Rotorcraft Center of Excellence The Pennsylvania State University 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 Research Proposal

Rotorcraft Center of Excellence The Pennsylvania State University 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

Rotorcraft Center of Excellence The Pennsylvania State University 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

Rotorcraft Center of Excellence The Pennsylvania State University 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)

Rotorcraft Center of Excellence The Pennsylvania State University 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

Rotorcraft Center of Excellence The Pennsylvania State University Frequency Spectrum for Helicopter Analysis Frequency Vibration Ground Resonance Acoustics Flight mechanics

Rotorcraft Center of Excellence The Pennsylvania State University 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

Rotorcraft Center of Excellence The Pennsylvania State University 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

Rotorcraft Center of Excellence The Pennsylvania State University Flapwise Load & Torsional Moment Control  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 2. Opposite action of dual flap 1. Deformed blade w/o control 3. Straightened blade lift due to outboard flap Opposite lift due to inboard flap

Rotorcraft Center of Excellence The Pennsylvania State University 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

Rotorcraft Center of Excellence The Pennsylvania State University 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 Composite Tailoring Pitch link loads

Rotorcraft Center of Excellence The Pennsylvania State University 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

Rotorcraft Center of Excellence The Pennsylvania State University 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 Illustration of an H-46 tunnel strike Rotational speed variations for engagement and disengagement

Rotorcraft Center of Excellence The Pennsylvania State University Sample Results

Rotorcraft Center of Excellence The Pennsylvania State University Sample Results: Active Loads Control using Active Flaps  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 Active control with 1/rev control input Flapwise moment harmonics along the radial station R, radial station x P Base 2P Base 1P Active 2P Active 4/rev vibratory hub loads

Rotorcraft Center of Excellence The Pennsylvania State University 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. Sample Results - dual flap w/ 1P Flapwsie bending moment and Flapping motion

Rotorcraft Center of Excellence The Pennsylvania State University Appendix

Rotorcraft Center of Excellence The Pennsylvania State University 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)

Rotorcraft Center of Excellence The Pennsylvania State University Global Fault Detection - using active flaps  Active interrogation using trailing edge flaps;  Excitation bandwidth of 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

Rotorcraft Center of Excellence The Pennsylvania State University 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 Finite element model of cracked beam Tunable Inductance Piezoelectric Patch Piezoelectric transducer for damage detection

Rotorcraft Center of Excellence The Pennsylvania State University 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 Substitute with Shear Piezoelectric Tube Segments poled along longitudinal direction, P 2 Electric field applied in the width direction, E 1 a’ Dead Leading Edge Mass (10 – 20% Weight of the Blade) a