FD AE2301-NOL

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    Y.K.SINHA

    RAJALAKSHI ENGINEERING COLLEGE

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    Why should we study properties of

    atmosphere?

    VariationofTemperature with Altitude

    VariationofPressure with Altitude

    VariationofDensity with Altitude

    Tables ofStandard Atmosphere

    TOPICS TO BE COVERED

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    Why should we study

    Atmospheric Properties Engineers designflight vehicles, turbine

    engines and rockets that willoperate at various

    altitudes.

    They cannot design these unless the

    atmospheric characteristics are not known.

    For example,

    SV

    LCL

    2

    2

    1

    g

    !

    V

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    What is a standard

    atmosphere? Weather conditions vary around the globe,

    from day today.

    Taking all these variations intodesign is

    impractical.

    A standard atmosphere is therefore defined,

    that relates fight tests, wind tunnel tests and

    general airplane design to a commonreference.

    This common reference is called a

    standard atmosphere.

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    International Standard Atmosphere

    Standard Sea Level Conditions

    Pressure 101325 Pa

    Density 1.225 Kg/m3Temperature 15oC or 288 K

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    Temperature vs. Altitude

    Temperature, degreesAltitude,

    km

    . 6

    km

    6.66

    km

    47 km, T= .66

    km

    79 km

    6 .66

    9 km

    Troposphere

    tratosphere

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    SYMMETRIC AND UNSYMMETRIC AIRFOIL

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    CL VS ANGLE OF ATTACK CURVE

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    Characteristic Curves

    Available for

    all classes of

    standard

    aerofoils.

    Include plots

    ofCD, CL, L/D, Example NACA 2421

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    DRAG

    DRAG IS THE RESOLVEDCOMPONENT OF THECOMPLETE AERODYNAMICFORCE WHICH IS PARALLEL TOTHE FLIGHT DIRECTION(OR

    RELATIVE ONCOMINGAIRFLOW).

    IT MUST ALWAYS ACT TOOPPOSETHE DIRECTION OFMOTION.

    IT IS THE UNDESIRABLE

    COMPONENT OF THEAERODYNAMIC FORCE WHILELIFT IS THE DESIRABLECOMPONENT

    LIFT

    DRAG

    RESULTANT FORCE

    C.P

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    TYPES OF DRAG

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    VARIATION OF DRAG WITH SPEED

    Induceddrag decreases as V

    increases, because we need less

    values of CL at high speeds.

    Otherdrag forces (form,

    skin friction , interference)

    increase.

    Result: Drag first drops, thenrises.

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    Minimum Drag & Power Speeds

    This gives a simple theoretical relationshipbetween the flight speeds requiredforminimum drag and power conditions.

    i.e. VP,min = (k2/3k1)1/4= 0. (k2/k1)

    1/4

    = % VD,min

    Also, at minimum powerspeed,

    3k1V2 = k2V

    -2

    @ 3CD0 = CL2 / (TAe)(orlift-induceddrag= 3 x parasite drag)

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    Altitude Effects on PR v Airspeed

    PR varies with 1/W (orVo /V). Minimum power required increases with

    altitude but VP,min fixed ifplotted as

    equivalent airspeeds. True airspeed

    for minimum

    power condition

    increases withaltitude.

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    Minimum Drag & Power Speeds

    Since P = D x V,@ D = P /V so a single plotofP against V may be used todetermine

    bothVP,min & VD,min.

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    Available Thrust & Power (TA, PA)

    Required thrust is determined byaerodynamics & weight considerations whileavailable thrust and power are functions ofthe propulsion system performance.

    Bigdifferences between piston-props &turbojets so considered separately. Turbojets & fans have reasonably constant thrust

    values sothrust-rated.

    Piston-props arepower-rated. Both thrust & power reduce with increased

    altitude (reduceddensity).

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    Available Thrust & Power

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    Maximum Velocity

    May be determinedfrom plots ofeitherTR (or PR) and TA (or PA) against V.

    Intersectionofcurves gives maximum

    speed capability and possibly alsominimum speed capability (if

    intersection is above stall speed).

    Piston-props and turbojets/fans usually

    considered separately.

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    Maximum Velocityfor Piston-Prop

    Most convenientlydeterminedfrom plots ofPR and PA against V.

    Dashedlines give

    curves atincreased altitude

    - both minimum

    and maximum

    speeds affected inthis case.

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    Maximum Velocityfor Jet/Fan

    Most convenientlydeterminedfrom plots ofTR and TA against V.

    Dashedlines give

    curves atincreased altitude

    - both minimum

    and maximum

    speeds againaffected in this

    case.

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    Breguet Formulae for

    Piston-Prop A/CRange FormulaR = (L/sfc).(CL/CD).ln(W0/W1)

    Where

    W0 =gross aircraft weight, WF=fuel weight

    W1 =W0 - WF, L = propeller efficiency

    Endurance Formula

    E = (L/sfc).(CL1.5

    /CD). (2VS)(W1-0.5

    - W0-0.5

    )

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    Range & Endurance Formulae

    for Jet/Fan A/C

    Endurance Formula

    E = (1/tsfc).(CL/CD).ln (W0/W1)

    Range Formula

    R = 2(2/VS). (1/tsfc).(CL0.5/CD).(W1-0.5 - W0-0.5)

    Note that range is altitude dependent while

    endurance is not - opposite for piston-props.

    However, tsfc also varies with altitude andeventually increases.

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    Climbing

    Consider aircraft in a steadyunacceleratedclimb with vertical climb speedofVc.

    Force balance gives:cos c

    L WK!

    sinc

    T D W K!

    ( ) /

    sin /c c

    W

    V VK

    @ !

    !

    ( ) /c

    V T D V W @ !

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    Ceilings

    Absolute ceiling- altitude forVc,max = 0

    Service ceiling- altitude forVc,max = 100

    ft/min

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    Diving

    Similar to the steadyunaccelerated climbcase.

    Force balance fordive speedor sink rate

    (Vd)gives:cos d

    L WK!

    sind

    T D W K!

    ( ) /

    sin /d c

    D T W

    V VK

    @ !

    !

    ( ) /d

    V D T V W @ !

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    AIRCRAFT STABILITY

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    THANK YOU