Research Proposal

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

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

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

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)

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

Frequency Spectrum for Helicopter Analysis Flight mechanics Ground Resonance Acoustics Vibration Frequency

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

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

Flapwise Load & Torsional Moment Control 1. Deformed blade w/o 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 lift due to outboard flap Opposite lift due to inboard flap 3. Straightened blade

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

Composite Tailoring Pitch link loads 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

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

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

Sample Results

-4 x 10 2.5 1P Base 2P Base 2 1P Active 2P Active 1.5 1 0.5 0 0 0.2 0.4 0.6 0.8 1 Sample Results: Active Loads Control using Active Flaps Active control with 1/rev control input • 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 Flapwise moment harmonics along the radial station 4/rev vibratory hub loads R, radial station

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

Appendix

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)

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

Tunable Inductance Piezoelectric Patch 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

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

Research Proposal