Winglets, 737MAX and the MD-12

737MAX and the MD-12
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First unveiled publically in May 2012, the advanced 737 MAX winglet, which Boeing first described as a 'dual feather," was designed to provide up to an additional 1.5% fuel burn improvement on long flights with the promise of even more if a proposed laminar flow surface treatment worked as planned. The MAX wingtip is an all-Boeing design which extends divergently both above and below the wingtip.

For long range cruise missions up to 3,000 naut. mi., the new winglet on the 737-8 carrying 162 passengers in a dual class configuration will have up to a 1.8% better block fuel than a blended winglet equipped aircraft, says Boeing. The advantage grows the longer the flight, but even on shorter ranges of 500 naut. mi. the new winglet shows around a 1% benefit at Mach 0.79 and slightly more than 1% at long range cruise speeds. 

While the design caused quite a stir when it was first unveiled, the configuration is not new.  The winglet is designed to maximize lift for a wing span restricted to the same Category C sized gates as current 737s. The design traces its origins to the split wingtip adopted for similar gate restraint reasons for the proposed, but never built, MD-12 twin-deck concept devised by McDonnell Douglas in the 1990s before the merger with Boeing.

"The span considerations of the MD-12 determined that it had to live within the 213 ft. span of the 747-400," says Boeing Flight Sciences Chief Aerodynamicist and former Douglas designer Robert Gregg. Inboard of the winglet and outboard of the aileron the MAX will also incorporate a divergent trailing edge. "This puts more load into winglet and makes it work harder," he adds.

The MD-12 was all-new aircraft designed to compete with the 747-400 which, in 1992, was unchallenged in the long range, high capacity arena. The double-decker was designed to seat up to 511 in a three-class arrangement and aimed at ranges over 7,000 naut. mi. Douglas planned to launch the program in early 1993 and build the aircraft at a 'green-field' start, somewhere in the U.S. but not at Long Beach where its main facility was based.  First flight was set for mid-1996, with first deliveries in late 1997. Of course none of that was to happen and, instead of flight testing what arguably would have been a potential game changer for the waning Douglas line, the company was being integrated into Boeing.

McDonnell Douglas built a full-scale mock-up of the double-deck cross section. This is an illustration of the upper deck concept which bears a strong resemblance to the A380 of today.

The double-decker MD-12 succeeded an earlier MD-12 concept which, in late 1991, was based on a double-stretch of the MD-11 trijet. Configured with seats for 375 in a triclass arrangement, the jet was designed for routes up to 9,000 naut. mi, but failed to attract much interest. Ironically it did not sport winglets.

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