NASA Technical Paper 2857 1 1988 Development and Flight Test Experiences With a Flight-Crucial Digital Control System Dale A. Mackall Ames Research Center Dryden Flight Research Facility Edwards, Calgornia I National Aeronautics I and Space Administration I Scientific and Technical Information Division I CONTENTS Page ~ SUMMARY ................................... 1 I 1 INTRODUCTION . 1 2 NOMENCLATURE . 2 3 SYSTEM SPECIFICATION . 5 3.1 Control Laws and Handling Qualities ................. 5 3.2 Reliability and Fault Tolerance ................... 5 4 DESIGN .................................. 6 4.1 System Architecture and Fault Tolerance ............... 6 4.1.1 Digital flight control system architecture .......... 6 4.1.2 Digital flight control system computer hardware ........ 8 4.1.3 Avionics interface ...................... 8 4.1.4 Pilot interface ........................ 9 4.1.5 Actuator interface ...................... 10 4.1.6 Electrical system interface .................. 11 4.1.7 Selector monitor and failure manager ............. 12 4.1.8 Built-in test and memory mode ................. 14 4.2 ControlLaws ............................. 15 4.2.1 Control law development process ................ 15 4.2.2 Control law design ...................... 15 4.3 Digital Flight Control System Software ................ 17 4.3.1 Software development process ................. 18 4.3.2 Software design ........................ 19 5 SYSTEM-SOFTWARE QUALIFICATION AND DESIGN ITERATIONS ............ 19 5.1 Schedule ............................... 20 5.2 Software Verification ........................ 21 5.2.1 Verification test plan .................... 21 5.2.2 Verification support equipment . ................ 22 5.2.3 Verification tests ...................... 22 5.2.4 Reverifying the design iterations ............... 24 5.3 System Validation .......................... 24 5.3.1 Validation test plan . ............... 24 5.3.2 Support equipment ....................... 25 5.3.3 Validation tests ....................... 25 5.3.4 Revalidation of designs .................... 33 5.4 Qualification Issues ......................... 33 6 CONFIGURATION CONTROL . 33 17 FLIGHTTEST ................................ 34 I 7.1 General ............................... 35 1 7.2 Fault-Tolerant Design ........................ 37 I 7.2.1 In-flight experience ..................... 37 7.2.2 Ground experience ....................... 39 7.2.3 Summary ............................ 40 I 7.3 Control Laws ............................. 41 I iii i PRECEDING PAGE BLANK NOT FILMED 7.4 Hardware ............................... 42 7.5 Software ............................... 43 8 OBSERVATIONS AND RECOMMENDATIONS . 44 8.1 Anomaly of Flight 44, A Case Study .................. 44 8.1.1 Specifcation ......................... 44 8.1.2 Design ............................ 45 8.1.3 Qualification ......................... 45 8.2 Observations and Recommendations by development Phase .......................... 45 8.2.1 Specification ......................... 45 8.2.2 Design ............................ 46 8.2.3 Qualification ......................... 47 8.2.4 Flight test .......................... 48 9 CONCLUDINGREMARKS . 49 APPENDIX -CONTROL LAW VERIFICATION REQUIREMENTS 50 iv SUMMARY 1 INTRODUCTION Engineers and scientists in the advanced The advanced fighter technology integra- fighter technology integration (AFTI) tion (AFT11 F-16 program provided the F-16 program investigated the integra- opportunity to investigate the bene- tion of emerging technologies into an fits and complexities of integrating advanced fighter aircraft. AFTI'S three advanced aircraft technologies into a major technologies included (1 ) flight- fighter aircraft. The study was a crucial digital control, (2) decoupled joint National Aeronautics and Space aircraft flight control, and (3) inte- Administration (NASA), U.S. Air Force, gration of avionics, flight control, and and U.S. Navy program and was managed pilot displays. In addition to investi- by the Air Force Flight Dynamics Labo- gating improvements in fighter perform- ratory. NASA goals were to ensure ance, researchers studied the generic safety during flight testing and to problems confronting the designers of provide an independent assessment of highly integrated f light-crucial digital the advanced technologies. control systems. The primary subject of this report The author provides an overview of is the digital flight control system both the advantages and problems of in- (DFCS) and its integration with the tegrated digital control systems. An avionics and pilot displays. An intro- examination of the specification, de- duction to the history, rationale, and sign, qualification, and flight test nomenclature of digital flight control life-cycle phase is provided. An over- systems can be found in Szalai (1978). view is given of the fault-tolerant The AFTI F-16 DFCS development objec- design, multimoded decoupled flight tives included assessment of a triplex control laws, and integrated avionics dual-fail operate architecture, integra- design. The approach to qualifying the tion of avionics and pilot displays with software and system designs is discussed, the DFCS, and development of mission- and the effects of design choices on specific decoupled flight control modes. system qualification are highlighted. Operating a DFCS without mission AFTI F-16 flight test results are impairment after any two failures summarized for the fault-tolerant, de- required a minimum of four channels of coupled flight control, hardware, and redundancy in previously designed sys- software requirements. The effects of tems. If a triplex system could cor- design choices and qualification proce- rectly choose between the remaining dures on flight test operations are de- two channels when the second failure tailed, based on AFTI flight experience. occurred, acquisition and maintenance costs for the flight control system Observations and recommendations are could be reduced. Reducing pilot work- given for each development phase - speci- load and increasing weapon effectiveness fication, design, qualification, and were the goals of integrating the DFCS flight test. and its mission-specific decoupled con- trol modes with the avionics system and pilot displays. In previously designed A/S airspeed systems, the flight controls did not have specific modes for the different ASB air-to-surface bombing missions. The pilot was required to individually configure each avionic ASG air-to-surface gunnery system for a mission. ATP acceptance test procedure This report includes an historical review of the development and flight lateral acceleration, ft/sec2 test of this integrated DFCS program. AY The historical review is structured to ac alternating current provide an adequate background of the development process and the resulting alpha angle of attack, deg design needed to comprehend the flight test results. The author addresses each an normal acceleration, ft/sec2 of the development phases - specifica- tion, design, qualification, and flight BIT built-in test test. Important lessons learned are illustrated with examples from flight beta angle of sideslip, deg test experience. CADC central air data computer The increasing use of system integration to increase aircraft ccv control configured vehicle performance, and the flight crucial nature of these systems, dictates a CHGR charger, battery thorough assessment of this inte- grated DFCS program. CPC computer program component CPDS computer program development 2 NOMENCLATURE specification CPPS computer program product AAG air-to-air gunnery specification ~ ACK acknowledge CPU central processing unit i ( A-D analog to dig1tal c.g. center of gravity, percentage mean aerodynamic chord I AD I atti tude directional i indicator D-A digital to analog I AFT1 advanced fighter tech- DAAG decoupled air-to-air gunnery 1 nology integration DASB decoupled air-to-surface I AGL above ground level, ft bombing I I AIU actuator interface unit DASG decoupled air-to-surface I gunnery ALT altimeter I DFCS digital flight control system ~ AMUX avionics multiplex bus 2 DGFT dog fight HS I horizontal situation indicator DN down HUD head-up display DNRM decoupled normal HZ hertz DST device status table hr hours dc direct current I BU independent back-up unit degrees I FFC integrated flight fire control deg/sec degrees per second ILS instrument landing system EMIC electromagnetic interference and compatibility INU inertial navigation unit EPU emergency power unit I oc input-output controller ETSE engineering test support I SA integrated servoactuator equipment KCAS knots calibrated airspeed FCC fire control computers k thousand FCR fire control radar LARAP low-altitude radar autopilot FDIR fault detection, indentifica- tion, and reconfiguration LAT-DIR lateral-directional FLCC flight control computer LCND left canard FM failure manager, a software LEF leading-edge flap component L FLP left trailing edge flap FMET failure modes and effects testing LH left hand FPME f lightpath maneuver L HT left horizontal tail enhancement LOC location in memory flt flight LQS linear quadratic synthesis ft feet LRU line replaceable unit good channel average lb pounds G command M Mach longitudinal acceleration, g MAX maximum afterburner power 3 MHz mi1 lion hertz RCND right canard MIL military power RFLP right flap MPD multipurpose display RH right hand MSL median select log C RHT right horizontal tail MSOV missile override RM redundance managment msec millisecond ROM read only memory NX longitudinal