The split winglets on the Boeing 737 MAX are among the aircraft’s most recognisable external features, but their purpose is not cosmetic. Boeing calls them Advanced Technology, or AT, winglets and states that they can reduce fuel use and carbon-dioxide emissions by up to 2% compared with the same aircraft without their benefit.[1][2] That improvement comes from manipulating the three-dimensional flow around the wingtip so the aircraft produces the required lift with less induced drag. The distinctive upper and lower elements are a way of increasing the wing’s effective aerodynamic span without simply extending a very long horizontal tip that would create additional structural and airport-clearance problems.
The short answer
A winglet works because the end of a lifting wing is a region where high-pressure air from beneath the wing curls around toward the lower-pressure upper surface. That spanwise flow rolls into a wingtip vortex and changes the direction of the local lift force, creating induced drag. The 737 MAX AT winglet reshapes that tip flow, producing useful aerodynamic force on both an upward and downward element while reducing the energy lost into the vortex system.[1]
Why a wing produces induced drag
An ideal infinitely long wing would not have tips, but real aircraft wings do. Pressure beneath the wing is generally higher than pressure above it when lift is being produced. Near the tip, air moves around the end and rolls into a rotating wake. The resulting downwash tilts the wing’s lift vector slightly rearward, and that rearward component is induced drag.
Induced drag is greatest when lift demand is high
Induced drag is especially important at lower speeds and higher lift coefficients, such as climb. At fast cruise, parasitic drag from skin friction, pressure and interference becomes relatively more important, but wingtip design still contributes to total aircraft efficiency over the mission.
Why simply extending the wing helps
For a given wing area and lift, increasing span generally increases aspect ratio and reduces induced drag. This is why gliders use long, slender wings. A transport aircraft, however, cannot increase span without limit because longer wings create higher bending loads and can exceed airport gate and taxiway geometry.
The airport constraint
The 737 has to fit infrastructure designed around established single-aisle dimensions. A large increase in horizontal span could change the aircraft’s aerodrome reference category and reduce compatibility with existing gates. A winglet provides some of the aerodynamic benefit of extra span while keeping the physical horizontal extension smaller.
What the original 737 wingtip looked like
Early 737 generations used relatively simple wingtip geometry. Later 737 Next Generation aircraft became widely associated with blended winglets, which curve smoothly upward from the wing. Boeing states that winglet technology on the 737NG improved range, payload, takeoff and landing performance and fuel economy.[3]
Why the MAX winglet is different
The MAX uses two principal aerodynamic branches at the wingtip: an upper element and a lower element. Boeing’s own technical explanation says the design generates useful lift components while using natural-laminar-flow design features to reduce skin-friction drag on the winglet itself.[1]
The upper element
The upward winglet modifies the pressure field and vortex formation in much the same broad way as earlier vertical winglets. Its aerodynamic force includes a component that effectively reduces the rearward induced-drag force acting on the aircraft.
The lower element
The downward-swept element exploits airflow beneath the wingtip that would otherwise contribute to the vortex. Boeing’s design uses that flow to generate additional useful force. The two surfaces work as one aerodynamic system rather than two independent decorative fins.
Why the lower winglet does not strike the runway
The lower element is sized and angled around the aircraft’s landing-gear geometry and certified ground-clearance envelope. Wing flex, bank angle during ground contact, tyre compression and landing attitudes all have to be considered. It would be unacceptable to achieve cruise efficiency at the cost of ordinary runway clearance.
Natural laminar flow
Boeing specifically highlights natural-laminar-flow characteristics on the AT winglet.[1] Laminar flow is smoother and more orderly than turbulent boundary-layer flow and generally creates lower skin-friction drag. Maintaining laminar flow over a useful part of a real aircraft surface requires careful shape, surface finish and contamination control.
Laminar does not mean no turbulence anywhere
Boundary layers naturally transition from laminar to turbulent as they move over a surface. Bugs, dirt, manufacturing tolerances and pressure gradients can encourage earlier transition. The aerodynamic objective is to preserve favourable flow over as much of the intended surface as practical, not to make the entire winglet perfectly laminar under every condition.
Surface finish therefore matters
Boeing says detailed design, surface materials and coatings contribute to the winglet’s laminar-flow performance.[1] Maintenance quality matters because dents, erosion or poor repair geometry can change local airflow even if the structure remains strong enough.
Winglet forces enter the wing structure
Any aerodynamic surface generating useful force also creates structural load. The AT winglet applies bending and torsional loads at the outer wing. Engineers therefore reinforce and substantiate the tip structure so it can carry repeated gust, manoeuvre and landing loads throughout the aircraft’s approved life.
Why every efficiency feature has a weight penalty
Winglets themselves have mass, and the supporting wing structure may need additional strength. Their aerodynamic gain must exceed the fuel penalty caused by carrying that extra mass. This is one reason winglet geometry is heavily optimised rather than simply made as large as possible.
Wing bending
A wing bends upward under aerodynamic lift. A winglet at the tip moves with that structure and adds its own force vector. Certification analyses combine wing bending, torsion, gust response and winglet loads so the entire outer-wing structure remains within limit and ultimate-load requirements.
Flutter
Adding mass and aerodynamic area near the wingtip can affect aeroelastic behaviour. Engineers must demonstrate adequate flutter margin because the combination of aerodynamic forces and structural vibration can become unstable under certain conditions if poorly designed. Ground vibration testing, analysis and flight test are part of aircraft-level substantiation.
Why the winglet can improve climb
During climb the aircraft is producing relatively high lift, so induced drag is a meaningful part of total drag. Reducing it means more engine thrust can contribute to climb or less thrust is required for a given climb profile. This can improve fuel use and potentially noise-management flexibility.
Cruise benefit
At cruise, lower induced drag still reduces total drag, especially at heavier weights and higher lift coefficients early in a long sector. The percentage benefit varies with mission length and aircraft weight, which is why no single fuel-saving number applies identically to every flight.
Boeing’s 2% figure
Boeing states that the MAX AT winglets can reduce fuel use and CO₂ emissions by up to 2%.[2] The phrase “up to” matters. It is a manufacturer performance claim based on defined assumptions, not a promise that every flight saves exactly two percent compared with an otherwise identical operational mission.
Two percent is substantial in airline economics
A single flight saving a small fraction of fuel may not sound dramatic, but commercial aircraft can fly several sectors each day for decades. Repeated across thousands of flights, small aerodynamic improvements can represent very large fuel and cost reductions.
Why winglets also affect emissions
Burning less hydrocarbon fuel for the same mission reduces carbon dioxide emissions almost directly in proportion to fuel saved. Winglets do not make an aircraft emission-free; they reduce the energy required to perform the transport task.
Winglets and range
Lower drag can be traded in several ways. An airline might carry the same payload farther, carry more payload over the same distance, reduce fuel uplift, or preserve additional reserve margin. Aircraft performance engineering determines the actual operational benefit for a particular route.
Winglets and takeoff
Takeoff performance is influenced by lift-to-drag ratio as the aircraft accelerates and climbs. The winglet contributes to the complete aerodynamic configuration, but runway performance also depends on engines, flaps, weight, temperature, wind and obstacle clearance.
Why the MAX wing changed elsewhere too
The AT winglet is not the only aerodynamic change on the MAX. Boeing also redesigned the aft body and integrated the LEAP-1B nacelle with the wing to reduce drag.[2] The aircraft’s efficiency improvement therefore cannot be attributed solely to the wingtip.
The LEAP-1B interaction
The larger LEAP-1B engine changed local airflow, weight and structural loads. Boeing had to integrate engine, pylon and wing aerodynamics while preserving the winglet’s intended performance. Aircraft-level optimisation is always more complex than adding independent efficient components.
Why winglets are not identical across aircraft
Airbus uses different tip designs on the A320neo family; Boeing uses raked tips on some widebodies and folding tips on the 777X. The optimum solution depends on wing sweep, span, structural stiffness, airport restrictions, mission and manufacturing constraints.
Raked tips versus vertical winglets
A raked wingtip extends the wing largely outward and backward, increasing effective span efficiently, but requires more physical gate width. A vertical or split winglet can obtain some span-efficiency benefit in a smaller horizontal footprint. Neither concept is automatically superior in every application.
Why the 777 can use raked tips
Boeing’s 777 design highlights describe raked wingtips that extend span and improve aerodynamic efficiency.[4] A widebody already occupies a larger airport code category, so the infrastructure trade differs from the 737’s single-aisle mission.
Wingtip vortices still exist
A winglet cannot eliminate the physics of finite-wing lift. The aircraft still creates a wake and requires wake-turbulence separation. The winglet changes the strength and distribution of the vortex system; it does not make induced drag or wake turbulence disappear.
Why winglets cannot replace span entirely
A vertical device is not aerodynamically identical to adding the same amount of horizontal wing. The benefits come from a different force orientation and flow interaction. Designers choose the combination of span, sweep and tip geometry that gives the best aircraft-level result.
Manufacturing tolerances
The complex curved surfaces must be manufactured accurately because their aerodynamic performance depends on shape. Composite materials can be useful for producing efficient thin structures while controlling weight, although exact material construction should be taken from Boeing-approved structural documentation.
Lightning protection
Wing tips are exposed to lightning attachment. Composite or mixed-material structures therefore include conductive paths, bonding and protection so current can pass into the broader aircraft structure without unacceptable damage or ignition risk.
Navigation lights
The wingtip region also contains navigation and strobe lighting. Wiring and light installations must coexist with the aerodynamic surface without creating excessive drag or compromising structural and lightning-protection requirements.
Ground damage risk
Winglets can be vulnerable to contact with vehicles, hangars or other aircraft because they sit at the outermost part of the wing. Airports use stand-clearance rules and ground-handling procedures to protect wingtip areas during towing and parking.
Maintenance after a strike
A winglet impact requires inspection under Boeing structural documentation. Damage may involve skins, internal structure, fasteners or the wingtip attachment even if the visible mark appears minor. Composite structures can also sustain damage beneath the surface.
Why repairs must preserve aerodynamic shape
A structurally adequate repair that leaves an unacceptable step or contour could degrade laminar-flow performance. Repair limits therefore consider both strength and aerodynamic smoothness where relevant.
Painting and contamination
Paint thickness, erosion and surface cleanliness can influence boundary-layer behaviour. Operators maintain the surface primarily for corrosion, appearance and structural protection, but the winglet’s aerodynamic design also depends on maintaining appropriate contour quality.
Why the split shape attracts so much attention
Most aerodynamic optimisation is invisible to passengers. Small changes in airfoil contour, fuselage fairings or pressure distribution are hard to see. The MAX winglet turns the same physics into an obvious external shape, making it a useful visual example of how engineers trade drag, span, load and airport compatibility.
The engineering lesson
The AT winglet is not simply a vertical fence that “blocks” a vortex. It is a lifting aerodynamic surface designed to reshape the three-dimensional pressure field at the wing tip. Its upper and lower elements produce forces that reduce the rearward component associated with induced drag, while laminar-flow design tries to minimise the winglet’s own skin-friction penalty.
Conclusion
The Boeing 737 MAX winglet demonstrates why modern aircraft efficiency is often won in small percentages. Boeing did not simply extend the wing until induced drag fell; that would have increased bending load and airport span. Instead, the Advanced Technology winglet uses a split upper-and-lower geometry and carefully controlled airflow to increase effective aerodynamic span within the 737’s established operating footprint. Boeing attributes up to a 2% fuel and CO₂ benefit to the feature.[2] Across the lifetime of a high-utilisation airliner, that apparently small aerodynamic improvement can become a very large operational saving.
Sources / Technical References
- [1] Boeing, “737 MAX AT Winglet — The most efficient winglet on any airplane” — https://www.boeing.com/commercial/737max/737-max-winglets
- [2] Boeing, 737 MAX By Design — https://www.boeing.com/commercial/737max/by-design
- [3] Boeing, 737 Next Generation Design Highlights — https://www.boeing.com/commercial/737ng/737-next-generation-design-highlights
- [4] Boeing, 777 Design Highlights — https://www.boeing.com/commercial/777/design-highlights
- [5] Boeing, 737 MAX Airplane Characteristics for Airport Planning — https://www.boeing.com/commercial/airports/plan-manuals
- [6] FAA, transport-category airplane certification and aeroelastic guidance — https://www.faa.gov/regulations_policies/advisory_circulars
Disclaimer: Cockpit King provides general aviation education and reference information. Aerodynamic performance, structural limits, inspection criteria and aircraft operating data must always be verified against current approved Boeing, operator and regulatory documentation. This article is not engineering or maintenance instruction.