Integral Twist Actuation of Helicopter Rotor Blades for Vibration Reduction SangJoon Shin

174 Pages·2013·16.52 MB·English

Integral Twist Actuation of Helicopter Rotor
Blades for Vibration Reduction
by
SangJoon Shin
B.S., Aerospace Engineering, Seoul National University (1989)
M.S., Aerospace Engineering, Seoul National University (1991)
S.M., Aeronautics and Astronautics, Massachusetts Institute of Technology (1999)
Submitted to the Department of Aeronautics and Astronautics
in partial fulfillment of the requirements for the degree of
Doctor of Philosophy in Aeronautics and Astronautics
at the
MASSACHUSETTS INSTITUTE OF TECHNOLOGY
August 2001
@ Massachusetts Institue of Technology 2001. All rights reserved.
Author
Department of Aeronautics and Astronautics
August 24, 2001
Certified by..................
!Carlos E. . Cesnik,Committee Chair
Associate Professor of Aeronautics aniAstrbnaatics
Certified by.............................
Steven R. Hall
Professo"Aeronauticsnd Astronautics
Certified by......
Edward F. Crq4eT
Professor of Ap ronantics and Astronantics
Certified by......
Nesbitt W. Hagood
A 6ci49 Professor of Aieronaut/cs an Adg0nautics
Accepted by...........
Wallace E. Vander Velde
Professor of Aeronautics and Astrona tics
MASSACHUSETTS INSTI UTE Chair, Committee on Graduate Students
OF TECHNOLOGY
AUG 1 3 2002
AERO 1
LIBRARIES
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Integral Twist Actuation of Helicopter Rotor Blades for Vibration
Reduction
by
SangJoon Shin
Submitted to the Department of Aeronautics and Astronautics
on August 24, 2001 in Partial Fulfillment of the
Requirements for the Degree of
Doctor of Philosophy in Aeronautics and Astronautics
ABSTRACT
Active integral twist control for vibration reduction of helicopter rotors during forward
flight is investigated. The twist deformation is obtained using embedded anisotropic
piezocomposite actuators. An analytical framework is developed to examine integrally-
twisted blades and their aeroelastic response during different flight conditions: fre-
quency domain analysis for hover, and time domain analysis for forward flight. Both
stem from the same three-dimensional electroelastic beam formulation with geometrical-
exactness, and are coupled with a finite-state dynamic inflow aerodynamics model. A
prototype Active Twist Rotor blade was designed with this framework using Active
Fiber Composites as the actuator. The ATR prototype blade was successfully tested
under non-rotating conditions. Hover testing was conducted to evaluate structural
integrity and dynamic response. In both conditions, a very good correlation was ob-
tained against the analysis. Finally, a four-bladed ATR system is built and tested to
demonstrate its concept in forward flight. This experiment was conducted at NASA
Langley Transonic Dynamics Tunnel and represents the first-of-a-kind Mach-scaled
fully-active-twist rotor system to undergo forward flight test. In parallel, the impact
upon the fixed- and rotating-system loads is estimated by the analysis. While discrep-
ancies are found in the amplitude of the loads under actuation, the predicted trend
of load variation with respect to its control phase correlates well. It was also shown,
both experimentally and numerically, that the ATR blade design has the potential for
hub vibratory load reduction of up to 90% using individual blade control actuation.
Using the numerical framework, system identification is performed to estimate the
harmonic transfer functions. The linear time-periodic system can be represented by
a linear time-invariant system under the three modes of blade actuation: collective,
longitudinal cyclic, and lateral cyclic. A vibration minimizing controller is designed
based on this result, which implements classical disturbance rejection algorithm with
some modifications. The controller is simulated numerically, and more than 90% of
the 4P hub vibratory load is eliminated.
By accomplishing the experimental and analytical steps described in this thesis,
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the present concept is found to be a viable candidate for future generation low-
vibration helicopters. Also, the analytical framework is shown to be very appropriate
for exploring active blade designs, aeroelastic behavior prediction, and as simulation
tool for closed-loop controllers.
Thesis supervisor: Carlos E. S. Cesnik, Chair
Title: Associate Professor of Aeronautics and Astronautics
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Acknowledgments
I greatly appreciate Dr. Carlos E. S. Cesnik, who is my advisor, for his guidance and
supervision throughout the entire process of this thesis. Without his encouragement,
this thesis would not exist. I would also like to express my gratefulness to Dr. Steven
R. Hall for sharing his profound knowledge with me regarding the helicopter and its
control problems. Also, I would like to express my thankfulness to Dr. Nesbitt W.
Hagood for his support during the period of my graduate study. I appreciate Dr. Ed-
ward F. Crawley and Dr. John Dugundji for the discussion and recommendations on
my work.
I would definitely like to thank Mr. Matthew L. Wilbur for the financial sup-
port and all the wind-tunnel experiments, as well as CAMRAD II analysis. I also
would like to express my thankfulness to Mr. Paul H. Mirick, Mr. William T. Yeager,
Jr., Mr. Chester W. Langston, and Dr. W. Keats Wilkie for their support on the
experiments.
I am profoundly grateful to Dr. Olivier A. Bauchau for providing DYMORE code
and the help on its modification. Also, I wish to thank Dr. Xiaoyang Shang for his
help on modifying the one-dimensional beam code.
I am grateful to Dr. John P. Rodgers, Dr. Eric F. Prechtl, Mr. Mads C. Schmidt,
and Mr. Viresh K. Wickramasinghe for their support on the experiments of the ATR
test blade and providing the updated AFC data. Special thanks to Ms. Afreen Siddiqi
for her help on the blade signal generation and providing the system identification
routine.
I would appreciate my parents for their love and support, and also, my sister,
brother, brother-in-law, and twin nieces. Especially, I would like to profoundly thank
my wife, JeeYoung, for her encouragement and understanding, and my daughter,
SoMin, for her love and smile.
This work was sponsored by NASA Langley Research Center under the cooperative
agreement # NCC1-323.
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Contents
1 Introduction 27
1.1 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
1.2 Helicopter Vibration Reduction . . . . . . . . . . . . . . . . . . . . 29
1.3 Previous Work Related with Integral Twist Actuation . . . . . . . . 31
1.3.1 Actuators Applicable for the Integral Concept . . . . . . . . 31
1.3.2 Previous Integral Helicopter Blades . . . . . . . . . . . . . . 32
1.3.3 ATR Blade - Previous Work . . . . . . . . . . . . . . . . . . 33
1.4 Present Wo rk . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
2 Analytical Framework 39
2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
2.2 Cross-Sectional Analysis . . . . . . . . . . . . . . . . . . . . . . . . 42
2.3 Global Beam Analysis . . . . . . . . . . . . . . . . . . . . . . . . . 45
2.3.1 Mixed Form for Hover Analysis . . . . . . . . . . . . . . . . 45
2.3.2 Displacement-based Form for Forward Flight Analy sis . . . . . 50
2.4 Aerodynamic Analysis . . . . . . . . . . . . . . . . . . . . . . . . . 53
2.4.1 Hover Aerodynamics . . . . . . . . . . . . . . . . . . . . . . 53
2.4.2 Forward Flight Aerodynamics . . . . . . . . . . . . . . . . . 55
2.5 Solution of the Aeroelastic System . . . . . . . . . . . . . . . . . . . 56
2.5.1 Frequency Domain Solution for Hover Analysis . . . . . . . . 56
2.5.2 Time Domain Solution for Forward Flight Analysis . . . . . 59
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3 Experimental Setup 61
3.1 Overview ............................. 61
3.2 Blade Design . . . . . . . . . . . . . . . . . . . . . . 62
3.2.1 ATR Prototype Blade . . . . . . . . . . . . . 62
3.2.2 ATR Test Blade with Modification . . . . . . 65
3.3 Prototype Blade Manufacturing . . . . . . . . . . . . 66
3.4 Aeroelastic Tests . . . . . . . . . . . . . . . . . . . . 67
3.4.1 Wind Tunnel . . . . . . . . . . . . . . . . . . 67
3.4.2 Test Apparatus . . . . . . . . . . . . . . . . . 67
3.4.3 Hover Testing . . . . . . . . . . . . . . . . . . 70
3.4.4 Forward Flight Testing . . . . . . . . . . . . . 72
4 Characteristics of the ATR Blade on the Bench and in Hover 75
4.1 O verview . . . . . . . . . . . . . . . . . . . . . . . . . 75
4.2 Basic Bench Testing . . . . . . . . . . . . . . . . . . 75
4.3 Non-Rotating Frequency Response . . . . . . . . . . 77
4.4 Hover Frequency Response . . . . . . . . . . . . . . . 80
4.4.1 Collective pitch sensitivity . . . . . . . . . . . 80
4.4.2 Medium density sensitivity . . . . . . . . . . . 81
4.4.3 Rotational speed sensitivity . . . . . . . . . . 82
4.4.4 Discussion . . . . . . . . . . . . . . . . . . . . 84
5 Dynamic Characteristics of the ATR System in Forward Flight 87
5.1 O verview . . . . . . . . . . . . . . . . . . . . . . 87
5.2 Non-Rotating Frequency Response . . . . . . . 88
5.3 Forward Flight Response ............. 90
5.3.1 Analysis Model without Pitch Link . 90
5.3.2 Individual Blade Control Signal..... 92
5.3.3 Results of the Model without Pitch Link 93
5.3.4 Analysis Model with Pitch Link . . . . . 106
5.3.5 Results from the Model with Pitch Link 108
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5.4 Correlation of Forward Flight Analyses with Experiments . . . . . . . 113
6 System Identification of the ATR System in Forward Flight 115
6.1 O verview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115
6.2 Input Signals for System Identification . . . . . . . . . . . . . . . . . 116
6.3 Results of the ATR System Identification . . . . . . . . . . . . . . . . 119
6.3.1 Collective Mode of Actuation . . . . . . . . . . . . . . . . . . 119
6.3.2 Cyclic Mode of Actuation . . . . . . . . . . . . . . . . . . . . 124
7 Closed-loop Controller for Vibration Reduction in Forward Flight 127
7.1 O verview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127
7.2 LTI Feedback Compensator for Disturbance Rejection . . . . . . . . . 128
7.3 Stability of the Closed-loop System . . . . . . . . . . . . . . . . . . . 130
7.3.1 Original Feedback Controller . . . . . . . . . . . . . . . . . . . 130
7.3.2 Modified Feedback Controller . . . . . . . . . . . . . . . . . . 133
7.4 Numerical Demonstration of the Closed-loop Controller . . . . . . . . 134
8 Conclusions and Recommendations 139
8.1 Summ ary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139
8.2 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141
8.3 Recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142
A State-space Formulation for Hover Analysis 145
B Time Integration Formulation for Forward Flight Analysis 147
C AFC Distribution in the ATR Prototype Blade 149
D Material Properties of the ATR Test Blade Constituents 151
E LTP System and its Identification 153
E.1 Characteristics of LTP system . . . . . . . . . . . . . . . . . . . . . . 153
E.2 Identification Methodology of the LTP System . . . . . . . . . . . . . 156
E.3 Implementation of the Developed Methodology . . . . . . . . . . . . . 160
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