Propulsion and Flight Controls Integration for the Blended Wing Body Aircraft
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Cranfield University Naveed ur Rahman Propulsion and Flight Controls Integration for the Blended Wing Body Aircraft School of Engineering PhD Thesis Cranfield University Department of Aerospace Sciences School of Engineering PhD Thesis Academic Year 2008-09 Naveed ur Rahman Propulsion and Flight Controls Integration for the Blended Wing Body Aircraft Supervisor: Dr James F. Whidborne May 2009 c Cranfield University 2009. All rights reserved. No part of this publication may be reproduced without the written permission of the copyright owner. Abstract The Blended Wing Body (BWB) aircraft offers a number of aerodynamic perfor- mance advantages when compared with conventional configurations. However, while operating at low airspeeds with nominal static margins, the controls on the BWB aircraft begin to saturate and the dynamic performance gets sluggish. Augmenta- tion of aerodynamic controls with the propulsion system is therefore considered in this research. Two aspects were of interest, namely thrust vectoring (TVC) and flap blowing. An aerodynamic model for the BWB aircraft with blown flap effects was formulated using empirical and vortex lattice methods and then integrated with a three spool Trent 500 turbofan engine model. The objectives were to estimate the effect of vectored thrust and engine bleed on its performance and to ascertain the corresponding gains in aerodynamic control effectiveness. To enhance control effectiveness, both internally and external blown flaps were sim- ulated. For a full span internally blown flap (IBF) arrangement using IPC flow, the amount of bleed mass flow and consequently the achievable blowing coefficients are limited. For IBF, the pitch control effectiveness was shown to increase by 18% at low airspeeds. The associated detoriation in engine performance due to compressor bleed could be avoided either by bleeding the compressor at an earlier station along its ax- ial length or matching the engine for permanent bleed extraction. For an externally blown flap (EBF) arrangement using bypass air, high blowing coefficients are shown to be achieved at 100% Fan RPM. This results in a 44% increase in pitch control authority at landing and take-off speeds. The main benefit occurs at take-off, where both TVC and flap blowing help in achieving early pitch rotation, reducing take-off field lengths and lift-off speeds considerably. With central flap blowing and a lim- ited TVC of 10◦, the lift-off range reduces by 48% and lift-off velocity by almost 26%. For the lateral-directional axis it was shown that both aileron and rudder control powers can be almost doubled at a blowing coefficient of Cu = 0.2. Increased roll authority greatly helps in achieving better roll response at low speeds, whereas the increased rudder power helps in maintaining flight path in presence of asymmetric thrust or engine failure, otherwise not possible using the conventional winglet rudder. i ii Acknowledgments I would like to dedicate this thesis to my parents who worked tirelessely throughout their lives and are still making all efforts to support me and my family in every possible way. I am here at this stage of my carrier only because of them. It would be very hard for me to pay them back for what they have done, probably the best way would be to try and match what they did for us, for our children. My deepest acknowledgments to my supervisor and mentor Dr. James F. Whid- borne who guided me throughout my research and made this thesis possible. I am greatly indebted to him. In addition, it would not be fair not to mention Dr. Alastair K. Cooke whom I bothered many a times to seek guidance with regards to flight dynamics and aerodynamic model building. I found his NFLC Jetstream model very valuable in understanding flight dynamics in an entirely new perspective. Last but not the least, I would like to thank my wife, Zahra, and my kids, Sarah and Saad, for their patience, understanding and support during the last three years. I hope I would be able to give more time to them after my studies. My time here at Cranfield has been memorable, except for the cold British weather I have enjoyed every aspect of this country. Once again, I would like to thank, ev- erybody who helped me finish this work and made this Cranfield experience a most pleasurable one. Naveed ur Rahman. May, 2009 iii Contents Abstract i Acknowledgments iii Contents v List of Tables x List of Figures xii Abbreviations and Symbols xxi 1 Introduction 1 1.1 Introduction................................ 1 1.2 ProblemDescription ........................... 2 1.3 Objectives................................. 2 1.4 Methodology ............................... 4 1.5 ThesisOutline............................... 5 2 Literature Review 7 2.1 Literature Review - Tailless Aircraft . .... 7 2.1.1 AHistoricalPerspective . 8 2.1.2 Tailless Aircraft and Longitudinal Stability . ..... 11 2.1.3 Tailless Aircraft and Lateral-Directional Stability ....... 17 2.2 ALiteratureReviewonJet-Flaps . 22 2.2.1 PastandthePresent . .. .. 22 v CONTENTS 2.2.2 Jet-Flaps and Mechanism of High Lift . 23 2.2.3 Achievable Lift Coefficients . 26 2.2.4 SomeBlownFlapArrangements . 27 2.3 A Review on Propulsion/Controls Integration . .... 28 2.3.1 MD-11 Propulsion Controlled Transport Aircraft . ... 28 2.3.2 Boeing - Propulsion/Flight Control System . .. 30 2.3.3 PropulsionControlforF-15Aircraft . 31 2.3.4 Hunting H-126 - Jet Flap Research Aircraft . 33 2.3.5 UAV Flight Control through Circulation Control . ... 34 2.3.6 Embedded Wing Propulsion (EWP) . 35 2.4 Conclusions-LiteratureReview . 35 3 Identification of Control Problems 37 3.1 ControlAuthorityAnalysis. 37 3.1.1 Longitudinal Control Power and Trim . 37 3.1.2 Lateral-Directional Control Power and Trim . .. 41 3.2 VariationinDynamicModes. 45 3.2.1 Variation in Dynamic Modes - Longitudinal Axis . 46 3.2.2 Varition in Dyanmic Modes - Lateral Directional Axis . .... 49 3.3 BWB - Handling Qualities Assessment . 52 3.3.1 Longitudinal Handling Qualities (BWB) . 52 3.3.2 Lateral-Directional Handling Qualities (BWB) . .... 57 3.4 ChapterSummary ............................ 62 4 Transient Engine Model and Effects of Controls Integration 63 4.1 AHybrid3SpoolTurbofanEngineModel . 66 4.1.1 EngineStationsandStateVector . 66 4.1.2 Calculation of Pressure Derivatives - (P˙i)............ 67 4.1.3 Calculation of Speed Derivatives - (N˙ ) ............. 72 4.1.4 Iterative Solution of Compressor Thermodynamics . .... 73 4.1.5 Iterative Solution of Turbine Thermodynamics . ... 75 vi CONTENTS 4.1.6 MatlabImplementation . 75 4.2 ModelValidation ............................. 77 4.2.1 DesignPointValidation . 77 4.2.2 Validation of Engine Transients . 78 4.3 Thrust Vectoring and Engine Performance . .. 85 4.3.1 Thrust Vectoring and Engine Transients . 85 4.3.2 Thrust Vectoring and Steady State Performance . 87 4.4 Effect of Engine Bleed on its Performance . 88 4.4.1 Transient Engine Performance with Step Bleed . .. 88 4.4.2 Engine Performance under Steady State Bleed . 91 4.5 Chapter-Summary............................ 93 5 A BWB Model with Blown Flaps 95 5.1 Introduction................................ 95 5.2 GeneralDescription.. .. .. 96 5.3 Building the BWB Aircraft Model . 97 5.3.1 The BWB Planform and Wing Sections . 97 5.3.2 ValidationofBWBAirfoilprofiles. 99 5.3.3 WingForcesandMoments . .102 5.3.4 VerticalFinForcesandMoments . 113 5.4 ModelValidation .............................116 5.4.1 TornadoResults. .116 5.4.2 Validation of Spanwise Lift and Pitching Moment . 118 5.4.3 Validation of Aero Derivatives w.r.t Air Angles . .120 5.4.4 Validation of Aero Derivatives w.r.t Body Rates (p,q,r) ...123 5.4.5 ValidationofControlDerivatives . 124 5.5 Effect of Blown Flaps on Aero Derivatives . 126 5.5.1 Effect on Spanwise Lift and Pitch moment . 126 5.5.2 Lift and Pitch moment (CL,Cm) with Flap Blowing . 128 5.5.3 Increase in Roll moment (Cl) with Flap Blowing . 130 5.5.4 Increase in Yawing moment (Cn) with Flap Blowing . 130 5.5.5 RelativeFlapEffectiveness . .131 5.6 Chapter-Summary............................132 vii CONTENTS 6 Propulsion and Controls Integration 133 6.1 Engine Bleed and Lift/Pitching Moment . 134 6.1.1 Internally Blown Flaps (IBF) - Using IPC Bleed . 134 6.1.2 Externally Blown Flaps (EBF) - Using LPC/Fan Bleed . 150 6.1.3 Engine Matched for Additional Bleed at Design Point . .154 6.2 Controls Performance with Flap Blowing . 156 6.2.1 Control of Pitch Axis with Blown Flaps . 156 6.2.2 RollControlandBlownFlaps . .157 6.2.3 Directional Control and Blown Flap Rudder . 159 6.3 Controls Performance with Thrust Vectoring . .162 6.4 Trim Results with Flap Blowing and TVC . 166 6.4.1 Trimming with AFC + Fixed TVC . 166 6.4.2 TrimmingwithBlownFlaps . .168 6.5 ChapterSummary ............................170 7 Landing and Take-off Performance 173 7.1 GeneralDescription . .. .. .173 7.2 Landing with TVC and Flap Blowing . 175 7.2.1 LandingwithFixedTVC . .176 7.2.2 Landing with Fixed TVC + Flap Blowing . 177 7.3 Take-offPerformance . .178 7.3.1 DescriptionofTake-offPhases . .178 7.3.2 Forces and Moments on BWB During Take-off . 179 7.3.3 Nominal Un-Assisted Take-off . 180 7.3.4 Take-off Performance with TVC and Flap Blowing . 182 7.4 ChapterSummary ............................184 8 Conclusions and Further Research 185 8.1 Conclusions ................................185 8.2 FurtherResearch .............................190 8.3 DisseminationofResults . .192 viii CONTENTS A BWB Data - Baseline 193 A.1 GeneralDescription. .193 A.2 MassandInertiaProperties . .194 A.3 Geometricproperties . .195 A.4 AerodynamicProperties . .196 A.4.1 Normal Force Coefficient, CZ ..................196 A.4.2 Axial Force Coefficient, CX ...................197 A.4.3 Side Force Coefficient, CY ....................198 A.4.4 Roll Moment Coefficient, Cl ...................199 A.4.5 Pitch Moment Coefficient, Cm ..................199 A.4.6 Yaw Moment Coefficient, Cn ...................200 B BWB Linear Model 203 B.1 DimensionalDerivatives . .203 B.1.1 Axial Force (X)Derivatives . .204 B.1.2 Side Force (Y )Derivatives .