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«ABSTRACT DESIGN AND PERFORMANCE PREDICTION Title of dissertation: OF SWASHPLATELESS HELICOPTER ROTOR WITH TRAILING EDGE FLAPS AND TABS Jaye Falls, ...»

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ABSTRACT

DESIGN AND PERFORMANCE PREDICTION

Title of dissertation:

OF SWASHPLATELESS HELICOPTER ROTOR

WITH TRAILING EDGE FLAPS AND TABS

Jaye Falls, Doctor of Philosophy, 2010

Professor Inderjit Chopra

Dissertation directed by:

Department of Aerospace Engineering This work studies the design of trailing edge controls for swashplateless helicopter primary control, and examines the impact of those controls on the performance of the rotor. The objective is to develop a comprehensive aeroelastic analysis for swashplateless rotors in steady level flight. The two key issues to be solved for this swashplateless control concept are actuation of the trailing edge controls and evaluating the performance of the swashplateless rotor compared to conventionally controlled helicopters. Solving the first requires simultaneous minimization of trailing flap control angles and hinge moments to reduce actuation power. The second issue requires not only the accurate assessment of swashplateless rotor power, but also similar or improved performance compared to conventional rotors. The analysis consists of two major parts, the structural model and the aerodynamic model.

The inertial contributions of the trailing edge flap and tab are derived and added to the system equations in the structural model. Two different aerodynamic models are used in the analysis, a quasi-steady thin airfoil theory that includes arbitrary hinge positions for the flap and the tab, and an unsteady lifting line model with airfoil table lookup based on wind tunnel test data and computational fluid dynamics simulation.

The design aspect of the problem is investigated through parametric studies of the trailing edge flap and tab for a Kaman-type conceptual rotor and a UH-60A swashplateless variant. The UH-60A model is not changed except for the addition of a trailing edge flap to the rotor blade, and the reduction of pitch link stiffness to imitate a soft root spring. Study of the uncoupled blade response identifies torsional stiffness and flap hinge stiffness as important design features of the swashplateless rotor. Important trailing edge flap and tab design features including index angle, aerodynamic overhang, chord and length are identified through examination of coupled trim solutions in wind tunnel conditions at high speed. Flap and tab configurations that minimize both the control angles and hinge moments required to trim are developed for both the Kaman-type and UH-60A models, and the rotors are successfully trimmed across the range of forward flight speed.

The conventionally controlled UH-60A rotor model is validated with data from the UH-60A Flight Test Program. Excellent correlation is obtained for rotor power in hover and in forward flight. It is shown that the magnitude of the predicted power, but not the trend versus forward speed, is affected by the calculation of inflow distribution. Both uniform inflow and a pseudo-implicit free wake model are used to calculate the inflow distribution for the swashplateless rotor. Using the free wake model, the predicted swashplateless rotor power is sensitive to the pattern of trailed vorticity from the rotor blade. Trailed vortices are added at the inboard and outboard boundaries of the trailing edge flap, and the flap deflection is used to calculate an effective angle of attack for the calculation of the near and far wake. This wake model predicts the swashplateless rotor requires less main rotor power than the conventional UH-60A helicopter from hover to µ = 0.25. As the forward flight speed increases, the swashplateless predicted power increases above the conventional rotor, and the rotor lift-to-drag ratio decreases below that of the conventional rotor.

Design and Performance Prediction of Swashplateless Helicopter Rotor with Trailing Edge Flaps and Tabs

–  –  –

Advisory Committee:

Professor Inderjit Chopra, Chair/Advisor Dr. Anubhav Datta, Co-Advisor Professor Darryll Pines Professor Norman Wereley Associate Professor James Baeder Professor Michael Coplan, Dean’s Representative c Copyright by Jaye Falls Acknowledgments I am pleased to acknowledge all those who have contributed to this work as I finally bring it to completion.

My deepest thanks to my advisor, Inderjit Chopra, for his many years of encouragement and support. He convinced me to add aerospace engineering to my education at a point when an easier topic might have been tempting for a young parent with a full complement of suburban distractions, and I have never regretted the undertaking. His contributions to my research, from the general to the detail level, have been large and greatly appreciated.

Dr. Anubhav Datta has acted as both my colleague and mentor in rotor dynamics. The excellence of his scholarship is well known, but his patience and kindness should also earn him fame. The thought-provoking discussions we had about rotor dynamics frequently clarified my thinking and bolstered my motivation.

I would also like to thank the other members of my advisory committee, Drs.

Baeder, Coplan, Pines and Wereley, for their ongoing interest in and support for this work.





This work was supported in part by Kaman Aerospace Corporation. John Wei and Mike Bielefield provided useful discussion, guidance and data in the initial stages of the project. The Alfred P. Sloan Foundation and the Vertical Flight Foundation of the American Helicopter Society provided generous financial support for several years.

My colleagues from the Alfred Gessow Rotorcraft Center have been a welcome

–  –  –

the CFD research group led by Dr. Baeder. Arun Jose contributed to the success of this work by enabling my use of CFD. His analysis of trailing edge flaps was of great benefit to me. My ideas about the effect of a trailing edge flap on rotor wake were improved and sharpened in discussion with Dr. Shreyas Ananthan. Drs.

Jinwei Shen and Judah Milgram helped me understand trailing edge flaps and ways to implement them in UMARC. Beatrice Roget, Jayant Sirohi and Jinsong Bao were particularly generous with their time during my years in the lab. Many others, including Ron, Jason, Abhishek, Felipe, Julie, Anne, Paul, Beerinder, Carlos, Ben, Peter and Brandon, were the sources of much friendly interaction and intellectual cross-pollination.

My husband, Britton Ward, and our children, Hunter and Schuyler, have been a wellspring of support and joy. Without them, the process may have been shorter but the achievement would not be nearly as sweet. For the last two years in particular, Hunter has exhibited patience far beyond his years as his mother spent far more time working and less time playing video games than he would have preferred.

Thanks also to my grandmother, aunts and cousins, and to my sisters- and brothersin-law, who have made brief holidays into concentrated occasions of happiness. To my mother who has always been my inspiration, gratitude and my assurance that I believe my student days may be over. Finally, thanks to my parents-in-law, who have so ably shown Britt and me how to earn a PhD while raising a family.

–  –  –

1.4 Schematic Diagram of Generic Rotor Blade with Varying Trailing Edge Flap Configurations........................ 21

2.1 Measured Drag for the NACA 23012 (Ames and Sears [1]) and Apache HH-06 and HH-10 (Hassan et al. [2]) Flapped Airfoils. Positive (4◦ ) and Negative (−4◦ ) Flap Deflections Shown............... 113

2.2 Measured Drag for Flapped HH-06 Airfoil, M = 0.6.......... 113

–  –  –

2.4 Empirical Model of Drag for Flapped SC1095R8 Airfoil, M = 0.3, Showing ±10◦ TEF Deflections..................... 114

2.5 Extended Empirical Model of Drag for Flapped SC1095R8 Airfoil, Showing ±10◦ TEF Deflections..................... 114

2.6 Grid for 2-D CFD Analysis of Flapped SC1095R8 Airfoil. Shown with Flap Chord cf = 0.15c, Positive Flap Deflection.......... 114

2.7 Comparison of CFD Predicted and Measured Baseline SC1095R8 Airfoil Properties at M = 0.3, No Flap.................... 115

–  –  –

2.9 Comparison of CFD Drag Prediction and Empirical Model for Flapped SC1095R8, cf = 0.15c, No Overhang, M = 0.3............. 116

–  –  –

2.15 Radial Distribution of Bound Circulation at 0◦, 90◦, 180◦ and 270◦ Azimuth Angles, µ = 0.11........................ 121

–  –  –

3.2 Effect of Index Angle on Tab Control Angles for Kaman-type Rotor, µ = 0.35, CT /σ = 0.062, Rigid Blades.................. 155

–  –  –

3.4 Effect of Advance Ratio on Tab Control Angles for Kaman-type Rotor, θidx = 5◦, CT /σ = 0.062, Rigid Blades............... 156

3.5 Effect of Advance Ratio on Tab Hinge Moments for Kaman-type Rotor, θidx = 5◦, CT /σ = 0.062, Rigid Blades............... 157

3.6 Effect of Combined Chord on Tab Control Angles for Kaman-type Rotor, µ = 0.35, θidx = 5◦, CT /σ = 0.062, Rigid Blades........ 157

3.7 Effect of Combined Chord on Tab Hinge Moments for Kaman-type Rotor, µ = 0.35, θidx = 5◦, CT /σ = 0.062, Rigid Blades........ 158

3.8 Effect of Radial Position on Tab Control Angles for Kaman-type Rotor, µ = 0.35, θidx = 5◦, CT /σ = 0.062, Rigid Blades.......... 158

3.9 Effect of Radial Position on Tab Hinge Moments for Kaman-type Rotor, µ = 0.35, θidx = 5◦, CT /σ = 0.062, Rigid Blades........ 159

3.10 Effect of Flap Overhang on Tab Control Angles for Kaman-type Rotor, µ = 0.35, θidx = 5◦, CT /σ = 0.062, Rigid Blades.......... 159

3.11 Effect of Flap Overhang on Tab Hinge Moments for Kaman-type Rotor, µ = 0.35, θidx = 5◦, CT /σ = 0.062, Rigid Blades........ 160

3.12 Effect of Tab Overhang on Tab Control Angles for Kaman-type Rotor, µ = 0.35, θidx = 5◦, CT /σ = 0.062, Rigid Blades............ 160

–  –  –

3.14 Comparison of Baseline and Improved Tab Control Angles for Kamantype Rotor, CT /σ = 0.062, Rigid Blades................ 161

3.15 Comparison of Baseline and Improved Tab Hinge Moments for Kamantype Rotor, CT /σ = 0.062, Rigid Blades................ 162

–  –  –

3.17 Fan Plot of Swashplateless Rotor Model................ 164

3.18 Uncoupled Blade Pitch Response to TEF Input for Varying Torsional Frequency, UH-60A type Rotor µ = 0.0, θidx = 15◦........... 165

3.19 Uncoupled Blade Loading Response to TEF Input for Varying Torsional Frequency, UH-60A type Rotor µ = 0.0, θidx = 15◦....... 166

3.20 Effect of Advance Ratio on Flap Control Angles and Hinge Moment, UH-60A Type Rotor, θidx = 15◦, CT /σ = 0.084............. 167

3.21 Effect of Index Angle on Flap Control Angles and Hinge Moment, UH-60A Type Rotor, overhang = 0.0cf, µ = 0.368, CT /σ = 0.084.. 168

–  –  –

3.23 Effect of Flap Overhang on Flap Control Angles and Hinge Moment, UH-60A Type Rotor, θidx = 15◦, µ = 0.368, CT /σ = 0.084...... 170

–  –  –

3.26 Effect of Advance Ratio on Improved Flap Configuration, UH-60A Type Rotor, θidx = 20◦, ovh = 0.33cf, CT /σ = 0.084.......... 173

3.27 Uncoupled Blade Pitch Response to Tab Input for Varying Torsional Frequency, UH-60A type Rotor µ = 0.0, θidx = 15◦, Aileron Frequency = 2.15/rev............................ 174

–  –  –

3.29 Uncoupled Blade Loading Response to Tab Input for Varying Torsional Frequency, UH-60A type Rotor µ = 0.0, θidx = 15◦, Aileron Frequency = 2.15/rev........................... 176

3.30 Uncoupled Blade Pitch Response to Tab Input for Varying Aileron Frequency, UH-60A type Rotor µ = 0.0, θidx = 15◦, Torsional Frequency = 1.9/rev............................. 177

–  –  –

3.32 Uncoupled Blade Loading Response to Tab Input for Varying Aileron Frequency, UH-60A type Rotor µ = 0.0, θidx = 15◦, Torsional Frequency = 1.9/rev............................. 179

3.33 Effect of Index Angle on Tab Control Angles and Hinge Moment, UH-60A Type Rotor, µ = 0.368, CT /σ = 0.084............. 180

3.34 Effect of Tab Chord Ratio on Tab Control Angles and Hinge Moment, UH-60A Type Rotor, µ = 0.368, θidx = 15◦, CT /σ = 0.084...... 181

3.35 Effect of Combined Chord Ratio on Tab Control Angles and Hinge Moment, UH-60A Type Rotor, µ = 0.368, θidx = 15◦, CT /σ = 0.084. 182

3.36 Effect of Flap Overhang on Tab Control Angles and Hinge Moment, UH-60A Type Rotor, µ = 0.368, θidx = 15◦, CT /σ = 0.084...... 183

3.37 Effect of Tab Overhang on Tab Control Angles and Hinge Moment, UH-60A Type Rotor, µ = 0.368, θidx = 15◦, CT /σ = 0.084...... 184

3.38 Effect of Advance Ratio on Improved Trailing Edge Flap and Tab Configuration, UH-60A Type Rotor, θidx = 18◦, CT /σ = 0.084.... 185

–  –  –

4.2 Predicted and Measured Power for UH-60A in Forward Flight, CW /σ = 0.0783 (FW: free wake, Uniform: uniform inflow).......... 217

4.3 Effect of Reduced Torsional Frequency on Pitch Collective for Rotor in Forward Flight, CW /σ = 0.0783................... 218

–  –  –

4.5 Effect of Reduced Torsional Frequency on Predicted Power for Rotor in Forward Flight, CW /σ = 0.0783................... 220

4.6 Effect of Reduced Torsional Frequency on Predicted Shaft Angles for Baseline in Forward Flight, CW /σ = 0.0783.............. 221



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