1. Conceptual Design and Configuring Airplanes Some basic principles of airplane design
John H. McMasters
Technical Fellow
The Boeing Company
and
Affiliate Professor
Department of Aeronautics and Astronautics
University of Washington
Seattle, WA
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.

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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.
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4. Notation and Symbols Used
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)

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

6. The Aerospace System Designer’s Bible
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. (One Person’s Dream may be Another’s Nightmare)
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
Politics
Manufacturing
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. Perspectives on Airplane System Design (With the specific or implicit objective of improving the air transportation system.)
Traditional System View
A “System of Systems” Approach
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. Airplane Design Taxonomy
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.
Conceptual Design
Preliminary Design
Detail Design
Design Support
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”)
Meets
DR&Os ??
Systems
Manufacturing
Trade
Studies
&
Testing
Other
external
factors
The
Design
Controls
Integration
Software
Propulsion
Yes !
Proceed
No !
Aerodynamics
Structures
Reject ? or
What would happen if:
Requirements change
Constraints change
Change assumptions
Marketing

13. Initial Decisions Affect the Slope of the “Locked In” Curve
Life Cycle Cost – Airplane Design Like Aerodynamics is an “Initial Value Problem”
175%
150%
125%
Cost
Avoidance
Area
Potential Cost Overrun Curve
Cumulative Percent of Life Cycle Cost
100% • •
75%
Locked In Curve •
50%
$ expenditure
The initial slope of the locked in curve is set in the initial phases.
Cannot determine the slope at the very beginning, in fact, it’s tangent to the y-axis
The people involved in product design have to have lots of experience
The configurator should be in charge of the early process
The configurator role goes away as the project proceeds.
The configurators job is to set the initial curve. After that, it’s just general arrangement maintenance
The initial decisions affect the slope of that curve.
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. On the Nature of Optima
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)
“Performance” Δ
“Flat” Optimum
“Size/Shape”

15. Exploring the Design Space
Boundary of the feasible design 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 First operational jet fighter
Arado Ar First operational jet bomber
Heinkel He 162
Messerschmitt (Lippisch) Me 163
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

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) = ½ ρ 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
Weight - W
Pitch
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)
Weight (W)
Airplane geometric
Reference axis
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 – V = constant
Lift (L) = Weight (W)
Thrust (T) = Drag (D) 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)
CD0
“Zero-lift” drag coefficient
Drag Coefficient CD

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 X
Power
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