MAE3241 Ch01 Introduction (1)

8/13/2019 MAE3241 Ch01 Introduction (1)

1/20

MAE 3241 AERODYNAMICS &FLIGHT MECHANICS

Introduction

Mechanical & Aerospace Engineering

Yongki Go


2/20

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


3/20

TextbooksPrimary:

Other useful books:

John Anderson,AircraftPerformanceand Design,1998

John Bertin,

Aerodynamicsfor Engineers,4th edition, 2001

John Anderson, Fundamentals ofAerodynamics, 5 th edition, 2011


4/20

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 )


5/20

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


6/20

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


7/20

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


8/20

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!


9/20

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


10/20

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


11/20

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 =


12/20

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


13/20

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

=


14/20

Sample of SA Table


15/20

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


16/20

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


17/20

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


18/20

Aspect Ratio

Definition: S b

AR

2

b: wingspanS : wing area

S

b

T i p


19/20

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)


20/20

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

Documents

MAE3241 Ch01 Introduction (1)