MAE3241 Ch01 Introduction (1)
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MAE 3241 AERODYNAMICS &FLIGHT MECHANICS
Introduction
Mechanical & Aerospace Engineering
Yongki Go
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MAE 3241 OverviewCourse contents:
Aerodynamics (70%)Forces and momentsFundamental principles and equationsInviscid incompressible flow
Flow over airfoils (2D)Flow over finite wings (3D)Effect of compressibility and viscosity
Flight mechanics (30%)Modeling concept in flight performance analysisSteady flight performanceAccelerated flight performance
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TextbooksPrimary:
Other useful books:
John Anderson,AircraftPerformanceand Design,1998
John Bertin,
Aerodynamicsfor Engineers,4th edition, 2001
John Anderson, Fundamentals ofAerodynamics, 5 th edition, 2011
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Lecture StylePpt lecture notes will be posted in ANGEL before the
lecture timeSome parts may be delivered by writing on whiteboard
Lecture notes are in summary form and contain parts thatyou will need to complete during lecture
Not a replacement for textbookIt is best to have the relevant lecture notes while attendinglectureIt is strongly suggested that you add your own notes toenhance your understanding on certain topicsSome of the exams may be open notes (open lecture notes andyour own notes but not open book )
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Aerodynamics Overview Aerodynamics : study of interaction of air and object due to
their relative motionPurpose of learning aerodynamics:
Calculate and predict: lift, drag, moments, heat transferUnderstand how these forces and moments are generatedUnderstand how interaction depends on flow conditions
Fluid propertiesRelative velocitiesTemperature, pressure, densityBody geometry
Knowledge of aerodynamics is very important in aircraftdesign
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Flight Mechanics OverviewFlight Mechanics : the science of predicting and controlling
the motion that results from the forces and moments actingon a flying object
Flying object of interest in this course: fixed-wing aircraft
Sub-areas of flight mechanics:Flight performanceFlight stability (statics and dynamics) and controlFlight simulationFlight control systems
MAE 3241 covers fundamental flight performance of fixed-wing aircraft
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Flight PerformanceFlight Performance concerns about how an aircraft responds
to the forces experienced during its motion through theatmosphere
Mainly looks at translational motionOften sufficient to consider aircraft as point mass at its CG
with all forces acting through it
Thrust 1
Thrust 2
Weight
Lift
Drag
CGCG
Weight
Lift
Thrust
Drag
Four forces of flight
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Importance of Flight PerformanceExamples of questions of concern in aircraft performance:
How fast, how slow and how high can it fly?How rapidly can it climb?How far and how long can it fly?How maneuverable is it?How long a runway is needed for its takeoff and landing?
Performance is one of the main drivers in aircraft design!
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The Four Forces of Flight
Aircraft flight performance estimation/analysis is based onthese four forces
Aerodynamic and propulsive characteristics of the aircraftdepend on airflow conditions
Depend on the atmospheric properties and aircraft motionitself
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Earths Atmosphere Earths atmosphere is a mixture of several gases
78% nitrogen, 21% oxygen, 1% othersAtmospheric properties ( pressure, temperature, density ) areconstantly varying
These variations affect aerodynamics and aircraft performance
Need a standard for aircraft performance comparison andflight testing purposesStandard Atmosphere (SA) is defined
Commonly used:International Standard Atmosphere (ISA)US Standard Atmosphere
Identical up to32 km
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Standard Atmosphere (SA)
RTp =
Based on defined averagevariation of T with altitude
From observational dataSA consists of isothermal andconstant gradient layers
Assumed to behave as perfectgas
Standard sea-level values for pressure, density, andtemperature:
R)g.ft.lb/(slu1716 J/(kg.K)287
=
= R RT p =
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Layers in ISA (1976)Layer Level
NameBaseGeopotential
Heighth (in km)
BaseGeometric
Heightz (in km)
LapseRate
(inC/km)
BaseTemperature
T (in C)
Base Atmospher ic
Pressurep (in Pa)
0 Troposphere 0 0 -6.5 15 101,325
1 Tropopause 11 11.019 0 -56.5 22,632
2 Stratosphere 20 20.063 1 -56.5 5,474.90
3 Stratosphere 32 32.162 2.8 -44.5 868.02
4 Stratopause 47 47.35 0 -2.5 110.915 Mesosphere 51 51.413 -2.8 -2.5 66.939
6 Mesosphere 71 71.802 -2 -58.5 3.9564
7 Mesopause 84.852 86 -86.2 0.3734
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Calculation of SA PropertiesIn the gradient layer:
a is the lapse rate (-6.5 x 10 -3 K/m in the troposphere)
g0 = 9.81 m/s 2 In the isothermal layer:
Software for SA properties calculation can easily be found in theinternet (beware of which SA model is used!)Properties of SA are usually tabulated
)( 11 hhaT T +=aRg
T T
p p
0
11
=
+
=1
11
0aRg
T T
constant=T ( )10
1
hh RT g
e p
p =( )10
1
hh RT g
e
=
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Sample of SA Table
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Aerodynamics = Fluid Dynamics?Aerodynamics: subset of fluid dynamics
Fluid dynamics encompass all fluids, aerodynamics focus onair
Specifically:Aerodynamics focus on the forces generated on bodies in airflow (i.e. lift and drag)Aerodynamics typically concern more to external flows (i.e.flows around bodies like aircraft, car, etc.)Aerodynamics provide the necessary parameters for flightmechanics and control studies
Much of the governing concepts between aerodynamics andfluid dynamics are similar
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Some Fundamentals Aerodynamic Variables
Variable Symbol Dimension SI Unit English Unit
Pressure p ml -1t -2 Pa (N/m 2) psf (lb/ft 2)
Density ml -3 kg/m 3 lb/ft 3 Temperature T K oR
Viscosity(dynamic)
ml -1t -1 Pas (kg/( sm )) lbs /ft2
m: dimension of mass
l: dimension of lengtht : dimension of time
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Airfoil vs. WingAirfoil: cross-section geometry of aerodynamic force
generator elements (wings, tails, control surfaces)
In analysis:Airfoil 2D flow (part of infinitely-long wing)Wing 3D flow
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Aspect Ratio
Definition: S b
AR
2
b: wingspanS : wing area
S
b
T i p
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Some Important Dimensionless Parameters (1) Reynolds number : ratio of inertia forces to viscous forces
Reynolds number indicates when viscous forces areimportant and when viscosity may be neglected
High Re: viscosity can be neglectedLow Re: viscosity cannot be neglected
Vl=Re V : flow speedl: reference length
Within B.L. flow:highly viscous(low Re)
Outside B.L. flow(high Re)
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Some Important Dimensionless Parameters (2)Another important quantity that is usually extracted from the
flow property is the speed of soundSpeed of sound depends on temperature only
Mach number : ratio of flow velocity to the speed of sound
RT a =v
p
c
c=
For perfect gas: 4.1=
aV
M =
Mach number, M
1.0 2.0 3.0 0.3 4.0 5.0 M crit
Subsonic Transonic Supersonic Hypersonic
Compressible Incom- pressibl e