University of Tennessee, Knoxville TRACE: Tennessee Research and Creative Exchange Masters Theses Graduate School 5-2008 The Effect of Tailboom Strakes and Vertical Fin Modifications on the Performance and Handling Qualities of OH-58 Helicopters John A. Wade University of Tennessee - Knoxville Follow this and additional works at: https://trace.tennessee.edu/utk_gradthes Recommended Citation Wade, John A., "The Effect of Tailboom Strakes and Vertical Fin Modifications on the erP formance and Handling Qualities of OH-58 Helicopters. " Master's Thesis, University of Tennessee, 2008. https://trace.tennessee.edu/utk_gradthes/477 This Thesis is brought to you for free and open access by the Graduate School at TRACE: Tennessee Research and Creative Exchange. It has been accepted for inclusion in Masters Theses by an authorized administrator of TRACE: Tennessee Research and Creative Exchange. For more information, please contact [email protected]. To the Graduate Council: I am submitting herewith a thesis written by John A. Wade entitled "The Effect of Tailboom Strakes and Vertical Fin Modifications on the erP formance and Handling Qualities of OH-58 Helicopters." I have examined the final electronic copy of this thesis for form and content and recommend that it be accepted in partial fulfillment of the equirr ements for the degree of Master of Science, with a major in Aviation Systems. Richard Ranaudo, Major Professor We have read this thesis and recommend its acceptance: Stephen Corda, Uwe P. Solies Accepted for the Council: Carolyn R. Hodges Vice Provost and Dean of the Graduate School (Original signatures are on file with official studentecor r ds.) To the Graduate Council: I am submitting herewith a thesis written by John A. Wade entitled “The Effect of Tailboom Strakes and Vertical Fin Modifications on the Performance and Handling Qualities of OH-58 Helicopters.” I have examined the final electronic copy of this thesis for form and content and recommend that it be accepted in partial fulfillment of the requirements for the degree of Master of Science, with a major in Aviation Systems. Richard Ranaudo Major Professor We have read this thesis and recommend its acceptance: Stephen Corda Uwe P. Solies Accepted for the Council: Carolyn R. Hodges Vice Provost and Dean of the Graduate School (Original signatures are on file with official student records) The Effect of Tailboom Strakes and Vertical Fin Modifications on the Performance and Handling Qualities of OH-58 Helicopters A Thesis Presented for the Master of Science Degree The University of Tennessee, Knoxville John A. Wade May 2008 ACKNOWLEDGEMENTS My sincerest thanks must be expressed to all those who have helped with this project. Tom Thompson of the Aeromechanics department of the Army’s Aviation Engineering Department (AED) supported and added his considerable expertise throughout this project and it would not have been possible without him. Joe McKay and his handling qualities team at AED added the drive and engineering insight that kept the project alive and moving forwards. Dennis Boyer and Tim Parker of the Program Executive Office – Aviation sponsored and believed in this test from the beginning. Their wonderful mentorship and drive kept the team motivated. Bob Desroche and his team at BLR Aerospace never gave up and went to almost unbelievable lengths to keep the project funded and on track. My deepest appreciation goes to Mark Miller and the management of Dynetics Inc. who allowed me the time, encouragement and space to pursue this thesis. It is a pleasure to be associated with such professionals. Special thanks must also go to my thesis advisor, Rich Ranaudo who provided sage advice and counseling throughout my time at UTSI. Rich is a magnificent teacher and mentor whom I deeply respect. Thanks also to those fantastic instructors at USNTPS, without whose training I would not have had this opportunity. To J. Kevin Heineke who got me started, I express my sincere appreciation. Lastly, the greatest of all thanks must go to my wife Carolyn, who stood beside me through all the troubles and turmoil of 23 years of military service and many years of college. ii ABSTRACT The Bell OH-58D helicopter is used in the armed reconnaissance role by the U.S. Army worldwide. Operations in support of this mission require the aircraft to be operated at a hover for extended periods of time at high altitude and in hot conditions. This places large demands on a power limited aircraft and increases pilot workload, especially in the pointing task so important to weapons delivery. The addition of aerodynamic modifications provides an inexpensive and effective method of reducing power required and pilot workload. An investigation was conducted to determine the effects of adding tailboom strakes and a vertical fin modification (FastFin®) to a Bell OH-58D. The effect of the combined devices on helicopter performance, vibration and handling qualities was evaluated to determine any decrease in power required vs. power available (increased power margin). The strakes and modified fin were attached to the tailboom in such a manner as to alter the flow pattern of air passing over the tailboom. This change in flow pattern reduced the anti-torque requirements of the tail rotor. This in turn reduced the overall power requirement. The modified fin and strake combination reduced the vortices and turbulence at the tailboom and resulted in lower pilot workload and vibration in an out-of-ground-effect hover. This study also evaluated the effects on performance and handling characteristics of the helicopter. Testing included hover, low airspeed forward, rearward, sideward flight and level forward flight power measurements and handling qualities using modified Cooper-Harper and Vibration Assessment Rating (VAR) scales. Results showed an overall improvement in handling qualities and vibration levels at critical wind azimuth angles in low airspeed flight. For out-of-ground effect (OGE) hover, there was also a 2-3% reduction in power required due to the improved aerodynamic efficiency of the modified fin and strake combination. iii DISCLAIMER The views, opinions and/or findings contained in this report are those of the author and should not be construed as an official Department of Army position, or decision, unless so designated by other official documentation. iv TABLE OF CONTENTS 1. INTRODUCTION.....................................................................................................1 1.1 Aircraft description ...............................................................................................1 2. BACKGROUND .......................................................................................................5 2.1 Strake Theory of Operation ..................................................................................5 2.2 Estimating the Effects of Strake Installation. .....................................................12 2.3 Estimating the Effects of Fin Modifications.......................................................13 Figure 5. Comparison of Modified OH-58D Fin (orange) to Original Fin..............14 3. TEST AND TEST METHODS..............................................................................22 3.1 Test Configuration and Methodology.................................................................22 3.1.1 Test Aircraft.................................................................................................22 3.1.2 Aerodynamic Modifications ........................................................................24 3.1.3 Instrumentation ............................................................................................24 3.2 Methodology.......................................................................................................26 3.2.1 Description of Test Conditions and Maneuvers...........................................26 3.2.2 Data Reduction and Analysis.......................................................................28 3.2.3 Pilot Handling Qualities Ratings .................................................................29 3.2.4 Vibration Assessment Ratings .....................................................................29 4. DATA, RESULTS AND DISCUSSION................................................................32 4.1 Hover Performance .............................................................................................32 4.2 Low Airspeed Evaluation ...................................................................................35 4.2.1 Handling Qualities and Vibration Assessment Ratings...............................35 5. CONCLUSIONS .....................................................................................................46 5.1 Handling Qualities and Vibration Assessment Ratings......................................46 5.2 Low Airspeed Performance ................................................................................46 5.3 Hover Performance. ............................................................................................48 6. RECOMMENDATIONS........................................................................................49 LIST OF REFERENCES...........................................................................................50 APPENDICES.............................................................................................................54 APPENDIX 1...............................................................................................................55