Synthesis of Subsonic Airplane Design

Since the education of aeronautical engineers at Delft University of Technology started in 1940 under the inspiring leadership of Professor H.J. van der Maas, much emphasis has been placed on the design of aircraft as part of the student's curriculum. Not only is aircraft design an optional subject for thesis work, but every aeronautical student has to carry out a preliminary airplane design in the course of his study. The main purpose of this preliminary design work is to enable the student to synthesize the knowledge ob­ tained separately in courses on aerodynamics, aircraft performances, stability and con­ trol, aircraft structures, etc. The student's exercises in preliminary design have been directed through the years by a number of staff members of the Department of Aerospace Engineering in Delft. The author of this book, Mr. E. Torenbeek, has made a large contribution to this part of the study programme for many years. Not only has he acquired vast experience in teaching airplane design at university level, but he has also been deeply involved in design-oriented re­ search, e.g. developing rational design methods and systematizing design information. I am very pleased that this wealth of experience, methods and data is now presented in this book.

1. General Aspects of Aircraft Configuration Development.- 1.1. Introduction.- 1.2. Aircraft design and development.- 1.3. Configuration development.- 1.3.1. The design concept.- 1.3.2. Initial configuration design and configuration variations.- 1.3.3. Baseline configuration development.- 1.3.4. The preliminary design department.- 1.4. The initial specification.- 1.4.1. The need for a new type of aircraft.- 1.4.2. Transport capacity.- 1.4.3. Design cruising speed and range.- 1.4.4. Low-speed characteristics and field performance.- 1.4.5. Other requirements.- 1.5. A continuous thread running through the design process.- 1.5.1. The iterative character of design.- 1.5.2. Searching for the optimum.- 1.5.3. A suggested scheme for preliminary design.- 1.6. Impact of civil airworthiness requirements, and operating and flight rules.- 1.6.1. General.- 1.6.2. Federal Aviation Regulations.- 1.6.3. British Civil Airworthiness Requirements.- 1.6.4. Airworthiness standards and design.- 1.7. Conclusion.- 2. The General Arrangement.- 2.1. Introduction.- 2.2. High, low or mid wing?.- 2.2.1. High wing.- 2.2.2. Mid wing.- 2.2.3. Low wing.- 2.2.4. Effects of wing location on the general arrangement.- 2.3. Location of the engines.- 2.3.1. Propeller aircraft.- 2.3.2. Jet-propelled transport aircraft.- 2.3.3. Single-engine subsonic jet aircraft.- 2.4. Arrangement of the tailplane.- 2.4.1. Classification of tail surface configurations.- 2.4.2. The location of tail surfaces.- 2.5. Arrangement of the undercarriage.- 2.5.1. Tailwheel undercarriage.- 2.5.2. Nosewheel undercarriage.- 2.5.3. Tandem undercarriage.- 2.6. Some unconventional aircraft configurations.- 2.6.1. The flying wing.- 2.6.2. Tailless aircraft.- 2.6.3. Tail-first (or canard) layout.- 3. Fuselage Design.- 3.1. Introduction.- 3.1.1. Function and design requirements.- 3.1.2. Drag and optimization of the external shape.- 3.1.3. A design procedure for fuselages with cylindrical mid-section.- 3.2. The fuselage of airliners and general aviation aircraft.- 3.2.1. Importance of comfort and payload density.- 3.2.2. Cabin design.- 3.2.3. Passenger seats.- 3.2.4. Passenger emergency exits, doors and windows.- 3.2.5. Cargo holds.- 3.2.6. Services.- 3.3. The fuselage of cargo aircraft.- 3.3.1. The case for the civil freighter.- 3.3.2. Payload density and volume of the freight hold.- 3.3.3. Loading systems.- 3.3.4. Accessibility of the freight hold.- 3.4. Flight deck design.- 3.4.1. Location of the pilot’s seat and the flight controls.- 3.4.2. Visibility from the cockpit.- 3.4.3. Flight deck dimensions and layout.- 3.4.4. Emergency exits for crew members.- 3.5. Some remarks concerning the external shape.- 3.5.1. Fuselages with a cylindrical mid-section.- 3.5.2. Fuselages for relatively small useful loads.- 4. An Appreciation of Subsonic Engine Technology.- 4.1. Introductory comparison of engine types.- 4.2. Current reciprocating engines.- 4.2.1. Some characteristics of the four stroke engine.- 4.2.2. Engine design and its influence on flight performance.- 4.2.3. Engine classification by cylinder arrangement.- 4.2.4. Two-stroke and Rotary Combustion engines.- 4.3. Basic properties of aircraft gas turbines for subsonic speeds.- 4.3.1. The gas producer.- 4.3.2. The propulsive device.- 4.3.3. The pure jet engine.- 4.3.4. The turbofan engine.- 4.3.5. The turboprop engine.- 4.3.6. Overall efficiency, specific fuel consumption and specific thrust (power).- 4.3.7. Analysis of the engine cycle.- 4.4. Assessment of turbojet engines.- 4.4.1. Overall Pressure Ratio.- 4.4.2. Turbine Entry Temperature.- 4.4.3. Bypass ratio.- 4.4.4. Engine noise.- 4.4.5. Summary and prognosis for the turbofan engine.- 4.4.6. Engine performance in non-standard atmosphere.- 4.5. Assessment of turboprop engines.- 4.5.1. Performance.- 4.5.2. Weight and drag.- 4.5.3. Turboprop engine configurations.- 5. Design for Performance.- 5.1. Introduction.- 5.2. Initial weight prediction.- 5.2.1. Stages in the estimation of airplane weight.- 5.2.2. Examples of weight “guesstimates”.- 5.3. Initial estimation of airplane drag.- 5.3.1. Drag breakdown.- 5.3.2. Low-speed drag estimation method.- 5.3.3. Compressibility drag.- 5.3.4. Retracing a drag polar from performance figures.- 5.3.5. Drag in takeoff and landing.- 5.4. Evaluation of performance requirements.- 5.4.1. High-speed performance.- 5.4.2. Range performance.- 5.4.3. Climb performance.- 5.4.4. Stalling and minimum flight speeds.- 5.4.5. Takeoff.- 5.4.6. Landing.- 5.5. Aircraft synthesis and optimization.- 5.5.1. Purpose of parametric studies.- 5.5.2. Basic rules.- 5.5.3. Sizing the wing of a long-range passenger transport.- 5.5.4. Wing loading and thrust (power) loading diagrams.- 5.5.5. Optimization for low operating costs.- 5.5.6. Community noise considerations.- 6. Choice of the Engine and Propeller and Installation of the Powerplant.- 6.1. Introduction.- 6.2. Choice of the number of engines and the engine type.- 6.2.1. Engine installation factors.- 6.2.2. Engine failure.- 6.2.3. Engine performance and weight variations.- 6.2.4. Choice of the engine type.- 6.3. Characteristics, choice and installation of propellers.- 6.3.1. General aspects.- 6.3.2. Propeller coefficients and diagrams.- 6.3.3. Blade angle control.- 6.3.4. Propeller geometry.- 6.4. Installation of propeller engines.- 6.4.1. Location of the propellers.- 6.4.2. Tractor engines in the nose of the fuselage.- 6.4.3. Wing-mounted tractor engines.- 6.5. Installation of turbojet engines.- 6.5.1. General requirements.- 6.5.2. Fuselage-mounted podded engines.- 6.5.3. Wing-mounted podded engines.- 6.6. Miscellaneous aspects of powerplant installation.- 6.6.1. Thrust reversal.- 6.6.2. Auxiliary Power Units (APU).- 7. An Introduction to Wing Design.- 7.1. Introduction and general design requirements.- 7.2. Wing area.- 7.2.1. Wing loading for optimum cruising conditions.- 7.2.2. Wing loading limits and structural aspects.- 7.3. Some considerations on low-speed stalling.- 7.3.1. Stall handling requirements and stall warning.- 7.3.2. Design for adequate stall characteristics.- 7.3.3. Stalling properties of airfoil sections.- 7.3.4. Spanwise progression of the stall.- 7.4. Wing design for low-subsonic aircraft.- 7.4.1. PIanform.- 7.4.2. Aspect ratio.- 7.4.3. Thickness ratio.- 7.4.4. Wing taper.- 7.4.5. Airfoil selection.- 7.4.6. Stalling characteristics and wing twist.- 7.5. Wing design for high-subsonic aircraft.- 7.5.1. Wing sections at high-subsonic speeds.- 7.5.2. Wing design for high speeds.- 7.5.3. Low-speed problems of high-speed wings.- 7.5.4. Planform selection.- 7.6. High lift and flight control devices.- 7.6.1. General considerations.- 7.6.2. Trailing-edge flaps.- 7.6.3. Leading-edge high lift devices.- 7.6.4. Flight control devices.- 7.7. Dihedral, anhedral and wing setting.- 7.7.1. The angle of dihedral (anhedral).- 7.7.2. Wing/body incidence.- 7.8. The wing structure.- 7.8.1. Types of wing structure.- 7.8.2. Structural arrangement in plan.- 8. Airplane Weight and Balance.- 8.1. Introduction; the importance of low weight.- 8.2. Weight subdivision and limitations.- 8.2.1. Weight subdivision.- 8.2.2. Weight limitations and capacities.- 8.2.3. Operational weights and the payload-range diagram.- 8.2.4. The choice of weight limits.- 8.3. Methodology of empty weight prediction.- 8.4. Weight prediction data and methods.- 8.4.1. Airframe structure.- 8.4.2. The propulsion group.- 8.4.3. Airframe services and equipment.- 8.4.4. Useful Load and the All-Up Weight.- 8.5. Center of gravity.- 8.5.1. The load and balance diagram.- 8.5.2. Loading flexibility and restrictions.- 8.5.3. Effects of the general arrangement and layout.- 8.5.4. Design procedure to obtain a balanced aircraft.- 9. Preliminary Tailplane Design.- 9.1. Introduction to tailplane design, control systems and stabilization.- 9.2. Static longitudinal stability and elevator control forces.- 9.2.1. Stick-fixed static stability and neutral point.- 9.2.2. Stick-free static stability and neutral point; the stick force gradient.- 9.2.3. Stick-fixed and stick-free maneuver points and maneuver control forces.- 9.2.4. Reduction of control forces.- 9.2.5. Effects of compressibility and powerplant operation.- 9.3. Some aspects of dynamic behavior.- 9.3.1. Characteristics of the SP oscillation.- 9.3.2. Criteria for acceptable SP characteristics.- 9.3.3. A simple criterion for the tailplane size.- 9.3.4. The phugoid.- 9.4. Longitudinal control at low speeds.- 9.4.1. Control capacity required to stall the aircraft.- 9.4.2. Control capacity required for takeoff rotation and landing flareout.- 9.4.3. Out-of-trim conditions.- 9.5. Preliminary design of the horizontal tailplane.- 9.5.1. Tailplane shape and configuration.- 9.5.2. Design procedures.- 9.6. Design of the vertical tailplane.- 9.6.1. Control after engine failure: multi-engine aircraft.- 9.6.2. Lateral stability.- 9.6.3. Crosswind landings.- 9.6.4. The spin.- 9.6.5. Preliminary design of the vertical tailplane.- 10. The Undercarriage Layout.- 10.1. Introduction.- 10.2. Tailoring the undercarriage to the bearing capacity of airfields.- 10.2.1. Runway classification.- 10.2.2. The Equivalent Single Wheel Load (ESWL).- 10.2.3. Multiple wheel undercarriage configurations.- 10.3. Disposition of the wheels.- 10.3.1. Angles of pitch and roll during takeoff and landing.- 10.3.2. Stability at touchdown and during taxying: tricycle undercarriages.- 10.3.3. Gear length, wheelbase and track: tricycle undercarriages.- 10.3.4. Disposition of a tailwheel undercarriage.- 10.4. Type, size and inflation pressure of the tires.- 10.4.1. Main wheel tires.- 10.4.2. Nosewheel tires.- 10.4.3. Inflation pressure.- 10.5. Gear geometry and retraction.- 10.5.1. Energy absorption on touchdown.- 10.5.2. Dimensions of the gear.- 10.5.3. Gear retraction.- 11. Analysis of Aerodynamic and Operational Characteristics.- 11.1. Introduction.- 11.2. Terminology in relation to the determination of drag.- 11.2.1. Pressure drag and skin friction drag.- 11.2.2. Wake drag, vortex-induced drag, and wave drag.- 11.2.3. Form drag, profile drag, and induced drag.- 11.2.4. Zero-lift drag and lift-dependent drag.- 11.2.5. Breakdown for drag analysis.- 11.2.6. Bodies with internal flow.- 11. 3. Determination of aerodynamic characteristics.- 11.3.1. Reynolds number effects.- 11.3.2. Mach number effects.- 11.3.3. Low-speed polars.- 11. 4. The flight envelope.- 11. 5. Flight profile analysis and payload-range diagram.- 11.5.1. Operational climb.- 11.5.2. Cruise performance.- 11.5.3. Descent.- 11.5.4. Payload-range diagram and block time.- 11.6. Climb performance.- 11.6.1. Maximum rate of climb, time to climb and ceilings.- 11.6.2. Takeoff and landing climb.- 11.7. Airfield performance.- 11.7.1. Takeoff field length.- 11.7.2. Landing field length.- 11.8. Some aspects of operating economy.- 11.8.1. Economic criteria.- 11.8.2. Estimation of DOC.- 12. Evaluation and Presentation of a Preliminary Design.- 12.1. Presentation of the design.- 12.2. External geometry and structural arrangement.- 12.3. Layout drawings.- 12.4. Conclusion.- References.- Appendix A. Definitions Relating to the Geometry and Aerodynamic Characteristics of Airfoils.- A-1. General.- A-2. Wing sections.- A-2.1. Geometric definitions.- A-2.2. Aerodynamic definitions.- A-2.3. Nomenclature for some NACA sections.- A-3. Wings.- A-3.1. Wing planform.- A-3.2. (Wing) twist and incidence.- A-3.3. Aerodynamic definitions.- References.- Appendix B. The Computation of Circumferences, Areas and Volumes of Curves, Sections and Bodies.- B-1. Fuselage.- B-1. 1. General method.- B-1. 2. Quick method for bodies of revolution.- B-2. Wings and tailplanes.- B-3. Fuel tank volume.- B-4. Engine nacelles and air ducts.- References.- Appendix C. Prediction of Wing Structural Weight.- C-1. Introduction.- C-2. Basic wing structure weight.- C-3. High lift devices, spoilers and speedbrakes.- C-4. Wing group weight.- Appendix D. The Weight Penalty Method for Fuselage Structural Weight Prediction.- D-1. Survey of the methodology.- D-2. Gross shell weight.- D-2.1. Gross skin weight.- D-2.2. Gross stringer and longeron weight.- D-2.3. Gross standard frame weight.- D-3. Gross shell modifications.- D-3.1. Removed material.- D-3.2. Doors, hatches, windows and enclosures.- D-4. Flooring.- D-4.1. Passenger cabin and freight hold floors.- D-4.2. Various other floors.- D-5. Pressure bulkheads and frames.- D-5.1. Pressure cabin bulkheads.- D-5.2. Wheelbays for retractable undercarriages.- D-6. Support structure.- D-6.1. Wing/fuselage connection.- D-6.2. Engine support structure.- D-6.3. Other support structures.- D-7. Additional weight items.- References.- Appendix E. Prediction Methods for Lift and Pitching Moment of Aircraft in the En Route Configuration.- E-1. Applicability of the methods.- E-2. Contributions to the lift.- E-3. Lifting properties of airfoil sections.- E-3.1. The zero-lift angle.- E-3.2. Lift-curve slope.- E-3.3. Maximum lift.- E-4. Wing lift and lift distribution.- E-4.1. Lift-curve slope.- E-4.2. Spanwise lift distribution.- E-4.3. Zero-lift angle.- E-4.4. Maximum lift.- E-5. Pitching moment of the wing.- E-5.1. Aerodynamic center.- E-6. Wing/fuselage interference effects on lift.- E-7. Wing/fuselage pitching moment.- E-7.1. Aerodynamic center.- E-8. Nacelle and propeller contributions.- E-9. Lift of the complete aircraft.- E-9.1. Tailplane lift.- E-9.2. Total trimmed airplane lift.- E-9.3. Wing/body incidence.- E-9.4. Trimmed lift curve.- E-10. Airplane pitching moment and neutral point (stick fixed).- E-10.1. The stick-fixed neutral point.- E-10.2. Horizontal stabilizer incidence.- E-10.3. Pitching moment curve.- References.- Appendix F. Prediction of the Airplane Polar at Subcritical Speeds in the en Route Configuration.- F-1. Drag components.- F-2. Primary components of vortex-induced drag.- F-2.1. Untwisted plane wings.- F-2.2. Drag due to twist.- F-2.3. Wing tip correction on vortex-induced drag.- F-2.4. Vortex drag induced by fuselage lift.- F-2.5. Nacelle contribution.- F-2.6. Horizontal tailplane contribution.- F-3. Profile drag of smooth, isolated major components.- F-3.1. The flat plate analogy.- F-3.2. Wing sections.- F-3.3. Wings.- F-3.4. Fuselages and tail booms.- F-3.5. Engine nacelles.- F-3.6. Tailplane profile drag.- F-4. Subcritical interference effects and corrections.- F-4.1. Wetted area corrections.- F-4.2. Wing/fuselage interference.- F-4.3. Nacelle/airframe interference.- F-4.4. Tailplane/airframe interference.- F-5. Protuberances, surface imperfections and other extra’s.- F-5.1. Fixed undercarriages.- F-5.2. Canopies and windshields.- F-5.3. Wheel-well fairings and blisters.- F-5.4. External fuel tanks.- F-5.5. Streamlined struts.- F-5.6. Powerplant installation drag.- F-5.7. Excrescences, surface imperfections and other extra’s.- References.- Appendix G. Prediction of Lift and Drag in the Low-Speed Configuration.- G-l. Introduction.- G-2. Effect of trailing-edge flap deflection on airfoil section lift.- G-2.1. General aspects.- G-2.2. Lift increment at zero angle of attack.- G-2.3. Maximum lift coefficient.- G-2.4. Lift-curve slope.- G-3. Lift of aircraft with deflected trailing-edge flaps.- G-3.1. Wing lift.- G-3.2. Various contributions.- G-3.3. Contribution of the horizontal tailplane.- G-4. Prediction of the low-speed drag polar.- G-4.1. Profile drag.- G-4.2. Vortex-induced drag.- G-4.3. Trim drag.- G-5. Leading-edge high-lift devices.- G-5.1. Sections with plain leading-edge flaps.- G-5.2. Sections with slats and Krueger flaps.- G-5.3. Wing lift with leading-edge devices.- G-5.4. Drag due to leading-edge devices.- G-6. Drag due to extension of a retractable undercarriage.- G-7. Ground effects.- G-7.1. Ground effect on lift.- G-7.2. Ground effect on drag.- G-8. Drag due to engine failure.- G-8.1. Engine windmilling drag.- G-8.2. Propeller drag.- G-8.3. Drag due to the asymmetric flight condition.- References.- Appendix H. Procedures for Computing Turbo-Engine Performance for A...