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Winglet benefits

Winglets could bring operational benefits to the Boeing 747-200F.

Guy Norris/SEATTLE

Aviation Partners, a Seattle-based modification company specialising in advanced winglet designs, is developing a lightweight winglet for the Boeing 747-200F. The company predicts that the revised wing could yield a 7% cruise-drag reduction, among other operational benefits. The company bases its predictions on performance data gathered from flight tests on the Gulfstream II, modified with a scaled version of the same winglet design. Kim Frinell, director of engineering, says: "Freight operators are very sensitive to cost. If you can save these guys fuel, then you're making sense to them."

Company president Joe Clark estimates that the overall benefits would produce fuel savings of around $1 million a year per aircraft for a typical 747-200F operator. The economic trade-offs include a 1h endurance increase, or additional payload. "In our experiences with business-jet operations it's been like having a 30-35kt [55-65km/h] permanent tailwind. This technology deserves to be....on the 747, where it would make a dramatic difference," he says.

The fuel-saving potential "...would allow operators to be more flexible". On a typical transpacific mission, for example, they could opt to use the benefit for longer range and overfly some fuel stops. Alternatively, they could choose instead to land at the refuelling stop and consume less fuel getting there. Fuel could be traded for a larger payload, or a reduced take-off weight, because of a reduced fuel load.

The proposed winglets would be directly scaled up from the units now fitted to more than 30 modified GIIs. The composite device would measure 4.4m in height and add around 3.3m to the overall span. Unlike the current 2m-high winglets on the production 747-400 and -400F, which yield a 3% range improvement, the Aviation Partners design is a high-aspect-ratio "blended winglet."

This differs from most conventional winglets in being more slender, with a high ratio of height to average chord. In addition, the blended transition geometry between the blended winglet and the wing is smoother than that of other "add-on" designs. The Aviation Partners winglet has a large transition radius coupled with a gradual change in chord. The company believes that this helps achieve optimum aerodynamic loading, and cuts induced drag, by avoiding unwanted concentrations of trailing vortices. The result, according to Aviation Partners, is a 60% increase in effectiveness over that of other winglets.

OTHER OBJECTIVES

Other design objectives laid out in the company's proposal to Boeing and -200F operators include a second-segment-climb weight-limit improvement of 4.5% and a reduced time to initial cruise altitude. This would be of considerable benefit to long-range freight haulers, which are often "trapped" at lower altitudes for long periods on busy routes to and from Asia.

Aviation Partners also predicts a 2,000ft (600m) higher cruise altitude at all weights and an increase in long-range cruise of about Mach 0.01. The winglet modification would also yield a 15% improvement in climb gradient at maximum landing weight, and a reduction in balanced field length of around 150m.

Frinell, says that the -200F test programme will be based directly on the GII effort. "We'll do back-to-back and before-and-after testing, to quantify the performance benefits," he says. The test programme will also be used to confirm predictions that wing strength needs enhancing in selected areas to offset the increased bending moment induced by the winglets.

Aviation Partners is talking to Boeing about assisting directly with a test programme, which it is targeting for the fourth quarter of 1996. "We certainly hope that we can work directly with Boeing on this," comments Clark, who does not see the development as a conflict of interests. "We make the economic life of the aircraft more productive - we don't necessarily extend its economic life."

Outline proposals have been sent to all -200F operators, including Cargolux and Atlas. Aviation Partners sees a potential market for around 50 aircraft, a figure which could grow as the number of -200 conversions increases. The outline cost per shipset of winglets is expected to be around $1.5 million.

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