The Evolution of Winglets

Why Winglets Work

At the wingtip, high-pressure air below the wing spills upward around the tip toward the lower-pressure region above, creating a strong rotating wingtip vortex. This vortex has two negative consequences: it represents energy wasted from the engine's output (induced drag), and it creates hazardous wake turbulence for following aircraft. Induced drag can account for 30–40 percent of total drag in cruise on a conventional unswept low-wing aircraft like a regional jet.

The theoretical solution — extending the wingspan — reduces induced drag because a longer span spreads lift more evenly, producing weaker tip vortices. But wingspan is limited by airport gate dimensions (the ICAO Code Letter system limits wingspan based on aircraft size) and structural weight increases with span cubed. A winglet achieves much of the span extension benefit with a fraction of the structural weight penalty by turning the extension vertical: it effectively increases the aerodynamic span while minimizing the bending moment increase at the wing root.

Types of Winglets

Winglet design has evolved through several generations:

• Winglet (classic): The original Boeing 747-400 blended winglet — an upward-canted surface with a smooth curve at the root to minimize interference drag. Also used on the original Boeing 737 Classic optionally and the BBJ (737 business jet). Reduces induced drag by 3–5 percent.
• Blended winglet (split canted): The familiar design on the Boeing 737 NG and most modern regional jets. A smooth curve blends the tip into a canted winglet at approximately 65–70° from vertical. Developed by Aviation Partners and licensed widely.
• Sharklet (Airbus): Airbus's term for the large, curved split-winglet design on the A320neo family and A350. Named for their shark fin appearance. The A320neo sharklets extend 2.4 meters above the wingtip and deliver 3.5–4 percent fuel savings over the plain-tip A320.
• Split-tip winglet / Raked wingtip: Boeing's preferred design for the 787 and 777X. Instead of a vertical surface, the tip curves and fans into a raked, swept extension. Boeing argues the raked tip provides similar efficiency benefits with less structural complexity than a wingtip fence.
• Split Scimitar winglet: An evolution of the blended winglet for retrofit, adding a downward-canted strake below the existing winglet. Developed by Aviation Partners Boeing, providing an additional 1.5–2 percent fuel burn improvement on 737 NGs already fitted with blended winglets.
• Folding wingtip (Boeing 777X): The 777X's 105-foot wingspan exceeds ICAO Code E (80 m) limits for common airport gates. Boeing's solution: the outer 3.5 meters of each wing folds upward hydraulically on the ground, reducing ground footprint to 64.8 m. This is the first folding-wing commercial jet since the F4U Corsair's carrier-landing design.

Fuel Savings

Fuel savings from winglets depend on aircraft type, route profile, and existing wingtip design:

• Boeing 747-400 classic winglets: 3.5 percent reduction.
• Boeing 737 NG blended winglets: 3–5 percent, saving approximately 800 kg of fuel per flight on medium-haul routes.
• Airbus A320neo sharklets: 3.5 percent over plain-tip, 5 percent over wing alone (combined with other aerodynamic improvements).
• Boeing 787 raked wingtips: estimated 2 percent contribution within the aircraft's overall 20 percent improvement package.

On a single-aisle jet flying 4 hours per day for 20 years, a 3 percent fuel saving translates to roughly 1,200 tonnes of fuel saved per aircraft — an enormous financial and environmental benefit that explains why airlines invested heavily in winglet retrofits on existing fleets.

Retrofit vs. OEM

Winglets can be certified either as original equipment from the manufacturer (OEM) or as Supplemental Type Certificates (STCs) for retrofit to existing aircraft. Aviation Partners' blended winglet STC for the 737 Classic and NG was one of the most commercially successful retrofits in aviation history, with thousands of aircraft modified. The retrofit market allowed airlines to improve efficiency without full fleet replacement.

OEM winglets (like the 747-8's raked tips) are designed integrally with the wing structure and aerodynamics. Retrofit winglets must work with an existing wing structure, sometimes requiring reinforcement of the wing-to-fuselage attachment or wingtip structure. The economic case for retrofit winglets typically shows payback in 2–5 years depending on fuel price and utilization.