# Principles of Flight - 1

First chapter of ATPL Principles of Flight

- Created by: Gul
- Created on: 01-06-09 10:32

## Newton's Laws of Motion

**1) A body at rest will remain at rest & moving body will continue to move at same speed in same direction unless an external force is applied to it.**

**2) F = m * a**

**To change state of body, a force must be exerted on it.**

**3) F = m * g**

**For every action there is an equal and opposite reaction.**

## Work Done + Power

**Work Done = F * Distance Moved (Nm or J)**

**Power = Work Done/Time (J/s or W)**

## Properties of Atmosphere

**Properties of air mass defined by:**

**-Pressure**

**-Temp**

**-Density**

**-Viscosity**

## Pressure (atmosphere)

**1) Pressure decrease with altitude**

**2) Pascal's Law: In fluid at rest - pressure acts in all directions equally**

**3) Pressure = Force/Area (N/m^2)**

## Temperature (atmosphere)

**1) Temp of fluid = measure of it's molecular motion**

**2) Temp at which molecular motion occurs = ABSOLUTE ZERO (-273K)**

## Density (atmosphere)

**1) Density = ratio between mass of fluid and it's volume**

**2) Density = Mass/Volume (kg/m^3)**

## Viscosity (atmosphere)

**1) Viscosity of air = measure of resistance of one layer of air to movement over neighbouring layer**

**2) Heavy oil more viscose than water so takes longer to flow.**

**3) Air as fluid --> fluid free flowing + no definite shape but conforms to shape of container**

## Relationship Between Presure/Temp/Density

**Density of air mass changed by:**

**1) Changing volume occupied by air**

**2) Varying pressure/temp of air**

**ρ α P/T**

**( ρ = rho )**

**Density directly proportional to Pressure**

**Density inversely proportional to Temp**

## Fluid Compressibility

**1) Liquids --> incompressible --> nearly constant Density**

**2) Gases --> compressible --> variable Density**

**3) Air mostly incompressible at speeds below speed of sound**

**4) > 300 KTS air starts to behave like compressible fluid.**

## Local Speed of Sound (LSS)

**1) Speed at which small pressure disturbances propagated through air.**

**2) Solely a function of air temp**

**LSS = 38.94 * square root of Temp Kelvin**

**To predict compressibility the Mach Number must be known!**

**(MN = TAS/LSS)**

## Static Pressure

**1) Exerted in all directions**

**2) Static P of atmosphere caused by weight of air acting on surface equally in all directions**

## Dynamic Pressure - (q)

**½ρV²**

**Dynamic pressure increases as Static pressure decreases.**

## Bernoulli's Theorem

**1) Pstat +** **½ρTAS² = constant**

**2) Ptot = p + q**

**(Total Pressure = Static Pressure + Dynamic Pressure)**

**3) Increased speed (q) = decreased p**

**Decreased speed (q) = increased p**

**4) At zero speed Ptot = Ps**

## Equation of Continuity

**Principle of mass conservation = mass is constant (cannot be created or destroyed)**

**ρ A V = constant**

**Stationary subsonic streamline flow pattern, streamlines converge so Ps decreases and velocity (Pd) increases.**

**In convergent tube with incompressible subsonic flow:**

**Ps decreases**

**Pd increases**

**Ptot constant**

**ρ1 =** **ρ2 if cross-sectional area of tube changes**

## Venturi Tube

1) Constriction in tube - speed of flow increased to maintain same mass flow

2) As V increased, q increased and p decreased

(Speed increased, Pd increased and Ps decreased)

3) As air flows through converging section of venturi tube:

Ps decreases -----> V increases -----> Mass flow constant

## Airspeed Measurement

**Pitot Tube**

**Measures total pressure (stagnation pressure)**

**Air PRESSURE travels down pitot tube - NOT AIR.**

**Static Vent**

**Measures local static pressure on side of fuselage**

**Ps + Pd = Ptot therefore Ptot - Ps = Pd**

**Dynamic pressure is directly proportional to IAS (if IAS increased then Pd increased)**

**Pressure diff measuring device = capsule/diaphragm.**

## Airspeeds

**IAS** - Actual reading on instrument

**CAS** - IAS corrected for **Position** + **Instrument** error

**EAS** - CAS corrected for **Compressibility**

**TAS** - EAS corrected for **Density**

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