Winglets

Presented by

Dan ShaferJames Pembridge

Mike Reilly

Outline

• Introduction

• History

• Pros / Cons

• Force Diagram

• Design Considerations

• Case Study

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

Solution

Winglets

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

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

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

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.

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

• 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

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

Design of Winglets

Geometry of Winglet1. Airfoil

2. Chord distribution

3. Height

4. Twist

5. Sweep

6. Toe angle

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

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

Winglet Height

• Determined by the optimal induced drag and profile drag relationship

Twist/Sweep• Have similar effects on the winglet

• Tailor the load distribution

Toe Angle

• Mounting angle– Controls overall loading on winglet– Effects the load distribution on main wing– Only optimum for one flight condition

Winglet Modeling

Tornado© VLM code for MATLAB

b/20, b/10

Taper => 0.3

= 57 deg

Winglet Geometry

Winglet Modeling

Aircraft Configuration

dihedral = 4.6o

1/4 = 20o

Winglet ModelingOriginal Configuration

= 8o

L/D = 51

Winglet ModelingSmall Version

11% drag reduction

(7% when compared to an extended wing)

8% drag reduction

(4% when compared to an extended wing)

Winglet ModelingLarge Version

22% drag reduction

(14% when compared to an extended wing)

12% drag reduction

(4% when compared to an extended wing)

Winglet ModelingSide View

Conclusions

• Drag reductions up to 20%

• Winglets only needed on designs with higher than normal induced drag

• Beneficial in canard configuration

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/

Questions?