BLENDED WINGLETS

ROBERT FAYE

TECHNICAL DIRECTOR

BOEING BUSINESS JETS

BOEING COMMERCIAL AIRPLANES

FOR IMPROVED AIRPLANE PERFORMANCE

TECHNOLOGY / PRODUCT DEVELOPMENT

New blended winglets on the Boeing Business Jet and the737-800 commercial airplane offer operational benefits tocustomers. Besides giving the airplanes a distinctive appear-ance, the winglets create more efficient flight characteristicsin cruise and during takeoff and climbout, which translateinto additional range with the same fuel and payload.

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ROBERT LAPRETE

ASSOCIATE TECHNICAL FELLOW

AERODYNAMICS TECHNOLOGY

BOEING COMMERCIAL AIRPLANES

MICHAEL WINTER

PRINCIPAL ENGINEER

STATIC AEROELASTIC LOADS

BOEING COMMERCIAL AIRPLANES

FOR IMPROVED AIRPLANE PERFORMANCE

vertical height of the lifting system (i.e., increasing the length of the TEthat sheds the vortices). The wingletsincrease the spread of the vortices along the TE, creating more lift at thewingtips (figs. 2 and 3). The result is areduction in induced drag (fig. 4). Themaximum benefit of the induced dragreduction depends on the spanwise liftdistribution on the wing. Theoretically,for a planar wing, induced drag is opti-mized with an elliptical lift distributionthat minimizes the change in vorticityalong the span. For the same amount ofstructural material, nonplanar wingtipdevices can achieve a similar induceddrag benefit as a planar span increase;however, new Boeing airplane designsfocus on minimizing induced drag withwingspan influenced by additionaldesign benefits.

On derivative airplanes, performancecan be improved by using wingtipdevices to reduce induced drag (see“Wingtip Devices” on p. 30). Selectionof the wingtip device depends on thespecific situation and the airplane model.

An important consideration when designing the wingtip device for theBBJ was that it could be retrofittedon BBJs already in service. A blendedwinglet configuration (patented and de-signed by Dr. L. B. Gratzer of AviationPartners, Inc., Seattle, Washington) was selected because it required fewerchanges to the wing structure. The aerodynamic advantage of a blendedwinglet is in the transition from theexisting wingtip to the vertical winglet.The blended winglet allows for thechord distribution to change smoothlyfrom the wingtip to the winglet, whichoptimizes the distribution of the spanload lift and minimizes any aerodynam-ic interference or airflow separation.

STRUCTURAL DESIGN CONSIDERATIONS

The aerodynamic benefits of a wingletapplication are determined in part by the extent of the wing modificationsmade to accommodate the winglet. This especially is the case when an airplane model has been designed and certifiedwithout winglets. The magnitude of the

AERODYNAMICS OF WINGLETS

From an engineering point of view —and ultimately that of mission capabilityand operating economics — the mainpurpose and direct benefit of wingletsare reduced airplane drag.

Winglets affect the part of drag calledinduced drag. As air is deflected by

Not applicable

Not applicable

CFM56-727,300 lb (12,394 kg)

10,695 U.S. gal (40,480 L)10,443 U.S. gal (39,525 L)

171,000 lb (77,565 kg)174,200 lb (79,015 kg)

6,200 nmi (11,480 km)5,750 nmi (10,650 km)

0.785 Mach (530 mi/h)

117 ft 5 in (35.79 m)

110 ft 4 in (33.63 m)129 ft 6 in (39.48 m)41 ft 2 in (12.55 m)11 ft 7 in (3.53 m)

PassengersCargoEnginesMaximum thrust

Maximum fuel capacityBBJBBJ 2

Maximum takeoff weightBBJ BBJ 2

Maximum rangeBBJ BBJ 2

Cruise speed at 35,000 ftBasic dimensionsWingspan (with winglets)Overall length

BBJBBJ 2

Tail heightInterior cabin width

BBJ TECHNICAL CHARACTERISTICS

Passengers3-class configuration2-class configuration1-class configuration

Cargo

EnginesMaximum thrust

Maximum fuel capacity

Maximum takeoff weight

Maximum range

Cruise speed at 35,000 ft

Basic dimensionsWingspan (with winglets)Overall lengthTail heightInterior cabin width

Not applicable162189

1,555 ft3 (44 m3)

CFM56-727,300 lb (12,394 kg)

6,875 U.S. gal (26,035 L)

174,200 lb (79,015 kg)

3,383 statute mi (5,449 km)

0.785 Mach (530 mi/h)

117 ft 5 in (35.79 m)129 ft 6 in (39.48 m)41 ft 2 in (12.55 m)11 ft 7 in (3.53 m)

737-800 TECHNICAL CHARACTERISTICS

Direction of flight

Liftforce vector

Lift component

Induced drag component

Induced angle

AERO

19AERO

18

INDUCED DRAG

FIGURE

1

Boeing offers blendedwinglets — upward-sweptextensions to airplane wings —as standard equipment on itsBoeing Business Jet (BBJ) andas optional equipment on its737-800 commercial airplane.Winglets also are available forretrofit on in-service airplanes.The 8-ft, carbon graphitewinglets allow an airplane to extend its range, carry asmuch as 6,000 lb morepayload from takeoff-limitedairports, and save on fuel.

Understanding the benefitsof blended winglets requiresknowledge of the following:

1. Aerodynamics of winglets.

2. Structural design considerations.

3. Design and testing.

4. Retrofit and maintenance.

The 737-800 commercial airplaneis one of four 737s introduced in the late 1990s for short- tomedium-range commercial air-line operations. Demonstratingexceptional flexibility in size and mission, the four models —737-600/-700/-800/-900 —essentially are four sizes of thesame airplane. Two convertiblemodels are available for conver-sion to an all-freighter configu-ration. All the new 737s can flyhigh-frequency, high-utilizationflights as well as transcontinentaland extended-range twin-engineoperation missions.

1

The Boeing Business Jet (BBJ) was launched in 1996 as a joint venture betweenBoeing and General Electric.Designed for corporate andindividual use, the BBJ is ahigh-performance derivative of the 737-700 commercialairplane. The BBJ marries the737-700 fuselage with thestronger wing and gear of the737-800 commercial airplane.A second version of the BBJ,called BBJ 2, was launched in1999. Based on the 737-800commercial airplane, the BBJ 2has 25 percent more cabinspace and twice the cargo spaceof the BBJ. Both provide thehighest levels of space, com-fort, and utility. BBJ customersare individuals, corporations,governments, armed forces,and heads of state.

2the lift of the wing, the total lift vector tilts back. The aft component of this lift vector is the induced drag (fig. 1). The magnitude of the induced drag isdetermined by the spanwise distributionof vortices shed downstream of the wing trailing edge (TE), which is related in turn to the spanwise lift dis-tribution. Induced drag can be reducedby increasing the horizontal span or the

Flutter. The flutter characteristics of an airplaneare evident at high speed when the combined structural and aerodynamicinteraction can produce a destabilizing or divergent condition. Under such cir-cumstances, an airplane with winglets is sensitive to the weight and center of gravity (CG) of the winglets and asso-ciated structural wing changes. Additionalweight near the wingtip, either higherthan or aft of the wing structural neutralaxis, will adversely affect flutter.

DESIGN AND TESTING

To design a satisfactory product thatintegrated performance and structuralrequirements, the design team gatheredtechnical data on aerodynamics, loads,and flutter through wind tunnel andflight tests.

The loads on a 737-600/-700/-800/-900 airplane with winglets wereanalyzed through wind tunnel testingusing a standard model constructed in the 1.0-g cruise shape and a uniquemodel. The unique wing model,complete with a full set of pressureports, was built in the deflected shape for the 2.5-g design maneuver

winglet-induced load increase and itsdistribution along the wing can signifi-cantly affect the cost of modifying thewing structure. From the perspective ofloads and dynamics, the three areas thataffect structural change are static loads,dynamic flight loads, and flutter.

With winglet

Baseline

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0.00.0 0.2 0.4 0.6 0.8 1.0

Sect

iona

l lift

coe

ffici

ent x

loca

l win

g ch

ord

/ ref

eren

ce

737 BBJMach = 0.78, lift coefficient = 0.50

Span

SPANWISE LIFT DISTRIBUTION

FIGURE

3

With winglet

Baseline

Mas

kell’

s in

duce

d dr

ag x

loca

l win

g ch

ord

/ ref

eren

ce

737 BBJMach = 0.78, lift coefficient = 0.50, delta CDinduced = 0.00105

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0.0

– 0.10.0 0.2 0.4 0.6 0.8 1.0

Span

Calculated using Maskell’s induced drag integrand, which is proportional to the first moment of the slope of the spanwise change in the TE wake circulation

REDUCTION IN INDUCED DRAG

FIGURE

4

AERO

21AERO

20

Span

Heig

ht

Heig

ht

4.0

2.0

0.0

0.0 0.2 0.4 0.6 0.8 1.0 1.2– 2.0

Span

4.0

2.0

0.0

0.0 0.2 0.4 0.6 0.8 1.0 1.2– 2.0

737 BBJ wingletMach = 0.78, lift coefficient = 0.50, alpha = 2.43°

737 BBJ baseline Mach = 0.78, lift coefficient = 0.50, alpha = 2.55°

Streamwise vorticity x spanfree-stream velocity

15.0

7.5

0

-7.5

-15.0

VORTICITY CONTOURS BEHIND WING TE WITH AND WITHOUT WINGLETS

FIGURE

2

WIND TUNNEL TEST

FIGURE

5

Image of wind tunnel model constructedin the shape of the 2.5-g deflected wingsuperimposed over an image of the wing in the nominal 1.0-g cruise shape

3

reaches its highest loads in the cleanwing configuration (i.e., with speedbrakes retracted).

The outboard tip of the wing generallyis designed for roll maneuvers. However,when winglets are added, the high loadson the winglets during sideslip maneu-vers cause the wingtip area to be morehighly loaded. Therefore, sideslip ma-neuvers became the design case for thewingtip and winglet.

Dynamic flight loads.Dynamic flight loads also contribute to the maximum load envelope of theoutboard wing. The response of the airframe to gusts or turbulence createsdynamic flight loads on the wing andwinglet. During turbulence, the airframeresponds at different frequencies de-pending on its aerodynamics, inertia,and stiffness. Modifications to theseparameters change how the airframeresponds to turbulence, which in turnchanges the loads. In addition to thewinglet-induced increase in air load,the weight of the winglet itself and itsextreme outboard location also increasethe loads for the outboard wing. Theheavier the winglets are, the higher thedynamic loads.

maneuver. Although these maneuvers all contribute to the wingbox design,most of the wingbox is designed for 2.5-g maneuvers. The highest loads onthe mid- to outboard part of the wingoccur when speed brakes are extended.The inboard portion of the wing

Static loads. Static loads are determined by Boeing and U.S. Federal AviationAdministration (FAA) design require-ments, such as a symmetric 2.5-gmaneuver, a roll maneuver, or an abruptrudder input that results in a sideslip

condition (fig. 5). The test data from this configuration were used to determinethe change in air load distribution on thewing in the deflected shape. This infor-mation was used to refine the analysisand helped minimize the adverse effectsof the higher loads that resulted from the winglets.

Flight tests were conducted todetermine the cruise drag reduction of the winglets and provide data on loads,handling qualities, and aerodynamic performance. Strain gages and rows ofpressure taps placed on the winglet andoutboard wing were used to indicate thechanges in bending moment on the out-board wing resulting from the winglet.Data from these flight tests were used to adjust and validate the aerodynamicdatabase derived from the wind tunneltests. Table 1 summarizes the aero-dynamic flight test results.

Gross fuel mileage improvement with winglets was recorded in the rangeof 4 to 5 percent. Taking into account the weight of the winglet and the relatedwing structural modifications, the netperformance improvement was approxi-mately 4 percent for long-range flights(fig. 6). Low-speed testing showed a significant reduction in takeoff and

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23

6

5

4

3

2

1

0

Per

cent

age

impr

ovem

ent i

n bl

ock

fuel

Range, nmi

0 1,000 2,000 3,000 4,000 5,000 6,000

Average of eastbound and westbound block fuel improvement

Weights include winglets 737-800 BBJCruise LRC LRCOEW 91,660 lb 94,350 lbPassengers 162 12Mission rules Typical mission NBAA 5% contingency None 200-nmi alternate 200-nmi alternate 30-min hold at 1.5 k 30-min hold at 5 k

737-800

BBJ

BLOCK FUEL IMPROVEMENTS RESULTING FROM WINGLETS

FIGURE

6

737-800/CFM56-7B24 engines Without winglet With winglet

14

12

10

8

6

4

290 100 110 120 130 140 150 160 170 180

Takeoff gross weight, lb (000s)

Take

off f

ield

leng

th, f

t (00

0s)

Air conditioning offZero slopeZero wind30°CCategory C brakesDry runway

Takeoff at 5,000-ft altitude

Takeoff at sea level

EFFECT OF WINGLETS ON TAKEOFF FIELD LENGTH

FIGURE

7

PROTOTYPE WINGLET AERODYNAMICFLIGHT TEST RESULTS

TABLE

1

Performance■ Four to five percent cruise drag reduction

■ No change to initial buffet boundary

■ No change to stall speeds

■ No pilot-perceived buffet before stick shaker

■ Flaps-down lift increase

■ Significant drag reduction for takeoff flaps

Handling qualities■ Improved Mach tuck

■ Improved directional stability

■ Improved longitudinal and lateral trim stability

■ Increased pitch stability

■ No degradation of stall characteristics and stall identification

■ Unchanged rudder crossover speed

■ Unchanged Dutch roll damping

■ Unchanged manual reversion roll characteristics

PROCESS FOR WINGLET AND WING MODIFICATION DESIGN

FIGURE

8landing drag and a significantbenefit in payload capability for certain operations (fig. 7).

Using the informationgleaned from the wind tunneland flight tests, a winglet configuration was developedthat balanced the benefits of aerodynamic performanceagainst the weight and cost of modifying the airplane. The optimal configurationreduced loads and minimizedweight and structural modifi-cations without sacrificing significant winglet perfor-mance. It was achieved by an iterative process during which tradeoffs among criticaldesign functions were con-tinually reviewed by expertsin aerodynamics, loads, flutter,design, and stress (fig. 8).

Five major issues wereaddressed in the develop-ment of the optimal wingletconfiguration.

Toe angle. The initial winglet configuration with a 0-deg toe angle was designed to mini-mize induced drag but resulted in highwing loads. Therefore, the winglet wastoed out 2 deg to reduce wing-bendingloads. The 2-deg toe angle, while reducing the loads, did not compromisethe cruise drag. Figure 9 shows a break-down of the total drag of the wingletinstallation as a function of toe-out angle at the cruise condition. Theincrease in induced drag from unloadingthe winglet was offset by the reductionin trim, profile, and wave drag. A performance flight test showed the dragwas equivalent for a 0-deg toe angle and a 2-deg toe-out angle.

The toe-out angle change did slightlyreduce the winglet-induced lift when theflaps were down. Induced drag is muchgreater during flaps-down operation thanat cruise because of the higher lift of thewing. However, this loss in improvedperformance during flaps-down opera-tion was considered an acceptable trade-off for reduced structural modifications.

Speed-brake angle. The mid- to outboard portion of thewing was designed for speed-brakes-upmaneuver loads of 2.5 g. Loads in thisarea can be lowered by reducing the in-flight speed-brake angle. The reductionin the acceptable speed-brake angledepended on airplane utilization by the

operators: The angle was reduced by 50 percent for the BBJ; the 737-800commercial airplane required full useof the speed brakes to the in-flightdetent position for emergency descentcertification requirements. For 737-800retrofits, a load alleviation system wasdeveloped to reduce the speed-brake

angle automatically at heavy weights and high speeds for critical design loadconditions. For airplanes in production,a strengthened wing allows for fullspeed-brake capability to be retained.Figure 10, which shows the net loadreduction from changing the toe angleand reducing the speed-brake angle,depicts how structural changes to thewing were minimized.

Structural changes. After completing the studies of the toeangle and speed-brake angle, structuralmaterial for the mid- to outboard wing-box was still required. (Because theinboard wing had sufficient strengthmargins, structural changes to that area were minimal or unnecessary.) To minimize the adverse effects of thewing structural modifications on flut-ter, wing torsional stiffness was maxi-mized in relation to bending stiffness.

Weight and CG control. To address the effects of both flutterand dynamic load, the weight and CGcontrol of the winglet were considered

Winglet installation■ Includes navigation and anticollision lights Wing modifications

■ New outboard panels and spar fittings

Avionics revision■ FMC performance update

Strengthened wing

AIRPLANE-LEVEL CONFIGURATION CHANGES — PRODUCTION 737-800

FIGURE

11b

APB winglet installation■ Includes navigation and anticollision lights

Wing interface with winglet■ New rib 25 and closure rib 27 (wingbox only)■ New spar fittings to interface with winglet■ Replace upper and lower surface panels with new, thicker honeycomb panels

In-flight speed-brake detent adjustment■ Reduce detent 50 percent to limit in-flight speed-brake deployment

Modified avionics■ Update FMC for new aerodynamics

AIRPLANE-LEVEL CONFIGURATION CHANGES — BBJ

FIGURE

11a

AERO

25AERO

24

2.5

2.0

1.5

1.0

0.5

0.0

– 0.5

– 1.0

– 1.5

– 2.0

Toe-out angle (deg)

Total drag

Trim drag

Wave drag

Induced drag

Profile drag

Drag

cou

nts

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5

TOTAL DRAG OF THE WINGLET INSTALLATION AS A FUNCTION OF TOE-OUT ANGLE AT THE CRUISE CONDITION

FIGURE

9

2.5-g clean wing2.5-g speed brakes up

Roll, gust, sideslip

Percentage of wing semispan

2-deg toe out

Base winglet with full speed brakes

50% speed brakes

Perc

enta

ge c

hang

e in

win

g-be

ndin

g m

omen

t

Wing root Wingtip

Design conditions typically vary throughout the wingspan. ■ Inboard wing: symmetric 2.5-g maneuver ■ Midwing: 2.5-g speed brakes deployed ■ Outboard wing: roll, gust, or sideslip maneuver

10

20

2.5-g clean wing 2.5-g speed brakes up Roll, gust, sideslip

WINGSPAN DESIGN CONDITIONS

FIGURE

10

Retrofit of the 737-800 commercial airplane includes aload alleviation system to obtain full use of the speed brakesto the in-flight detent position during typical airline opera-tions. The system, which is installed in the flight deck aislestand, arms at heavy weights and high speeds at extreme portions of the flight envelope. When armed, the system

■ Installation of the new center section of rib 27 and thenew winglet attach fitting (fig. 12c).

■ Installation of the spar attach fittings (fig. 12d).

■ Installation of the aft-position light.

■ Installation of the winglet (fig. 12e).

RETROFIT AND MAINTENANCE

The wing modification was designedwith retrofit in mind. Once the wing has been modified for winglets, thewinglet itself can be replaced withinthree hours. The more time-consumingpart of the retrofit is installation of thewing modification to accommodate thewinglet. For example, a BBJ retrofit,accomplished according to an FAA supplemental-type certificate, involvesthe following tasks. (This listing doesnot constitute a complete work instruc-tion package.)

■ Removal and replacement of the outboard upper and lower skin panels(fig. 12a).

■ Removal and replacement of rib 25,which is third from the outermost rib(fig. 12b).

■ Installation of stiffeners across rib 25.

■ Cutting of the closure rib (rib 27) andtrimming of the two spars (fig. 12b).

4

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27AERO

26

Winglet installation■ Includes navigation and anticollision lights

Wing modifications■ New outboard panels and fittings■ Strengthened stringers■ Revised fasteners

Avionics revision■ FMC performance update

In-flight speed-brake load limiter■ Does not affect normal operations

AIRPLANE-LEVEL CONFIGURATION CHANGES — RETROFIT 737-800

FIGURE

11c REMOVAL OF OUTBOARD UPPERAND LOWER SKIN PANELS

FIGURE

12a

REMOVAL AND REPLACEMENT OF RIB 25AND THE CENTER SECTION OF RIB 27

FIGURE

12b

INSTALLATION OF THE NEW CENTER SECTION OF RIB 27 AND THE NEW WINGLET ATTACH FITTING

FIGURE

12c

INSTALLATION OF THE SPAR ATTACH FITTINGSAND FINAL ASSEMBLY OF WING MODIFICATION

FIGURE

12d

INSTALLATION OF WINGLET

FIGURE

12e

carefully, including the location of thewinglet lights and specifications for the painting and possible repair of thewinglet. To meet flutter requirementswith minimal structural changes, addi-tional wingtip ballast was mounted onthe front spar to counteract the incre-mental weight of the winglet located afton the wing. The use of wingtip ballastdepended on the structural configurationof the wing. In some cases, ballast wassimpler and more cost effective thanstructural modification of the wingbox.No wingtip ballast is required for theBBJ configuration; 75 lb of ballast perwing is required for each productionwinglet on the 737-800 commercial air-plane; 90 lb of ballast is required perwing for 737-800 retrofit.

Damage tolerance and fatigue.The winglet and the wing modificationswere designed to meet Boeing and FAA criteria for damage tolerance andfatigue. Any unchanged structure affect-ed by the increased loads was analyzedto ensure that all requirements were met.

Analysis indicated that no additionalrework was required for the BBJ.Because of the higher cycles of air-plane utilization and takeoff weights of the 737-800 commercial airplane,some wing panel fastener holes requirerework for fatigue considerations onretrofitted airplanes. The inspectionintervals for the wing modificationand winglet structure are the same asthose for all 737-600/-700/-800/-900airplanes.

The overall scope of the wing modification for the BBJ involves 10 percent of the outboard wing. Thissmall percentage results from the 2-degchange in winglet toe angle and the 50 percent reduction in the in-flightspeed-brake angle. For the 737-800retrofit, the modification involves 35 percent of the outboard wing. Theproduction airplane with full speed-brake capability involved wing panelchanges that affect 60 percent of thespan. Figure 11 shows airplane-levelconfiguration changes.

actuates the in-flight speed-brake handles and retracts them to 50 percent.

For airplanes in production, thewings are strengthened throughout thewingbox to accommodate the wingletloads with full use of the speed brakesto the in-flight detent position. The in-production modification meets the samedesign criteria as those for the retrofit.However, during production, structuralstrengthening is accomplished byincreasing the gage of spars, stringers,ribs, and panels. Rib 27 incorporatesbolt hole patterns that allow attachmentof either a winglet or a standard wingtip.The winglet is installed in final assembly.

Navigation and strobe lights aremounted on the leading edge (LE) ofthe winglet in a way similar to that of the basic wingtip for production.Replacement of the winglet forward-position light, strobe light, and lensrequires removal of the LE assemblyfrom the winglet. The winglet aft-position lights are easily accessible for maintenance.

Except for replacement of the wingletforward-position lights and strobe lights,the winglets minimally affect in-servicemaintenance of the airplane, and thedesign allows for a wide range of structural repairs.Primary materialsare graphite spars,honeycomb gra-phite panels, andaluminum LE and interface joints (fig. 13). Designedto meet Boeing andFAA criteria forfatigue and damagetolerance, the wing-let structure andsystems fit withincurrent airplanemaintenance inter-vals and life cycles,with the exceptionof the 737-800 lens, which has atemporary certifi-cation maintenancerequirement.

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SUMMARYBlended winglets offer operational and economic benefits to BBJ and 737-800 customers. Mission blockfuel is improved approximately 4 percent. Range capability isincreased by as much as 200 nmi on the BBJ and 130 nmi on the 737-800 commercial airplane. Thereduction in takeoff flap drag duringthe second segment of climb allowsincreased payload capability at takeoff-limited airports.

Environmental benefits include a 6.5 percent reduction in noise levelsaround airports on takeoff and a 4 percent reduction in nitrogen dioxideemissions on a 2,000-nmi flight.

The blended winglets now are available as standard equipment on BBJs, as optional equipment on 737-800 commercial airplanes, and by retrofit for BBJs, 737-800, and 737-700 commercial airplanesalready in service. Because thewinglet structure and systems followestablished maintenance intervalsand life cycles, winglets have a mini-mal effect on airplane maintenance.

Graphite sparsAluminum tip

Aluminuminterchangeableinterface joint

FWD

INBD

Aluminum ribsTitanium splice plates

Position andstrobe lights

Aluminum LE skins

Aluminum TE arrowhead

Aft position light

■ Blind fasteners upper skin attach■ Huck bolts lower skin attach■ No bonding

Graphite with honeycomb upper and lower skins

BLENDED WINGLET STRUCTURE

FIGURE

13

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Editor’s note: The 737 BBJ blended winglets are patented by Dr. L. B. Gratzer of Aviation Partners, Inc. (API), Seattle, Washington. Boeing and API formed a joint venture, Aviation Partners Boeing, during the development of the 737 BBJ blended winglet design. This article was provided solely by Boeing.

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30AERO

31AERO

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Wingtip devices on derivative airplanes can improve performance byreducing induced drag. Selection of thewingtip device depends on the specificsituation and the airplane model.

747-400. The 747-400 commercial airplane needed a significant span increase tomeet the range requirement. However,structural constraints prevented the totalspan increase, so a combination ofwinglet and span increase was used.

767-400. Following a business-case study of the benefits of adding winglets orincreasing wingspan, the 767-400 program chose a span increase in theform of a raked tip.

BBJ and 737-800.The wingtip device for the BBJ and737-800 commercial airplane involved a retrofit of existing wings. The blendedwinglet was selected because it required minimal changes to the wingstructure and provided improved aesthetic appeal for the BBJ.

MD-11.The MD-11 program chose a wingletbased on wingspan constraints and minimum structural weight.

KC-135.The U.S. Air Force and the NationalAeronautics and Space Administrationconducted a winglet development program in 1978 to understand howwinglets could improve performance.

767-400

MD-11

Percentage increase in horizontal and vertical span

Perc

enta

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f dra

g re

duct

ion

at a

vera

ge c

ruis

e

6

5

4

3

2

1

00 2 4 6 8 10 12 14 16 18

KC-135 winglet

MD-11 extended winglet

747-400 tip plus winglet

737-800 blended winglet

767-400 raked tip

Drag Reduction of Wingtip Device

747-400

WINGTIP DEVICES

KC-135

BBJ and 737-800