A Study in Aircraft Efficiency Enhancements via Prandtl-Tailored Dynamically Aerocompliant Wingtip Extensions
Schueler, Samantha Katelyn
University of Kansas
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In 2008, the commercial aerospace industry saw substantial reductions in aircraft operating hours because of the struggling economy and high operating costs. Recurring fuel costs range from 10-40% of total operating cost revealing an inherent need for increased fuel efficiency for in-service aircraft. Current methods, such as control system improvements and winglet installments, yield little improvement. Wingtip extensions using a new design philosophy, however, indicate significant progress in the area through large scale reductions in the span loading of the aircraft thereby dramatically reducing induced drag. The adaptability of the wingtip extension allows for the span limitations set by the aircraft group classification to be met through the inclusion of a folding mechanism. Unlike currently used folding mechanisms, the Prandtl-tailored dynamically aerocompliant wingtip extension, explored herein, maintains the aerodynamic surface on both the upper and lower surface, thereby reducing drag further over the state of the art in active hinge mechanisms. The philosophy behind the Prandtl-tailored dynamically aerocompliant wingtip extensions follows technology commonly used in the helicopter and missile communities along with an approach by Ludwig Prandtl for reductions in induced drag. Strong pitch-flap coupling in the folding region results in reduced flapping tendencies and reduced fatigue while the shaping of the wingtip extension reduces the force increase due to the retrofit. By combining these techniques and adaptive materials, the benefits predicted through the retrofit of in-service aircraft with the wingtip extensions include: fatigue reduction, gust load alleviation, improved fuel burn efficiency, iv improved marketability through an increase in the design range, and improved safety during adverse flying conditions. This study uses the Boeing 727-200 as an analytical proof of concept aircraft to retrofit with the Prandtl-tailored dynamically aerocompliant wingtip extensions. This aircraft was used due to the abundance of publicly available technical data while the aircraft is still in-service but out of production, therefore the study is applicable while being "non-controversial". The aerodynamic results of this study indicate substantial improvement in the fuel efficiency of the aircraft during the cruise segment of the flight profile. The smallest span wingtip extension which was analyzed resulted in a 2% cruise fuel consumption reduction while the largest span wingtip extension analyzed resulted in a 48% cruise fuel consumption reduction. Although the Boeing 727-200 was used as the basis for this analysis, this wingtip extension design philosophy can be applied to most commercial aircraft with slight modifications to the layout and design. By proving the concept with wingtip extensions, the market can become accustomed to adaptive wing technology in commercial applications which, eventually, could lead to fundamentally new wing designs.
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