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737MAX and the MD-12


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 - but its roots go back far further than most know - in fact deep into the company's Douglas heritage.

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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. 

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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.  But more than 20 years ago Douglas faced a smiliar problem on a much bigger scale with its huge MD-12 - a twin deck concept studied in the 1990s before the merger with Boeing. In response it devised the split wingtip to cope with similar gate restraints.

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“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.  So when it came to how to squeeze the 737 into today's gates but still maximize the wing's aerodynamic efficiency, Boeing knew where to look for solutions. 

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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’ site, 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.

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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.

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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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