BLENDED WINGLETS FORFOR IMPROVEDIMPROVED AIRPLANEAIRPLANE PERFORMANCEPERFORMANCE New blended winglets on the Boeing Business Jet and the 737-800 commercial airplane offer operational benefits to customers. Besides giving the airplanes a distinctive appear- ance, the winglets create more efficient flight characteristics in cruise and during takeoff and climbout, which translate into additional range with the same fuel and payload. ROBERT FAYE ROBERT LAPRETE MICHAEL WINTER TECHNICAL DIRECTOR ASSOCIATE TECHNICAL FELLOW PRINCIPAL ENGINEER BOEING BUSINESS JETS AERODYNAMICS TECHNOLOGY STATIC AEROELASTIC LOADS BOEING COMMERCIAL AIRPLANES BOEING COMMERCIAL AIRPLANES BOEING COMMERCIAL AIRPLANES TECHNOLOGY/PRODUCT DEVELOPMENT AERO 16 vertical height of the lifting system (i.e., increasing the length of the TE that sheds the vortices). The winglets increase the spread of the vortices along the TE, creating more lift at the wingtips (figs. 2 and 3). The result is a reduction in induced drag (fig. 4). The maximum benefit of the induced drag reduction depends on the spanwise lift distribution on the wing. Theoretically, for a planar wing, induced drag is opti- mized with an elliptical lift distribution that minimizes the change in vorticity along the span. For the same amount of structural material, nonplanar wingtip 737-800 TECHNICAL CHARACTERISTICS devices can achieve a similar induced drag benefit as a planar span increase; however, new Boeing airplane designs Passengers focus on minimizing induced drag with 3-class configuration Not applicable The 737-800 commercial airplane wingspan influenced by additional 2-class configuration 162 is one of four 737s introduced BBJ TECHNICAL CHARACTERISTICS The Boeing Business Jet design benefits. 1-class configuration 189 in the late 1990s for short- to (BBJ) was launched in 1996 On derivative airplanes, performance Cargo 1,555 ft3 (44 m3) medium-range commercial air- Passengers Not applicable as a joint venture between can be improved by using wingtip Boeing and General Electric. line operations. Demonstrating Boeing offers blended Cargo Not applicable Engines CFM56-7 devices to reduce induced drag (see Designed for corporate and Maximum thrust 27,300 lb (12,394 kg) exceptional flexibility in size winglets — upward-swept Engines CFM56-7 “Wingtip Devices” on p. 30). Selection individual use, the BBJ is a and mission, the four models — Maximum thrust 27,300 lb (12,394 kg) Maximum fuel capacity 6,875 U.S. gal (26,035 L) of the wingtip device depends on the extensions to airplane wings — high-performance derivative 737-600/-700/-800/-900 — Maximum takeoff weight 174,200 lb (79,015 kg) specific situation and the airplane model. as standard equipment on its Maximum fuel capacity of the 737-700 commercial essentially are four sizes of the BBJ 10,695 U.S. gal (40,480 L) An important consideration when airplane. The BBJ marries the Maximum range 3,383 statute mi (5,449 km) Boeing Business Jet (BBJ) and BBJ 2 10,443 U.S. gal (39,525 L) same airplane. Two convertible designing the wingtip device for the 737-700 fuselage with the Cruise speed at 35,000 ft 0.785 Mach (530 mi/h) models are available for conver- as optional equipment on its Maximum takeoff weight BBJ was that it could be retrofitted stronger wing and gear of the sion to an all-freighter configu- on BBJs already in service. A blended 737-800 commercial airplane. BBJ 171,000 lb (77,565 kg) Basic dimensions BBJ 2 174,200 lb (79,015 kg) 737-800 commercial airplane. Wingspan (with winglets) 117 ft 5 in (35.79 m) ration. All the new 737s can fly winglet configuration (patented and de- A second version of the BBJ, Winglets also are available for Maximum range Overall length 129 ft 6 in (39.48 m) high-frequency, high-utilization signed by Dr. L. B. Gratzer of Aviation retrofit on in-service airplanes. BBJ 6,200 nmi (11,480 km) called BBJ 2, was launched in Tail height 41 ft 2 in (12.55 m) flights as well as transcontinental Partners, Inc., Seattle, Washington) BBJ 2 5,750 nmi (10,650 km) 1999. Based on the 737-800 Interior cabin width 11 ft 7 in (3.53 m) and extended-range twin-engine was selected because it required fewer The 8-ft, carbon graphite commercial airplane, the BBJ 2 Cruise speed at 35,000 ft 0.785 Mach (530 mi/h) operation missions. changes to the wing structure. The winglets allow an airplane has 25 percent more cabin aerodynamic advantage of a blended Basic dimensions space and twice the cargo space to extend its range, carry as Wingspan (with winglets) 117 ft 5 in (35.79 m) winglet is in the transition from the of the BBJ. Both provide the much as 6,000 lb more Overall length 1 INDUCED DRAG Induced drag existing wingtip to the vertical winglet. BBJ 110 ft 4 in (33.63 m) highest levels of space, com- component The blended winglet allows for the FIGURE payload from takeoff-limited BBJ 2 129 ft 6 in (39.48 m) fort, and utility. BBJ customers chord distribution to change smoothly airports, and save on fuel. Tail height 41 ft 2 in (12.55 m) are individuals, corporations, from the wingtip to the winglet, which Understanding the benefits Interior cabin width 11 ft 7 in (3.53 m) governments, armed forces, optimizes the distribution of the span and heads of state. of blended winglets requires load lift and minimizes any aerodynam- Lift ic interference or airflow separation. knowledge of the following: the lift of the wing, the total lift vector component AERODYNAMICS OF WINGLETS STRUCTURAL DESIGN 1. Aerodynamics of winglets. 1 tilts back. The aft component of this Lift 2 lift vector is the induced drag (fig. 1). force CONSIDERATIONS vector 2. Structural design From an engineering point of view — The magnitude of the induced drag is Induced The aerodynamic benefits of a winglet considerations. and ultimately that of mission capability determined by the spanwise distribution angle application are determined in part by and operating economics — the main of vortices shed downstream of the the extent of the wing modifications 3. Design and testing. purpose and direct benefit of winglets wing trailing edge (TE), which is made to accommodate the winglet. This are reduced airplane drag. related in turn to the spanwise lift dis- especially is the case when an airplane 4. Retrofit and maintenance. Winglets affect the part of drag called tribution. Induced drag can be reduced Direction of flight model has been designed and certified induced drag. As air is deflected by by increasing the horizontal span or the without winglets. The magnitude of the AERO AERO 18 19 reaches its highest loads in the clean Flutter. condition (fig. 5). The test data from 2 VORTICITY CONTOURS BEHIND WING TE WITH AND WITHOUT WINGLETS wing configuration (i.e., with speed The flutter characteristics of an airplane this configuration were used to determine 15.0 FIGURE brakes retracted). are evident at high speed when the the change in air load distribution on the 7.5 wing in the deflected shape. This infor- Streamwise vorticity x span The outboard tip of the wing generally combined structural and aerodynamic free-stream velocity 0 is designed for roll maneuvers. However, interaction can produce a destabilizing mation was used to refine the analysis when winglets are added, the high loads or divergent condition. Under such cir- and helped minimize the adverse effects 737 BBJ winglet 737 BBJ baseline -7.5 cumstances, an airplane with winglets of the higher loads that resulted from Mach = 0.78, lift coefficient = 0.50, alpha = 2.43° Mach = 0.78, lift coefficient = 0.50, alpha = 2.55° on the winglets during sideslip maneu- -15.0 vers cause the wingtip area to be more is sensitive to the weight and center the winglets. 4.0 4.0 highly loaded. Therefore, sideslip ma- of gravity (CG) of the winglets and asso- Flight tests were conducted to neuvers became the design case for the ciated structural wing changes. Additional determine the cruise drag reduction of wingtip and winglet. weight near the wingtip, either higher the winglets and provide data on loads, 2.0 2.0 than or aft of the wing structural neutral handling qualities, and aerodynamic Dynamic flight loads. axis, will adversely affect flutter. performance. Strain gages and rows of Height Height Dynamic flight loads also contribute pressure taps placed on the winglet and 0.0 0.0 to the maximum load envelope of the 3 DESIGN AND TESTING outboard wing were used to indicate the outboard wing. The response of the changes in bending moment on the out- – 2.0 – 2.0 airframe to gusts or turbulence creates To design a satisfactory product that board wing resulting from the winglet. 0.0 0.2 0.4 0.6 0.8 1.0 1.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 dynamic flight loads on the wing and integrated performance and structural Data from these flight tests were used Span Span winglet. During turbulence, the airframe requirements, the design team gathered to adjust and validate the aerodynamic responds at different frequencies de- technical data on aerodynamics, loads, database derived from the wind tunnel pending on its aerodynamics, inertia, and flutter through wind tunnel and tests. Table 1 summarizes the aero- and stiffness. Modifications to these flight tests. dynamic flight test results. 3 SPANWISE LIFT DISTRIBUTION 4 REDUCTION IN INDUCED DRAG parameters change how the airframe The loads on a 737-600/-700/-800/ Gross fuel mileage improvement FIGURE FIGURE responds to turbulence, which in turn -900 airplane with winglets were with winglets was recorded in the range changes the loads.