Aerodynamic Issues of Unmanned Air Vehicles Workshop · Unmanned Air Vehicles Workshop. Report...

Air Force Institute of Technology

AeroAero--Structural Coupling Structural Coupling and Sensitivity of a Joinedand Sensitivity of a Joined--

Wing SensorCraftWing SensorCraft

Lt Jennifer Schwartz (AFRL/AFIT) Lt Col Robert Canfield (AFIT) Dr Maxwell Blair (AFRL)

5 Nov 2002

Aerodynamic Issues of Unmanned Air Vehicles Workshop

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Standard Form 298 (Rev. 8-98) Prescribed by ANSI Std Z39-18

5 November 2002 Lt Jennifer Schwartz 2

� Background on Joined-Wing SensorCraft� History of the Joined-Wing� SensorCraft Background� Configuration Issues

� Modeling� Parametric Modeling & Design Method� Aerodynamic Panel Model

� PanAir� FlightLoads

� Structural Finite Element Model

� Related Studies

� Conclusion

Overview


History of Joined Wings

� Advantages Claimed� Reduce induced drag� Improve Stability� Strengthen Wing� Prevent Flutter

Staggered Wing, Staggered Wing, RatonyRatony, 1977, 1977

Lockheed MartinLockheed Martin

�New Strategic �New Strategic Aircraft� ConceptAircraft� Concept


Joined / Box Wing Studies

� Wolkovitch (1986)� Highly Integrated Structures &

Aerodynamics Concept

� Gallman & Kroo (1996)� Buckling Critical

� Livne (2001)� Survey� Complex

Aeroelastic Behavior

NASA : Box Wing Airliner (325 Passenger)NASA : Box Wing Airliner (325 Passenger)

Lockheed Martin Lockheed Martin Concept to Concept to

Replace Replace CC--141 & KC141 & KC--135135


SensorCraft Background

� Air Force Requirement� A UAV for continuous, long term intelligence,

surveillance, and reconnaissance (ISR) missions� Joined wing magnifies sensor footprint by providing

360 degree coverage of the area of interest

Notional UAV Joined Wing SensorCraft Concept (Boeing)


Notional Mission Profile

50,000 ft55,000 ft

Climb200 nm

IngressM=0.63,000 nm

LoiterM=0.5

65,000 ft

EgressM=0.6

3,000 nm

65,000 ft

Descend200 nm Max

� L/D = 24� CD = 0.04� TOGW = 63,000 lbs� Fuel Weight = 41,000 lbs

� L/D = 24� CD = 0.04� TOGW = 63,000 lbs� Fuel Weight = 41,000 lbs

= −

i

i

WW

DL

CVR 1lnBreguet Range Equation:


SensorCraft Concept

� Developed by a team of AFRL in-house engineers� Designed with the concept of designing an aircraft

around the desired sensor package, rather than trying to pack sensors into an already existing platform

� Provides the required 360 deg coverage in a joined-wing configuration

� Further analysis is now being performed by students at the Air Force Institute of Technology


SensorCraft Complexity

� SensorCraft Issues� Many current tools are unable to process unusual

configurations� Need to examine several points in the mission profile� Complex aerodynamics at the joints� Conformal, load bearing antenna integration� Non-linear structural analysis

� Wing buckling and bending� Interaction of structural and aero loads

� Solution requires simultaneous, interactive examination of:� Sensors, including the structural characteristics� Structural analysis� Flexible aerodynamic loads






� Related Studies

� Conclusion

Overview � Modeling


Design Tools

AML Design Environment:� Object-oriented With Native Geometric Modeling� Dependency-tracking & Demand Driven Process� Run-time Object Creation

PanAir Aerodynamic Solver:� Linear panel geometry for complex configurations� High order continuous singularity distribution� Wake shaping capability

MSC.Nastran:� Non-Linear Analysis� Gradient-Based Buckling Design

ASTROS:� Structural Optimization� Linear Fully-Stressed Design (FSD)

MSC.FlightLoads Solver:� Combined structural-aerodynamic model


Joined-Wing Design Flowchart

Generate Geometric Model

Flexible Air Loads

Σ Weights

FEA

Trim α, δ

Drag & Fuel Buckling & Nonlinear Analysis

Generate Aero Model Generate FEM

FSD

Aero-StructuralInterface

Antenna Structure


5) Wing Panel

Start withBasic Building Blocks:1) curve2) contour3) surface

4) Airfoil

6) Web Geometry

7) Surface Geometry

Object-Oriented Wing Building~ AML Design Environment ~


Fully Associative Parametric Variations~ AML Design Environment ~

52.2 m3Wing Volume

145.0 m2Planform Area

FX-60-126-1Airfoil

30 degSweep (Λib, Λob)

7.0 mWing Offset (zfa)

22.0 mWing Separation (xfa)

2.5 mChord (crf, cra, cm, ct)

6.3 mOutboard Span (Sob)

26.0 mInboard Span (Sib)


Joined-Wing Aero Model~ PanAir Aerodynamic Solver ~

Rigid Trimmed PanAir Pressure Vectors on the Top Skin

PanAir Panel Model


MSC.FlightLoads Architecture~ FlightLoads ~

Geometry

Loads Browser

Aero Modeling

Structural Modeling

Aerodynamics Aeroelasticity External Structural Loads & Dynamic

ResponseAeroelastic

DBAerodynamics

DB

� Begin with geometry from user-preferred sources (i.e. IGES, CAD, etc)� Define the aerodynamic and structural models� Perform aerodynamic calculations� Analyze the combined structural-aerodynamic model to provide both component

and total vehicle aeroelastic responses� View the results and produce external loads that can be passed to the stress

group for detailed design and verification


Analysis Process~ FlightLoads ~

� Input a simple structural geometry� Include degrees of freedom

� Build a flat-plate aero model, including control surfaces

� Spline the aero model to the structure� Identify aero and structural monitoring points

� Examine the model at various points in the mission profile� Takeoff, ingress, mid-loiter, 2-g turn, egress, and landing

� Export to NASTRAN for structural analysis

� Use NASTRAN results to complete the aerodynamic analysis


Aero-Structural Model~ FlightLoads ~


Joined-Wing FEM

Rigid Trimmed Forces at the Structural Grid Points






� Related Studies

� Conclusion

Overview � Related Studies


Related Research

� Previous Work� Joined-Wing Structural Weight Modeling Study

(Blair/Canfield)

� Concurrent Work� Stochastic Finite Element Analysis (Pettit/Ghanem)� Reliability Based Structural Design (Roberts)� Structurally Integrated Conformal Antennas (Smallwood)


Linear Results Non-Linear Results

� FEM Resized (Fully-Stressed): Linear FEA� Aeroelastic Load was Applied in

Geometrically Nonlinear FEA

Conclusion: Non-linear Analysis Critical in Designing Joined-Wing

Joined-Wing FEM~ Joined-Wing Structural Weight Modeling Study ~


Linear FSD Flexible Loads Iter. 1~ Joined-Wing Structural Weight Modeling Study ~

X

YZ

281702400.

264096297.

246490194.

228884092.

211277989.

193671886.

176065783.

158459680.

140853578.

123247475.

105641372.

88035269.

70429166.

52823064.

35216961.

17610858.

4755.

V2L200C1

Output Set: MSC/NASTRAN Case 1Deformed(3.151): Total TranslationContour: Plate Top VonMises Stress

X

YZ

1.764E+10

1.654E+10

1.544E+10

1.434E+10

1.323E+10

1.213E+10

1.103E+10

9.925E+9

8.822E+9

7.719E+9

6.616E+9

5.514E+9

4.411E+9

3.308E+9

2.205E+9

1.103E+9

523.9

V1L200C1

Output Set: Eigenvalue 2 1.208545Deformed(1.001): Total TranslationContour: Plate Top VonMises Stress

Buckling Deformation of Linear FSD

Linear FSDStatic Deformation


Conclusions

� The joined-wing SensorCraft presents designers with unique technical issues

� Accomplishments� Design Environment for Nonlinear Flexible Trim

� Interactive Aero-Structural Model

� Next Steps� Un-Sweep Outboard or Aft Wing

� Design for Buckling and Non-Linear FSD

� Tailor Aft Wing Buckling to Alleviate Flexible Load

� Verify aerodynamic results with CFD


Joined-Wing Analysis Flowchart

Generate Parametric Geometry

Rigid Air Loads

Σ Weights

FEA

Trim α, δ

Drag & Range

Flexible Air Loads


Negative Aft Wing Lift Positive Lift

Un-Sweep Outboard Wing

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