Master thesis in Aeronautical Engineering Development of a Flight Dynamics Model of a Flying Wing Configuration Candidate Supervisor Jacopo Tonti Prof. Guido De Matteis External supervisor Prof. Arthur Rizzi (Kungliga Tekniska högskolan) Academic Year 2013/2014 cbn 2014 by Jacopo Tonti Some rights reserved. This thesis is available under a Creative Commons CC BY-NC-3.0 IT License. (creativecommons.org/licenses/by-nc/3.0/it/) Alla mia musa , a Vale «As ailerons, these damn spoilers make great rudders!» Bruce Miller, after flying the Marske Pioneer 1A Abstract The subject of UCAV design is an important topic nowadays and many countries have their own programmes. An international group, under the initiative of the NATO RTO AVT-201 Task group, titled “Extended Assessment of Reliable Stability & Control Pre- diction Methods for NATO Air Vehicles”, is currently performing intensive analysis on a generic UCAV configuration, named SACCON. In this thesis the stability and control characteristics of the SACCON are investigated, with the purpose of carrying out a compre- hensive assessment of the flying qualities of the design. The study included the generation of the complete aerodynamic database of the aircraft, on the basis of the experimental data measured during TN2514 and TN2540 campaigns at DNW-NWB low speed wind tunnel. Moreover, system identification techniques were adopted for the extraction of dynamic derivatives from the time histories of forced oscillation runs. The trim of the aircraft was evaluated across the points of a reasonable test envelope, so as to define a set of plausible operative conditions, representing the reference conditions for subsequent linearization of the dynamic model. The study provided a thorough description of the stability and control characteristics and flying qualities of the unaugmented SACCON, laying the groundwork for future improvement and validation of the configuration in the next design stages. Keywords: Aerodynamic Modelization, System Identification, Stability & Control, Linear Dynamics, Flying Qualities, Flying Wing, UCAV, SACCON. Table of Contents Contents i List of Figuresv List of Tables ix Nomenclature and Symbols xi Frames of reference................................... xi Notations ........................................ xii 1 Introduction1 1.1 Background of the NATO RTO program.................... 2 1.2 Problem description ............................... 4 1.3 Objective and methodology ........................... 5 1.4 Thesis outline................................... 7 2 Literature review9 2.1 Historical perspective............................... 9 2.1.1 Modern stealth UCAVs.......................... 14 2.2 An overview on flight mechanics analysis.................... 15 2.2.1 Static stability .............................. 15 2.2.2 Dynamic stability............................. 18 2.2.3 Flying and handling qualities...................... 20 2.2.3.1 Cooper-Harper rating scale.................. 20 2.2.3.2 MIL-HDBK-1797A....................... 22 2.2.3.3 CAP criterion ......................... 27 2.3 Flying wing design issues ............................ 28 2.3.1 Longitudinal issues............................ 29 2.3.2 Lateral-directional issues......................... 30 3 Aerodynamic database 33 3.1 Foreword ..................................... 33 3.2 Wind tunnel campaigns ............................. 35 i TABLE OF CONTENTS 3.2.1 Wind tunnel model............................ 35 3.2.2 Experimental setup............................ 37 3.2.3 Tests and results............................. 38 3.3 Database generation ............................... 42 3.3.1 Database format ............................. 45 3.3.2 Static data processing .......................... 47 3.3.3 Dynamic data processing ........................ 49 3.4 Aerodynamic analysis .............................. 50 3.4.1 Baseline.................................. 51 3.4.2 Dynamic behavior ............................ 53 3.4.3 Control authority............................. 56 4 Static analysis 63 4.1 Flight envelope definition ............................ 64 4.1.1 Airspeed limitations ........................... 65 4.1.2 Altitude limitations ........................... 66 4.1.3 CG limitations .............................. 66 4.2 Longitudinal static stability........................... 68 4.3 Trim assessment ................................. 70 4.4 Limitations .................................... 79 5 Dynamic analysis 81 5.1 Aerodynamic identification............................ 81 5.2 Dynamic modes.................................. 87 5.2.1 Longitudinal dynamics.......................... 88 5.2.2 Lateral-directional dynamics....................... 95 5.3 Flying qualities assessment ...........................106 5.3.1 Longitudinal flying qualities.......................108 5.3.1.1 Short period ..........................108 5.3.1.2 Phugoid.............................110 5.3.2 Lateral-directional flying qualities....................112 5.3.2.1 Roll subsidence.........................112 5.3.2.2 Dutch roll............................113 5.3.2.3 Spiral..............................114 5.3.3 Control dynamics.............................115 5.3.3.1 Response to step elevator...................115 5.3.3.2 Response to step aileron....................116 5.3.3.3 Response to step rudder....................118 5.4 Chapter summary ................................120 ii TABLE OF CONTENTS 6 Concluding remarks 123 6.1 Conclusions....................................123 6.2 Further research .................................127 Appendices 131 A SACCON configuration 131 A.1 General description................................131 A.2 Mass and inertia properties ...........................132 A.3 Geometric properties...............................133 B Theoretical basis and definitions 135 B.1 Physical model ..................................135 B.1.1 Assumptions ...............................135 B.1.2 Coordinate systems and transformations . 136 B.1.3 Mathematical relations..........................138 B.2 Conventions and customs ............................140 B.2.1 Control sign convention and definitions . 140 B.2.2 Aerodynamic parameters convention ..................142 B.2.3 Propulsion system customs .......................143 B.2.4 Mass and geometry............................143 C Linearized Model 145 D XML database structure 151 D.1 Overview .....................................151 D.1.1 Fundamental table structure.......................151 D.2 Database structure................................152 D.2.1 Aerodynamics...............................153 D.2.2 Geometry and mass ...........................157 D.2.3 Propulsion.................................158 D.2.4 Flight control system...........................159 Bibliography 163 iii List of Figures 2.1 Nature’s noteworthy flying wing designs..................... 9 2.2 The Penaud and Gauchot “Amphibian” - 1876 [46]............... 10 2.3 Dunne’s D.8 flying wing biplane - 1912 [52]................... 11 2.4 Chyeranovskii BICh-17 experimental fighter - 1934............... 12 2.5 The Horten Vc - 1941............................... 12 2.6 The Northrop-Grumman B-2 “Spirit” - 1989................... 13 2.7 Modern stealth flying wing UCAV designs.................... 14 2.8 Pitching moment curves (fixed elevator) [2]................... 16 2.9 Conventional wing-tail arrangement [2]. .................... 17 2.10 Dynamic response of a statically stable aircraft [52]. ............. 18 2.11 Cooper-Harper rating scale [52].......................... 21 2.12 MCH-UVD diagnosis tool [33]. ......................... 22 2.13 CAP requirements for Category B flight phase [35]............... 28 2.14 Northrop N-1M. ................................. 31 2.15 The drag rudder deployed on the wing tip of the Northrop N-9M. 32 3.1 Planform and geometric parameters of the DLR-F17SACCON [16]. 36 3.2 The DLR-F17/SACCON in the DLR-NWB with yaw link support [47]. 37 3.3 Lateral coefficients of the DLR-F17 versus α at different β [15]. 41 3.4 Influence of sting mounting on longitudinal coefficients (Body axes) [38]. 42 3.5 The frame of reference convention adopted in TN 2514 and TN 2540 [20]. 43 3.6 Baseline drag and lift coefficients versus α, varying β. ............ 51 3.7 Baseline pitching moment coefficient versus α, varying β............ 52 3.8 Baseline lateral-directional coefficients (Body frame) versus β, varying α. 53 3.9 1-cycle average of lift driven by pitch oscillations [20]. ............ 54 3.10 1-cycle average of pitching moment driven by pitch oscillations [20]. 54 3.11 1-cycle average of lateral coefficients driven by 1 Hz roll oscillations [20]. 55 3.12 1-cycle average of lateral coefficients driven by yaw oscillations. 55 3.13 Elevator contribution to lift............................ 57 3.14 Elevator contribution to pitching moment.................... 58 3.15 Total lift and pitching moment with elevator. ................. 58 3.16 Rolling and yawing moments induced by the ailerons.............. 59 v LIST OF FIGURES 3.17 Rolling and yawing moments induced by the drag rudders........... 60 3.18 LCDP........................................ 62 3.19 Cnβ DYN....................................... 62 4.1 The analysis envelope of the SACCON..................... 67 4.2 Limit locations of the CG of the SACCON (in red the ARP). 67 4.3 Variation in static margin with CG position and angle of attack. 69 4.4 Variation of static margin with CG position and velocity............ 70 4.5 Flow chart diagram of the double variable iteration procedure.