NASA Technical Paper 3537 1995 Flight Test of the X-29A at High Angle of Attack: Flight Dynamics and Controls Jeffrey E. Bauer Robert Clarke John J. Burken Dryden Flight Research Center Edwards, California National Aeronautics and Space Administration Office of Management Scientific and Technical Information Program CONTENTS ABSTRACT ........................................................................ 1 INTRODUCTION .................................................................... 1 AIRCRAFT DESCRIPTION ........................................................... 1 Flight Control System .............................................................. 2 Mode Logic ................................................................... 2 Design Requirements ............................................................ 2 Design Technique .............................................................. 3 Longitudinal Control Law Design .................................................. 3 Roll and Yaw Control Law Design ................................................. 4 Pilot-Selectable Gain ............................................................ 4 Flow Angle and Pitot-Static Measurement Systems .................................... 5 Simulation ....................................................................... 5 TEST AND PROCEDURES ............................................................ 6 Envelope Expansion ............................................................... 6 Piloted Simulation and Updates ...................................................... 6 RESULTS AND DISCUSSION ......................................................... 7 Flight Characteristics and Correlation With Preflight Predictions ............................ 7 Wing Rock and Lateral Control Power .............................................. 7 Pitching Moment Characteristics ................................................... 8 Yaw Asymmetries .............................................................. 9 Flying Qualities Research .......................................................... 10 Structural Dynamics Interaction With the Flight Control System ........................... 13 SUMMARY OF RESULTS ........................................................... 14 APPENDIX A--LINEAR MODELS .................................................... 16 APPENDIX B--PILOT COMMENTS .................................................. 17 NOMENCLATURE ................................................................. 22 REFERENCES ..................................................................... 23 iii P_ PAGE .BL,_tI'K NOT FIL_',,_E';..' TABLES 1 The X-29A no. 2 geometry and mass characteristics .................................... 25 2 High-angle-of-attack design guidelines .............................................. 26 3 Longitudinal and lateral stick characteristics .......................................... 26 4 Matrix of test points for flying qualities research ...................................... 26 A- 1 An s-plane description of continuous dynamic elements ................................ 27 iv FIGURES 1 The X-29A no. 2 test airplane ..................................................... 29 2 The X-29A no. 2 cockpit displays .................................................. 30 3 The X-29A no. 2 spin chute assembly ............................................... 31 4 The X-29A longitudinal control system ............................................. 32 5 The X-29A lateral-directional control system ......................................... 32 6 Time histories of the angle-of-attack redundancy management failure from flight 27 .......... 33 7 The X-29A high-angle-of-attack envelope ........................................... 34 8 Drop-model wing rock with a 0.88 deg/(deg/sec) roll damping gain ....................... 35 9 Wing drop time history .......................................................... 36 10 Wing rock time history .......................................................... 40 11 Magnitude of bank angle oscillation as a function of angle of attack during wing rock ......... 41 12 Open-loop dutch roll pole locations ................................................. 41 13 Pitch rate comparison ............................................................ 42 14 Simulation match to flight data for pitching maneuver .................................. 43 15 Surface rates during pitching steps ................................................. 45 16 Minimum nosedown aerodynamic pitching moment ................................... 47 17 The X-29A high-angle-of-attack lateral--directional flight control system with variable gains highlighted ............................................................... 47 18 Stability axis roll rate (at 200 kn and an altitude of 20,000 ft) as a function of angle of attack... 48 19 Body axis yaw rate required (at 200 kn and an altitude of 20,000 ft) for coordination of stability axis roll rate of figure 18 .................................................. 48 20 Effect of sideslip on roll coordination for a typical bank angle maneuver ................... 49 21 Roll coordination data (all data represented as if roll were negative (to the left)) ............ 51 V 22 Maximum rudder deflection during 180 ° roll captures at 200 kn equivalent airspeed .......... 52 23 Maximum aileron deflection during 180 ° roll captures at 200 kn equivalent airspeed .......... 53 24 Angle of sideslip buildup during position limiting ..................................... 54 25 Effects of filtering on lateral acceleration components ................................. 55 26 Cockpit lateral acceleration at roll initiation .......................................... 56 27 Largest cockpit lateral acceleration components during maneuver ......................... 56 28 Flight data fit to determine roll mode time constant .................................... 57 29 Roll mode time constant as a function of stability axis roll rate at a 30 ° angle of attack ........ 58 30 Proposed criteria for a 30 ° angle of attack ........................................... 58 31 Roll rate gyroscope signal power spectral density ...................................... 59 A-1 Linear matrices ................................................................. 60 A-2 Longitudinal control system ...................................................... 63 A-3 Lateral--directional control system .................................................. 63 vi ABSTRACT has several advantages in this flight regime. 5' 6 The configuration was designed to be departure resistant and to maintain significant roll control at high angles of The NASA Dryden Flight Research Center has flight tested two X-29A aircraft at low and high angles of attack. To further investigate the potential of a forward- swept wing at high angles of attack, the X-29A military attack. The high-angle-of-attack tests evaluate the fea- utility and agility test program was initiated in 1986 as sibility of integrated X-29A technologies. More specif- a follow-on to the low-angle-of-attack program, l' 2 7-10 ic objectives focus on evaluating the high-angle-of- This paper provides results from the envelope expan- attack flying qualities, defining multiaxis controllabili- ty limits, and determining the maximum pitch-pointing sion and handling qualities testing at intermediate angles of attack. Topics include envelope expansion, capability. A pilot-selectable gain system allows exam- ination of tradeoffs in airplane stability and maneuver- flight test techniques, and flight test results. Compari- ability. Basic fighter maneuvers provide qualitative sons of the flight test results to the predictions are made where appropriate. evaluation. Bank-angle captures permit qualitative data analysis. This paper discusses the design goals and approach AIRCRAFT DESCRIPTION for high-angle-of-attack control laws and provides results from the envelope expansion and handling qual- The X-29A aircraft is a single-seat, single-engine ities testing at intermediate angles of attack. Compari- fighter class aircraft (fig. 1). An F-5 forebody is used sons of the flight test results to the predictions are made forward of the pilot station, and F-16 integrated servo- where appropriate. The pitch rate command structure actuators are used for all except the strake actuators. of the longitudinal control system is shown to be a val- The cockpit has conventional dial display gauges id design for high-angle-of-attack control laws. Flight (fig 2). No cathode-ray-tube screens or head-up dis- test results show that wing rock amplitude was over- plays are used. predicted and aileron and rudder effectivenesses were The wing has a thin, 4.9 percent-thick streamwise underpredicted. Flight tests show the X-29A airplane supercritical airfoil section with a 29.27 ° forward to be controllable in all axes, with no nose wandering, sweep along the leading edge and a -33.73 ° quarter- up to 40 ° angle of attack. chord sweep. The wing structure includes aeroelastical- ly tailored graphite-epoxy covers to help provide the INTRODUCTION stiffness needed to overcome the torsional divergence problems associated with forward-swept wings. The The NASA Dryden Flight Research Center (NASA wing is relatively simple, employs full-span trailing- Dryden) X-29A program was structured to test the edge flaps, and does not use leading-edge devices. X-29A no. 1 airplane at low angles of attack and the These double-hinged flaps also provide discrete vari- able camber. no.