8.1 Physics of the Atmosphere Flashcards
What are the four base quantities used in aerodynamics?
Mass
Length
Time
Temperature
1 KG is the same mass as what ?
1 litre of water at 4 degrees c
What is one metre more precisely defined as ?
A certain number of wavelengths of a particular colour of light
What is a second now defined as ?
A fraction of the unchangeable speed of light
The unit for temperature is ?
The Kelvin
What is a derived quantity ?
A quantity made up from the base units, e.g. speed as it is made up of distance(m) over time(s)
What are the six derived quantities ?
Speed Acceleration Force Work Power Pressure
What is the formula for velocity?
V = distance divided by time
What is the formula for acceleration?
A = change of velocity divided by the time taken
What unit is for acceleration under gravity?
G
What is the value of acceleration under gravity?
G = 9.8 M PER S squared
What is the second law of Newton?
Force = mass multiplied by the acceleration
What is force measured in?
Newtons or deca-newtons which is 10 Newtons
What is the formula for weight?
Mass times the acceleration due to gravity
What is the unit of weight?
N
What is the formula for force?
F = Mass times acceleration
What is the formula for work?
Work = N x m (force multiplied by the distance)
What is work denoted by?
The Joule (J)
What is the formula for power?
Power = N x m divided by s ( force times distance divided by time)
What is the SI unit for power?
Watts and kilowatts
What is the unit of pressure?
The Pascal (Pa)
What is Pa measured in?
Newtons per square metre
What is static pressure denoted by?
A small p measured in Newtons per square metre
How do you calculate static pressure?
Static pressure is calculated as height multiplied by density multiplied by gravity ( p = h times density times g )
What is dynamic pressure denoted by?
A small q measured in Newtons per square metre
How is dynamic pressure calculated?
Dynamic pressure is calculated as half the density multiplied by the speed squared ( q = density half times v squared)
One bar is equal to how many pascals?
100,000 Pascals
What is the formula for pressure?
Pressure = force divided by area
What denotes the speed of sound?
a
Sound waves are the same as what?
Pressure waves
The speed of sound depends on what?
The temperature (k)
The speed of sound is lower at ?
High altitudes (low temps)
The speed of sound is higher at ?
Low altitudes (high temps)
Below the speed of sound where are the pressure waves around the aircraft?
Both in front and behind it
At the speed of sound where are the pressure wave around the aircraft?
The pressure wave cannot escape at the front of the aircraft, forming a big pressure wave. This pressure wave is known as a shock wave
Above the speed of sound where are the pressure wave around the aircraft?
In this case the pressure waves increase behind the aircraft and shock waves form outside the periphery of the pressure waves
What can be said about the relationship between the speed of sound, the aircraft speed and altitude?
The aircraft at fixed speed of say 300 m/s at low altitude will reach the speed of sound if it climbs to a high altitude due to decreased ambient temperature
What is Mach number used for?
Mach number M, is used to keep the pilot
informed of the relationship between the speed of the aircraft and the speed of sound
How is Mach number calculated?
The Mach number is the speed of the aircraft divided by the speed of sound
What is considered subsonic?
In the subsonic region all speeds around the aircraft are below the speed of sound. This is the region up to the critical Mach number
What is considered transonic?
In the transonic region some speeds around the aircraft are below the speed of sound and some are higher than the speed of sound. This is the region between the critical Mach number and 1.3 Mach.
What is considered supersonic?
Finally, we have the supersonic region. Here, all speeds around the aircraft are higher than the speed of sound. This is the region at Mach numbers higher than 1.3
In the atmosphere which is the lowest layer?
The troposphere is the lowest of these layers. In the troposphere we have clouds and rain and many different weather conditions
What is the layer above the troposphere?
The stratosphere is the layer above the troposphere. There are no rain clouds in the stratosphere and the temperature does not change as the altitude increases
What is the boundary between troposphere and the stratosphere?
The tropopause is the name given to the boundary between the troposphere and the stratosphere
What is the height of the tropopause?
Approximately 8 kilometres over the north and south poles and 16 kilometres over the equator
Who created the ISA?
A standard atmosphere was introduced by the International Civil Aviation Organisation, the ICAO
What is the ISA altitude for the tropopause?
11 Kilometres
Under standard conditions the temperature decreases at what rate?
6.5 degrees c per KM
What’s the standard conditions temp at the tropopause?
Minus 56.5 degrees c
In the stratosphere is there any temperature changes?
No
According to the ISA what is the standard temperature at sea level?
14 or 15 degrees c
According to the ISA what is the density at sea level?
1.225 KG per metre cubed
According to the ISA what is the pressure at sea level?
1013.25 hecto pascals
What is the base unit and symbol of the base quantity luminous intensity is?
base unit = candela
base symbol = Cd
What is the base unit and symbol of the base quantity amount of substance?
Base unit = Mole
Base symbol = Mol
What is the base unit and symbol of the base quantity current?
Base unit = Ampere
Base symbol = A
The formula for the speed of sound is?
A = 20 times the square root of temperature in kelvin
20 times square of t m/s
