Rotorcraft Airloads Measurements—Extraordinary Costs, Extraordinary Benefits William G

Rotorcraft Airloads Measurements—Extraordinary Costs, Extraordinary Benefits William G

NASA/TP–2014-218374 Rotorcraft Airloads Measurements—Extraordinary Costs, Extraordinary Benefits William G. Bousman U.S. Army Aeroflightdynamics Directorate Ames Research Center, Moffett Field, California August 2014 The NASA STI Program Office . in Profile Since its founding, NASA has been dedicated to the • CONFERENCE PUBLICATION. Collected advancement of aeronautics and space science. The papers from scientific and technical conferences, NASA Scientific and Technical Information (STI) symposia, seminars, or other meetings spon‑ Program Office plays a key part in helping NASA sored or cosponsored by NASA. maintain this important role. • SPECIAL PUBLICATION. Scientific, technical, The NASA STI Program Office is operated by or historical information from NASA programs, Langley Research Center, the Lead Center for projects, and missions, often concerned with NASA’s scientific and technical information. The subjects having substantial public interest. 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NASA/TP–2014-218374 Rotorcraft Airloads Measurements—Extraordinary Costs, Extraordinary Benefits William G. Bousman U.S. Army Aeroflightdynamics Directorate Ames Research Center, Moffett Field, California National Aeronautics and Space Administration Ames Research Center Moffett Field, California 94035‑1000 August 2014 Acknowledgments I obtained a great deal of help from many people while preparing this report. I thank them all, including Ed Austin, Ken Bartie, Ed Beno, Mahendra Bhagwat, Dave Conner, Jeff Cross, Joe Chambers, Bruce Charles, Frank Harris, Danny Hoad, Euan Hooper, Terry Hornbuckle, Larry Jenkins, Wayne Johnson, Andy Kerr, Bob Kufeld, Tom Lawrence, Al Lizak, Tom Maier, Wayne Mantay, Bobby Mathew, Jim McCroskey, Don Merkley, Jorge Morillo, Tom Norman, Bob Ormiston, Ray Piziali, Ray Prouty, Art Ragosta, Nischint Rajmohan, Mike Scully, Marilyn Smith, Karen Studebaker, Barbara Trippe, John Vorvald, John Ward, Bill Warmbrodt, Bob Wood, Gloria Yamauchi, and Hyeonsoo Yeo. This publication is an expanded version of the 31st Alexander Nikolsky Honorary Lecture, originally presented at the American Helicopter Society 66th Annual Forum, Virginia Beach, VA, May 3–5, 2011. Available from: NASA Center for Aerospace Information National Technical Information Service 7115 Standard Drive 5301 Shawnee Road Hanover, MD 21076‑1320 Alexandria, VA 22312 TABLE OF CONTENTS SUMMARY ...................................................................1 Nonlinear Aerodynamics—Each Rotor is Different ...................................................................38 INTRODUCTION .........................................................1 Remaining Deficiencies ...........................................39 ROTORCRAFT AIRLOADS ........................................2 Loss of Experimental Data ......................................40 EXTRAORDINARY COSTS, EXTRAORDINARY Alternatives to Full‑Scale Airloads Tests ................42 BENEFITS .....................................................................3 Model Rotor Tests ...............................................42 Full‑Scale Rotor Tests With Limited HISTORY OF AIRLOADS TESTING ..........................4 Instrumentation ...................................................43 Flight Envelope Limits ..............................................4 Simplified Measurements ....................................44 Early NACA Research Into Rotor Loads ..................6 New Measurement Techniques and The Twelve Airloads Tests .........................................7 Technologies ........................................................44 Technology and Airloads Testing ..............................9 Data Validation ........................................................13 APPENDIX 1—AIRLOADS TEST DESCRIPTIONS .........................................................45 Repeat Cases .......................................................13 Introduction .............................................................45 Steady Thrust Comparisons ................................15 NACA 15‑Foot‑Diameter Model Rotor ...................45 Test‑on‑Test Cases ...............................................17 CH‑34 Flight Test ....................................................47 BENEFITS OBTAINED FROM AIRLOADS UH‑1A Flight Test ...................................................50 TESTING .....................................................................20 CH‑34 Wind Tunnel Test .........................................53 Citations as a Measure of Benefits ..........................21 CH‑47A Flight Test..................................................54 Understanding Airloads ...........................................22 NH‑3A Compound Flight Test.................................57 First Problem: Vortex Wake Loading XH‑51A Compound Flight Test...............................59 at Low Speed .......................................................22 CH‑53A Flight Test..................................................62 Second Problem: Dynamic Stall .........................23 AH‑1G/Operational Loads Survey ..........................64 Third Problem: High‑Speed Structural Loads ...................................................................25 AH‑1G/Tip Aerodynamics and Acoustics Test ........67 UH‑60A Airloads Program and Workshops ............29 UH‑60A Airloads Program Flight Test ....................70 UH‑60A Airloads Program ..................................30 UH‑60A Airloads Wind Tunnel Test........................74 UH‑60A Airloads Workshop ...............................31 APPENDIX 2—CORRELATION Airloads Workshops and the New ACCURACY ...............................................................78 Calculations .........................................................31 Introduction .............................................................78 The Airloads Workshops Transformation ............33 Steady Data ..............................................................78 CONCLUDING REMARKS .......................................37 Time History Data ...................................................79 THE FIVE CHALLENGES .........................................38 REFERENCES ............................................................81 Integrating the New Methods ..................................38 iii iv Rotorcraft Airloads Measurements—Extraordinary Costs, Extraordinary Benefits William G. Bousman1 Ames Research Center SUMMARY The first airloads measurements were made in the 1950s at NACA Langley on a 15.3-foot-diameter model rotor, stimulated by the invention of miniaturized pressure transducers. The inability to predict higher harmonic loads in those early years led the U.S. Army to fund airloads measurements on the CH-34 and the UH-1A aircraft. Nine additional comprehensive airloads tests have been done since that early work, including the recent test of an instrumented UH-60A rotor in the 40- by 80-Foot Wind Tunnel at NASA Ames. This historical paper discusses the 12 airloads tests and how the results were integrated with analytical efforts. The recent history of the UH-60A Airloads Workshops is presented, and it is shown that new develop- ments in analytical methods have transformed our capability to predict airloads that are critical for design. INTRODUCTION It is traditional for the Nikolsky Lecturer to draw some connection between the lecturer and Professor Nikolsky, something that becomes more difficult to do with each passing year. I have no such connection, but I do have a link to the start of the honorary lectureship and that will have to suffice. In 1978, Dewey Hodges and I wrote a paper on the correlation

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