ASSESSMENT OF WINGTIP MODIFICATIONS TO INCREASE THE FUEL EFFICIENCY OF AIR FORCE AIRCRAFT

Committee on Assessment of Aircraft Winglets for Large Aircraft Fuel Efficiency

Air Force Studies Board

Division on Engineering and Physical Sciences

NATIONAL RESEARCH COUNCIL OF THE NATIONAL ACADEMIES

THE NATIONAL ACADEMIES PRESS

Washington, D.C.
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Assessment of Wingtip Modifications to Increase the Fuel Efficiency of Air Force Aircraft ASSESSMENT OF WINGTIP MODIFICATIONS TO INCREASE THE FUEL EFFICIENCY OF AIR FORCE AIRCRAFT Committee on Assessment of Aircraft Winglets for Large Aircraft Fuel Efficiency Air Force Studies Board Division on Engineering and Physical Sciences NATIONAL RESEARCH COUNCIL OF THE NATIONAL ACADEMIES THE NATIONAL ACADEMIES PRESS Washington, D.C. www.nap.edu

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Assessment of Wingtip Modifications to Increase the Fuel Efficiency of Air Force Aircraft THE NATIONAL ACADEMIES PRESS 500 Fifth Street, N.W. Washington, DC 20001 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. International Standard Book Number-13 978-0-309-10497-5 International Standard Book Number-10 0-309-10497-1 Limited copies are available from: Air Force Studies Board National Research Council 500 Fifth Street, N.W. Washington, DC 20001 (202) 334-3111 Additional copies are available from: The National Academies Press Box 285 500 Fifth Street, N.W. Washington, DC 20055 (800) 624-6242 or (202) 334-3313 (in the Washington Metropolitan Area) http://www.nap.edu Copyright 2007 by the National Academy of Sciences. All rights reserved. Printed in the United States of America

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Assessment of Wingtip Modifications to Increase the Fuel Efficiency of Air Force Aircraft THE NATIONAL ACADEMIES Advisers to the Nation on Science, Engineering, and Medicine The National Academy of Sciences is a private, nonprofit, self-perpetuating society of distinguished scholars engaged in scientific and engineering research, dedicated to the furtherance of science and technology and to their use for the general welfare. Upon the authority of the charter granted to it by the Congress in 1863, the Academy has a mandate that requires it to advise the federal government on scientific and technical matters. Dr. Ralph J. Cicerone is president of the National Academy of Sciences. The National Academy of Engineering was established in 1964, under the charter of the National Academy of Sciences, as a parallel organization of outstanding engineers. It is autonomous in its administration and in the selection of its members, sharing with the National Academy of Sciences the responsibility for advising the federal government. The National Academy of Engineering also sponsors engineering programs aimed at meeting national needs, encourages education and research, and recognizes the superior achievements of engineers. Dr. Charles M. Vest is president of the National Academy of Engineering. The Institute of Medicine was established in 1970 by the National Academy of Sciences to secure the services of eminent members of appropriate professions in the examination of policy matters pertaining to the health of the public. The Institute acts under the responsibility given to the National Academy of Sciences by its congressional charter to be an adviser to the federal government and, upon its own initiative, to identify issues of medical care, research, and education. Dr. Harvey V. Fineberg is president of the Institute of Medicine. The National Research Council was organized by the National Academy of Sciences in 1916 to associate the broad community of science and technology with the Academy’s purposes of furthering knowledge and advising the federal government. Functioning in accordance with general policies determined by the Academy, the Council has become the principal operating agency of both the National Academy of Sciences and the National Academy of Engineering in providing services to the government, the public, and the scientific and engineering communities. The Council is administered jointly by both Academies and the Institute of Medicine. Dr. Ralph J. Cicerone and Dr. Charles M. Vest are chair and vice chair, respectively, of the National Research Council. www.national-academies.org

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Assessment of Wingtip Modifications to Increase the Fuel Efficiency of Air Force Aircraft 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) 1 Member, National Academy of Engineering.

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Assessment of Wingtip Modifications to Increase the Fuel Efficiency of Air Force Aircraft 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 CHANDRA N. KUMAR PATEL, NAE/NAS,1,2 University of California 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 1 Member, National Academy of Engineering. 2 Member, National Academy of Sciences.

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Assessment of Wingtip Modifications to Increase the Fuel Efficiency of Air Force Aircraft ENITA A. WILLIAMS, Research Associate CHRIS JONES, Financial Associate WILLIAM E. CAMPBELL, Senior Program Associate LaNITA R. JONES, Program Associate

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Assessment of Wingtip Modifications to Increase the Fuel Efficiency of Air Force Aircraft 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 1 NRC, 2007, Improving the Efficiency of Engines for Large Nonfighter Aircraft, Washington, D.C.: The National Academies Press.

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Assessment of Wingtip Modifications to Increase the Fuel Efficiency of Air Force Aircraft 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

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Assessment of Wingtip Modifications to Increase the Fuel Efficiency of Air Force Aircraft 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

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Assessment of Wingtip Modifications to Increase the Fuel Efficiency of Air Force Aircraft 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.

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Assessment of Wingtip Modifications to Increase the Fuel Efficiency of Air Force Aircraft Contents     SUMMARY   1 1   BACKGROUND AND OVERVIEW   12      Introduction,   12      Statement of Task,   15      Scope and Committee Approach,   15      Structure of This Report,   17 2   WINGTIP MODIFICATIONS   18      History of Wingtip Devices,   18      Introduction to Wingtip Aerodynamics,   19      Design of Wingtip Devices,   22      Optimal Wingspan,   22      Wing Retrofits,   23      Benefits of Wingtip Modifications,   25      Reduced Fuel Burn,   25      Increased Payload-Range Capability,   25      Improved Takeoff Performance,   27      Challenges Associated with Wingtip Modifications,   27      Cost,   27      Added Weight,   28      Added Span and Height,   28      Interference with Other Wing Equipment,   29      General Observations,   29

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Assessment of Wingtip Modifications to Increase the Fuel Efficiency of Air Force Aircraft 3   PREVIOUS ANALYSES AND EXPERIENCE WITH WINGTIP MODIFICATIONS ON EXISTING AIRCRAFT   31      Early Research Programs,   31      NASA-Led Research: ACEE,   31      Commercial Experience,   32      Airframe Manufacturers,   33      Airlines,   43      Military Experience,   48      C-17,   48      C-32,   50      KC-135,   50      Summary of Commercial and Military Experience,   51 4   ASSESSMENT OF WINGTIP MODIFICATIONS FOR VARIOUS AIR FORCE AIRCRAFT AND POTENTIAL INVESTMENT STRATEGIES   53      Checklist for Making Wingtip Modification Decisions,   53      Technical Issues,   54      Economic Issues,   55      Putting It All Together,   56      Candidate Aircraft in the Air Force Inventory,   57      C-17,   58      KC-135R/T,   58      C-5,   59      KC-10,   59      C-130H/J,   60      Intelligence, Surveillance, and Reconnaissance Aircraft,   61      Other Air Force Aircraft,   61      Priority Aircraft to Be Considered for Wingtip Modification,   63      Preliminary Net Present Value Analysis,   63      Investment Strategies,   69      Performing Retrofit Studies and Implementing Modifications,   70      Financing Mechanisms,   72     APPENDIXES          A  Data Used in Net Present Value Analyses   75      B  Additional Methods for Improving Fuel Consumption   77      C  Presentations to the Committee   88      D  Biographical Sketches of Committee Members   90

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Assessment of Wingtip Modifications to Increase the Fuel Efficiency of Air Force Aircraft Figures and Tables FIGURES 1-1   A common wingtip modification is the “winglet,”   13 2-1   Wingtip modifications with a variety of geometries have been tested and deployed on both commercial and military aircraft,   20 2-2   The vortex wake behind lifting wings descending through a thin cloud layer,   21 2-3   Winglets increase payload-range capability of the Boeing 737-800,   26 3-1   Boeing 747-400 with swept, canted winglets,   33 3-2   Boeing 737-NG with blended winglets,   34 3-3   Boeing 757 with retrofit blended winglets,   36 3-4   Boeing 767-400ER with raked wingtips,   37 3-5   The Boeing 787 family, featuring various wingtip modifications,   38 3-6   McDonnell Douglas MD-11 with dual winglets,   39 3-7   Airbus A320 with tip fence,   42 3-8   Airbus A340 with swept, canted winglets,   42 3-9   The Air Force’s C-17 with winglets,   49 4-1   Fuel usage of selected Air Force aircraft (by fleet) in FY05,   57 4-2   KC-135R/T estimated cumulative inventory-level net savings,   67

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Assessment of Wingtip Modifications to Increase the Fuel Efficiency of Air Force Aircraft 4-3   KC-10 estimated cumulative inventory-level net savings,   68 4-4   KC-135R/T effect of cost of fuel on payback period,   69 TABLES S-1   Potential for Wingtip Modifications to Benefit Air Force Aircraft,   4 S-2   Winglet Status of Air Force Aircraft Derived from Commercial Airframes,   7 3-1   Southwest Airlines 737 Winglet Modification Summary,   45 3-2   American Airlines 737-800 and 757-200ER Winglet Modification Summary,   48 4-1   Winglet Status of Air Force Aircraft Derived from Commercial Airframes,   62 4-2   Potential for Wingtip Modifications to Benefit Air Force Aircraft,   63 4-3   Estimated Aircraft Modification Costs,   64 4-4   Payback Period for a KC-135R/T Using 649,000 gal/yr,   65 4-5   Payback Period for a KC-10 Using 2.057 million gal/yr,   66 A-1   KC-10 Data,   75 A-2   KC-135 R/T Data,   76

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Assessment of Wingtip Modifications to Increase the Fuel Efficiency of Air Force Aircraft 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

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Assessment of Wingtip Modifications to Increase the Fuel Efficiency of Air Force Aircraft 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