Winglets

Presented by Dan Shafer James 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 Thrust

The 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 Additional Thrust Inboard Force Resultant Force

Good idea

• 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

Design Challenges

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 of Winglets

Geometry of Winglet 1. 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 Winglet Geometry L = 57 deg b/20, b/10 Taper => l = 0.3

Winglet Modeling

Aircraft Configuration dihedral = 4.6

o L 1/4 = 20 o l = 0.6

Winglet Modeling

Original Configuration a = 8 o L/D = 51

Winglet Modeling

Small Version 11% drag reduction (7% when compared to an extended wing) 8% drag reduction (4% when compared to an extended wing)

Winglet Modeling

Large Version 22% drag reduction (14% when compared to an extended wing) 12% drag reduction (4% when compared to an extended wing)

Winglet Modeling

Side 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?