Virginia Tech TrussBraced Wing Studies J A Schetz
Virginia Tech Truss-Braced Wing Studies J. A. Schetz and R. K. Kapania and TBW Group at VT Multidisciplinary Analysis and Design Center for Advanced Vehicles, Virginia Polytechnic Institute and State University and Collaborators at Georgia Tech, Univ. Florida & UT Arlington and Vivek Mukhopadhyay (NASA) and B. Grossman (NIA) 1 Multidisciplinary Analysis and Design Center for Advanced Vehicles 1
Goal of the Research • Use Multidisciplinary Design Optimization (MDO) to explore the potential for large improvements in longand medium-range transonic, transport aircraft performance by employing truss-braced wings (TBW) combined with other synergistic advanced technologies. • Ground Rules for VT Studies: Mach 0. 85 cruise All-metal airplanes GE 90 type engines Focus on truss benefits Multidisciplinary Analysis and Design Center for Advanced Vehicles 2
Original Pfenninger Vision Fuselage profile For low wetted area Wing tip for vortex control Large span wing to reduce induced drag Thin wing at root for laminar flow Optimized truss support to reduce wing weight. Reduce interference drag Pfenninger, W. , “Laminar Flow Control Laminarization, ” AGARD Report 654, “Special Course on Concepts for Drag Reduction” , 1977 Multidisciplinary Analysis and Design Center for Advanced Vehicles 3
Main Mission (“ 777 ER”) Mach 0. 85 Cruise Mach 0. 85 140 Knots Approach Speed Climb 11, 000 FT T/O Field Length 7730 NMI Range 350 NMI 11, 000 FT LDG Reserve Range Field Length • Use MDO to design 305 -passenger, 7730 nmi range, Mach 0. 85 transport aircraft of Cantilever, Strut-Braced-Wing (SBW), and Truss-Braced Wing (TBW) configurations Multidisciplinary Analysis and Design Center for Advanced Vehicles 4
MDO Design Environment N^2 Diagram Model. Center Environment Design Environment Block Diagram Baseline Design Parametric Geometry Propulsion Aerodynamics Optimizer Fuel Loading TOGW Convergence Performance, Cost Function, Constraints Structural Optimization Weight Estimation Multidisciplinary Analysis and Design Center for Advanced Vehicles 5
Propulsion Model • Dimensions and weights – Simplified VT model similar to Mattingly Elements of Propulsion: Gas Turbines And Rockets • Performance: 1. Simplified model 2. NASA fixed deck • “GE-90 -like” 3. NPSS or Reduced-order NPSS from GT Multidisciplinary Analysis and Design Center for Advanced Vehicles M=0. 85 6
Aerodynamic Model • Calculates: – Aerodynamic drag – Aerodynamic loading (input for structural design module) • Drag breakdown models: – – Induced drag based on Trefftz plane model Friction/Profile drag based on semi-empirical methods Wave drag based on the Korn Equation Interference drag based on literature and response surfaces from offline CFD Multidisciplinary Analysis and Design Center for Advanced Vehicles 7
Structural Design Requirements • Total of 17 cases: 2. 5 g 100% / 50% fuel -1 g 100% / 50% fuel 2 g taxi bump 12 gust cases, 50% 100% fuel, various altitudes – Motivated by low wing loading MDO designs – Simplified discrete gust modeling – Using gust alleviation factor 40 35 Altitude (x 103 ft) • • Vc 30 25 20 Flutter Envelope 15 10 5 0 0 0. 5 Mach 1 1. 5 • Designs evaluated for flutter performance post MDO Multidisciplinary Analysis and Design Center for Advanced Vehicles 8
Structural Design Methodology • Estimation of load carrying structural weight z – Bending and shear material – Structural optimization t 0 t 1=(t/c) ·c /2 B t 2 A D C cst • Finite element analysis – Stress, displacement and buckling constraints – Flutter constraints with geometric stiffness influence • Structural response surface model used in MDO x Offline RSM generation Latin-Hypercube Sampling Kriging Surrogate Model Design Variables Wing Structural Weight Estimation Evaluate Response Surface Model Wing Weight Multidisciplinary Analysis and Design Center for Advanced Vehicles 9
TBW Weight Estimation • Detailed physics based wing system structural weight estimation – In-house tool optimizes for bending and shear material weight • Other components: – FLOPS: secondary weight – Folding wing penalty – Fuselage pressurization penalty Multidisciplinary Analysis and Design Center for Advanced Vehicles 10
Performance Constraints • • • Range ≥ 7730 [NM] + 350 [NM] (reserve) Initial Cruise ROC ≥ 500 [ft/min] Max. cl (2 -D) ≤ 0. 8 Available fuel volume ≥ required fuel volume 2 nd segment climb gradient (TO) ≥ 2. 4% (FAR) Missed approach climb gradient ≥ 2. 1% (FAR) Approach velocity ≤ 132. 5 [kn. ] Balanced field length (TO & Land. ) ≤ 11, 000 [ft] Cruise altitude ≤ 48, 000 [ft] Multidisciplinary Analysis and Design Center for Advanced Vehicles 11
Truss Topology Optimization Study • • Triangular Loading Two-dimensional analysis Buckling not included Single load case 15% Volume Fraction Fewer Members Larger tip deflection Larger strain energy • All designs with same volume fraction have same mass Multidisciplinary Analysis and Design Center for Advanced Vehicles 12
Muldisciplinary Design Optimization Study • Cost functions: Minimum fuel/emissions and TOGW • Configurations – Cantilever – Strut-Braced wing (SBW) – Single Jury TBW – 2 -Jury TBW – 3 -Jury TBW • Aggressive laminar flow • Aggressive junction fairing • Fuselage riblets Multidisciplinary Analysis and Design Center for Advanced Vehicles 13
Minimum Fuel/Emissions Design Study Active Constraints range, deflection range, clmax, Vapproach range, fuel range, clmax, Vapproach Multidisciplinary Analysis and Design Center for Advanced Vehicles 14
Minimum Fuel/Emissions Design Study B 777: 183 40 170 150 130 10 90 0 Cant. SBW 1 -Jury 2 -jury 3 -jury Cant. SBW 1 -Jury 2 -Jury 3 -Jury 40 550 30 B 777: 512 AR TOGW, klb 600 -8% 10 400 0 Cant. SBW 1 -Jury 2 -jury 3 -jury 140 200 120 150 100 +11% B 777: 71 60 +160% B 777: 10 Cant. SBW 1 -Jury 2 -Jury 3 -Jury Half Span, ft Wing Weight, klb 20 450 80 B 777: 20 20 110 500 +80% 30 -33% L/D Fuel Weight, klb 190 +70% B 777: 106 100 50 0 Cant. SBW 1 -Jury 2 -Jury 3 -Jury Multidisciplinary Analysis and Design Center for Advanced Vehicles 15
Minimum TOGW Design Study Active Constraints range, balanced field length, Vapproach range, initial cruise rate of climb, fuel range, initial cruise rate of climb, Vapproach, clmax range Multidisciplinary Analysis and Design Center for Advanced Vehicles 16
Minimum TOGW Design Study B 777: 183 150 40 -26% +50% 30 L/D Fuel Weight, klb 200 100 B 777: 20 20 50 10 0 0 Cant. SBW 1 -Jury 2 -Jury 3 -Jury 25 B 777: 512 20 510 490 -10% AR TOGW, klb 530 470 +80% 15 B 777: 10 10 450 5 430 0 Cant. SBW 1 -Jury 2 -Jury 3 -Jury 80 -17% 200 B 777: 71 60 Half Span, ft Wing Weight, klb Cant. SBW 1 -Jury 2 -Jury 3 -Jury 40 20 0 Cant. SBW 1 -Jury 2 -Jury 3 -Jury 150 +40% B 777: 106 100 50 0 Cant. SBW 1 -Jury 2 -Jury 3 -Jury Multidisciplinary Analysis and Design Center for Advanced Vehicles 17
Comparison of Designs: Min. Fuel and Min. TOGW B 777: 183 40 35 170 30 150 L/D Fuel Weight, klb 190 130 25 110 15 90 10 Cant. SBW 1 -Jury 2 -Jury 3 -Jury Cant. 500 B 777: 512 30 20 400 0 Cant. SBW 1 -Jury 2 -Jury 3 -Jury Cant. SBW 1 -Jury 2 -Jury 3 -Jury 200 B 777: 71 50 0 Half Span, ft 150 Wing Weight, klb B 777: 10 10 450 100 SBW 1 -Jury 2 -Jury 3 -Jury 40 AR TOGW, klb 600 550 B 777: 20 20 150 B 777: 106 100 50 0 Cant. SBW 1 -Jury 2 -Jury 3 -Jury Multidisciplinary Analysis and Design Center for Advanced Vehicles 18
1 -Jury TBW Configurations Minimum Fuel/Emissions Minimum TOGW Multidisciplinary Analysis and Design Center for Advanced Vehicles 19
MDO Configurations: Drag Breakdown Minimum Fuel 15000 Drag, lb 12000 Interference 9000 Wave 6000 Friction 3000 Induced Drag Component 100% Cant. SBW 1 -Jury 2 -Jury 40% 20% 3 -Jury Drag Component 12000 9000 6000 3000 0 Cant. SBW 1 -Jury 2 -Jury 3 -Jury Minimum TOGW 15000 Drag, lb 60% 0% 0 - 80% 100% 80% 60% 40% 20% 0% 1 -Jury 2 -Jury 3 -Jury All minimum fuel configurations cruise altitude is between 46, 000 to 48, 000 ft Increasing number of members reduces induced drag and increases profile drag Additional surface area from more members reduces system benefit Fuselage drag reduction is needed. Multidisciplinary Analysis and Design Center for Advanced Vehicles 20
Vc Flutter Envelope 0 0. 2 0. 4 0. 6 Mach 0. 8 1 1. 2 SBW 1 -Jury 40 35 30 25 20 15 10 5 0 2 -Jury Minimum Fuel 3 -Jury Altitude (x 103 ft) SBW 1 -Jury 40 35 30 25 20 15 10 5 0 2 -Jury Minimum TOGW 3 -Jury Altitude (x 103 ft) Flutter Boundary of TBW Airplane Designs Vc Flutter Envelope 0 0. 5 Flutter Mach numbers for 100% fuel at 2. 5 g pull-up maneuver Mach 1 • Flutter margin reduces with increasing number of members due to higher span • Passive and active control measures under investigation • Passive methods – Ballast mass – TBW geometry modification: parametric study – Aeroservoelasticity Multidisciplinary Analysis and Design Center for Advanced Vehicles 21
Flutter Ballast Mass Study: Ballast Mass is 2% of Wing Mass • SBW Flutter speed: VF=588 fps, MF=0. 526; 600 lb Ballast mass • Best improvement of 1. 1% with mass at 36% span, 98% chord • Very low sensitivity to ballast mass location Multidisciplinary Analysis and Design Center for Advanced Vehicles 22
Flutter Ballast Mass Study: Ballast Mass from 2% to 8% • Very low sensitivity to size and location of ballast mass Multidisciplinary Analysis and Design Center for Advanced Vehicles 23
Truss-Braced Wing Geometry Parametric Study • Influence of selected geometric parameters on aeroelastic performance of TBW – Strut-sweep (ΛS), Wing-strut span intersection (η) – SBW, TBW 1 -jury, TBW 2 -jury, TBW 3 -jury • Same cross-sectional dimensions for each configuration – Chord, t/c ratio – Values correspond to TBW 1 -jury configuration (from MDO) – Each configuration sized for same requirements Multidisciplinary Analysis and Design Center for Advanced Vehicles 24
Comparison of TBW Configurations (η=55%, b/2=175 ft, ΛW =10°) • Addition of jury strut members – Reduces wing weight – Largest reduction (21%) from SBW to TBW 1 -jury • TBW configurations have similar flutter boundary – Low sensitivity to strut-sweep • TBW 1 -jury and 2 -jury offer 19% increment in flutter boundary with 14% higher weight • TBW 3 -jury offers 49% increment in flutter boundary with 20% higher weight Multidisciplinary Analysis and Design Center for Advanced Vehicles 25
Comparison of TBW Configurations (η=70%, b/2=175 ft, ΛW =10°) • Addition of jury strut members – Reduces wing weight – Largest reduction (14%) from SBW to TBW 1 -jury • TBW configurations show strong sensitivity to strut-sweep – Significant flutter boundary increment from SBW • TBW 1 -jury and 2 -jury have similar weight and flutter boundary – 33% increment in flutter boundary with 20% higher weight • TBW 3 -jury offers 75% increment in flutter boundary with 8% higher weight Multidisciplinary Analysis and Design Center for Advanced Vehicles 26
SBW Flutter modes (sea-level, b/2=175 ft, ΛW =10°) Multidisciplinary Analysis and Design Center for Advanced Vehicles 27
TBW 3 -jury Flutter modes (sea-level, b/2=175 ft, ΛW =10°) Multidisciplinary Analysis and Design Center for Advanced Vehicles 28
Conclusions and Future Work • TBW airplane configurations offer significant performance benefits • Higher span increases weight and reduces flutter speed • Outboard wing-strut intersection location – Increases wing weight in present study due to active buckling – Increases flutter speed for TBW configurations • Larger difference in wing- & strut-sweep could be used to help flutter performance – Flutter speed sensitivity to strut-sweep increases with spanwise intersection location – Airplane MDO would show multidisciplinary influence • Large benefit in wing weight reduction and flutter boundary increment from SBW and TBW configurations – TBW 3 -jury offers highest benefit in flutter performance • Ongoing efforts and future work – Active control techniques – Body-freedom flutter and nonlinear aeroelasticity Multidisciplinary Analysis and Design Center for Advanced Vehicles 29
Backup Slides Multidisciplinary Analysis and Design Center for Advanced Vehicles 30
Minimum Fuel/Emissions Design Study 170 130 110 10 90 0 AR TOGW, klb 30 B 777: 512 -8% 20 450 10 400 0 200 120 150 Half Span, ft Wing Weight, klb 140 80 60 +11% B 777: 71 Cant. SBW 1 -Jury 2 -Jury 3 -Jury +160% B 777: 10 Cant. SBW 1 -Jury 2 -Jury 3 -Jury Cant. SBW 1 -Jury 2 -jury 3 -jury 100 2000 Cant. SBW 1 -Jury 2 -Jury 3 -Jury 40 550 B 777: 4340 4000 Cant. SBW 1 -Jury 2 -Jury 3 -Jury 600 +18% 0 B 777: 106 50 0 Cant. SBW 1 -Jury 2 -Jury 3 -Jury 0. 7 0. 6 0. 5 0. 4 0. 3 Cant. SBW 1 -Jury 2 -Jury 3 -Jury +70% 100 Strut Intersection Ratio Cant. SBW 1 -Jury 2 -jury 3 -jury 500 B 777: 20 20 6000 Specific Wing Weight lb/ft 150 8000 +80% 30 -33% L/D Fuel Weight, klb 40 Wing Area, ft^2 B 777: 183 190 450 400 350 300 250 200 150 Cant. SBW 1 -Jury 2 -Jury 3 -Jury Multidisciplinary Analysis and Design Center for Advanced Vehicles 31
Minimum TOGW Design Study B 777: 183 -26% 100 10 0 0 Cant. SBW 1 -Jury 2 -Jury 3 -Jury 470 430 0 Cant. SBW 1 -Jury 2 -Jury 3 -Jury B 777: 71 200 60 Half Span, ft Wing Weight, klb Cant. SBW 1 -Jury 2 -Jury 3 -Jury 40 20 0 Cant. SBW 1 -Jury 2 -Jury 3 -Jury 150 B 777: 4340 Cant. SBW 1 -Jury 2 -Jury 3 -Jury B 777: 10 10 5 -17% +80% 15 450 80 4500 Strut Intersection Ratio AR TOGW, klb 20 +12% 4000 25 510 -10% 5000 Cant. SBW 1 -Jury 2 -Jury 3 -Jury B 777: 512 490 B 777: 20 20 50 530 +80% 30 +40% Cant. SBW 1 -Jury 2 -Jury 3 -Jury B 777: 106 100 50 0 Cant. SBW 1 -Jury 2 -Jury 3 -Jury 0. 6 0. 5 0. 4 0. 3 0. 2 0. 1 0 Specific Wing Weight lb/ft 150 5500 Wing Area, ft^2 40 L/D Fuel Weight, klb 200 350 300 250 200 150 Cant. SBW 1 -Jury 2 -Jury 3 -Jury Multidisciplinary Analysis and Design Center for Advanced Vehicles 32
Comparison of Designs: Min. Fuel and Min. TOGW B 777: 183 40 130 25 15 20 400 0 Cant. SBW 1 -Jury 2 -Jury 3 -Jury B 777: 10 Cant. 0 150 0. 4 0. 2 0 Cant. SBW 1 -Jury 2 -Jury 3 -Jury B 777: 106 100 50 0 Cant. SBW 1 -Jury 2 -Jury 3 -Jury 0. 6 Specific Wing Weight lb/ft B 777: 71 0. 8 SBW 1 -Jury 2 -Jury 3 -Jury 200 Half Span, ft 150 Wing Weight, klb Cant. SBW 1 -Jury 2 -Jury 30 AR TOGW, klb B 777: 512 10 50 SBW 1 -Jury 2 -Jury 3 -Jury 40 450 100 0 Cant. 600 B 777: 4340 4000 10 Cant. SBW 1 -Jury 2 -Jury 3 -Jury Strut Intersection Ratio 90 6000 B 777: 20 2000 20 110 500 Wing Area, ft^2 30 150 550 8000 35 170 L/D Fuel Weight, klb 190 Cant. SBW 1 -Jury 2 -Jury 3 -Jury 450 400 350 300 250 200 150 Cant. SBW 1 -Jury 2 -Jury 3 -Jury Multidisciplinary Analysis and Design Center for Advanced Vehicles 33
Minimum Fuel/Emissions Design: 1 -Jury TBW Buckling and Flutter Mode Shapes Buckling Mode: 2. 5 g pull up Buckling factor = 1. 8 Buckling Mode: 2 g taxi-bump Buckling factor = 1. 0 • Global wing buckling mode for 2. 5 g pull-up • Strut buckling mode for 2 g taxi-bump • Flutter mode: combination of 3 modes: two bending + torsion Flutter Mode: 2. 5 g, 100% fuel, Sea-level Vf = 300 fps, 1. 7 Hz, reduced freq. = 0. 32 Multidisciplinary Analysis and Design Center for Advanced Vehicles 34
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