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Flexible-wing MAVsFlexible-wing MAVsDr. Peter Ifju, Bret StanfordMechanical and Aerospace EngineeringUniversity of Florida
Special ThanksSpecial ThanksStudents:
Bret StanfordRoberto AlbertaniKyu-Ho LeeSewoong JungScott EttingerMujahid AbdulrahimDon McArthurDan ClaxtonFrank BoriaMike SytsmaJos CoquytDragos ViieruBaron JohnsonMike MortonJames CliftonScott Bowman
UF Faculty:
Rick LindWarren DixonPaul HubnerWei ShyyRafi HaftkaDavid JenkinsAndy KurdilaCarl CraneWarren DixonFranklin PercivalMike Nechyba
Sponsors:
Air Force Office of Scientific ResearchAFRL at Eglin Air Force BaseUS Special Operations CommandNASA Langley Research CenterUS Geological SurveyUS Dept of Fisheries and Wildlife
James DavisYongsheng LianThomas RamboAlbert LinBrandon Evers
Design Concept: Flexible, Thin, Design Concept: Flexible, Thin, UndercamberedUndercambered Wing Wing
Undercambered wing provides better aerodynamic characteristics at Reynolds No. below 100,000.
Flexibility can be tuned for smoother flight in gusty wind conditions “adaptive washout”.
We have built wings with improved longitudinal stability.
Delayed/gentle stall has been documented
Flexible wing can be morphed efficiently.
Flexible wings can be folded for storage and deployed without assembly.
Wing configuration can be engineered to be lightweight as well as durable
Benefits of the UF DesignsBenefits of the UF Designs
MorphingMorphing
Gust AlleviationGust AlleviationStorageStorage
DurabilityDurability
Stability, high liftStability, high lift
Outline:Outline:
• Introduction•Fabrication methodologies•Flight testing•Experimental program•In-situ deformation measurements•Structural model•Fluid structure interaction models•Model validation via deformation measurements•Optimization •Conclusions and future work
Custom MAV Design SoftwareCustom MAV Design Software
• Span• Chord• Twist• Sweep• Airfoil
geometry• Virtually any
planformshape
MAVLab: rapid wing generation
CAD Model, Tool Path and Milling CAD Model, Tool Path and Milling
Finished Tooling andFinished Tooling andComposite ConstructionComposite Construction
Finished tool with layout pattern Prepreg unidirectional, woven carbon fiberand Kevlar composite construction
Composite Construction ContinuedComposite Construction Continued
Vacuumbagging
Fuselagelayup
Componentinstallation
Assembly
Finished MAV in Less Than One DayFinished MAV in Less Than One Day
• Latex rubber membrane material is applied
• Fins are attached • Off to be flight tested
International Micro Air Vehicle International Micro Air Vehicle Surveillance Competition HistorySurveillance Competition History
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
10
25
50MLB
MLBUF
UFUF
UFUF
UF
BYU
KKU
UF 4.5 in. (11.4 cm)record
Max
imum
Dim
ensi
on, c
m
15
Smallest MAV toidentify target at 600m
Year
30 cm US European MAV Competition30 cm US European MAV Competition
Three Wings were then Studied Three Wings were then Studied
[±453] [±452]
Latex Skin[02]
Rigid Batten-Reinforced BR Perimeter-Reinforced PR
• Composite wings constructed from carbon fiber composites, and latex rubber skin
• All three wings have the same nominal shape:– AR = 1.25, root chord = 130 mm, wing span = 150 mm
• Rigid wing: nominal aerodynamics• Batten-reinforced wing: adaptive washout• Perimeter-reinforced: adaptive inflation
Coefficient of Lift vs. Angle of AttackCoefficient of Lift vs. Angle of Attack
• The low aspect ratio accounts for high stall angles• After stall, the lift of the perimeter reinforced wing is greater than
The other wings before stall•The perimeter reinforced wing has higher CLmax
Moment Coefficient Moment Coefficient vsvs Coefficient of LiftCoefficient of Lift
• The perimeter reinforced wing has a higher negative slope• The rigid wing has the lowest• Static longitudinal stability of the perimeter reinforced wing is
substantially higher than the rigid case with the batten reinforcedwing intermediate
Wing Deformation Measurements UsingWing Deformation Measurements UsingVisual Image CorrelationVisual Image Correlation
• The stereo-triangulation is achieved through twin synchronized cameras (35 mm lens, 1.3 mega pixels, 5-10 ms exposure times) each looking at a different angle
• After a random speckling pattern is applied to the surface of the 3-D geometry in question, the VIC system digitally acquires the pattern, and tracks the deformation of each speckle
Synchronizedcameras
Wind tunnel
Model250 Watt lamp
Wind Tunnel VIC Tests ProcedureWind Tunnel VIC Tests Procedure
VIC Results: BR Wing OutVIC Results: BR Wing Out--OfOf--Plane Plane DisplacementsDisplacements
12° AOA, Wind Speed = 13 m/s
Wing fixed here: Non-zero displacement implies a small rigid body rotation of entire model
Primary region of deformation:battens are forced to bend upwards due to wind loading
Deformation patterns here imply that the wind load subjects the leading edge to torsion
VIC Results: PR Wing OutVIC Results: PR Wing Out--OfOf--Plane Plane DisplacementsDisplacements
12° AOA, Wind Speed = 13 m/s
Wing fixed here: Non-zero displacement implies a smallrigid body rotation of entire model
The primary region ofdeformation occurs as the membrane billows upwards dueto the aerodynamic forces
The carbon fiber perimeter exhibits substantial bending
MAV Structural ModelingMAV Structural Modeling• Accurate finite element wing modeling can provide insight into the
complicated fluid-structure interaction over a flexible MAV• In keeping with the composite nature of the wing, three different
elements are used: shells to model the carbon fiber weave (red),beams to model the battens (green), and membranes to model the latex skin (blue)
Static MAV Model ValidationStatic MAV Model Validation
• Visual image correlation is an ideal tool for finite element validation• Static model validation was conducted by hanging small weights from
the wing, and comparing numerical and experimental displacement fields
Out-of-plane displacements caused by a 7 g load at the tip of the outer left batten (MAV clamped at trailing edge)
Experimental (VIC) Numerical (FEA)
High fidelity finite elementanalysis (FEA) structural model
With nonlinear membrane properties
Navier Stokes basedcomputational fluid dynamics
(CFD) model with master/slaveperturbation techniques for remeshing
Define rigid wing geometry
Conduct CFD on rigid wing
Apply aero loads from CFD to FEA
Deformed shape analyzed by CFD
Apply new aero loads to FEA
Fluid Structure Interaction ModelFluid Structure Interaction Model
Stop when wing geometry converges
Fluid Structure Interaction Model Fluid Structure Interaction Model ConvergenceConvergence
Comparing BR Model and ExperimentComparing BR Model and Experiment
Out-of-plane displacement
Chord-wise strain
Comparing BR Model and Experiment Comparing BR Model and Experiment
Span-wise strain
Shear strain
Comparing PR Model and Experiment Comparing PR Model and Experiment
Out-of-plane displacement
Chord-wise strain
Comparing PR Model and Experiment Comparing PR Model and Experiment
Span-wise strain
Shear strain
0AOA, top
0AOA, bottom
Pressure, Streamlines and Deformation Pressure, Streamlines and Deformation Rigid Batten Perimeter
Rigid Batten Perimeter
15AOA, top
Pressure, Streamlines and Deformation Pressure, Streamlines and Deformation Rigid Batten Perimeter
Rigid Batten Perimeter
15AOA, bottom
Comparing BR Model and Experiment Comparing BR Model and Experiment
Pressure, Streamlines and Deformation Pressure, Streamlines and Deformation
PR Membrane Pretension vs. Deformation PR Membrane Pretension vs. Deformation
BR Membrane Pretension vs. Deformation BR Membrane Pretension vs. Deformation
PR Pretension vs. Performance PR Pretension vs. Performance
BR Membrane Pretension vs. Deformation BR Membrane Pretension vs. Deformation
Conclusions and Future WorkConclusions and Future Work•The design space can be greatly increased by employing flexibility
•Flight tests and wind tunnel tests have shown appreciable gains in some flight parameters with both the batten reinforced and perimeter reinforced membrane wing
•Advanced structural deformation measurement techniques provide high fidelity information that can give insight into the mechanisms that lead to enhanced flight performance
•Fluid structure interaction models can give insight into how to improve specific flight characteristics
•However no flexible wing design is the best at everything
•Topological optimization is currently being used for determiningbetter ways to reinforce the wing for specific objective functions
•Future work to validate the fluid structure interaction model byexperimentally characterizing the flow field is desired.