Calhoun: The NPS Institutional Archive Theses and Dissertations Thesis Collection 1989-09 Helicopter controllability Carico, Dean Monterey, California. Naval Postgraduate School http://hdl.handle.net/10945/27077 DTfltttf NAVAL POSTGRADUATE SCHOOL Monterey , California THESIS C2D L/5~ HELICOPTER CONTROLLABILITY by Dean Carico September 1989 Thesis Advisor: George J. Thaler Approved for public release; distribution unlimited lclassified V CLASSi^'CATiON QF THIS PAGE REPORT DOCUMENTATION PAGE ORT SECURITY CLASSIFICATION 1b RESTRICTIVE MARKINGS assif ied IURITY CLASSIFICATION AUTHORITY 3 DISTRIBUTION /AVAILABILITY OF REPORT Approved for public release :lassification t DOWNGRADING SCHEDULE Distribution is unlimited ORMING ORGANIZATION REPORT NUMBER(S) 5 MONITORING ORGANIZATION REPORT NUMBER(S) ME OF PERFORMING ORGANIZATION 6b OFFICE SYMBOL 7a. NAME OF MONITORING ORGANIZATION il Postgraduate School (If applicable) 62 Naval Postgraduate School DRESS {City, State, and ZIP Code) 7b ADDRESS (C/fy, State, and ZIP Code) :erey, California 93943-5000 Monterey, California 93943-5000 9 PROCUREMENT INSTRUMENT IDENTIFICATION NUMBER DRESS (City, State, and ZIP Code) 10 SOURCE OF FUNDING NUMBERS IE (include Security Claudication) HELICOPTER CONTROLLABILITY RSONAL AUTHOR(S) ICO, G. Dean YPE OF REPORT 4 DATE OF REPORT (Year, Month. Day) ter ' s Thesis 1989, September ipplementary notation T h e views expressed in this thesis are thos e of the hor and do not reflect the official policy or position of the Department r,nyprninpnf npfpnsp nr ___ , COSATi CODES 18 SUBJECT TERMS {Continue on reverse if pecessary and identify Helicopter Controllability, Helicop Flight Control Systems, Helicopter Flying Qualities and Flying Qualities Spec if ications i 3STRACT {Continue I reverse if necessary and identify by block number) 'he concept of helicopter controllability is explained. A background ,dy reviews helicopter development in the U.S. General helicopter ^ igurations linearized eguations of motion, stability, and piloting ;uirements a re discussed. Helicopter flight controls, handling qualities and i associated specifications are reviewed. Analytical, simulation, ght test me thods for evaluating helicopter automatic flight control terns are di scussed. A generic simulation is also conducted. This sis is inte nded to be used as a resource document for a helicopter bility and control course at the Naval Postgraduate School. ISTRIBUTION /AVAILABILITY OF ABSTRACT 21 ABSTRACT SECURITY CLASSIFICATION UNCLASSIFIED-UNLIMITED SAME AS RPT D dtic users UNCLASSIF IED JAME OF RESPONSlE .E INDIVIDUAL 22b TELEPHONE (Include Area Code) 22c OFFICE SYMBOL •of George Jr.. Thaler (408) 646-2134 62Tr >rm1473, JUN 86 Previous editions are obsolete f CLASSIFICATION OF THIS PAGE Unclassified S/N 0102-LF-014-6603 245433 Approved for public release; distribution unlimited Helicopter Controllability by Dean Carico Aerospace Engineer B.S., ASE, VPI and SU, 1967 M.S., ASE, Princeton University, 1976 Submitted in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE IN ENGINEERING SCIENCE NAVAL POSTGRADUATE SCHOOL September 1989^"^ . ABSTRACT The concept of helicopter controllability is explained. A background study reviews helicopter development in the U.S. General helicopter configurations, linearized equa- tions of motion, stability, and piloting requirements are discussed. Helicopter flight controls, handling qualities, and associated specifications are reviewed. Analytical, simulation, and flight test methods for evaluating helicop- ter automatic flight control systems are discussed. A generic simulation is also conducted. This thesis is intended to be used as a resource document for a helicopter stability and control course at the Naval Postgraduate School . C.i TABLE OF CONTENTS I INTRODUCTION 1 A. HELICOPTER CONTROLLABILITY DEFINED 1 II BACKGROUND 3 A. HELICOPTER DEVELOPMENT IN THE U.S 3 III HELICOPTER DESIGN 22 A. HELICOPTER CONFIGURATIONS 22 1 General 22 2 Rotor Systems 2 2 B FORCE BALANCE 31 1 General 31 2 Axis Systems 3 5 IV. EQUATIONS OF MOTION 40 A. ASSUMPTIONS 40 1. Complete Linearized Equations of Motion .. 43 2 Simplified Equations of Motion 45 3 Definitions 46 4. Stability Derivative Calculations 52 5 Hover Case 53 6 Summary Equations 54 V. SYSTEM CHARACTERISTICS 56 A. CHARACTERISTIC EQUATIONS 56 B. TRANSFER FUNCTIONS 59 . .. "- DTTDLEY KTTOX LIBRARY " - 0Tj NAV, • 1 . Block Diagrams 60 C STABILITY 62 1. Stability in the S Plane 64 D. PILOTING REQUIREMENTS 72 VI HELICOPTER FLIGHT CONTROL SYSTEMS 75 A. GENERAL 75 B. IMPLEMENTATION OPTIONS 76 1 Digital Systems 76 2. Fly-by-Wire and Fly-by-Light Systems 76 C MECHANICAL SYSTEMS 78 D. MECHANICAL STABILITY 80 1 Bell Bar 80 2. Hiller Airfoil 84 3 Lockheed Gyro 84 E ELECTROMECHANICAL STABILITY 85 1. Stability Augmentation System 86 2 . Automatic Stabilization Eguipment 88 3. Autopilot 89 4 Automatic Flight Control System 89 F. FLIGHT SPECIFICATIONS 91 1 Background 91 2. Handling Qualities Specifications 93 3. Flight Control System Specifications .... 103 VII. METHODS OF EVALUATING HELICOPTER AFCS 105 A. COMPUTATIONAL OPTIONS 105 . 1 General 105 2 ALCON 106 3 Program CC 107 4. TUTSIM 108 B. ANALYTICAL PROCEDURES 109 1 General 109 2 S Plane Analysis 110 a . Root Locus 110 3 Frequency Response Analysis 115 a Bode Analysis 115 b. Nyquist Analysis 120 c. Nichols Chart Analysis 122 4 Transient Response Analysis 124 5 Compensation 128 a Lead Networks 129 b. Lag Networks 130 c. Lag-Lead Networks 131 d. Notch Filters 132 6. Example of Analytical Procedures 133 C SIMULATION 150 D. FLIGHT TEST 151 VIII. SIMULATION OF GENERIC HELICOPTER AND AFCS 157 A. CONTROL INPUT TRANSFER FUNCTIONS 157 1. Pitch Attitude Feedback - Hover 157 2. Pitch Attitude Feedback - Forward Flight. 168 . 3. Altitude Feedback - Forward Flight 172 B. ALTITUDE HOLD AUTOPILOT 179 IX. CONCLUSIONS AND RECOMMENDATIONS 186 A. CONCLUSIONS 186 B. RECOMMENDATIONS 186 APPENDIX A CHRONOLOGY OF HELICOPTER AFCS DEVELOPMENT . 187 APPENDIX B MIL-H-8501A SUMMARY 193 APPENDIX C CHRONOLOGY OF EVENTS LEADING TO MIL-F-87242. 200 LIST OF REFERENCES 203 INITIAL DISTRIBUTION LIST 207 ACKNOWLEDGEMENT I thank the Naval Air Test Center for sponsoring my year of long-term training at the Naval Postgraduate School (NPS) . I also thank the NPS for providing all the interest- ing and challenging courses related to control systems and to helicopters. The cross training between the Department of Electrical and Computer Engineering and the Department of Aeronautics and Astronautics was greatly appreciated. My biggest gripe was that there were just too many good courses for me to take in the one year time-frame. I wish there had been classes on helicopter stability and control and heli- copter automatic flight control systems. I thank Professor D. Layton for suggesting the thesis topic of Helicopter Controllability to be used in conjunction with an earlier thesis by H. O'Neil, as reference documents for starting a course on helicopter stability and control. I regret that Professor Layton retired before the effort was completed. A special thanks goes to Professor George J. Thaler for pro- viding guidance and motivation to keep the project going. I thank all the individuals and companies that provided infor- mation for this thesis, including M. Murphy, C. Griffis, D. Rubertus, and G. Gross. I also want to thank Prof. J. Powers, Prof. H. Titus, Prof. G. Thaler, Prof. L. Schmidt, L. Corliss, E. Gulley, R. Miller, and Dr. L. Mertaugh for their comments on the thesis. I . INTRODUCTION A. HELICOPTER CONTROLLABILITY DEFINED Helicopter controllability refers to the ability of the pilot to fly a series of defined flight maneuvers required for a specific mission. The minimum time it takes to com- plete the flight maneuver profiles is a measure of the helicopter's agility . Helicopter maneuverability determines how closely the aircraft can follow rapidly varying flight profiles. The number and magnitude of tracking errors made in following the specified flight profiles is indicative of the precision with which the helicopter can be flown. The pilot effort expended in achieving the desired control is a measure of pilot workload . Ideally, the desired controlla- bility can be achieved with minimum pilot workload. Both aircraft controllability and pilot workload will depend on the specific helicopter configuration, specific mission or task, and environmental conditions. Control of the helicop- ter will be a function of basic aircraft flying qualities and performance, level of augmentation, level of displays, task, environment, and pilot skill. For a given helicopter configuration the mission may require precise control of parameters like airspeed, altitude, and heading. Control may be required under visual meteorological conditions (VMC) or under instrument meteorological conditions (IMC) under calm or turbulent atmospheric conditions, as illustrated in Table 1-1. TABLE 1-1 RANGE OF GENERAL CONTROL PARAMETERS FLIGHT TIME PILOT HIGH < > LOW CURRENT STATE SKILL LEVEL HIGH < > LOW AUGMENTATION HIGH < > LOW BASIC HELICOPTER DISPLAYS HIGH < > LOW CALM < > TURBULENT ENVIRONMENT DAY < > NIGHT VMC < > IMC EASY < > DIFFICULT WORKLOAD LEVEL LOW < > HIGH PERFORMANCE LEVEL GOOD < > BAD TASK ACCOMPLISHED YES OR NO II. BACKGROUND A. HELICOPTER DEVELOPHENT IN THE UNITED STATES Man has always dreamed of soaring like the eagle and hovering like the hummingbird. It was not until the begin- ning of the twentieth century that science and technology in the United States progressed to the point where these