Design, Analyses, and ,. Simulation Results

NASA Technical Paper 3446 _:i,2 _ .,/, ! High-Alpha Research Vehicle (HARV) Longitudinal Controller: Design, Analyses, and ,. Simulation Results Aaron J. Ostroff Langley Research Center • Hampton, Virginia Keith D. Hoffler ViGYAN, Inc. • Hampton, Virginia Melissa S. Proffitt Lockheed Engineering & Sciences Company • Hampton, Virginia :' National Aeronautics and Space Administration Langley Research Center • Hampton, Virginia 23681-0001 • : J July 1994 /: The use of trademarks or names of manufacturers in this i! report is for accurate reporting and does not constitute an official endorsement, either expressed or implied, of such products or manufacturers by the National Aeronautics and Space Administration. Acknowledgment The authors wish to acknowledge the following individuals who made important contributions to the research described in this paper: Philip W. Brown, Michael R. Phillips, and Robert A. Rivers, all from NASA Langley Research Center, who served as test pilots and provided ratings and insightful comments for the piloted simulation tasks. Michael D. Messina, Lockheed Engineering & Sciences Company, Hampton, VA, who maintained the nonlinear batch simulation and organized test cases for transportingreal-time code. Susan W. Carzoo, Unisys Corporation, who maintained the real- time software for the piloted simulation. Dr. Barton J. Bacon, NASA Langley Research Center, who constructed and tested the real-lt algorithms used for robustness analysis. John V. Foster, NASA Langley Research Center, who performed some engineering-test pilot evaluations. J ! i • Contents Summary .................................. 1 Introduction ................................. 1 Symbols ................................... 2 Description of Facilities ............................ 5 Airplane ................................. 5 Simulation ................................. 5 Piloted Simulator .............................. 5 Feedback Controller Design .......................... 6 Modeling ................................. 6 Continuous model ............................. 6 Discrete model .............................. 7 Cost _nction ............................... 7 Stochastic-Weighting Process ......................... 8 Design Conditions ............................... 8 Design Weights ............................... 8 Feedback-Gain Matrix ............................ 9 Linear Analysis of Feedback Controller ..................... 9 Feedback Gains ............................... 9 Closed-Loop Eigenvalues ........................... 9 Stability Margins ............................. 10 Robustness ................................ 10 Loop Transfer and Servoelastic Frequency Response .............. 10 Feed-Forward Controller Design ........................ 11 Feed-Forward Command Generator (FFCG) ................. 11 Command Generator Tracker (CGT) .................... 12 Nonlinear Configuration ........................... 12 Nonlinear Batch Simulation Results ...................... 13 Design Guidelines ............................. 13 Pitch-Up Agility ............................. 13 Pitch-Down Agility ............................ 13 Angle-of-Attack Capture .......................... 13 Angle-of-Attack Regulation ........................ 14 Piloted Simulation Results .......................... 14 Nose-Up Angle-of-Attack Capture Tasks ................... 15 i Nose-Down Angle-of-Attack Capture Tasks .................. 15 g-Heading Capture Task .......................... 16 Coupling-During-Roll Evaluation Tasks .................. 16 Tracking Evaluation Tasks ......................... 17 Departure Resistance ........................... 17 Conclusions ........ : ............. .......... 18 Appendix--Open-Loop Models ........................ 20 References ................................. 31 Tables ................................. 32 Figures .................................. 38 111""° i_i _ Summary which generates very high nose-turning rates. Simu- lation studies have shown that operational capability This paper describes the design, analysis, and and good controllability in this high-a flight regime nonlinear simulation results (batch and piloted) for provide tactical maneuver advantages during close- a longitudinal controller scheduled to be flight-tested in air combat (refs. 1-4) with current missiles and on the High-Alpha Research Vehicle (HARV). The guns. The success in simulated air combat studies HARV is an F-18 airplane modified for and equipped have lead to research airplanes that have the capa- with multiaxis thrust vectoring. The longitudinal bility to maneuver at poststall angles of attack. controller consists of feedback and feed-forward controllers. The paper includes a description of the fa- In recent years, four high-c_ flight test airplanes cilities, a detailed review of the feedback controller (i.e., X-29, X-31, the High-Alpha Research Vehicle design, linear analysis results of the feedback con- (HARV), and the F-16 Multi-Axis Thrust Vector- troller, a description of the=feed-forward controller ing (MATV)) have been maneuvering successfully at design, nonlinear batch simulation results, and pi- poststall angles of attack which was not previously loted simulation results. achievable. (See ref. 5.) The X-29 airplane can main- tain controlled flight up to a = 40°; the X-31 airplane Linear analysis shows that the feedback controller and HARV are designed to maneuver at a's up to 70 ° meets the stability design guidelines, is highly robust with the application of multiaxis thrust vectoring. to stability and control derivative parameter changes, The F-16 MATV airplane has done sustained ma- has good closed-loop damping ratios, and attenuates neuvers up to a = 84 ° with excursions beyond that. the structural modes well below the design guideline. Thrust-vectored controls provide the X-31, HARV, and F-16 MATV with the added control power re- Batch simulation results include maximum pitch stick agility responses, angle-of-attack c_ captures, quired to maneuver in the high-a flight regime which and a regulation for full lateral stick rolls at several is not achievable with purely aerodynamic controls. c_'s. The controller meets most of the agility guide- The HARV is a modified F-18 airplane that began lines throughout the a range, has good c_ regulation, flight evaluation in midyear 1991. The main modifi- and has consistently good transient response for all cation is the addition of thrust-vectored controls in altitudes within the design region. the pitch and yaw axes, which resulted in an airplane that is approximately 4000 lb heavier than an un- Piloted simulation results include task descrip- modified F-18 airplane. The original thrust-vectored tions for several types of maneuvers, task guidelines, control laws were developed jointly by NASA and the corresponding Cooper-Harper ratings from three McDonnell Aircraft Company and are being used test pilots, and some pilot comments. The ratings show that desirable criteria were achieved for almost during the initial HARV flight evaluations that include flight envelope expansion and maneuvering ca- all of the piloted simulation tasks, most of which pability. Revised controllers based upon modern con- had very stringent criteria. The control system was trol design methodologies and processes (ref. 6) will shown to be extremely departure resistant. then be installed on the HARV after the initial flights are completed. One of these revised controllers is the Introduction lofigitudinal controller described in this paper. Development of the short-to-medium range all- For completeness, much of the information in ref- aspect missiles have increased the need for a fighter erence 7 which pertains to the longitudinal controller airplane to rapidly point its nose at an opponent design is also contained in this paper. In particular, to obtain first shot opportunity during air combat reference 7 contains the following: maneuvering. Rapid nose pointing is of particular 1. An overview of the feedback controller with importance within visual range. Even though long- the application of variable-gain output feedback range missiles are also continually improving, fail- ures and rules of engagement will inevitably produce which generates a feedback gain functional that close-in encounters. During close-in air combat, the incorporates optima ! gain scheduling need to acquire a position in the opponent's rear 2. A derivation and description of the feed-forward quarter has diminished with the continual improve- command generator (FFCG) for pilot stick sensi- ment of short-to-medium range all-aspect missiles. tivity and mode selection Due to the enhanced capability of these missiles, a 3. Formulation of the command generator tracker great deal of research has gone into developing high- (CGT), which is a feed-forward control performance airplanes that can rapidly maneuver at angles of attack c_ greater than the maximum lift, 4. Control system design guidelines 5. Some linear analysis and nonlinear batch simula- scenarios, task guidelines, and Cooper-Harper rat- tion analysis ings (CHR) for the various maneuvers. Piloted tasks were developed to evaluate the longitudinal control A key part of reference 7 is the design procedure /, / : law acquisition capability, tracking capability, and for selection and adjustment of the optimal weights resistance to coupling (regulation of a during rolling used in the variable-gain output feedback design al- maneuvers). Cooper-Harper ratings and pilot com- gorithm. Note that the

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