AERODYNAMICS

INTRODUCTION- Aerodynamics is a branch of fluid mechanics. - A fluid is defined as a substance, liquid or gas, that readily and continuously changes shape when acted upon by external forces.

- Aerodynamics deals with

- Study of the properties of air

-Effect of forces upon it

-Analysis of forces that govern the relative movement between air and a body.

DEFINITIONS & UNITSMass - Matter - kilogram, Pounds, Slugs

Inertia – Quality - Newton’s first Law

Velocity – Rate of change of position m/s, ft/s

Momentum = Mass x Velocity

Force – Push or Pull to change momentum

Forces in equilibrium

• Acceleration = Force/Mass, m/s² or ft/sec²

• Gravity constant – 9.81 m/s² or 32 ft/s²

• Acceleration due to gravity - Same units

• Terminal velocity

• Weight - Force due to gravity, Newton

• C of G – Point through which weight acts

• Density - Mass/unit volume [ kilogram]/v³

Motion in: Force required,curved Magnitude depends on massPath and acceleration needed

: Rate of change of momentum in direction of force applied: Acceleration even when speed constant: Vertical Circle

Centripetal Force = mv² where v²(Centre seeking) r r

is the accelerationCentrifugal Force: Outgoing; Equilibrium

Work : Force x distance (Newton meter) 1 Newton meter = 1 Joule

Power : Rate of doing work Newton meter/ sec or Joule/ sec

1 Joule/ sec is = 1 watt ; 1 HP = 745.7 watts

Energy : Ability to do work; unit as work

Kinetic Energy = ½ mV² Joules

Energy & momentum : ½mv² (dissipated) mv (constant)

UNITSTemp : ºC, ºF, KForce : NewtonWeight : Newton (mass x g)

or (Kg x 9,81 m/s²)Nautical mile = 6280 ftStatute mile = 5280 ftKilometer = 3280 ft

SYMBOLSTemp : t ; Time (sec) : t ;Distance : S ; Acceleration : a .Initial velocity : u ; Final velocity : v ;

FORMULAEs = ut ; v = u + at ;s = ut + ½ at² ; v² = u² + 2as

Force : vector Qty (magnitude & direction), can be added, subtracted or resolved

Moment : Force x ┴ distance from point to line of force In moments there is no movement

Pressure : Force/unit area(Newton/sq meter)

Pressure in a fluid : Only magnitudeNo direction; ┴ to the surface

Force due to pressure has direction,Pressure increases with depth

Pressure : Pressure due to height of fluidhead : 760mm of Hg or 10mtrs of H2O

(instead of Newton/Sq mtr) proper unit is N/m² also called Pascal (Pa) 100 Kn/m² = 1 bar

Archimedes : Upward ThrustPrinciple = Weight of thefluid displaced

increases with depth

Gas Law :

Pressure = Gas constant x Absolute temp density

OR P = R x Tρ

OR P x V (volume) = K (constant) T

THE ATMOSPHERE

Atmosphere is a column of air extending vertically up to a height of 500 miles above the earth’s surface.

Air is a viscous, compressible fluid, which is assumed to be incompressible and ideal gas up to a speed of 300 knots or 0.4M

Some of the important properties of air exhibited in the atmosphere are:

QUALITIES OF AIR

Visibility of air : Invisible

Density : Low ; 1/800 of water ; Flights possible due to density.

It reduces with height.It varies in proportion to the pressure and isinversely proportional to the temperature.

Inertia : Obeys all laws of mechanics

Pressure : Average at sea level due to weight of the atmosphere is 101 kN/m² or 760 mm of Hg ; Reduces with height. Rate is much greater at ground due to compressibility.

Humidity : Is the amount of water vapour present in the air. Density of water vapor is about 5/8th that of dry air.

Temperature : Reduces with height @ 6.5º C per 1000 m (Lapse rate)

up to 11,000m (Troposphere) OR 1.98º C/1000ft upto 36,090 ft.

The temp is constant above (Stratosphere). Tropopause is the interface in between. Lapse rate & height of

tropopause change with latitude.

Viscosity: Resistance of one layer to movement over next layer

International Standard Atmosphere (ISA): For aircraft performance

At sea level

Temp is +15º C,

Pressure is 101.325 kN/m²

Tropopause is 11,000 m

Lapse rate is 6.5º C per 1,000 m.