Assessment of Wingtip Modifications to Increase the Fuel Efficiency of Air Force Aircraft (2007) / Chapter Skim
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4 Assessment of Wingtip Modifications for Various Air Force Aircraft and Potential Investment Strategies
4 Assessment of Wingtip Modifications for Various Air Force Aircraft and Potential Investment Strategies
Pages 53-72
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From page 53... ...
This is followed by a discussion of specific aircraft in the Air Force inventory, including those that are responsible for the greatest fuel consumption as well as those that are derived from commercial aircraft. The committee then identifies those aircraft that appear most promising for wingtip modification.
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From page 54... ...
, and the empty weight of the aircraft, which will increase when the winglets are installed. The viability of a winglet installation is different for each aircraft configuration, and sophisticated design studies are required to achieve the proper balance between aerodynamic efficiency and weight efficiency.
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From page 55... ...
This is particularly important when analyzing the economic life cycle of winglets. design Information Aailability Developing a winglet design for an existing aircraft requires a deep understanding of the characteristics of the original aircraft design.
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From page 56... ...
Independent variables in the assessment include the following: • Winglet unit price ($/airplane) , • Fuel burn reduction (%)
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From page 57... ...
The five that stand out most clearly are, in order of annual fuel usage by fleet, the C-17, KC-135R/T, C-5, KC-10, and C-130H/J. As noted in Chapter 3, the C-17 already has winglets, and the KC-135 and KC-10, which are closely related to the Boeing 707 and DC-10 commercial airframes, respectively, have been studied previously for wingtip modifications.
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From page 58... ...
While a newly designed winglet for the C-17 might result in somewhat improved cruise fuel efficiency, the magnitude of that improvement is likely to be in the 1 to 2 percent range,1 and it would only make sense if combined with other efficiency improvement modifications. The considerable data already developed for the C-17 could also be considered for further wing upgrades beyond winglets.
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From page 59... ...
The committee believes that the C-5 has the potential for drag reduction with wingtip modifications because of its current large fuel consumption, its missions, wing design, etc. Aerodynamic improvements, combined with orphan weight and obsolete component removal, would contribute to operating efficiency increases for the aircraft.
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From page 60... ...
The DC-10 flight test program that was conducted identified approximately 3 percent cruise efficiency improvement, which was later replicated on the MD-11 design.2 In addition, recent winglet design experience using modern CFD methods and high Reynolds number (RN) wind tunnels may provide lessons that could have applicability for winglet designs that may be more effective on the KC-10 and other government transport aircraft.
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From page 61... ...
Other drag reduction approaches, such as aft body strakes and revised wing fillets, have been identified in other studies and should be considered in any fuel consumption reduction study. Intelligence, Surveillance, and Reconnaissance Aircraft The committee was asked explicitly to consider the suitability of ISR aircraft for wingtip modifications.
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From page 62... ...
The remaining Air Force aircraft that are derivatives of commercial aircraft do not appear to be good candidates for wingtip modifications.
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From page 63... ...
PRELIMINARy NET PRESENT VALuE ANALySIS To illustrate the types of benefits and costs that might be realized through wingtip modifications (e.g., winglets) that would produce a reduction in fuel burn, the committee shows here, as examples, the results of its preliminary net present value (NPV)
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From page 64... ...
The NPV results are shown in Figure 4-2 for the KC-135R/T and in Figure 4-3 for the KC-10. The figures show the estimated cumulative fleet net savings over time from the start of aircraft modification to when the last aircraft is retired from service.
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From page 65... ...
5 ASSESSmENt FoR AIRCRAFt ANd PotENtIAL INVEStmENt StRAtEgIES TABLE 4-4 Payback Period for a KC-135R/T Using 649,000 gal/yr Fuel Usage Reduction Estimated Cost from Fuel Cost of Modification Modification Fuel Saved Saved Payback Period (Fy07 $M)
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From page 66... ...
ASSESSmENt oF wINgtIP modIFICAtIoNS TABLE 4-5 Payback Period for a KC-10 Using 2.057 million gal/yr Fuel Usage Reduction Estimated Cost from Fuel Cost of Modification Modification Fuel Saved Saved Payback Period (Fy07 $M)
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From page 67... ...
Finding: The committee's analysis for a broad range of fuel prices and with the data available to it on potential improvements in block fuel savings, modification cost estimates, operational parameters for the
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From page 68... ...
aircraft, and so forth indicates that wingtip modifications offer significant potential for improved fuel economy in certain Air Force aircraft, particularly the KC-135R/T and the KC-10. Recommendation: The Air Force should initiate an engineering analysis with the original equipment manufacturers (OEMs)
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From page 69... ...
The committee also suggests that the Air Force evaluate the fuel economy practices of commercial aircraft operators, some of which are described in Appendix B, and implement those that are applicable and
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From page 70... ...
Performing Retrofit Studies and Implementing Modifications Fuel economy has been a primary focus of commercial aircraft operators for a number of years. They have done an excellent job of working with the airframe manufacturers to perfect the aerodynamic design of aircraft to include wingtip modifications that will reduce drag, of implementing maintenance and operations procedures that save fuel, and of making fuel conservation a part of everyone's job and a factor in every decision.
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From page 71... ...
Also, as noted in Chapter 3, aerodynamic studies of wingtip modifications were done in the 1970s, and a test aircraft was modified with winglets and flight tested. Since the analysis and tests were done so many years ago and there are some uncertainties surrounding the condition of the KC-135 wings and their ability to handle the load increases from wingtip modifications, a sample of the fleet would have to be inspected.
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From page 72... ...
The same factors discussed in the investment strategies for the KC-10 and the KC-135R/T should be part of the planning process for these fleets as well. Financing Mechanisms Wingtip modification programs and other fuel economy investments are examples of long-term investments that may require a significant initial investment that provides returns over time.
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