Aeronautical Eng.

8/18/2019 Aeronautical Eng.

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Week 01: The Atmosphere


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SUMARY

Characteristics of the Atmosphere Hydrostatic Equation

Manometric Equation

Standard Atmosphere


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CHARACTERISTICS OF

THE ATMOSPHERE

04 Fundamental Properties (describe the state of air): DENSITY: Amount of mass per unit of volume (KG/M3) or

(SLUG/FT3). Symbol (ρ, RHO).

PRESSURE: It is the force exerted by a fluid (liquid or gas) per unitarea. (N/M2) or (LB/FT2). Symbol (P).

TEMPERATURE: Is a measure of the average kinetic energy of theair molecules as they . Celsius (°C), Fahrenheit (°F), Kelvin (°K) andRankine (°R). Symbol (T).

VELOCITY: Is the net motion of the air. Velocity is a vector.(magnitude and direction). Symbol (V o V).


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CHARACTERISTICS OF

THE ATMOSPHERE

Equation of State: Describes the relationships between thedensity, temperature and pressure of a gas, or a mixture of gasessuch as air.

= ρ

R: the proportionality constant is called the gas constant:

= 287

()(°) 1716

()()

()(°)

THIS EQUATION IS CALLED THE PERFECT GASEQUATION


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HYDROSTATIC EQUATION Consider an infinitesimal mass of air in a static (all velocities are zero)

atmosphere.

= y = 0

ρ =

= ρ

(P+dP) dA

dA

dh

PdA


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MANOMETRIC EQUATION

Fluid Pressure = Constant

The two reservoirs

at different pressures

The pressure at point 1

must be the same as P1

= ρ

(Hydrostatic Equation)

=

(Density and Gravity are Constant)

= (Manometric Equation)


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BAROMETER

It is a special type of manometer in which one end (thehigher end) of the tube is completely sealed off and filledwith fluid.

Barometers are usually filled with mercury and are often

used to measure atmospheric pressure


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PITOT – STATIC TUBE


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Altimeter

Airspeed Indicator

FLIGHT INSTRUMENTS


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Vertical Speed Indicator

FLIGHT INSTRUMENTS

Air flowing out of the bottle

indicates that the altitude of theaircraft is increasing.

Air flowing into the bottleindicates that the aircraft is

descending


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STANDARD ATMOSPHERE

The atmosphere is asumed to be static so that the velocity inthe model is everywhere zero.

The other three point properties, density, pressure andtemperature, must be determined everywhere in the

atmosphere to define the model The starting point is established at mean seal level (MSL)

TEMPERATURE (T0): 288,16°K = 518,69°R

PRESSION (P0): 101,325 N/m2 = 2116,2 lb/ft2 DENSITY (ρ0): 1,225 kg/m

3 = 0,002377 slug/ft3


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Temperature Model An algebraic model is defined for the variation of

temperature with altitude in the atmosphere

STANDARD ATMOSPHERE


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Gradient Layers In altitude bands where temperature varies, the variation with altitude is linear

and given by:

=

≡

=

=

−

=

−

+

Ing. Carlos Saito Villanueva

STANDARD ATMOSPHERE


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Common Uses of the Standard Atmosphere

The properties of the standard atmosphere are used frequently as

reference conditions for aircraft performance predictions.

For example, aircraft takeoff performance depends in part on the air density.The density for a given takeoff calculation is often given as a density altitude.Density altitude, which is given the symbol (h

ρ), is that altitude in the standard

atmosphere that has the correspoding density. If the density is for instant,0.00199 slug/ft3, then the density altitude would be given as 6000ft.

Likewise, pressure altitude (hP) and temperature altitude (ht).

STANDARD ATMOSPHERE

Aeronautical Eng.

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