171000 1 P 171000 1 AGA RD-R-5779' AGARD REPORT No. 577 on (V/STOLHandling I -Criteria and Discussion DlSTRlBUT10 N AND AVAl LAB1LlTY ON BACK COVER NORTH ATLANTIC TREATY ORGANIZATION ADVISORY GROUP FOR AEROSPACE RESEARCH AND DEVELOPMENT (ORGANISATION DU TRAITE DE L’ATLANTIQUE NORD) ,//- V/STOL HANDLING-QUALITIES CRITERIA This report was prepared at the request of the Flight Mechanics Panel of AGARD-NATO. Published December 1970 629.7.014.16:629.7.0a3 Printed by Technical Editing and Reproduction Ltd Harford House, 7-9 Charlotte St, London. WiP iHD This report prepared by a V/STOL Handling Qualities Committee sponeored by the ACARD Fqght Mechanics PanelGsents criteria on handling-7 qualities for VTOL and'STOL aircraft. Included wlth each criterion is a discussion pointing out the pilot's reasons for including a particular handling quality feature. The criteria are based on results of tests using piloted ground-based simulators, variable stability aircraft, particular models of VTOL and STOL aircraft, ani variable stability helicopters. -I ii i ACKNOWLEDGMENTS The following personnel were members of the V/STOL Handling Qualities Committee who helped prepare this report: Seth B. Anaerson, U.S.A., NASA, Ames Research Center , H. William Chinn, U.K., RAE, Bedford Antonio Filisetti, Italy, Fiat Dr. Xavier Hafer, W. Germany, Lehrstuhl und Institut fiir Flugtechnik Douglas M. McGregor, Canada, NAE Laurel G. Schroers, U.S.A., Army Aeronautical Laboratory George Ville, France, Service Technique de 1’ Aeronautique iv TABLE OF CONTENTS Introduction 1 Background 1 Revision Procedures 1 Report Format 1 Criteria Ap p 1i c a t i on 2 Interpretation 2 Level of Criteria 2 Wind Conditions 2 Classification of Aircraft 2 Terminology 2 Basic Terms 2 Flight Regimes . 3 Control Systems 3 Engineering Terms 3 Symbols 4 Pilot Rating Scale 5 References 5 1.0 Characteristics of the Control Systems 6 1.1 General 6 1.2 Control Breakout Forces 6 1.3 Control Force Gradients 6 1.4 Control System Free Play 8 1.5 Powered Control Systems 8 1.6 Trim Systems 8 1.7 Height Control Systems 8 1.8 Thrust Vector Controls 8 1.9 Control Travel Limits 9 1.10 Augmentation Systems 9 2.0 Longitudinal Stability and Control 11 2.1 General 11 2.2 Pitch Control Power 11 2.3 Control Sensitivity 12 2.4 Pitch Damping 13 2.5 Control System Time Lags 13 . 2.6 Static Longitudinal Stability Characteristics 14 2.6.1 Trim Speed Stability 14 2.6.2 Stability with Respect to Speed 14 2.6.3 Thrust Vector Stability 14 2.7 Longitudinal Control Characteristics in Maneuvering Flight 14 2.8 Dynamic Stability 15 . 2.9 Longitudinal Control Characteristics in Takeoff 15 2.10 Longitudinal Control Characteristics in Sideslip 15 2.11 Longitudinal Control Characteristics in Landing 16 3.0 Lateral Directional Stability and Control 17 3.1 General 17 3.2 Roll Control Power 17 3.3 Translational Control 18 3.4 Roll Control Sensitivity 18 3.5 Cross-Coupling 19 3.6 Roll Angular Damping 19 3.7 Roll Control System Time Lags 20 3.8 Peak Roll Control Forces 20 3.9 Spiral Stability 20 3.10 Dihedral Effect 21 3.11 Yaw Control Characteristics - General 21. 3.12 Yaw Control Power 21 3.13 Yaw Control Sensitivity 22 3.14 Control System Time Lag 23 3.15 Peak Yaw Control Forces 23 3 :16 Cross-Coupling 23 3.17 Directional Characteristics in Steady Sideslip 24 3.18 Side Force Characteristics in Steady Sideslips 24 3.19 Lateral-Directional Dynamic Stability 24 4.0 Hovering and Vertical Flight Path Characteristics 26 4.1 General 26 4.2 Ground Effect 26 4.3 Vertical Flight Path Control 26 4.4 Hovering Precision 27 4.5 Vertical Thrust Margins 27 4.6 Vertical Velocity and Thrust Response 28 V 5.0 Transition Characteristics 29 5.1 General 29 5.2 Acceleration-Deceleration 29 5.3 Flexibility of Operation 29 5.4 Tolerance in Conversion 29 5.5 Control Margins 30 5.6 Trim Changes 30 5.7 Rate of Control Movement 30 6.0 Miscellaneous Characteristics 31 6.1 General 31 6.2 Ground Handling - General 31 6.2.1 Landing Gear 31 6.2.2 Control Effectiveness During Takeoff, Landing Rollout, and Taxi 31 6.2.3 Power Checks Prior to Takeoff 31 6.3 Cross-Coupling Effects - General 31 6.3.1 Gyroscopic Effects 31 6.3.2 Inertial Cross-Coupling Effects 32 6.3.3 Mechanical Cross-Coupling 32 6.4 Minimum Flight Speeds - General 32 6.4.1 Loss of Lift 32 6.4.2 Warning of Approach of Vmin 32 6.5 Warning of Approach to Hazardous Flight Condition 33 6.6 Aircraft Behavior Following Systems Failure 33 Appendix 34 Maneuvers for V/STOL Aircraft Handling Qualities Evaluation 34 Summary of Criteria Tables 39 TABLE INDEX* 1.1 6 V/STOL Control Breakout Force Criteria 1.2 7 Control Force Gradients (lb/in.) for Hover 1.3 7 Control Force Gradients for STOL 1.4 7 Control Force Harmony Ratio Criteria 1.5 9 Cockpit Control Travel Limits (in.) 2.1 11 Pitch Control Power Characteristics 2.2 12 Pitch Control Sensitivity Characteristics 2.3 13 Pitch Angular Velocity Damping Criteria 2.4 13 Pitch Control System Time Lag Criteria 3.1 17 Roll Control Power Characteristics 3.2 18 Roll Control Sensitivity Characteristics 3.3 19 Cross-Coupling Characteristics in STOL Operation (Yaw Control Free) 3.4 19 Roll Angular Velocity Damping 3.5 20 Roll Control Lags 3.6 22 Yaw Control Power characteristics 3.7 23 Yaw Control Sensitivity Characteristics 3.8 24 Yaw Cross-Coupling Characteristics 4.1 26 Minimum Vertical Flight Path Control Characteristics in (STOL) Operation 4.2 28 Vertical Velocity and Thrust Response Characteristics FIGURE INDEX* 2.1 15 Longitudinal Dynamic Stability Criteria 3.1 25 Lateral-Directional Dynamic Stability Criteria 4.1 27 Vertical Thrust Margins Criteria *All tables and figures are summarized in the Appendix, Page 39. vi 1 V/STOL HANDLING-QUALITIES CRITERIA I - CRITERIA AND DISCUSSION INTRODUCTION Background. The first AGARD work relating to V/STOL handling-qualities criteria began in 1960; this work is documented in reference 1, published in October 1962. Following a general review in 1963, the report was revised to include comments on recommendations from industry, military services, and government agencies. This report (ref. 2), published in October 1964, has been used extensively as a guide in design-. ing new V/STOL aircraft. The report has received criticism, not unexpected, in two areas: scope and speci- fic recommendations. It was directed primarily toward VTOL aircraft and did not clarify a large number of requirements for STOL aircraft. In addition, recommendations did not include both VFR and IFR operation for all types of VTOL and STOL aircraft, because the background data used to establish many of the recommenda- tions had been obtained chiefly from helicopters. Perhaps the most serious deficiency was that the report attempted to provide quantitative requirements based on limited flight experience obtained for the most part from test-bed type aircraft. As a result, some inconsistencies would be expected when applications were made to operational V/STOL designs. In particular, the effect of vehicle gross weight or size on air- craft response was continually a source of disagreement. Further, the consequence of providing only minimum acceptable values of each handling-quality item was not fully appreciated (and perhaps is not yet under- stood); a VTOL aircraft that individually met all the recommendations could still be too demanding of pilot skill. In many cases, achieving a given set of numbers did not ensure a completely satisfactory aircraft, At the request of the Flight Mechanics Panel, a second AGARD V/STOL handling-qualities committee was organized in 1966 for the following purposes: 1. To revise and update AGARD Report No. 408A, changing its emphasis to reflect criteria rather than specifications. 2. To explore the latest VTOL flight-test techniques and recommend how to prepare a report on this activity . The committee consisted of one representative each from Canada, France, United Kingdom, West Germany, and Italy; the chairman and technical secretary were from the United States. Item (1) above was accomplished by (a) reviewing comments from users of TR No. 408A, (b) examining data from second-generation V/STOL air- craft, and (c) incorporating results from recent piloted simulator tests and analytical studies, Work directed at item (2) indicated an urgent need to standardize flight-test techniques to help reduce incon- sistencies in measurements of flight-test data. Although it was beyond the scope of this comittee to set up flight-test techniques, a set of standardized flight-test maneuvers was devised for pilots to use in evaluating handling qualities during flight tests of V/STOL aircraft. Revision Procedures. In revising TR 408A it was agreed that a more meaningful and useful document would include: 1. Evaluation of the various handling-qualities items in terms of criteria, rather than requirements or specifications 2. A discussion section to explain the purpose of each criterion 3. Data and reference material to support the criteria. Criteria can be defined as evaluation standards based on numbers that are meant only to be typical and can vary widely. Meaningful criteria can serve as a guide in establishing specifications to be used by a contractor for the design and testing of a particular aircraft. In the past, handling-qualities requirements have been presented without an explanation of why the pilot desires a particular characteristic; in many cases neither the purpose nor the various factors related to the requirements were understood.