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Pushing down fuel burn

Wingtip devices are the latest piece of innovation in aircraft design. Keith Mwanalushi examines how far this technology goes to meeting airline expectations for reduced fuel burn and improved performance

Winglets are aerodynamic surfaces mounted almost vertically at the wingtips. Their design is inspired from birds, which curl their wingtip feathers upward when in need of high lift. A well-designed winglet rises vertically and is swept back so that it significantly reduces the size of the wingtip vortex, thus reducing induced drag and increasing fuel efficiency.


Over the last few decades, rising fuel prices have often been followed by an increase in both fuel-saving initiatives and gadgets targeted at those who want to save at the pump – and airlines are no exception.


In February this year a United Airlines Boeing 737-800 freshly retrofitted with new Split Scimitar Winglets took to the skies, marking the first commercial flight worldwide to operate with the advanced winglet technology. The savings from the Split Scimitar Winglets is part of an initiative by United to reduce its fuel bill by $1 billion by 2017.


A number of years ago, Boeing’s attention was drawn to the fuel efficiency and the enhanced range of the Gulfstream II aircraft. This interest led to a joint venture with Aviation Partners to develop blended winglets for Boeing aircraft. Boeing assisted what is now Aviation Partners Boeing (APB) to pioneer the technology that is now available as an option on the 737NGs and as a retrofit option on the older 737, 757 and 767 models.


APB also received Supplemental Type Certification (STC) from the FAA for Split Scimitar Winglets to be installed on 737-800 aircraft in early February this year.


According to APB, the new Split Scimitar Winglet programme is the culmination of a five-year design effort. The process used the latest computational fluid dynamic technology to redefine the aerodynamics of the currently widely fitted Blended Winglet into an all-new Split Scimitar shape.


“The unique feature of the Split Scimitar Winglet is that it uses the existing Blended Winglet structure, but adds new strengthened spars, aerodynamic scimitar tips, and a large ventral strake,” says Mike Stowell, APB executive vice president and chief technical officer. “The APB team’s unique expertise combined with support from the FAA allowed STC issuance to come just weeks after the completion of the flight tests,” he recalls.


APB will develop and certify the Split Scimitar Winglet modification for all Boeing 737-700, 800 and 900 series aircraft, including Boeing Business Jets. APB started certification flight testing on the 737-900ER in mid-February and expects to achieve certification by late July 2014.


Ron Baur, United’s vice president of fleet, says this new winglet design demonstrated significant aircraft drag reduction over the basic Blended Winglet configuration United uses on its current fleet. The new design also reduces fuel consumption by up to 2% per aircraft. “We appreciate APB’s commitment to developing fuel-saving technology and look forward to realising savings that come from the improved fuel efficiency,” Baur affirms.


Unsurprisingly, Southwest Airlines is also an early adopter of the technology. In April 2014 the low-cost airline operated its first revenue flight using a 737-800 equipped with the Split Scimitar Winglets.


Kent Horton, Southwest’s director of engineering, explains his expectations to Low Cost & Regional Airline Business: “We expect annual fuel savings to increase from approximately 3.5% per aircraft from Blended Winglets to approximately 5 to 5.5% annually per aircraft with the Split Scimitar Winglets. In addition, the new winglet will reduce emissions.” >>

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