winglets presented by dan shafer james pembridge mike reilly
TRANSCRIPT
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Winglets
Presented by
Dan ShaferJames Pembridge
Mike Reilly
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Outline
• Introduction
• History
• Pros / Cons
• Force Diagram
• Design Considerations
• Case Study
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Problem
• Induced drag – Produced by 3-D
airflow around wing tips
– Large for high-lift, low speed flight conditions
– 50% of total drag for subsonic transports opperating at high subsonic speeds
Maughmer, D., Mark, “About Winglets”, Fig 3
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Solution
Winglets
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Origins
• Nature– Wingtip configuration on birds
• Numerous feathers at wing tips
• F.W.Lanchester• Vertical surfaces at wing tips reduced induced
drag(1897)• Vertical endplates produced a large reduction in
drag at high lift conditions
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Origins
• Richard T.Whitcomb– Inspired by birds– A properly cambered and angled surface
could reduce the strength of trailing vortex– “winglets” emphasize design process similar
to wings
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Winglets
• Reduce wingtip vortices• Cut back on drag up to
%20*
• Higher cruise speed• Increased fuel economy• Possibly double wings
lift to drag ratio *
• Good when wing extension
is not possible
*Richard Whitcomb NASA aerodynamicist
Picture courtesy of Cessna Aircraft
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Proven Performance• Mission block fuel is improved approximately 4
percent (BBJ)• Range increased by as much as 200 nm (BBJ)
and up to 130 nm (737-800)• 6.5 percent reduction in noise levels around
airports on takeoff• 4 percent reduction in nitrogen dioxide
emissions on a 2,000-nmi flight.
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Additional ThrustThe angle at which the winglets' airfoils diverge from the relative wind direction, determine the magnitude and orientation of the lift force generated by the winglet itself. By adjusting these so that the lift force points slightly forward, additional thrust is achieved
Inboard ForceResultant Force
Additional Thrust
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• Allow for steeper climb• Good for obstacle-limited, high, hot, weight-
limited, and/or noise-restricted airports• Lower wing spar bending moment than
wingspan extension• Eye catching• For the same amount of structural material,
nonplanar wingtip devices can achieve a
similar induced drag benefit as a planar span
increase
Good idea
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Cons• Have a tendency to cause wing flutter• Winglet design is very detailed and
complicated• Difficult to determine boundary layer effects
at wingtip/winglet junction (separation,
pressure gradient)• Usually not in initial design
Design Challenges
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Design of Winglets
Geometry of Winglet1. Airfoil
2. Chord distribution
3. Height
4. Twist
5. Sweep
6. Toe angle
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Winglet Airfoil
• Goal:– Generate enough lift while maintaining the lowest
possible drag
• Should not stall before wing during low speed flight
• Geometry driven by aerodynamic characteristics of the airfoil
• Limitation– Narrow chords yield low Re– Re range from 1E5 to 1E6
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Chord Distribution
• Sizing– Too small:
• Airfoil will require a large lift coefficient
– Too big :• High winglet loading• Causes outboard section of wing to stall prematurely
• Spanwise elliptical chord distribution– Elliptical planform will help with load distribution over
a large range of flight regimes
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Winglet Height
• Determined by the optimal induced drag and profile drag relationship
Twist/Sweep• Have similar effects on the winglet
• Tailor the load distribution
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Toe Angle
• Mounting angle– Controls overall loading on winglet– Effects the load distribution on main wing– Only optimum for one flight condition
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Winglet Modeling
Tornado© VLM code for MATLAB
b/20, b/10
Taper => 0.3
= 57 deg
Winglet Geometry
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Winglet Modeling
Aircraft Configuration
dihedral = 4.6o
1/4 = 20o
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Winglet ModelingOriginal Configuration
= 8o
L/D = 51
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Winglet ModelingSmall Version
11% drag reduction
(7% when compared to an extended wing)
8% drag reduction
(4% when compared to an extended wing)
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Winglet ModelingLarge Version
22% drag reduction
(14% when compared to an extended wing)
12% drag reduction
(4% when compared to an extended wing)
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Winglet ModelingSide View
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Conclusions
• Drag reductions up to 20%
• Winglets only needed on designs with higher than normal induced drag
• Beneficial in canard configuration
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References
• “Concept to Reality: Winglets”. http://oea.larc.nasa.gov/PAIS/Concept2Reality/winglets.html
• Maughmer, D., Mark, “Sailplane Winglet Design”.• Maughmer, D., Mark, “The Design of Winglets for High-Performance
Sailplanes”, AIAA Paper 2001-2406 • Melin, T., Tornado 1.23b, MATLAB code available at
http://www.flyg.kth.se/divisions/aero/software/tornado/
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Questions?