1. Propulsion Systems
Flight and Space
© 2011 Project Lead The Way, Inc.

2. Propulsion Systems
PLTW Gateway
Unit 4– Lesson 4.2– Aeronautics
Propulsion System
A machine that produces thrust to push an object forward
The amount of thrust depends on the mass flow through the engine and the exit velocity of the gas
On airplanes, thrust is usually generated through some application of Newton's third law of action and reaction. A gas, or working fluid, is accelerated by the engine, and the reaction to this acceleration produces a force on the engine.

3. Airplane Propulsion Systems
PLTW Gateway
Unit 4– Lesson 4.2– Aeronautics
Airplane Propulsion Systems
Propeller
Turbine (jet) engine
Ramjet or
Scramjet
Rocket Planes

4. Why Are There Different Types of Engines?
Propulsion Systems
PLTW Gateway
Unit 4– Lesson 4.2– Aeronautics
Why Are There Different Types of Engines?
Newton’s 1st Law
Objects in motion tend to stay in motion and objects at rest tend to stay at rest unless something pushes or pulls on the object.
Therefore:
Thrust from the propulsion system must balance the drag when the airplane is cruising.
Thrust from the propulsion system must exceed the drag for the airplane to accelerate.
You must have the correct type of engine (propulsion system) to provide the correct amount of thrust.

5. Aircraft Motion Propulsion Systems PLTW Gateway
Unit 4– Lesson 4.2– Aeronautics
Aircraft Motion

6. Propulsion System Piston Engines and Propellers
Propulsion Systems
PLTW Gateway
Unit 4– Lesson 4.2– Aeronautics
Propulsion System
Piston Engines and Propellers
Remember that internal combustion (gasoline) engines require oxygen to ignite the fuel, and therefore need to fly at lower altitudes
Used most commonly on smaller aircraft
They generally fly slower, and at lower altitudes

7. Propulsion System Piston Engines and Propellers Propulsion Systems
PLTW Gateway
Unit 4– Lesson 4.2– Aeronautics
Propulsion System
Piston Engines and Propellers
A propeller system takes the rotary motion from a motor and converts it into thrust. It has multiple blades attached to a central shaft, and works like a rotating screw or wing. The blades are often airfoil shaped, thus utilizing both Bernoulli’s principle and Newton’s third law to produce forward motion.

8. Airliners and Cargo Planes
Propulsion Systems
PLTW Gateway
Unit 4– Lesson 4.2– Aeronautics
Airliners and Cargo Planes
Spend most of the time in a cruise state
High engine efficiency and low fuel usage more important than excess thrust
Turboprop and turbofan propulsion used on airliners and cargo planes
Since thrust depends on both the amount of gas moved and the velocity, we can generate high thrust by accelerating a large mass of gas by a small amount, or by accelerating a small mass of gas by a large amount. Because of the aerodynamic efficiency of propellers and fans, it is more fuel efficient to accelerate a large mass by a small amount. That is why we find high bypass fans and turboprops on cargo planes and airliners.

9. Propulsion Systems
PLTW Gateway
Unit 4– Lesson 4.2– Aeronautics
Propulsion Systems
Jet propulsion is similar to the release of an inflated balloon.

10. Propulsion Systems Turbojet First really useful jet engine built
PLTW Gateway
Unit 4– Lesson 4.2– Aeronautics
Propulsion Systems
Turbojet
First really useful jet engine built
The turbojet was the first really useful jet engine to be built. The air flows into the engine through the air intak. The design of the inlet makes the air slow down and also raises the pressure. The air then goes through the compressor where sets of blades compress the air even more, greatly raising the pressure. The air then enters the combustion chamber where the fuel is added and ignited. The very hot, high pressure air rushes past the turbine blades, making them spin very fast. The turbine blades are connected back to the compressor blades by a shaft. The turbine blades take some of the energy from the air and return it to the compressor. The hot, high pressure air that gets past the turbine "jets" out the exhaust nozzle, thrusting the engine forward.
Turbojets are very inefficient and noisy at subsonic speeds. Most modern plans use turbofans and turboprops.

11. Propulsion Systems Turbofan Turboprop
PLTW Gateway
Unit 4– Lesson 4.2– Aeronautics
Propulsion Systems
Turbofan
Adds a large set of fan blades at the front of the inlet
Turboprop
The fan from turbofan is replaced with a propeller
The fan works much like a propeller, thrusting the engine forward and pushing a large amount of air backwards. As the air is pushed back by the fan, some of it goes into the engine and some bypasses the engine. The engine that sits behind the fan is basically a turbojet. The air that goes into this engine receives the same treatment as the air that goes through the turbojet.
The turboprop engine is essentially a turbofan engine where the fan is replaced by a propeller. The propeller is placed outside of the inlet.

12. Fighter Planes and Hypersonic Aircraft
Propulsion Systems
PLTW Gateway
Unit 4– Lesson 4.2– Aeronautics
Fighter Planes and Hypersonic Aircraft
Require high excess thrust to accelerate quickly and overcome high drag associated with high speeds
High thrust is more important than engine efficiency

13. Propulsion Systems
PLTW Gateway
Unit 4– Lesson 4.2– Aeronautics
A ramjet is a form of jet engine which uses the engine's forward motion to compress incoming air, without a rotary compressor. Ramjets cannot provide thrust at zero airspeed, and therefore, cannot move a plane from standstill. They require a forward speed of at least half the speed of sound (Mach 0.5)
A scramjet or” super combustion ramjet” uses the same principles as the ramjet. However, the minimum functional speed, requires acceleration by other means to hypersonic speed before the scramjet can become active. Ramjets slow the incoming air to a subsonic speed within the combustor. Scramjets require the airflow through the engine to be at hypersonic speed. Both function best at hypersonic (above Mach 3) speeds.
NASA is currently testing the X-43 at speeds of Mach 10.

14. Rocket Powered Airplanes
Propulsion Systems
PLTW Gateway
Unit 4– Lesson 4.2– Aeronautics
Rocket Powered Airplanes
Uses a rocket engine for propulsion
Has higher speeds
Propels only for a short period of time
Also known as a rocket plane, it is an aircraft that uses a rocket for propulsion, sometimes in addition to air-breathing jet engines (known as Jet Assisted Take Off). They can fly at much faster speeds than a jet aircraft of similar size, but only work for a few minutes, followed by a glide. Because they are powered by a rocket which does not need oxygen from the atmosphere, they are good for very high altitude flight. They also accelerate faster, and therefore have shorter takeoffs.
Unusual launch configurations
From another plane
Vertically – nose in the air and tail to the ground

15. Propulsion Systems
PLTW Gateway
Unit 4– Lesson 4.2– Aeronautics
Rocket Propulsion
Engine pushes itself forward or upward by producing thrust
A rocket engine uses only propellant carried within it
A rocket can operate in outer space, where there is almost no air
Unlike a jet engine, which draws in outside air, a rocket engine uses only the substances carried within it.
Click on Liftoff to show video of rocket launch.

16. 3 – 2 – 1 Liftoff! Propulsion Systems PLTW Gateway
Unit 4– Lesson 4.2– Aeronautics
3 – 2 – 1 Liftoff!

17. How Do Rocket Engines Work?
Propulsion Systems
PLTW Gateway
Unit 4– Lesson 4.2– Aeronautics
How Do Rocket Engines Work?
Newton’s 3rd Law:
For every action there is an equal and opposite reaction.
Rocket engines generate thrust by putting a gas under pressure.
The gas escaping the rocket is called exhaust.
As the rocket pushes the exhaust backward, the exhaust pushes the rocket forward.
The vast majority of rockets are chemical rockets. The two most common types of chemical rockets are solid-propellant rockets and liquid-propellant rockets. Engineers have tested a third type of chemical rocket, called a hybrid rocket, that combines liquid and solid propellants. Electric rockets have propelled space probes and maneuvered orbiting satellites. Researchers have designed experimental nuclear rockets.

18. Rocket Propellant Solid-Fuel Rockets
Propulsion Systems
PLTW Gateway
Unit 4– Lesson 4.2– Aeronautics
Rocket Propellant
Solid-Fuel Rockets
Burn a solid material called the grain
Engineers design grains with a hollow core
Propellant burns from the core outward
Unburned propellant shields the engine casing from the heat of combustion
Rocket designers often choose solid propellants for rockets that must be easy to store, transport, and launch. Military planners prefer solid-propellant rockets for many uses because they can be stored for a long time and fired with little preparation. Solid-propellant rockets often serve as sounding rockets and as boosters for launch vehicles and cruise missiles. They are also used in fireworks.

19. Rocket Propellant Solid-Fuel Rockets Hollow Core Solid Fuel
Propulsion Systems
PLTW Gateway
Unit 4– Lesson 4.2– Aeronautics
Rocket Propellant
Solid-Fuel Rockets
Hollow Core
Solid fuel rockets are currently being designed with an 11 point star as the hollow core. This provides more surface area which will burn faster, producing more thrust for a short period of time. Once it burns past the points of the star, the fuel will burn more uniformly and slower.
Solid Fuel

20. Rocket Propellant Liquid-Fuel Rocket
Propulsion Systems
PLTW Gateway
Unit 4– Lesson 4.2– Aeronautics
Rocket Propellant
Liquid-Fuel Rocket
Carries fuel and oxidizer in separate tanks
Fuel circulates through cooling jacket before entering combustion chamber
Circulation preheats the fuel for combustion and helps cool the rocket
Liquid propellants usually produce greater thrust than do equal amounts of solid propellants burned in the same amount of time. Scientists use liquid-propellant rockets for most space launch vehicles. Liquid-propellant rockets serve as the main engines of the space shuttle.
Fuel and oxidizer are cool. They are passed along side the combustion chamber to warm up to burn better.

21. Rocket Propellant Ion (Electric)
Propulsion Systems
PLTW Gateway
Unit 4– Lesson 4.2– Aeronautics
Rocket Propellant
Ion (Electric)
Coils are heated to change a fuel, such as xenon, into a vapor
Hot platinum or tungsten ionization grid changes the flowing vapor into a stream of electrically charged particles called ions
Electric rockets use electric energy to expel ions (electrically charged particles) from the nozzle. Solar panels or a nuclear reactor can provide the energy. An electric rocket cannot produce enough thrust to overcome Earth's gravity. Electric rockets used in space must therefore be launched by chemical rockets. Once in space, however, the low rate of mass flow becomes an advantage. It enables an electric rocket to operate for a long time without running out of propellant. Another type of electric rocket uses electromagnets rather than charged screens to accelerate xenon ions. This type of rocket powers the SMART-1 lunar probe, launched by the European Space Agency in 2003.
(Xenon is stripped of electrons by the ionization grid, making it positive. It then accelerates towards the accelerator, and then out the nozzle.)

22. Rocket Propellant Nuclear
Propulsion Systems
PLTW Gateway
Unit 4– Lesson 4.2– Aeronautics
Rocket Propellant
Nuclear
Uses heat from a nuclear reactor to change a liquid fuel into a gas
Some of the fuel, heated by the nozzle of the rocket, flows through the turbine
Turbine drives the fuel pump
The exhaust speed of a nuclear rocket might reach four times that of a chemical rocket. By expelling a large quantity of hydrogen, a nuclear rocket could therefore achieve high thrust. However, a nuclear rocket would require heavy shielding because a nuclear reactor uses radioactive materials. The shielding would weigh so much that the rocket could not be practically used to boost a launch vehicle. More practical applications would use small nuclear engines with low, continuous thrust to decrease flight times to Mars or other planets.
Nuclear rocket developers must also overcome public fears that accidents involving such devices could release harmful radioactive materials. Before nuclear rockets can be launched, engineers must convince the public that such devices are safe.

23. Our own experiments on jet propulsion!
Propulsion Systems
PLTW Gateway
Unit 4– Lesson 4.2– Aeronautics
What’s Next?
Our own experiments on jet propulsion!

24. Propulsion Systems
PLTW Gateway
Unit 4– Lesson 4.2– Aeronautics
Image Resources
Microsoft, Inc. (2008). Clip art. Retrieved September 10, 2008, from
National Aeronautics and Space Administration (NASA). (2008). Beginner’s guide to propulsion. Retrieved June 23, 2009, from
National Aeronautics and Space Administration (NASA). (2008). NASA TV Video Gallery. Retrieved June 23, 2009, from
National Aeronautics and Space Administration (NASA). (2008). NASA – A closer look at the X-43 mission. Retrieved June 23, 2009, from
National Aeronautics and Space Administration (NASA). (2007). NASA – Rocket. Retrieved June 23, 2009, from