Specific Impulse
Specific impulse is a measure of the efficiency of a rocket engine. It is defined as the thrust produced
per unit weight of propellant consumed per unit time. The higher the specific impulse, the more thrust can be
produced for a given amount of propellant. Specific impulse is typically measured in seconds, and is a key parameter in the
design of rocket engines and other propulsion systems.
Isp = F / (ṁ × g)
where:
• Isp is the specific impulse in seconds (s)
• F is the thrust in newtons (N)
• m is the propellant mass flow rate in kilograms per second (kg/s)
• g is the acceleration due to gravity at sea level, approximately 9.81 m/s²
Differences between piston engine and gas turbine engine
Feature Piston engine Gas turbine engine
Conversion of
chemical energy to Reciprocating motion Rotational motion
mechanical energy
Compressor, combustion
Mechanism Pistons, crankshaft
chamber, turbine, shaft
Power-to-weight
Lower Higher
ratio
Fuel efficiency Lower (generally) Higher (at high altitudes)
Emissions Higher Lower
Complexity Simpler More complex
Maintenance Easier More difficult
Cost Lower Higher
Larger aircraft, power
Smaller aircraft,
Applications generation, marine
automobiles, motorcycles
propulsion
Structure of Atmosphere - The different layers of the atmosphere
The atmosphere can be divided into layers based on its temperature, as shown in the figure
below. These layers are the troposphere, the stratosphere, the mesosphere and the thermosphere. A
further region, beginning about 500 km above the Earth's surface, is called the exosphere.
,The Troposphere
This is the lowest part of the atmosphere - the part we live in. It contains most of our weather - clouds,
rain, snow. In this part of the atmosphere the temperature gets colder as the distance above the earth
increases, by about 6.5°C per kilometre. The actual change of temperature with height varies from day to day,
depending on the weather.
The troposphere contains about 75% of all of the air in the atmosphere, and almost all of the water
vapour (which forms clouds and rain). Air in the troposphere thins as altitude increases.. The decrease
in temperature with height is a result of the decreasing pressure. If a parcel of air moves upwards it expands (because of
the lower pressure). When air expands it cools. So air higher up is cooler than air lower down.
The lowest part of the troposphere is called the boundary layer. This is where the air motion is determined by the properties
of the Earth's surface. Turbulence is generated as the wind blows over the Earth's surface, and by thermals rising from the
land as it is heated by the sun. This turbulence redistributes heat and moisture within the boundary layer, as well as
pollutants and other constituents of the atmosphere.
The top of the troposphere is called the tropopause. This is lowest at the poles, where it is about 7 -
10 km above the Earth's surface. It is highest (about 17 - 18 km) near the equator.
The Stratosphere
This extends upwards from the tropopause to about 50 km. It contains much of the ozone in the
atmosphere. The increase in temperature with height occurs because of absorption of ultraviolet (UV)
radiation from the sun by this ozone. Temperatures in the stratosphere are highest over the summer
pole, and lowest over the winter pole.
By absorbing dangerous UV radiation, the ozone in the stratosphere protects us from skin cancer and
other health damage. However chemicals (called CFCs or freons, and halons) which were once used in refrigerators,
spray cans and fire extinguishers have reduced the amount of ozone in the stratosphere, particularly at polar latitudes,
leading to the so-called "Antarctic ozone hole".
, Now humans have stopped making most of the harmful CFCs we expect the ozone hole will eventually recover over the 21st
century, but this is a slow process.
The Mesosphere
The region above the stratosphere is called the mesosphere. Here the temperature again decreases
with height, reaching a minimum of about -90°C at the "mesopause".
The Thermosphere and Ionosphere
The thermosphere lies above the mesopause, and is a region in which temperatures again increase
with height. This temperature increase is caused by the absorption of energetic ultraviolet and X-Ray
radiation from the sun.
The region of the atmosphere above about 80 km is also caused the "ionosphere", since the energetic
solar radiation knocks electrons off molecules and atoms, turning them into "ions" with a positive
charge. The temperature of the thermosphere varies between night and day and between the seasons,
as do the numbers of ions and electrons which are present. The ionosphere reflects and absorbs radio
waves, allowing us to receive shortwave radio broadcasts in New Zealand from other parts of the
world.
The Exosphere
The region above about 500 km is called the exosphere. It contains mainly oxygen and hydrogen
atoms, but there are so few of them that they rarely collide - they follow "ballistic" trajectories under
the influence of gravity, and some of them escape right out into space.
The Magnetosphere
The earth behaves like a huge magnet. It traps electrons (negative charge) and protons (positive),
concentrating them in two bands about 3,000 and 16,000 km above the globe - the Van Allen
"radiation" belts. This outer region surrounding the earth, where charged particles spiral along the
magnetic field lines, is called the magnetosphere.
Different Maneuvers of a typical fighter aircraft
Fighter aircraft perform a variety of maneuvers to gain an advantage in aerial combat. These
maneuvers can be divided into two main categories:
i) Basic maneuvers: These maneuvers are performed without respect to the position of an enemy.
They are often simple maneuvers, such as climbs, turns, aileron rolls, and slow rolls.
ii) Relative maneuvers: These maneuvers are performed in relation to the motion of another aircraft.
They are often used to outmaneuver the enemy, such as the high and low Yo-Yo, which are used to
adjust altitude, and the scissors, which are used to reverse roles and put the attacker on the defensive.
Some of the most common fighter aircraft maneuvers include:
Barrel roll: A barrel roll is a maneuver in which the aircraft rolls 360 degrees along its
longitudinal axis. This maneuver is often used to dodge enemy fire or to make a quick change
of direction.
Specific impulse is a measure of the efficiency of a rocket engine. It is defined as the thrust produced
per unit weight of propellant consumed per unit time. The higher the specific impulse, the more thrust can be
produced for a given amount of propellant. Specific impulse is typically measured in seconds, and is a key parameter in the
design of rocket engines and other propulsion systems.
Isp = F / (ṁ × g)
where:
• Isp is the specific impulse in seconds (s)
• F is the thrust in newtons (N)
• m is the propellant mass flow rate in kilograms per second (kg/s)
• g is the acceleration due to gravity at sea level, approximately 9.81 m/s²
Differences between piston engine and gas turbine engine
Feature Piston engine Gas turbine engine
Conversion of
chemical energy to Reciprocating motion Rotational motion
mechanical energy
Compressor, combustion
Mechanism Pistons, crankshaft
chamber, turbine, shaft
Power-to-weight
Lower Higher
ratio
Fuel efficiency Lower (generally) Higher (at high altitudes)
Emissions Higher Lower
Complexity Simpler More complex
Maintenance Easier More difficult
Cost Lower Higher
Larger aircraft, power
Smaller aircraft,
Applications generation, marine
automobiles, motorcycles
propulsion
Structure of Atmosphere - The different layers of the atmosphere
The atmosphere can be divided into layers based on its temperature, as shown in the figure
below. These layers are the troposphere, the stratosphere, the mesosphere and the thermosphere. A
further region, beginning about 500 km above the Earth's surface, is called the exosphere.
,The Troposphere
This is the lowest part of the atmosphere - the part we live in. It contains most of our weather - clouds,
rain, snow. In this part of the atmosphere the temperature gets colder as the distance above the earth
increases, by about 6.5°C per kilometre. The actual change of temperature with height varies from day to day,
depending on the weather.
The troposphere contains about 75% of all of the air in the atmosphere, and almost all of the water
vapour (which forms clouds and rain). Air in the troposphere thins as altitude increases.. The decrease
in temperature with height is a result of the decreasing pressure. If a parcel of air moves upwards it expands (because of
the lower pressure). When air expands it cools. So air higher up is cooler than air lower down.
The lowest part of the troposphere is called the boundary layer. This is where the air motion is determined by the properties
of the Earth's surface. Turbulence is generated as the wind blows over the Earth's surface, and by thermals rising from the
land as it is heated by the sun. This turbulence redistributes heat and moisture within the boundary layer, as well as
pollutants and other constituents of the atmosphere.
The top of the troposphere is called the tropopause. This is lowest at the poles, where it is about 7 -
10 km above the Earth's surface. It is highest (about 17 - 18 km) near the equator.
The Stratosphere
This extends upwards from the tropopause to about 50 km. It contains much of the ozone in the
atmosphere. The increase in temperature with height occurs because of absorption of ultraviolet (UV)
radiation from the sun by this ozone. Temperatures in the stratosphere are highest over the summer
pole, and lowest over the winter pole.
By absorbing dangerous UV radiation, the ozone in the stratosphere protects us from skin cancer and
other health damage. However chemicals (called CFCs or freons, and halons) which were once used in refrigerators,
spray cans and fire extinguishers have reduced the amount of ozone in the stratosphere, particularly at polar latitudes,
leading to the so-called "Antarctic ozone hole".
, Now humans have stopped making most of the harmful CFCs we expect the ozone hole will eventually recover over the 21st
century, but this is a slow process.
The Mesosphere
The region above the stratosphere is called the mesosphere. Here the temperature again decreases
with height, reaching a minimum of about -90°C at the "mesopause".
The Thermosphere and Ionosphere
The thermosphere lies above the mesopause, and is a region in which temperatures again increase
with height. This temperature increase is caused by the absorption of energetic ultraviolet and X-Ray
radiation from the sun.
The region of the atmosphere above about 80 km is also caused the "ionosphere", since the energetic
solar radiation knocks electrons off molecules and atoms, turning them into "ions" with a positive
charge. The temperature of the thermosphere varies between night and day and between the seasons,
as do the numbers of ions and electrons which are present. The ionosphere reflects and absorbs radio
waves, allowing us to receive shortwave radio broadcasts in New Zealand from other parts of the
world.
The Exosphere
The region above about 500 km is called the exosphere. It contains mainly oxygen and hydrogen
atoms, but there are so few of them that they rarely collide - they follow "ballistic" trajectories under
the influence of gravity, and some of them escape right out into space.
The Magnetosphere
The earth behaves like a huge magnet. It traps electrons (negative charge) and protons (positive),
concentrating them in two bands about 3,000 and 16,000 km above the globe - the Van Allen
"radiation" belts. This outer region surrounding the earth, where charged particles spiral along the
magnetic field lines, is called the magnetosphere.
Different Maneuvers of a typical fighter aircraft
Fighter aircraft perform a variety of maneuvers to gain an advantage in aerial combat. These
maneuvers can be divided into two main categories:
i) Basic maneuvers: These maneuvers are performed without respect to the position of an enemy.
They are often simple maneuvers, such as climbs, turns, aileron rolls, and slow rolls.
ii) Relative maneuvers: These maneuvers are performed in relation to the motion of another aircraft.
They are often used to outmaneuver the enemy, such as the high and low Yo-Yo, which are used to
adjust altitude, and the scissors, which are used to reverse roles and put the attacker on the defensive.
Some of the most common fighter aircraft maneuvers include:
Barrel roll: A barrel roll is a maneuver in which the aircraft rolls 360 degrees along its
longitudinal axis. This maneuver is often used to dodge enemy fire or to make a quick change
of direction.
