed solution up to 2
qt ( ;  ) 


a1
b1

cos(

)


sin
(1


)


sin
(1


)





  2  (1   ) 2

2  2
 2  (1   )2


 c

a2
b2
 2  2 2 2 cos( )  2
cos
(2


)


cos
(2


)

 O( 3 )





2
2
2
  (2   )
  (2   )
  

 Primary resonance at = (resonant frequency in hover)
 Resonances due to time-varying characteristics at 2 = 2, (1)2, (2)2
 Flap response qt includes other harmonics: (1), (2), …
 For example, if =4, then qt includes 2,3,4,5,6/rev harmonics
Rotorcraft Center of Excellence
Task Review, 2005
Frequency Responses in Forward Flight
Actuation system w/o circuitry
Actuation system with circuitry
Advance ratio
0.35
Hover
Advance ratio
0.15
Operating frequency, 4/rev, 26.6Hz
 RAS in hover
 Influence
of advance
ratios toincreased
the major
resonant
frequency
 The actuator
authority is significantly
from 1.25
degree to 4.5
degree
Flat significant
and wide shape near the resonant frequency (approximately 8 Hz).
is not
 RAS in forward flight
 RAS
can be applied to forward flight as well as hover
 Main characteristics of the RAS (high authority with wide bandwidth) are
achieved in forward flight
Rotorcraft Center of Excellence
Task Review, 2005
Flap Time Histories in Forward Flight (=0.35)
Nominal actuation system
Resonant Actuation System
 4/rev voltage signal input


4/rev harmonic component is increased from 1.5 to 3 degrees
Need to develop controller to resolve the side effects
Rotorcraft Center of Excellence
Task Review, 2005
Summary of Accomplishments in 04/05
Analysis and Experiment of Piezoelectric Resonant Actuation Systems
 Analysis is performed to explore the feasibility of a
resonant actuation system (RAS)


Dynamic characteristics of a RAS is examined via perturbation
method (forward flight)
Power consumption of a RAS is explored
 Experiment of a RAS with adaptive feed-forward
controllers – Bench Top Test



A voltage signal function is derived from the analytical model and
implemented using Matlab/dSPACE
A phase controller, so called ‘phaser’, is implemented to track the
phase variation near a resonant frequency
Actuator amplification mechanism of a RAS is modified to improve
the dynamic performance – 6.0 degrees are achieved
Rotorcraft Center of Excellence
Task Review, 2005
Feed-Forward Controller for RAS
Voltage Signal Function emulating of electric network
 Va

 Vc


 2 ˆ 2 /  2 (1  2 j   2 )


2
2
2
2
2 2
 (1    2 j   )(rj     )   ˆ
Adaptive “phaser” to track the phase variation
y (t )  cos( )u (t ) 
sin( )

u (t )
 Electric network is realized via
“Voltage Signal Function” which
is derived from the coupled
piezoelectric equations
Phase plot
Rotorcraft Center of Excellence
 The phase angle  is adaptively
corrected through the feedback
of the output signal
Task Review, 2005
Experiment Set-up
 8 inch PZT tube, 12 inch flap (inertia only)
 Amplification ratio: 5 (current), 15 (future)
 Mechanical tuning to 4/rev (26.6Hz)
Rotorcraft Center of Excellence
Task Review, 2005
Bench Top Test Results
Frequency Response
Phase Control at 24 Hz
w/o voltage signal function
Operating frequency
3.5
w/ voltage signal function
 Actuator authority at the tuned frequency (26.6Hz)

Increases about 3.5 times when compared to the static deflection (which
would be produced by nominal actuation system) with 8 Hz bandwidth
 The phase near a resonant frequency varies

Implemented adaptive controller is able to accurately follow the reference
Rotorcraft Center of Excellence
Task Review, 2005
Demonstration of RAS
 Full-scaled PZT tube actuator
Resonant Actuation System
fabricated (Jose Palacios and Edward Smith,
with simulated aerodynamic loads &
2005)
improved amplification mechanism
 PZT tube is 4 inches long

Simulated aerodynamic loads

Two springs (80 lb/in total)

Applied voltage: 2250 Volts
 Mechanical tuning: 33.3 Hz for
MD 900, 5/rev
 Flap deflections with simulated
aerodynamic loads

Mechanically tuned actuator w/o voltage signal function
Test with voltage signal function is scheduled in near future
Rotorcraft Center of Excellence
12 inches flap, 400 RPM
  6.0 degrees are achieved at
the operating frequency
 Nominal actuation authority is
0.2 degrees: 30 times increases
Task Review, 2005
Planned Efforts in 2005
 Controller design for flap responses in forward flight

Reduce the side effects due to time-varying characteristics
 Investigate the characteristics of a RAS further


Continue the test of a RAS with a voltage signal function
Nonlinear characteristics of a RAS
Controller for side effects
Rotorcraft Center of Excellence
Characteristics of a RAS
Task Review, 2005
Summary of Overall Accomplishments
Objective: To advance the state-of-the-art of rotor
vibration suppression and blade loads reduction
through combining the two approaches
1. High authority PZT actuators
2. Effective vibration/blade loads control system
1. Development of actuation systems for active flap rotors




A resonant actuation system (RAS) was developed
Bench top testing of full-scaled actuation system
Dynamic characteristics of a RAS in forward flight were explored
Actuator amplification mechanism of a RAS is modified to improve the
dynamic performance
2. Development of analytical tool for rotor analysis

Free-wake for main rotor, unsteady aero and finite wing effects for flaps
 Active load controls via dual flap (blade loads reduction)
 Vibration reduction via multiple trailing edge flaps controlled by resonant
actuation system
Rotorcraft Center of Excellence
Task Review, 2005
Future Work
 Hover or wind tunnel test of a RAS
 Active load controls for Heavy Lift Helicopters

Dual flap configuration together with RAS for light weight rotors
 Damage detection using active flaps in forward flight

Active interrogation could be combined with active loads control
Active load controls via dual-flap
Damage identification using trailing
edge flaps
1. Deformed blade
2. Straightened blade
Rotorcraft Center of Excellence
Task Review, 2005
External Interactions, Leveraging
and Technology Transfer
Have had discussions with
– US Army AFDD (Mark Fulton, smart rotor testing,
resonant actuator and circuit concept, flap aspect
ratio effect)
– Boeing (Friedrich Straub, actuator requirements)
– Sikorsky: visited (A. Bernhard, feasibility of
multiple-flap configuration)
– U. Maryland (I. Chopra et. al, hinge moments)
– U. Michigan (P.P. Friedmann, auto-weight control)
Rotorcraft Center of Excellence
Task Review, 2005
External Interactions, Leveraging
and Technology Transfer
 Novel, high authority flap actuation concepts using single
crystal stacks – SBIR (Small Business Innovation Research)


Invercon and PennState
Buckling beam actuator together with RAS – high actuation authority
Rotorcraft Center of Excellence
Task Review, 2005
Publications and Presentations
1.
Jun-Sik Kim, Edward C. Smith and Kon-Well Wang, "Active loads control of composite rotor blade via trailing
edge flaps", 44th AIAA/ASME/ASCE/AHS/ASC SDM Conference, Norfolk, Virginia, April 7-10, 2003.
2.
Jun-Sik Kim, Kon-Well Wang and Edward C. Smith, "Active authority enhancement of piezoelectric actuator
design via mechanical resonance and electrical tailoring", Fifth International Conference on Intelligent
Materials (ICIM) June 14 - 17, 2003, State College, Pennsylvania
3.
Jun-Sik Kim, Edward C. Smith and Kon-Well Wang , "Helicopter Vibration Suppression via Multiple Trailing
Edge Flaps Controlled by Resonance Actuation System", Tenth International Workshop on Dynamics and
Aeroelastic Stability Modeling of Rotorcraft System, November 3-5, 2003, Student Success Center, Georgia
Institute of Technology, Atlanta, GA.
4.
Jun-Sik Kim, Kon-Well Wang and Edward C. Smith, “High Authority Piezoelectric Actuator Synthesis through
Mechanical Resonance and Electrical Tailoring”, Adaptive Structures and Material Systems Symposium, The
Winter Annual Meeting of the ASME, November 16 - 21, 2003, Washington Marriott Wardman Park,
Washington DC
5.
Jun-Sik Kim, Edward C. Smith and Kon-Well Wang, “Helicopter Vibration Suppression via Multiple Trailing
Edge Flaps Controlled by Resonance Actuation System”, the AHS 60 th Annual Forum, Baltimore, MD, June 710, 2004.
6.
Jun-Sik Kim, Kon-Well Wang and Edward C. Smith, “High Authority Piezoelectric Actuator Synthesis through
Mechanical Resonance and Electrical Tailoring”, Journal of Intelligent Material Systems and Structures, Vol.
16, No. 1, pp. 21-3, 2005
7.
Jun-Sik Kim, Kon-Well Wang and Edward C. Smith, “Development of a Resonant Actuation System for Active
Flap Rotors,” the AHS 61st Annual Forum Gaylord Texas Resort, TX, June 1-3, 2005.
8.
Jun-Sik Kim, Kon-Well Wang and Edward C. Smith, “Design and Analysis of Piezoelectric Transducer Based
Resonant Actuation Systems,” Adaptive Structures and Material Systems Symposium, The Winter Annual
Meeting of the ASME , November 6-11, 2005, The Walt Disney World Swan & Dolphin Hotel, Orlando, Florida
Rotorcraft Center of Excellence
Task Review, 2005
Schedule and Milestones
Tasks
2001
2002
2003
2004
2005
Extension of hybrid analysis to
composite rotors, and actuatorcircuit model
Initial studies on composite rotor
and actuators with APPNs
Refinement for unsteady aero and
control algorithm(dual flap)
Near Term
Mid Term
Long Term
New actuator concept
development and integrated study
with rotor
Refine aerodynamic model
Design, fabrication of actuators
Methodology for robust design
and adaptive control
Refinement and testing of
resonance actuation system
Development of controller for flap
responses in forward flight and
investigation of nonlinear features
of a RAS
Rotorcraft Center of Excellence
Task Review, 2005
The End
Questions?
Rotorcraft Center of Excellence
Task Review, 2005
Appendix
Rotorcraft Center of Excellence
Task Review, 2005
Frequency Responses in Forward Flight
Actuation system w/o circuitry
Instantaneous frequencies
Advance ratio
0.35
Hover
Advance ratio
0.15
Operating frequency, 4/rev, 26.6Hz
 Influence of advance ratios to the major resonant frequency

Not significant
 Averaged frequencies along the azimuth

Almost constant with respect to the advance ratio
 RAS can be applied to forward flight as well as hover
Rotorcraft Center of Excellence
Task Review, 2005