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The Pennsylvania State University the Graduate School Department of Aerospace Engineering an INVESTIGATION of PERFORMANCE BENEFI

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The Pennsylvania State University the Graduate School Department of Aerospace Engineering an INVESTIGATION of PERFORMANCE BENEFI The Pennsylvania State University The Graduate School Department of Aerospace Engineering AN INVESTIGATION OF PERFORMANCE BENEFITS AND TRIM REQUIREMENTS OF A VARIABLE SPEED HELICOPTER ROTOR A Thesis in Aerospace Engineering by Jason H. Steiner 2008 Jason H. Steiner Submitted in Partial Fulfillment of the Requirements for the Degree of Master of Science August 2008 ii The thesis of Jason Steiner was reviewed and approved* by the following: Farhan Gandhi Professor of Aerospace Engineering Thesis Advisor Robert Bill Research Associate , Department of Aerospace Engineering George Leisuietre Professor of Aerospace Engineering Head of the Department of Aerospace Engineering *Signatures are on file in the Graduate School iii ABSTRACT This study primarily examines the main rotor power reductions possible through variation in rotor RPM. Simulations were based on the UH-60 Blackhawk helicopter, and emphasis was placed on possible improvements when RPM variations were limited to ± 15% of the nominal rotor speed, as such limited variations are realizable through engine speed control. The studies were performed over the complete airspeed range, from sea level up to altitudes up to 12,000 ft, and for low, moderate and high vehicle gross weight. For low altitude and low to moderate gross weight, 17-18% reductions in main rotor power were observed through rotor RPM reduction. Reducing the RPM increases rotor collective and decreases the stall margin. Thus, at higher airspeeds and altitudes, the optimal reductions in rotor speed are smaller, as are the power savings. The primary method for power reduction with decreasing rotor speed is a decrease in profile power. When rotor speed is optimized based on both power and rotor torque, the optimal rotor speed increases at low speeds to decrease rotor torque without power penalties. Optimization at high flight speeds shows that both power- and torque-weighted optimums occur at the same rotor speeds. This trend is independent of vehicle gross weight. For very high gross weight and high altitude operations, the flight envelope can be expanded by increasing the rotor speed, preventing rotor stall. Shaft torque was not seen to increase appreciably for moderate and high speed flight, with only a small increase in low speed flight. Main rotor collective pitch was seen to increase as rotor speed decreased to maintain thrust. In addition to main rotor collective pitch, main rotor longitudinal cyclic pitch was seen to increase at moderate to high cruise speeds when the rotor RPM was reduced. Blade coning also increased as RPM decreased due to reduction in centrifugal force, though first harmonic flapping angles remained nearly the same. iv TABLE OF CONTENTS LIST OF FIGURES.............................................................................................................. vi LIST OF TABLES................................................................................................................ vii LIST OF SYMBOLS ............................................................................................................ x ACKNOWLEDGEMENTS ................................................................................................... xi Chapter 1 Introduction........................................................................................................ 1 Background of Variable Speed Rotors ......................................................................... 1 Optimum Speed Rotor ......................................................................................... 2 Variable Span Rotor.............................................................................................2 Bell-Boeing V-22 Osprey...................................................................................... 3 Compound Helicopters......................................................................................... 4 Helicopter Controls .............................................................................................. 4 Stability................................................................................................................ 6 Proposed Concept....................................................................................................... 6 Chapter 2 Model and Analysis Methods ............................................................................ 8 Basic Helicopter Model ................................................................................................ 8 Operating Requirements ...................................................................................... 8 Model................................................................................................................... 9 Aerodynamic Environment ................................................................................... 9 Rotor Force and Moment Calculations.................................................................. 11 Rotor Motion ........................................................................................................ 15 Balance of Forces and Moments .......................................................................... 17 Simulation Model......................................................................................................... 19 Program Outline................................................................................................... 19 Basic Trim ....................................................................................................20 Flapping Calculations ................................................................................... 20 Force and Moment Calculations ................................................................... 20 Trim Procedure............................................................................................. 21 Analysis Methods................................................................................................. 22 Output from Simulation ................................................................................. 22 Examining Trends......................................................................................... 22 Optimization ................................................................................................. 22 Chapter 3 UH-60 results..................................................................................................... 24 Baseline Weight .......................................................................................................... 24 Sea Level Results ................................................................................................ 26 Results at Altitude................................................................................................ 44 Variation in Gross Weight ............................................................................................ 49 Reduced Gross Weight ........................................................................................ 49 Sea Level .....................................................................................................49 Results at Altitude......................................................................................... 54 Increased Gross Weight....................................................................................... 57 Sea Level .....................................................................................................57 v Results at Altitude......................................................................................... 59 Chapter 4 Conclusions and Recommendations .................................................................. 64 Summary..................................................................................................................... 64 Recommendations for Future Work ............................................................................. 66 Bibliography........................................................................................................................ 69 Appendix A Additional Figures............................................................................................ 71 18,300 lbs Gross Weight ............................................................................................. 71 16,000 lbs Gross Weight ............................................................................................. 77 22,000 lbs Gross Weight ............................................................................................. 82 Appendix B Helicopter Properties....................................................................................... 89 vi LIST OF FIGURES Figure 3.1: Main Rotor Power Contours, 18,300 lbs Gross Weight, Sea Level ..................... 27 Figure 3.2: Main Rotor Induced Power Profiles, 18,300 lbs Gross Weight, Sea Level .......... 29 Figure 3.3: Main Rotor Profile Power Contours, 18,300 lbs Gross Weight, Sea Level .......... 30 Figure 3.4: SC1095 Airfoil Drag Coefficient vs. Angle of Attack, Mach = 0.6 ........................ 31 Figure 3.5: Optimum RPM Schedule vs. Airspeed, 18,300 lbs Gross Weight, Sea Level...... 32 Figure 3.6: Torque Weighted Optimum RPM Schedules, 18,300 lbs Gross Weight, Sea Level ........................................................................................................................... 34 Figure 3.7: Torque Weighted Optimum Power Profiles, 18,300 lbs Gross Weight, Sea Level ..........................................................................................................................
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