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:
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)
1) Temp of fluid = measure of it's molecular motion
2) Temp at which molecular motion occurs = ABSOLUTE ZERO (-273K)
1) Density = ratio between mass of fluid and it's volume
2) Density = Mass/Volume (kg/m^3)
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
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)
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)
Dynamic pressure increases as Static pressure decreases.
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:
ρ1 = ρ2 if cross-sectional area of tube changes
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
Measures total pressure (stagnation pressure)
Air PRESSURE travels down pitot tube - NOT AIR.
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.
IAS - Actual reading on instrument
CAS - IAS corrected for Position + Instrument error
EAS - CAS corrected for Compressibility
TAS - EAS corrected for Density