Conceptual Design and Configuring Airplanes Some basic principles of airplane design

1. Conceptual Design and Configuring Airplanes Some basic principles of airplane design Affiliate Professor Department of Aeronautics and Astronautics University of Washington Seattle, WA John H. McMasters Technical Fellow The Boeing Company john.h.mcmasters@boeing.com and April 2007 Ed Wells Partnership Short Course Based on: American Institute of Aeronautics and Astronautics (AIAA) & Sigma Xi Distinguished Lectures & Von Kármán Institute for Fluid Dynamics Lecture Series: “Innovative Configurations for Future Civil Transports”, Brussels, Belgium June 6-10, 2005

2. Airplane Design: Past, Present and Future – • An Early 21st Century Perspective • John McMasters • Technical Fellow • Ed Wells Partnership • The central of several purposes of this course is to examine the co-evolution of our industry, aeronautical technology, and airplane design practice in a broad historical context. Attention then focuses on speculations on possible future trends and development opportunities within an unconventionally broad and multi-disciplinary context. It may then be shown that while aeronautics may be a “maturing industry”, there are numerous opportunities for further advance in our ever-changing enterprise. The emphasis throughout will be concepts and ways of thinking about airplane design in a systems sense rather than on the details of the methodologies one might use in design. The material for this course is a continuing work in progress and represents the instructor’s personal, sometimes idiosyncratic perspective which is in no way intended to reflect an official position of The Boeing Company or its current product development strategy. • Course Objectives: • Provide familiarization to non-specialists on the topics to be discussed • airplane design, • systems thinking, • the value of very broad multidisciplinary inquiry) • Present airplane design and its evolution in a very broad historical context • Present one perspective on a general approach to airplane configuration synthesis at the • conceptual level • Provide a basic aeronautics and airplane design “vocabulary” • Stimulate thought and imagination about the future of aeronautics • Target Audience: • Anyone interested in airplanes and aeronautical technology in a very broad, • multi-disciplinary system sense.

3. WARNING ITAR and EAR Compliance Important Security Information: Registration for this course (the following notes for which contain no ITAR/EAR-sensitive information) does not enforce the International Traffic in Arms Regulations (ITAR) and Export Administration Regulations (EAR) in any discussions that may result from it. Each attendee is responsible for complying with these regulations and all Boeing policies. EAR/Compliance Home Site: http://policyplus.boeing.com/PS/PDF/DDD/PRO-2805.pdf ITAR/Compliance Site: http://policyplus.boeing.com/PS/PDF/DDD/PRO-174.pdf

4. A Area (ft.2, m2) a Speed of sound (ft./sec., m/s) AR Aspect ratio, b/č = b2/S b Wing span (ft., m) č Average wing chord (ft.,m) CF Force coefficients (lift, drag, etc.) = F/qS Cℓ Section (2D) lift coefficient CM Moment coefficient = M/qSĉ Cp Pressure coefficient = Δp/q D Drag force (lb., N) E Energy (Ft.-lbs., N-m) e “Oswald efficency factor” ew Wing span efficiency factor (= 1/kw ) F Force (lift, drag, etc.) (lbs., N) H Total head (reservoir pressure) I Moment of inertia kw Wing span efficiency factor (= 1/ew) L Lift force (lb., N) ℓ Length (ft., m) M Mach number (V/a) M Mass (kg) M Moment (ft. lbs., N m) P Power (ft.-lbs./sec., N-m/sec.) p Static pressure (lbs./ft.2) q Dynamic pressure (lbs./ft.2) = ½ρV2 R Range (mi., km) Rn Reynolds number (ρVℓ / μ) S Wing area (ft.2, m2) T Thrust (lb., N) T Temperature (oF) u Local x-direction velocity component V Velocity, Speed (ft./sec., m/s, mph, km/h) v Local y-direction velocity component w Downwash velocity (ft./sec., m/s) ż Sink rate (vertical velocity) (ft./sec., m/s) Greek: α Angle of attack (deg.) Γ Circulation γ Climb or glide angle (deg., rad.) γ Ratio of specific heats in a fluid ε Wing twist angle (deg.) θ Downwash angle (deg.) φ Velocity potential Λ Wing sweep angle (deg.) μ Dynamic viscosity ν Kinematic viscosity (μ/ρ) ρ Fluid mass density (kg/m3) Notation and Symbols Used

5. Presentation Overview • Conceptual Design and Configuring Airplanes • Some basic principles of airplane design

6. The Book of Genesis From The Aerospace System Designer’s Bible By W.B. Gillette & J.H. McMasters And on the first day there was gravity and the spirit of Newton said: On the fifth day a tiny voice from the wilderness cried out: “…don’t forget Stability and Control.” And this was echoed by various multitudes crying: “…environmental control systems, ground support equipment, and etc.” far into the night of the sixth day. And on the final day, the spirit of Maynard Keynes proclaimed: “He who controls the purse strings, controls the Policy!” and there was Economic Reality. and Matter became weighty. And then there was boundless energy and it was consolidated and Einstein quoth: and there was Motion, but it was merely transverse. And on the third day, from the heavens, a voice cried out: and there was Lift. But on the fourth day, the Devil said: Caveat emptor, Amen. and there was Drag.

7. Special Interest Groups A completed airplane in many ways is a compromise of the knowledge, experience and desire of the many engineers that make up the various design and production groups of an airplane company. It is only being human to understand why the engineers of the various groups feel that their part in the design of an airplane is of greater importance and that the headaches in design are due to the requirements of the other less important groups. This cartoon “Dream Airplane” by Mr. C. W. Miller, Design Engineer of the Vega Aircraft Corporation, indicates what might happen if each design vs. production group were allowed to take itself too seriously.

8. Dream Airplanes (One Person’s Dream may be Another’s Nightmare) ..after dining with Airbus..Boeing Sauna Piano lounge Payloads Marketing Schizophrenia Aft Super computer Aerodynamics Fwd Super computer Structures Flight Controls Weights The Boeing Company Propulsion Manufacturing Noise Hecho en México y Chile J.H. McMasters (circa 1985)

9. Engineering (Design) Isn’t Done For Its Own Sake, It Is Practiced in a Context The “Design Onion” Societal Needs & Implications Tastes & Fashion • Philosophy • Why are we here? • Why are we doing • this ? Economics Manufacturing Politics Engineering (Design & Analysis) Business & Finance Marketing Customers (Operational Considerations) Resource Availability History Nationalism Tribalism Theology Environmental Impact & Consequences “Everything in this world is connected to everything else”. Think “system of systems”.

10. Traditional System View A “System of Systems” Approach Perspectives on Airplane System Design(With the specific or implicit objective of improving the air transportation system.) If one doesn’t consider the whole system, jumping to the conclusion that a particular sub-system is the best solution may result in a dumb or futile design effort. Design requirements, objectives and constraints Airplane System Life, the Universe And Everything Wing Sub-system World Economic System High-Lift Sub-system World Transportation System Flaps ? New Airplane System ? Flap Actuators Alternative System ? Somewhere down here is a sub-system an individual designer can deal with. A Suite of Systems ? Design requirements, objectives, and constraints.

11. Conceptual Design Preliminary Design Detail Design Design Support Design Objectives An optimized system, defined in sufficient detail to Offer to customers for sale Allow performance, cost, etc. guarantees to be written into legally binding contracts A complete design [the “drawings” ] including manufacturing requirements, etc. that meets guarantees and allows production of the required hardware Derivatives, modifications, up-grades, in-service deficiency corrections, etc. Airplane Design Taxonomy • A “configuration concept” that • appears to meet requirements • and constraints – as a system.

12. The Conceptual/Preliminary “Design Process” “ A problem properly posed is half solved” Resources Design Requirements (“musts”) & Objectives (“wants”) Systems Manufacturing Meets DR&Os ?? Trade Studies & Testing Other external factors The Design Controls Integration Software Propulsion Yes ! Proceed Aerodynamics No ! Structures • What would happen if: • Requirements change • Constraints change • Changeassumptions Reject ? or Marketing

13. 175% Potential Cost Overrun Curve 150% Cost Avoidance Area 125% Life Cycle Cost – Airplane Design Like Aerodynamics is an “Initial Value Problem” Cumulative Percent of Life Cycle Cost 100% • • 75% Locked In Curve • 50% $ expenditure 25% • • • 0% Concept Exploration Program Definition Engineering Development Production and Operational Support Program Phase Initial Decisions Affect the Slope of the “Locked In” Curve

14. The sum of a set of local optima is not necessarily a global optimum(e.g. an optimum wing doesn’t necessarily produce an optimum airplane) On the Nature of Optima “Performance” Δ “Flat” Optimum “Size/Shape”

15. Exploring the Design Space Boundary of the feasibledesign space Range of Past Experience & Data Terra incognita Performance (or cost) What might lurk in places we’ve never been before? We have become slaves to our data bases. “Configuration” (Size/shape)

16. The V/STOL Merry Go Round(A Now Classic “Configuration Matrix”) The more ideas you have, the more opportunities you’ve got.

17. German Aeronautical Progress (1944-45) Messerschmitt Me 262 First operational jet fighter Arado Ar 234 First operational jet bomber Messerschmitt (Lippisch) Me 163 Heinkel He 162 Junkers Ju 287 Swept-forward wing jet bomber Heinkel He 280 Messerschmitt P. 1101 DFS 228 Horton Ho 229

18. German Aeronautical Progress to 1945 Focke-Wulf Ta 283 Ramjet fighter Blohm und Voss P. 188 W-wing bomber Focke-Wulf Ta 183 Messerschmitt variable sweep fighter Blohm und Voss P.202 Oblique-wing fighter Lippisch P.13a Delta wing fighter Focke-Achgelis Fa 269 Tilt Rotor Sänger Antipodal Bomber http://www.luft46.com/

19. Some Basic “Laws” of Airplane Design • Innovation for mere innovation’s sake can be a great waste of time (and money) – never invent anything if you don’t have to • You never get something for nothing – someone, somewhere always pays for lunch • While the laws of economics are somewhat malleable, the laws of physics are not; thus • “If it looks good, it will fly good” is a myth that is sometime true • Simplicity is the essence of true elegance – it can also save weight and/or cost • If you can’t build it, you can’t sell or use it • They who control the purse strings control the policy– to avoid exercises in futility, learn how to close a business case • Grand concepts are easy – The devil is always in the details !

20. McDonnell XP-67 “Moonbat”

21. Fokker’s Rule: “If it looks good, it will fly good” is a myth that is sometime true….. McDonnell XP-67 “Moonbat” Dornier Do 335 “Anteater” To disparage a camel as a “horse designed by committee” is to completely ignore the obvious advantages of the camel over the horse in the environment in which the camel is intended to operate. Antonov An 2 (over 12,000 built since 1947) A-10 “Warthog” Boeing F-32 “Angry Frog”

22. Basic Laws of Airplane Design (cont’d) • In aeronautics, we live in a closed thermodynamic system in a largely Newtonian universe, thus: • Weight (W) < Lift (L) = ½ρ V2 CL S • Thrust (T) > Drag (D) = ½ ρ V2 CD S • D = Dparasite + Dinduced+ Dcompressibility + H.O.T. – 2/3 management requirements • DP ~ f(SWet, CL , Re) x speed (V)2 • Di ~ k [Lift (L)/span (b)]2x speed (V) -2 ~ k (nW/b)2 x V-2 • The sum of the moments equals the time-rate-of- change of angular moment (in a vector sense) • Rangejet = (M x L/D) x (tsfc)-1 x loge (Winitial/Wfinal) ew= 1/kw = theoretical wing span efficiency factor n = load factor = L/W Flying is easy; here lies the real challenge. (aerodynamics) ( propulsion) (structures/weights) • Grand concepts are easy – The devil is always in the details !

23. Force and Moments on an Airplane Yaw Velocity - V Lift - L Power [P] = TV If V = constant: L = W T = D Aerodynamic Efficiency = L/D Thrust - T Airplane longitudinal ref. axis D L F α V Angle of attack Drag - D Pitch Weight - W Roll

24. Forces on an Airplane in Steady [constant speed] Climb or Glide Lift (L) ~varies with airplane angle of attack Thrust (T) Angle of attack (α) Flight Velocity (V) Climb (or glide) angle (γ) γ Drag (D) Airplane geometric Reference axis Weight (W) Flight path axis In steady flight: Lift (L) = Weight (W) x cos γ Thrust (T) x cos α = Drag (D) + W sin γ Pavalilable > Prequired = T x V = [D + W sin γ ] x V γ(radians) ≈ T/W – (L/D)-1 By standard convention, the component of the total aerodynamic force on the airplane perpendicular to the flight path is the Lift (L) and that parallel to the flight path is Drag (D). The thrust need not align with with the flight path of the airplane reference axes, but by small angle approximations, the above relations hold well enough for conventional airplanes (or birds, etc.).

25. The Classic Breguet Range Equation Initial Weight (@ t =0) = Wi = W0 + Wpayload + Wfuel Final Weight (@ t= T) = WF = Wi – Wfuel For a jet aircraft: Thrust specific fuel consumption = tsfc (lbs. fuel/ lbs. thrust/ hr.) dR = V dt dW /dt = - T x tfsc = - D x tsfc dt = - dW/ D tsfc ∫0 dR = - [ V tsfc] ∫Wi dW/D T/ W = D /L (L/D) / W = 1/D R = + [V(L/D)/ tsfc] ∫ dW/W M = V/a For a Propeller-driven airplane: Power specific fuel consumption = psfc (lbs. fuel/unit power/hr.) Power (P) = TV = DV dt = - dW/ DV psfc Range – R @ V = constant Lift (L) = Weight (W) Thrust (T) = Drag (D) 0 T R WF Wi WF R = C1 [M (L/D) / tsfc] loge Winitial /WFinal (C1 is a numerical constant for range in mi., km, etc.) Payload Wpayload Max. Wpayload Range - R R = C2 [(L/D) / psfc] loge Winitial /WFinal (C2 is a numerical constant for range in mi., etc.) Max. range to include necessary fuel reserves.

26. Drag and Drag Estimation • Drag (D) = ½ ρ V 2 CD S CD = CDp + kwCL2/ π AR + CD wave • D = Dparasite + Dinduced + Dcompressibility + (trim, interference, excrescence,…) • Parasite drag: DP ~ f(Swet, CL , Re) x speed (V)2 • “Induced” Drag: Di ~ kw [Lift (L)/span (b)]2 x speed (V) -2 ~ kw (nW/b)2 x V-2 ew = 1/kw = theoretical wing span efficiency factor n = load factor = L/W AR = b2/S Parasite drag = Friction drag + “Form” (pressure) drag

27. The Parabolic Drag Polar Lift (L) = ½ ρ V2 CL S Drag (D) = ½ ρ V2 CD S Parabolic Drag Polar (Two-term polynomial curve fit ) Actual measured airplane drag polar Lift Coefficient CL L/Dmax CD = C1 + C2CL2 With: C1 = CDo C2 = 1/π AR e e = “Oswald” efficiency factor e = ew (theoretical wing span efficiency factor) 0 Drag Coefficient CD CD0 “Zero-lift” drag coefficient

28. Drag and Power Required Power (P) = Thrust (T) x Speed (V) Drag due to Lift (Induced Drag) - Di ~ W2( b V)-2 “Parasite” (viscous) Drag Dp ~ Swet V2 Power ( P)required = D x V Total Drag = Dp + Di Pavailable Power X Drag Vmin Vmax V*prop V*jet V*prop Speed – V Speed - V V* = Optimum Speed to Fly for Maximum Range

29. Dreams of Leonardo da Vinci

30. Fathers of Human Flight Wilbur Wright Orville Wright Otto Lilienthal 1867-1912 1871-1948 1848-1896