are much improved; the Navier-Stokes codes are considered capable of generating more accurate results and have been used in the latest aircraft designs to reach a successful design more quickly and with less wind tunnel testing.7 In both cases the selected design philosophies might have been different had the current CFD capabilities and design lessons learned been available. Nevertheless, both the 747-400 and DC-10/MD-11 winglet designs have provided substantial airplane performance benefits to their products. The dual winglet design developed for the DC-10 has only been incorporated into the production MD-11 aircraft. Although the winglet was not flight tested separately from other aerodynamic modifications, it has been credited with a performance benefit of 2.5 percent.8 To date, there has not been a retrofit program for the DC-10 aircraft.

The Douglas twinjet family has also been the subject of wingtip redesign studies. In the early 1980s, the DC-9 was redesigned as the MD-80, including a wing root insert and a wingtip extension. These changes provided more wing area, more wing span, and increased fuel volume, allowing increases in payload and range for this aircraft family. Also included in the MD-80 transformation were new, higher thrust/higher efficiency engines and an elongated fuselage. The wingtip extension for the MD-80 was notable in that it was a constant chord design, allowing the existing tip fairing and navigation light design to be retained. However, the wingtip extension and span loading were not optimized for efficient long-range cruise, as some other designs have been. The result of that is that the MD-80 wingtip devices do not show significant fuel economy benefits.

APB has investigated a retrofit design for the DC-9 family. Those design studies have not been successful in creating a viable business case. Projected block fuel burn reductions of less than 2 percent are offset by substantial modification costs. The limited potential for the DC-9 is a result of the existing wing structure, which hinders installation of a large winglet, as was possible on the Boeing 737 family. Since the DC-9 has been out of production since the early 1980s, the fleet size has shrunk and the fleet has aged, making the business case for a retrofit winglet or wingtip not as attractive as that for the Boeing 737 and 757 families.

7

Forrester T. Johnson, Edward N. Tinoco, and N. Jong Yu, 2003. “Thirty years of development and application of CFD at Boeing Commercial Airplanes, Seattle,” AIAA-2003-3439, 16th AIAA Computational Fluid Dynamics Conference, Orlando, Fla., June 23-26.

8

Robb Gregg, Senior Manager for Aircraft Programs, Boeing Phantom Works, “Drag improvement: A study of the DC-10/MD-11/C-17 winglet programs,” Presentation to the committee on December 13, 2006.



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