ASSESSMENT OF WINGTIP MODIFICATIONS TO INCREASE THE FUEL EFFICIENCY OF AIR FORCE AIRCRAFT
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NOTICE: The project that is the subject of this report was approved by the Governing Board of the National Research Council, whose members are drawn from the councils of the National Academy of Sciences, the National Academy of Engineering, and the Institute of Medicine. The members of the committee responsible for the report were chosen for their special competences and with regard for appropriate balance.
This is a report of work supported by Grant F49620-01-1-0269 between the U.S. Air Force and the National Academy of Sciences. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the views of the organizations or agencies that provided support for the project.
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COMMITTEE ON ASSESSMENT OF AIRCRAFT WINGLETS FOR LARGE AIRCRAFT FUEL EFFICIENCY
KENNETH E. EICKMANN, Chair,
U.S. Air Force (retired), Independent Consultant, Austin, Texas
NATALIE W. CRAWFORD, NAE,1 Vice Chair,
RAND Corporation, Santa Monica, California
MARK I. GOLDHAMMER,
Boeing Commercial Airplanes, Seattle, Washington
STEPHEN JUSTICE,
Lockheed Martin Aeronautics Company, Palmdale, California
CLYDE KIZER, Independent Consultant,
Nokesville, Virginia
ILAN KROO, NAE,1
Stanford University, Stanford, California
ELI RESHOTKO, NAE,1
Case Western Reserve University (emeritus), Denver, Colorado
RAYMOND VALEIKA, Independent Consultant,
Powder Springs, Georgia
Staff
MARTA VORNBROCK, Study Director
GREGORY EYRING, Senior Program Officer
JAMES C. GARCIA, Senior Program Officer
DETRA BODRICK-SHORTER, Administrative Coordinator
LaSHAWN SIDBURY, Program Associate (until March 2007)
AIR FORCE STUDIES BOARD
LAWRENCE J. DELANEY, Chair,
Titan Corporation (retired)
TAYLOR W. LAWRENCE, Vice Chair,
Raytheon Company
FRANK J. CAPPUCCIO,
Lockheed Martin Corporation
THOMAS DARCY, EADS
North America Defense Company
STEVEN D. DORFMAN, NAE,1
Hughes Electronics (retired)
PAMELA A. DREW,
Boeing Integrated Defense Systems
KENNETH E. EICKMANN,
U.S. Air Force (retired)
JOHN V. FARR,
Stevens Institute of Technology
RAND H. FISHER,
Titan Corporation
JACQUELINE GISH,
Northrop Grumman
KENNETH C. HALL,
Duke University
WESLEY L. HARRIS, NAE,1
Massachusetts Institute of Technology
LESLIE KENNE,
LK Associates
DONALD J. KUTYNA,
U.S. Air Force (retired)
GREGORY S. MARTIN,
GS Martin Consulting
DEBASIS MITRA, NAE,1
Bell Laboratories
ROBERT F. RAGGIO,
Dayton Aerospace, Inc.
GENE W. RAY,
GMT Ventures
LOURDES SALAMANCA-RIBA,
University of Maryland
MARVIN R. SAMBUR,
Headquarters, U.S. Air Force (retired)
LYLE H. SCHWARTZ, NAE,1
Air Force Office of Scientific Research (retired)
EUGENE L. TATTINI,
Jet Propulsion Laboratory
Staff
MICHAEL A. CLARKE, Director
GREGORY EYRING, Senior Program Officer
JAMES C. GARCIA, Senior Program Officer
DANIEL E.J. TALMAGE, JR., Program Officer
CARTER W. FORD, Associate Program Officer
MARTA VORNBROCK, Associate Program Officer
DETRA BODRICK-SHORTER, Administrative Coordinator
Preface
At the request of the U.S. Air Force, and in light of greatly increased government emphasis on the need for greater fuel efficiency in the fleet of military aircraft, the National Research Council (NRC) was asked to study whether business cases could be made for modifying engines or re-engining large Air Force aircraft. The Committee on Analysis of Air Force Engine Efficiency Improvement Options for Large Non-fighter Aircraft was formed and its report1 was provided to the Air Force on January 31, 2007.
While that study was under way, congressional interest in fuel efficiency increased, resulting in the inclusion of the following language in Report 109-452 of the House Armed Services Committee on H.R. 5122 (National Defense Authorization Act for FY07):
The committee commends the Air Force in its efforts to increase aircraft fuel efficiency and decrease fuel consumption. The committee notes that initiatives such as re-engining aircraft, modifying in-flight profiles, and revising aircraft ground operations contribute to decreased fuel consumption and increased life-cycle savings.
The committee is aware that winglet technology exists for aircraft to increase fuel efficiency, improve take-off performance, increase cruise altitudes, and increase payload and range capability. The committee notes that winglets are currently used on commercial aircraft and result in a five to seven percent increase in fuel efficiency. On September 16, 1981, the National
Aeronautics and Space Administration released the KC-135 Winglet Program Review on the incorporation of winglets for KC-135 aerial refueling aircraft. However, the Air Force concluded that the cost of adding winglets to the KC-135 did not provide sufficient payback in fuel savings or increased range to justify modification. Although the Air Force did conclude that modifying aircraft with winglets could increase fuel efficiency, the Air Force determined that re-engining the KC-135 aircraft produced a greater return on investment. The committee believes that incorporating winglets on military aircraft could increase fuel efficiency on certain platforms and that the Air Force should reexamine incorporating this technology onto its platforms.
Therefore, the committee directs the Secretary of the Air Force to provide a report to the congressional defense committees by March 1, 2007, examining the feasibility of modifying Air Force aircraft with winglets. The report shall include a cost comparison analysis of the cost of winglet modification compared to the return on investment realized over time for each airlift, aerial refueling, and intelligence, surveillance, and reconnaissance aircraft in the Air Force inventory; the market price of aviation fuel at which incorporating winglets would be beneficial for each Air Force platform; all positive and negative impacts to aircraft maintenance and flight operations; and investment strategies the Air Force could implement with commercial partners to minimize Air Force capital investment and maximize investment return.
In response to a subsequent request from the Air Force, the NRC appointed the Committee on Assessment of Aircraft Winglets for Large Aircraft Fuel Efficiency to examine the feasibility of modifying Air Force aircraft with winglets. Since this study is a follow-on effort to the earlier study examining methods to improve fuel efficiency in large Air Force aircraft, appropriate members of the original study committee, including the chair and vice chair, agreed to participate in this study. They were joined by new members with the expertise to address the necessary technical areas. This report responds to the request of Congress as outlined above.
The chair thanks the members of the committee for generously taking time from their demanding schedules and working hard to complete this report in the short time allotted. The entire committee, in turn, thanks the many organizations and the guest speakers who provided excellent briefings and background information, and it thanks the NRC staff members who supported the study. Primary among them were Marta Vornbrock, Gregory Eyring, Jim Garcia, Michael Clarke, LaShawn Sidbury, and Detra Bodrick-Shorter.
Kenneth E. Eickmann, Chair
Committee on Assessment of Aircraft Winglets for Large Aircraft Fuel Efficiency
Acknowledgments
This report has been reviewed in draft form by individuals chosen for their diverse perspectives and technical expertise, in accordance with procedures approved by the National Research Council’s (NRC’s) Report Review Committee. The purpose of this independent review is to provide candid and critical comments that will assist the institution in making its published report as sound as possible and to ensure that the report meets institutional standards for objectivity, evidence, and responsiveness to the study charge. The review comments and draft manuscript remain confidential to protect the integrity of the deliberative process. We wish to thank the following individuals for their review of this report:
William G. Agnew, NAE, General Motors Corporation (retired),
Kenneth C. Hall, Duke University,
Wesley L. Harris, NAE, Massachusetts Institute of Technology,
Frank T. Lynch, Independent Consultant, Yorba Linda, California,
Gregory S. Martin, GS Martin Consulting,
John P. Sullivan, Purdue University,
Charles F. Tiffany, NAE, The Boeing Company (retired), and
Henry T.Y. Yang, NAE, University of California, Santa Barbara.
Although the reviewers listed above have provided many constructive comments and suggestions, they were not asked to endorse the conclusions or recommendations, nor did they see the final draft of the report before
its release. The review of this report was overseen by Alexander H. Flax, NAE. Appointed by the National Research Council, he was responsible for making certain that an independent examination of this report was carried out in accordance with institutional procedures and that all review comments were carefully considered. Responsibility for the final content of this report rests entirely with the authoring committee and the institution.
The committee also acknowledges and appreciates the contribution of the members of the Air Force Studies Board (AFSB) of the National Academies for their support of this study.
The AFSB, established in 1996 by the National Research Council at the request of the Air Force, brings to bear broad military, industrial, and academic scientific, engineering, and management expertise on Air Force technical challenges and other issues of importance to senior Air Force leaders. The board discusses potential studies of interest, develops and frames study tasks, ensures proper project planning, suggests potential committee members and reviewers for reports produced by fully independent ad hoc study committees, and convenes meetings to examine strategic issues. The board members listed on page vi were not asked to endorse the committee’s conclusions or recommendations, nor did they review the final draft of this report before its release. Board members with appropriate expertise may be nominated to serve as formal members of study committees or to review reports.
Figures and Tables
FIGURES
1-1 |
A common wingtip modification is the “winglet,” |
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2-1 |
Wingtip modifications with a variety of geometries have been tested and deployed on both commercial and military aircraft, |
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2-2 |
The vortex wake behind lifting wings descending through a thin cloud layer, |
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2-3 |
Winglets increase payload-range capability of the Boeing 737-800, |
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3-1 |
Boeing 747-400 with swept, canted winglets, |
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3-2 |
Boeing 737-NG with blended winglets, |
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3-3 |
Boeing 757 with retrofit blended winglets, |
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3-4 |
Boeing 767-400ER with raked wingtips, |
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3-5 |
The Boeing 787 family, featuring various wingtip modifications, |
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3-6 |
McDonnell Douglas MD-11 with dual winglets, |
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3-7 |
Airbus A320 with tip fence, |
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3-8 |
Airbus A340 with swept, canted winglets, |
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3-9 |
The Air Force’s C-17 with winglets, |
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4-1 |
Fuel usage of selected Air Force aircraft (by fleet) in FY05, |
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4-2 |
KC-135R/T estimated cumulative inventory-level net savings, |
4-3 |
KC-10 estimated cumulative inventory-level net savings, |
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4-4 |
KC-135R/T effect of cost of fuel on payback period, |
TABLES
S-1 |
Potential for Wingtip Modifications to Benefit Air Force Aircraft, |
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S-2 |
Winglet Status of Air Force Aircraft Derived from Commercial Airframes, |
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3-1 |
Southwest Airlines 737 Winglet Modification Summary, |
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3-2 |
American Airlines 737-800 and 757-200ER Winglet Modification Summary, |
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4-1 |
Winglet Status of Air Force Aircraft Derived from Commercial Airframes, |
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4-2 |
Potential for Wingtip Modifications to Benefit Air Force Aircraft, |
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4-3 |
Estimated Aircraft Modification Costs, |
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4-4 |
Payback Period for a KC-135R/T Using 649,000 gal/yr, |
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4-5 |
Payback Period for a KC-10 Using 2.057 million gal/yr, |
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A-1 |
KC-10 Data, |
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A-2 |
KC-135 R/T Data, |
Acronyms
ACEE aircraft energy efficiency
APB Aviation Partners Boeing
API Aviation Partners Incorporated
APU auxiliary power unit
AWACS Airborne Warning and Command System
BBJ Boeing Business Jets
CFD computational fluid dynamics
CG center of gravity
DESC Defense Energy Support Center
DOD Department of Defense
DOE Department of Energy
EGT exhaust gas temperature
ESPC energy savings performance contract
FAA Federal Aviation Administration
ISR intelligence, surveillance, and reconnaissance
JSTARS Joint Surveillance Target Attack Radar System
L/D lift-to-drag ratio
NACA National Advisory Committee for Aeronautics
NASA National Aeronautics and Space Administration
NG Next-Generation
NPV net present value
NRC National Research Council
OEM original equipment manufacturer
RN Reynolds number
SOT statement of task
TACAMO take charge and move out
TOGW takeoff gross weight
USAF United States Air Force